Project Progress Report:Implementation of the IPM program using weaver ants as a major component for cashew growers in Vietnam - MS7 " ppt

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Ministry of Agriculture & Rural Development

Project Progress Report



029/05VIE:
Implementation of the IPM program using weaver ants as
a major component for cashew growers in Vietnam



MS7: Research/technical Report







Renkang Peng, Keith Christian, La Pham Lan and Nguyen Thanh Binh

31 July 2008

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1. Institute Information
Project Name
Implementation of the IPM program using weaver
ants as a major component for cashew growers in
Vietnam
Vietnamese Institution
Institute of Agricultural Science of South Vietnam

Vietnamese Project Team Leader
Mr La Pham Lan
Australian Organisation
Charles Darwin University
Australian Personnel
Prof. Keith Christian and Dr Renkang Peng
Date commenced
February 2006
Completion date (original)
January 2009
Completion date (revised)

Reporting period
July 2008

Contact Officer(s)

In Australia: Team Leader
Name:
Keith Christian
Telephone:
61 8 89466706
Position:
Professor
Fax:
61 8 89466847
Organisation
Charles Darwin
University
Email:


In Australia: Administrative contact
Name:
Jenny Carter
Telephone:
61 08 89466708
Position:
Research Manager
Fax:
61 8 89467199
Organisation
Charles Darwin University
Email:


In Vietnam

Name:
La Pham Lan
Telephone:
84 0913829560
Position:
Head of Plant Protection
Department
Fax:
84 8 8297650
Organisation
Institute of Agricultural
Science of South Vietnam
Email:



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Summary

To assist our cashew IPM TOT training program, field experiments, field surveys and
observations, laboratory experiments and rearing were conducted in Binh Phuoc,
Dong Nai and Dak Lac provinces between July 2006 and March 2008.

Data obtained from the field experiments and field surveys showed that
• The common insect pests damaging flushing terminals, cashew apples and/or
nuts were tea mosquito bugs, shoot borers, coreid bugs, thrips, apple-nut
borers, leaf rollers, leaf miners, aphids and mealy bugs, among which tea
mosquito bugs, shoot borers, leaf rollers and apple-nut borers were the major
pests during the flowering and fruiting period. The branch borer and the stem-
root borer were the major pests damaging branches and trunks.

• Weaver ants were similar to insecticides for controlling a range of insect pests,
such as tea mosquito bugs, shoot borers, apple-nut borers, leaf rollers and leaf
miners.
• Cashew yields were similar between the IPM plot and the farmer’s plot, but
nut quality was higher in the IPM plot than in the farmer’s plot because of the
foraging behaviour of weaver ants.
• Mealy bugs and aphids, that are currently determined to be minor pests, were
unlikely to become major ones after the main pests are controlled by weaver
ants. A total of 12 species of natural enemies of aphids and 9 species of natural
enemies of mealy bugs were determined, and these natural enemies were more
frequently seen in the IPM plot than in the farmer’s plot, showing that when
weaver ants were present, mealy bugs and aphids were present, and predators
and parasitoids of these pests were also present, resulting in very little damage
to the cashew crop.
• The key to successfully manage the IPM plot was to keep weaver ant
populations high and stable. The boundary fighting between weaver ant
colonies and the competition between weaver ants and other ant species were
determined to be very important for the reduction of weaver ant populations.
Solutions for these competitive interactions were provided and discussed.
Data obtained from field observations, laboratory experiments and rearing showed
that
• A soft chemical (Abamectine) was effective in controlling thrips, on which
weaver ants have a little effect, and it was not harmful to weaver ants.
• The bio-ecology of the branch borer and the stem-root borer were extensively
studied. Based on their ovipositing behaviour, initial damage symptoms and
their life cycles, an integrated management strategy for each of the pests was
recommended. These strategies include three components (monitoring,
removal of young larvae based on initial damage symptoms, and chemical
injection).
• Control strategies developed for thrips, branch borers and stem-root borers are

compatible with the other components of the cashew IPM program.

Based on the above results and general farming practice, a cashew IPM program
which is suitable for cashew growing conditions in Vietnam has been developed and
is described in Appendix 1.

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Introduction

To assist our cashew IPM TOT training program, field experiments, field surveys and
observations, laboratory experiments and rearing were conducted in Binh Phuoc,
Dong Nai and Dak Lac provinces (the three biggest cashew growing provinces in
Vietnam) between July 2006 and March 2008. The field experiments were conducted
in three demonstration orchards, each of which was divided into two plots: a farmer’s
plot that was managed with chemical insecticides, and an IPM plot that was managed
by using the weaver ants (Oecophylla smaragdina). The field surveys were also
conducted in three orchards at different time of the cashew developmental stage. At
each orchard, the main insect pest damage was assessed in tree groups: trees with
weaver ants, trees with other species of ants, and trees without ants. The objectives of
the field experiments and surveys were:
(1) letting TOT trainees observe and assess the main cashew insect pests and
diseases (morphs, damage symptoms and life history) and their natural
enemies at different cashew developmental periods, and make comparisons
between the farmer’s plot and the IPM plot,
(2) letting TOT trainees assess the effective control of the main insect pests by the
most important bio-control agent - weaver ants,
(3) demonstrating how to use weaver ant colonies properly in cashew orchards,
(4) demonstrating how to use different farming strategies at the different periods
of the year to grow healthy cashews, and
(5) collecting technical data to comprise the cashew IPM curriculum and the

cashew IPM photo book.
This report will summarise the effectiveness of weaver ants in controlling the main
cashew insect pests, which directly damage flushing terminals, apples and nuts, and
their effect on cashew yield and nut quality through comparisons between the farmer
managed plots and the IPM plots and between trees with weaver ants and trees
without the ants.
The following problems have been addressed during this period of the project:
(1) The branch borer (Rhytidodera integra) and the stem-root borer (Plocaederus
obesus) larvae cause the damage inside branches and the trunk, often resulting
in the death of main branches or even the whole tree. Our preliminary
observations revealed that although weaver ants can catch or repel some adults
from trees, they have no ability to control the larvae when they bore into
branch or tree trunk. In order to develop control methods that can manage the
pests without negative effect on weaver ants, the bio-ecology for each of these
two pests in southern Vietnam is needed. However, no such information is
available.
(2) Thrips (
Rhynchothrips sp and Scirtothrips dorsalis) that damage cashew
flowers, apples and nuts are not the main pests in insecticide control orchards
because insecticides used to control tea mosquito bugs (Helopeltis antonii and
H. theivora), shoot borers (Alcidodes sp) and flower caterpillars also control
thrips. However, the use of weaver ants is incompatible with the use of toxic
insecticides. Thrips damage on apples and nuts is increasing in some areas.
Weaver ants can reduce the thrips populations, but they cannot reduce the
thrips damage below the economic injury level. Therefore, it is necessary to
find locally available low toxic insecticides that are effective in controlling the
thrips, but that are not harmful to weaver ants.

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(3) Weaver ants have a mutual relationship with aphids (Toxoptera sp and Aphis

gossypii) and mealy bugs (Dysmicoccus brevipes and Ferrisia virgata), many
cashew growers are concerned about whether these minor insect pests will
become major ones after the weaver ant is used. The results from our research
in different cashew growing regions show that aphids and mealy bugs in
cashew orchards with weaver ants are unlikely to become major insect pests.
Their populations can be naturally reduced by their natural enemies on which
weaver ants have limited effect. To demonstrate this relationship for TOT
trainers and cashew farmers, apart from our regular monitoring on these pests
between the farmer’s plot and the IPM plot at our demonstration orchards,
determination of natural enemy species of aphids and mealy bugs in cashew
orchards is important. This work has never been done in Vietnam.
Extensive field observations, laboratory experiments and rearing were conducted in
Hong Loc Centre to understand the behaviour and the life cycle of the branch borer
and the stem-root borer, to select locally available soft chemicals to control thrips, and
to determine natural enemy species of aphids and mealy bugs. The results from this
work will also be summarised in this report together with a discussion of how the
suggested control methods of these pests fit the cashew IPM program, which uses
weaver ants as a major component.


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Materials and methods

Field experiments


Three long-term field experiments were conducted in three demonstration orchards:
Mr Ty’s orchard in Dong Phu District of Binh Phuoc province, Hong Loc Centre
orchard, and Mr Bi’s orchard in Trang Bom District of Dong Nai province.

Mr Ty’s orchard

This orchard has about 2 ha of cashew trees grown from seeds. To limit the effect of
soil nutrition, half of this orchard was equally divided into two plots across the slight
slope: farmer’s plot (70 trees) and IPM plot (70 trees). Around the IPM plot, a row of
cashew trees was used as a buffer zone. For insect pest control, chemical insecticides
were used in the farmer’s plot, and sprays were done by the orchard owner based on
his own experience. In the IPM plot, weaver ants were used, and they were managed
by an experimentalist. The other farming activities, such as weeding, pruning,
fertilizer application and the use of fungicides, were done the same for the farmer’s
plot and the IPM plot and were conducted by the orchard owner.
Due to regular insecticide use, this orchard had no weaver ants before it was
used as our demonstration orchard. To establish and manage weaver ant colonies in
the IPM plot, the following 5 steps were followed:
(1) the dominant ant species in each tree of the plot was determined. We found all
the trees were fully occupied by the crazy ant (Anoplolepis gracilipes
), which
is a competitor with weaver ants;
(2) to reduce the crazy ant populations, a contact-killing insecticide (Motox
®
)
was sprayed at the tree bases while fallen leaves were raked to expose the ant
nests;
(3) a week later, about 5 - 10 trees were grouped together with twisted polystrings
if their side branches were not attached in preparation for receiving new
weaver ant colonies. Due to the fighting behaviour of weaver ants between
colonies, each group of trees received only one colony;
(4) a total of 10 weaver ant colonies were transplanted to the trees at a rate of 4 –
5 nests /tree in November 2006; and
(5) fresh minced fish meat was provided to each ant colony during the period of

tree dormancy.

Two weeks later and onwards after weaver ant colonies were transplanted, all the ant
colonies were regularly monitored. Weaver ant abundance was expressed as a percent
per tree by the following method: (the number of main branches with a weaver ant
trail in a tree / the number of the main branches in the tree) x 100. Weaver ants on a
tree were treated as

“Abundant”, if > 50% of the main branches had ant trails.
The major insect pest damage between the two plots was regularly monitored.
The damage symptoms for each of the major insect pests on flushing shoots, flowers
and nut was easily recognized and separated in the field by experimentalists who were
preliminarily trained with such knowledge. All the trees in each plot were numbered
in sequence. Two-weekly monitoring occasions were also numbered in sequence. In
each plot, trees with odd numbers were inspected in odd numbered weeks, and trees
with even numbers were inspected in even numbered weeks, so that freshly damaged
shoots would not be repeatedly counted (because soft foliar or floral flushes were

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hardened before the next monitoring occasion). Preliminary observations suggested
that all the main insect pests were more active in the lower tree canopy than in upper
levels. Therefore, the monitoring was concentrated in the lower level of the tree
canopy. For each tree, we recorded the total number of flushing shoots (including
foliar or/and floral flushing terminals) and the number of freshly damaged shoots by
each major pest, and percent damage was calculated.
The cashew yields were measured in each plot one week before harvest by the
following formula: total numbers of nuts counted on the half canopy of each tree on
the same side × canopy score. Four canopy scores (1, 1.33, 2 and 4) were used based
on the size and thickness of each tree canopy: score = ‘1’, if the canopy was 100%
goodness (the canopy being biggest and thickest); score = ‘1.33’, if the canopy was

75% goodness; score = ‘2’, if the canopy was 50% goodness; score = ‘4’, if the
canopy was 25% goodness. Cashew nut quality was generally assessed on site based
on overall nut appearance: shine and clean skin.

Hong Loc Centre orchard

The orchard is next to Dong Nai TOT training Centre, which is very convenient for
TOT trainees to do field experiments and observations. The orchard had ten cultivars,
each of which occupied one row, and each row was divided into two parts (farmer’s
part and IPM part). A total of 10 farmer’s parts made a farmer’s plot, with 67 trees. A
total of 10 IPM parts made an IPM plot, with 71 trees. There were 14 existing weaver
ant colonies randomly distributed in this orchard. In the farmer’s plot, weaver ants on
most of the trees were manually removed to the trees without weaver ants in the IPM
plot, and then chemical insecticides were used to remove the remaining ants to make
sure no weaver ants were in the farmer’s plot. In the IPM plot, after existing weaver
ant colonies were combined with the transplants from the farmer’s plot, almost every
tree had weaver ants. Apart from weaver ants, we also found ghost ants (Tapinoma
melanocephalum
), small sized crematogaster ants (Crematogaster sp) and an
unidentified black ant in this orchard, but we did not bait them because they were not
found to compete with weaver ants. The experiment began in September 2007. The
field management, weaver ant monitoring, insect pest monitoring, and yield, and nut
quality assessment followed the same protocol as Mr Ty’s orchard (see above).

Mr Bi’s orchard

This orchard has two blocks next to each other, and each block is about one ha. Block
1 was used from September 2006 to July 2007, and because of the disturbance of the
site caused by the owner, block 2 was used from September 2007 to May 2008. In
each block, 120 cashew trees of the same cultivar and similar size were used, and they

were divided into two plots (farmer’s plot – 60 trees and IPM plot – 60 trees). Due to
regular insecticide use, cashew trees in this orchard had no weaver ants, but they were
occupied by mud-nesting crematogaster ants (Crematogaster sp), ghost ants and an
unidentified black ant.
In 2006, to establish weaver ant colonies in the IPM plot, these ant species
were baited by an ant bait (fresh minced fish meat mixed with Regent
®
). A week after
baiting, these ant populations were greatly reduced, and weaver ant colonies were
transplanted into the IPM plot in early December 2006. The field experimental design,
field management, weaver ant monitoring, insect pest monitoring and yield
assessment followed the same protocol as Mr Ty’s orchard (see above).

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Surprising results were obtained from December 2006 to July 2007, showing
lower cashew yield and nut quality and heavier pest damage on foliar and floral
shoots in the IPM plot compared to the farmer’s plot. Through a detailed examination
in April 2007, the following phenomenon was observed:
(1) boundary fighting between weaver ant colonies and weaver ants dispersal to
orchard boundary trees resulting in 30% of the trees being without weaver
ants, and 30% of the trees had very low numbers of weaver ants (the ant
abundance being < 30%). These trees were either fully or partly occupied by
ghost ants, and they were heavily damaged by tea mosquito bugs, shoot borers
and fruit-nut borers.
(2) on the remaining 40% of the trees, weaver ants were abundant on tree trunks
and the main branches, but they did not forage on aphid-free foliar and floral
shoots, resulting in the heavy damage on flushing shoots, flowers and
developing nuts by tea mosquito bugs, shoot borers and fruit-nut borers.

The first phenomenon was mainly due to the experimentalist who lacked the

experience in managing weaver ant colonies. Ghost ants are very small (about 1.1
mm), and they were incorrectly thought not to be very competitive with weaver ants.
For the second phenomenon, 7 field surveys were conducted in different types of
cashew orchards with weaver ants together with interviews of the orchard owners for
information about farming practice. Through comparisons, it seemed that heavy leaf
fertilizer sprays (3 applications done in the IPM plot between December 2006 and
January 2007) may suppress or change the level of extra floral nectar secreted by
flushing terminals, which made them unattractive to weaver ants.
In 2007, therefore, more attention was paid to weaver ant colony management
and no leaf fertilizers were used in the IPM plot. The other management, such as
baiting other ant species, weaver ant transplantation, weaver ant monitoring, insect
pest monitoring and yield assessment, followed the same protocol as in the first year.

Field survey


A total of 6 field surveys were done in three cashew orchards: Mr Quang’s orchard in
Dong Xoai district of Binh Phuoc province, Mr Be’s orchard and Mr Sau’s orchard in
Trang Bom District of Dong Nai province.

Mr Quang’s orchard

This orchard had 60 cashew trees grown from seeds (14 trees over 10 years old and 46
trees about 3 years old). This orchard was surrounded by two patches of mahogany
trees and cassava crop. Because no insecticides were used, there were three existing
weaver ant colonies on big cashew trees and mahogany trees, and the ants had
dispersed to some of the young cashew trees when we did the first survey in July
2006. As big cashew trees were too tall to make an accurate assessment of the main
pest damage, each survey was concentrated on the 46 small trees. On each survey, all
the 46 trees were inspected, and for each tree, we recorded the dominant ant species

on the tree, the total numbers of flushing foliar and/or floral terminals on the tree and
the number of terminals damaged by each major pest, and the percentage damage was
calculated. A total of three surveys were done in this orchard: July 2006, December
2006 and April 2007.


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Mr Be’s orchard

Two surveys were done in this orchard which has several blocks of cashews. The first
survey was conducted in July 2006 in a block of about 3 ha. In this block, trees were
over 20 years old, but there were 18 young trees (about three years old) randomly
growing among the big trees due to the replacement of the dead trees. Insecticides
were not regularly used in this block (about one or two times a year), and therefore,
there were some existing weaver ant colonies on big trees, and they had dispersed to
some of the young trees. Because big cashew trees were too tall to make assessment
of the main pest damage, this survey was concentrated on the 18 small trees.
The second survey was conducted in another block of the orchard in August
2007 in collaboration with a field practical of the TOT training. This block was about
one ha, and trees were 4 years old of similar size. This block was closely surrounded
by old cashew trees (> 10 years). There were several weaver ant colonies on the big
trees, and they had dispersed to some of the young trees. A total of 50 young trees
were surveyed.
For each survey, the methods used were the same as in Mr Quang’ orchard.

Mr Sau’s orchard

This is an abandoned orchard, and it had 53 medium sized cashew trees of unknown
age. There were three existing weaver ant colonies: one in the orchard, and another
two colonies originally on the Eucalyptus trees on the edge of the orchard, which had

dispersed to a few cashew trees. A survey was done in July 2006. The survey methods
used were the same as in Mr Quang’ orchard.

Field observations and laboratory rearing


Field observations and laboratory rearing were conducted in Hong Loc centre, Hong
Loc Centre orchard, Mr Sau’s orchard and some orchards in Dak Lac province. The
observations concentrated on the bio-ecology of the branch borer and the stem-root
borer, including the behaviour of larvae and their life cycle. This was done by
dissecting branches and stems at different cashew developmental periods. The adult
emergence, activity and oviposition were also observed in evenings.
The laboratory rearing was concentrated on natural enemy species of aphids,
mealy bugs and shoot borers.
In order to find a suitable soft chemical that will reduce thrips populations on
developing nuts, but will not be harmful to weaver ants, lab experiments were
conducted using the locally available soft chemicals using four treatments: developing
nuts and apples with thrips were treated with Applaud, D.C. Tron oils, Abamectine
and water, respectively.

Data analysis


For field experimental data analyses, on each monitoring occasion, two plots (farmer
and IPM) were ranked, based on mean percentage damage by each major pest. All the
monitoring occasions in the flowering and fruiting period and in the dormant or leaf
flushing period were separately compared by a non-parametric Friedman 2-way
ANOVA by ranks using SYSTAT statistics software. The percentage yield data and

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field survey data were analysed by a Kruskal-Wallis one-way ANOVA by ranks to
test for a difference between plots and between trees with or without weaver ants.

Results

Field experiments


Mr Ty’s orchard

The weaver ant populations in the IPM plot were high and stable from December
2006 to July 2007, and the average ant abundance was over 80% (Fig. 1). However,
from August 2007 to January 2008, the ant populations gradually decreased from 70%
to 28% (Fig. 1). This was mainly due to fighting between weaver ant colonies.
0
20
40
60
80
100
120
140
23
Jan
31
Jan
7
Feb
23
Feb

7
Mar
23
Mar
1
Apr
7
Apr
23
Apr
7
May
23
May
7
Jun
23
Jun
7 Jul 14
Nov
24
Dec
4
Jan
12
Jan
% Weaver ant abundance

| 2007 | 2008 |
Fig. 1. Average weaver ant abundance in the IPM plot at Binh Phuoc province,

Vietnam.

Although the numbers of flushing terminals per tree were higher in the IPM
plot than in the farmer’s plot, the difference between the two treatments was
statistically similar (P > 0.05; Table 1).

Table 1. The average number of flushing shoots per tree for the farmer’s plot and the
IPM plot during the period of pre-flowering flush and nut development (November –
March), Binh Phuoc province, Vietnam.
Plot Mean number of shoots
/tree +
SD
Rank sum
Farmer 86.6 + 28.3 12.0
IPM 102.3 + 39.7 18.0

Friedman two–way ANOVA

X
r
2
=3.600; df = 1; P = 0.058

Based on the monitoring data, the common insect pests in this orchard were
tea mosquito bugs, shoot borers, leaf miners (Acrocercops syngramma), aphids, the
apple-nut borer (Nephopteryx sp), leaf rollers and branch borer. The population
fluctuations in the IPM plot and the farmer’s plot for tea mosquito bugs, shoot borers,
leaf miners and aphids, are shown in Figs 2, 3, 4, and 5, respectively.

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0
10
20
30
40
22
Dec
23
Jan
31
Jan
7
Feb
23
Feb
7
Mar
23
Mar
1
Apr
7
Apr
23
Apr
7
May
23
May

7
Jun
23
Jun
7 Jul 24
Dec
4
Jan
12
Jan
% shoots damaged by tea
mosquito bugs
Farmer
IPM

| 06 | 2007 | 08 |
Fig. 2. Mean % foliar or floral flushing shoots damaged by tea mosquito bugs in the
farmer’s plot and the IPM plot at Binh Phuoc province, Vietnam.

0
5
10
15
20
25
22
Dec
23
Jan
31

Jan
7
Feb
23
Feb
7
Mar
23
Mar
1
Apr
7
Apr
23
Apr
7
May
23
May
7
Jun
23
Jun
7 Jul 24
Dec
4
Jan
12
Jan
% shoots damaged by shoot

borer
Farmer
IPM

|-06-| 2007 |-2008 |
Fig. 3. The mean % flushing shoots damaged by shoot borers in the farmer’s plot and
the IPM plot at Binh Phuoc province, Vietnam.









|-06-| 2007 |-2008-|
Fig. 4. The mean % shoots damaged by leaf miners in the farmer’s plot and the IPM
plot at Binh Phuoc province, Vietnam.

0
5
10
15
20
25
30
22
Dec
23

Jan
31
Jan
7
Feb
23
Feb
7
Mar
23
Mar
1
Apr
7
Apr
23
Apr
7
May
23
May
7
Jun
23
Jun
7 Jul 24
Dec
4
Jan
12

Jan
% shoots with aphids
Farmer
IPM

|-06-| 2007 | 2008 |
Fig. 5. The mean % shoots with aphids in the farmer’s plot and the IPM plot at Binh
Phuoc province, Vietnam.

During the period of pre-flowering flush to nut development (November to March),
the damage level of cashew flushing shoots, flowers or young nuts by tea mosquito
0
1
2
3
4
5
22
Dec
23
Jan
31
Jan
7
Feb
23
Feb
7
Mar
23

Mar
1
Apr
7
Apr
23
Apr
7
May
23
May
7
Jun
23
Jun
7
Jul
24
Dec
4
Jan
12
Jan
% shoots damaged by lea
f
miners
Farmer
IPM

12

bugs, shoot borers, leaf miners, aphids and leaf rollers was similar between the
farmer’s plot and the IPM plot (P > 0.05; Figs 2-5; Table 2). However, the average
level of developmental nuts damaged by the fruit-nut borer was lower in the IPM plot
than in the farmer’s plot (P = 0.018; Table 2)

Table 2. The mean % shoots damaged by insect pests in the farmer’s plot and the IPM
plot of the demonstration orchard at Binh Phuoc province, Vietnam.
Friedman two–way ANOVA Pest name Treatment Mean % shoots
damaged /tree +
SD
Rank sum Statistic
Farmer 6.5 + 3.8 14.0 Tea mosquito
bugs
IPM 6.7 +
3.2 16.0
X
r
2
= 0.400; df =
1; P = 0.527
Farmer 8.3 + 7.0 14.0 Shoot borers
IPM 7.9 +
5.1 16.0
X
r
2
= 0.400; df =
1; P = 0.527
Farmer 1.8 + 1.6 15.5 The leaf miner
IPM 1.8 +

1.5 14.5
X
r
2
= 0.111; df =
1; P = 0.739
Farmer 11.5 + 11.9 14.5 Aphids
IPM 12.4 +
11.8 15.5
X
r
2
= 0.111; df =
1; P = 0.739
Farmer 0.11 + 0.69 57608.0 The fruit-nut
borer*
IPM 0.01 +
0.15 56395.0
U = 29405.0; df
= 1; P = 0.018
Farmer 0.4 + 1.2 56575.5 Leaf rollers*
IPM 0.7 +
3.4 57427.5
U = 28372.5; df
= 1; P = 0.933
*, Mann-Whitney U test is used.

During the cashew dormant or leaf flush period (April to July), the damage on
flushing shoots by tea mosquito bugs, shoot borers and leaf miners was significantly
lower in the IPM plot than in the farmer’s plot (Figs 2-4; Table 3). However, the

average level of shoots with aphids was more in the IPM plot than in the farmer’s plot
(Fig 5; Table 3).

Table 3. The mean % shoots damaged by insect pests in the farmer’s plot and the IPM
plot during the tree dormancy or leaf flush period at Binh Phuoc province, Vietnam.
Friedman two–way ANOVA
Pest name Treatment Mean % shoots
damaged /tree +
SD
Rank sum Statistic
Farmer 6.5 + 11.2 16.0 Tea mosquito
bugs
IPM 2.4 +
4.3 8.0
X
r
2
= 8.000; df =
1; P = 0.005
Farmer 5.0 + 2.0 16.0 Shoot borers
IPM 2.4 +
0.9 8.0
X
r
2
= 8.000; df =
1; P = 0.005
Farmer 1.2 + 1.0 15.0 The leaf miner
IPM 0.5 +
0.3 9.0

X
r
2
= 4.500; df =
1; P = 0.034
Farmer 9.0 + 5.9 8.0 Aphids
IPM 13.3 +
9.6 16.0
X
r
2
= 8.000; df =
1; P = 0.005

In 2007, we missed the opportunity to assess the number of nuts on tree
canopies before harvest. However, after the harvest, the orchard owner told us that the
nuts produced were cleaner and shinier in the IPM plot than in the farmer’s plot.
In 2008, the assessment of the number of nuts on tree canopies was done one
week before harvest, and it showed that the number of nuts per tree was significantly

13
higher in the farmer’s plot than in the IPM plot (Table 4). Based on regular
monitoring, we found that weaver ant populations in the IPM plot were very low
(from 48% in December 2007 to 28% in January 2008; Fig. 1), and the trees with low
numbers of ants were heavily damaged by tea mosquito bugs and shoot borers during
the flowering and fruiting time. However, there were 20 trees which had reasonable
numbers of weaver ants (the ant abundance was > 35%), and these were much less
damaged by these pests. When comparing the 20 trees in the IPM plot with the 70
trees in the farmer’s plot, there was no significant difference in the numbers of nuts
per tree (Table 5).

Table 4. The average number of cashew nuts per half canopy in the farmer’s plot and
the IPM plot of the demonstration orchard at Binh Phouc province, Vietnam.
Plot (Treatment) Mean number of nuts
/tree +
SD
Number of
trees
Rank sum
Farmer (use insecticides) 558.3 + 380.3 70 5482.5
IPM (use weaver ants only) 431.5 + 336.3 70 4387.5

Mann-Whitney U test

U = 2997.5; df = 1; P = 0.022

Table 5. The average number of cashew nuts per half canopy in the farmer’s plot and
the IPM plot of the demonstration orchard at Binh Phouc province, Vietnam.
Plot (Treatment) Mean number of nuts
/tree +
SD
Number of
trees
Rank sum
Farmer (use insecticides) 558.3 + 380.3 70 3200
IPM (use weaver ants only) 526.9 + 332.3 20 894

Mann-Whitney U test

U = 7150500; df = 1; P = 0.880

Hong Loc Centre orchard

Fig. 6 shows that weaver ant abundance was over 60%, and the ant populations were
stable during the period of cashew flowering and fruiting (December 2007 – February
2008).


Fig. 6. Average abundance
of weaver ants in the IPM plot
at Hong Loc Centre, Dong Nai
province, Vietnam.



The average number of flushing shoots was more in the IPM plot than in the
farmer’s plot, but they were not statistically different (Table 6).

0
20
40
60
80
100
120
22 Dec 07 5 Jan 08 19 Jan 08 2 Feb 08 16 Feb 08
% weaverv ant abundance

14
Table 6. The average number of shoots per tree in the farmer’s plot and the IPM plot

of the demonstration orchard at Hong Loc Centre, Dong Nai province, Vietnam.
Plot (Treatment) Mean number of shoots
/tree +
SD
Rank sum
Farmer (use insecticides) 29.9 + 10.2 6
IPM (use weaver ants only) 36.4 + 15.4 9

Friedman two–way ANOVA

X
r
2
= 3.000; df = 1; P = 0.083

Based on regular monitoring, the main insect pests in this orchard are tea
mosquito bugs, leaf rollers, leaf miners, aphids and branch borers. The minor pests are
shoot borers and mealy bugs. The mean damage level on cashew flowers and young
nuts by each of these pests was similar between the farmer’s plot and the IPM plot
(Table 7). In a field observation, a branch borer adult was chased away by weaver ants
from a mature shoot (branch borer preferred oviposition location).

Table 7. The mean % shoots damaged by insect pests in the farmer’s plot and the IPM
plot of the demonstration orchard at Hong Loc Centre, Dong Nai province, Vietnam.
Friedman two–way ANOVA
Pest name Treatment Mean % shoots
damaged /tree +
SD
Rank sum Statistic
Farmer 1.25 + 2.64 6 Tea mosquito

bugs
IPM 2.49 +
3.40 9
X
r
2
= 3.000; df
= 1; P = 0.083
Farmer 0.64 + 1.79 5273.5 The shoot
borer*
IPM 0.26 +
1.06 5166.5
U = 2788.5; df
= 1; P = 0.135
Farmer 3.13 + 3.85 7 Leaf rollers
IPM 3.42 +
3.93 8
X
r
2
= 0.333; df
= 1; P = 0.564
Farmer 2.75 + 3.83 7 The leaf miner
IPM 2.65 +
4.49 5
X
r
2
= 2.000; df
= 1; P = 0.157

Farmer 0.69 + 2.03 4780.5 Mealy bugs*
IPM 1.96 +
5.49 5659.5
U = 2295.5; df
= 1; P = 0.088
Farmer 0.75 + 2.47 6.5 Aphids
IPM 1.96 +
4.33 8.5
X
r
2
= 1.000; df
= 1; P = 0.317
*, Mann-Whitney U test is used.

The average number of nuts per tree were similar between the farmer’s plot
and the IPM plot (P = 0.206; Table 8). The nuts were cleaner and shinier in the IPM
plot than in the farmer’s plot.

Table 8. The number of cashew nuts per half canopy in the farmer’s plot and the IPM
plot of the demonstration orchard at Hong Loc Centre, Dong Nai, Vietnam.
Plot (Treatment) Mean number of nuts /tree
+
SD
Rank sum
Farmer (use insecticides) 179.2 + 104.7 17
IPM (use weaver ants only) 177.9 + 143.9 13

Friedman two–way ANOVA

Xr2 = 1.600; df = 1; P = 0.206

Mr Bi’s orchard

15

The regular pest monitoring showed that the common insect pests in this orchard were
tea mosquito bugs, shoot borers, leaf miners, leaf rollers, thrips, aphids, fruit-nut
borers and branch borers. The general farming practice of this orchard was very well
managed; farmer’s and IPM plots were free from any weeds (two applications of
herbicide spray and one time manual weeding each year) and 6 applications of
insecticide sprays per year were applied in the farmer’s plot during the pre-flowering
time and nut developmental period (later October – early March). The results obtained
from November 2006 to July 2007 are summarised below:
(1) The average abundance of weaver ants was < 40% in the IPM plot, which was
low,
(2) during the period from pre-flowering flush to nut development (December –
March), the average damage level for each of the main pests was greater in the
IPM plot than in the farmer’s plot; and
(3) the yield and nut quality was significantly lower in the IPM plot than in the
farmer’s plot.

As of late January 2008, regular weaver ant and insect pest monitoring, together with
field observations, showed that:
(1) Weaver ant colonies were, in general, managed well, and the average
abundance of the ants was > 50%,
(2) Although trees did not receive any leaf fertilizer sprays, weaver ants were still
abundant on tree trunks and the main branches, and they were rarely seen
foraging on aphid-free foliar and floral shoots as observed last year, which
resulted in over 50% of flushing shoots, flowers and developing nuts being

damaged by tea mosquito bugs, shoot borers and leaf rollers and fruit-nut
borers in the IPM plot,
(3) Slight taps on the tree bases resulted in abnormal aggressive behaviour by the
ants,
(4) Competition between weaver ants and ghost ants for food was observed. Ghost
ants were originally thought to be too small (only 1.1 mm) to be effective
competitors against weaver ants. In fact, we found that on cashew trees, these
ants only feed on extra floral nectar secreted by flushing shoots, flower
panicles and young nuts. They nest underground in complicated network
systems with huge numbers of individuals. They foraged actively and
collectively in very large numbers on cashew tender terminals. Cashew extra
floral nectar is a preferred food for weaver ants. In an observation, we
observed that when a weaver ant fed on nectar of a tender flower shoot on
which there were some ghost ants, it was attacked by several ghost ants, which
grasped the legs, antenna and mandibles. Two minutes later, two legs and two
antenna of the weaver ant were cut off, resulting in the death of the ant. Ghost
ants did not eat or take the dead weaver ant back to their nest, but they let it
drop down on the orchard floor. Following this clue, we found quite a few
dead weaver ants on the orchard floor. During such encounters, some weaver
ants acted quickly and escaped from ghost ant attack, but they were scared off
flushing shoots, flowers and young nuts, resulting in the large numbers of
weaver ants walking on tree trunks and branches in an aggressive posture.
(5)
We also found that numbers of ghost ants went up and down, travelling over
the tree trunk and branches where a lot of weaver ants were present, but they
did not actively attack the weaver ants.

16

Having determined this competition, we immediately took two actions; (1) to spray

engine oil around each tree base to stop ghost ants coming up from the ground, and
(2) to bait the ghost ants with fresh fish meat mixed with Regent
®
. The engine oil was
only effective for 12 hours. The fish bait was very attractive to ghost ants, and their
populations were greatly reduced in the first 3 - 4 days. At the same time, however,
the bait also attracted a lot of flies, and these flies died in a couple of hours and fell on
the orchard floor or on the tree leaves. Due to great reduction of ghost ants, weaver
ants started to actively forage on flower terminals and tender leaf shoots. We found
that a lot of dead flies were carried by weaver ants to their nests. As a result, the
weaver ant populations were greatly reduced two days later, and a lot of weaver ants
were found dead in their nests because of the poison from dead flies. This led to a
great reduction of weaver ant abundance from 65% to below 15% within a period of 2
weeks. Because of this, the average damage level of flushing terminals by each of the
main pests was much higher in the IPM plot than in the farmer’s plot, and the yield
and nut quality in 2008 were much lower in the IPM plot than in the farmer’s plot.

Field survey


Mr Quang’s orchard

Three surveys conducted in this orchards in 2006 and 2007 showed that shoot borers,
tea mosquito bugs, leaf rollers and fruit-nut borer are the common pests (Table 9).
The mean damage level by the common pests was between 0.8% and 8.6% on trees
with weaver ants, but between 3.4% and 36.0% on trees without the ants (Table 9).
This damage level for each of the pests at the different survey times was highly
significant (Table 9).

17

Table 9. The mean % flushing terminals or developmental nuts damaged by the main
insect pests in trees with weaver ants (WA) and trees without the ants at Mr Thiem
Truong Quang’s orchard, Dong Xoai, Binh Phuoc province, Vietnam.
Mann-Whitney U test
Survey
date
Pest
name
Trees
with
No. of
trees
Mean %
damage /tree
+
SD
Rank sum Statistic
No WA 29 36.0 + 20.3 890.5 Shoot
borers
WA 17 4.6 +
8.9 190.5
U = 455.5; df =
1; P < 0.001
No WA 29 8.0 + 7.6 813.0
July
2006
Mosquito
bugs
WA 17 2.2 +
3.7 268.0

U = 378.0; df =
1; P = 0.002
No WA 12 6.5 + 7.0 358.5 Shoot
borers
WA 33 2.3 +
3.4 676.5
U = 280.5; df =
1; P = 0.025
No WA 12 3.4 + 4.2 375.5
Dec.
2006
Mosquito
bugs
WA 33 0.3 +
1.1 659.5
U = 297.5; df =
1; P = 0.001
No WA 19 18.2 + 15.7 532.0 Shoot
borers
WA 25 8.6 +
12.0 458.0
U = 342.0; df =
1; P = 0.013
No WA 19 17.0 + 21.6 522.0 Mosquito
bugs
WA 25 2.5 +
6.8 468.0
U = 332.0; df =
1; P = 0.008
No WA 19 16.5 + 18.6 527.0 Leaf

rollers
WA 25 5.3 +
8.7 463.0
U = 337.0; df =
1; P = 0.014
No WA 9 16.4 + 20.6 145.0
April
2007
Fruit-nut
borer
WA 15 0.8 +
2.6 155.0
U = 100.0; df =
1; P = 0.016

Mr Be’s orchard

The common pests in this orchard were shoot borers, tea mosquito bugs and coreid
bugs. The mean damage level of flushing shoots for each of these pests was much
lower on trees with weaver ants (< 5%) than on trees without weaver ants or with
other species of ants (> 19%; Table 10).

Table 10. The mean % flushing shoots damaged by the main insect pests in trees with
and without weaver ants at Mr Be’s orchard, Dong Nai province, Vietnam.
Mann-Whitney U test
Survey
date
Pest
name
Trees

with
1

No.
of
trees
Mean %
damage /tree
+
SD
Rank sum Statistic
No WA 10 26.2 + 14.0 134.0 Shoot
borers
WA 8 0.9 +
1.4 37.0
U = 79.0; df =
1; P < 0.001
No WA 10 24.3 + 17.2 129.0
July
2006
Mosquito
bugs
WA 8 1.4 +
2.6 42.0
U = 74.0; df =
1; P = 0.002
WA 15 4.3 + 4.0 154.0
Ghost ant 10 25.7 + 13.2 332.0
No ant 13 23.3 + 10.0 410.0
Cremat 4 19.6 + 8.3 107.0

Aug.
2007
The
coreid
bug
2

Black ant 8 26.0 +
13.2 272.0
H = 24.175; df
= 4; P < 0.001

1
, WA = weaver ants; Cremat = Crematogaster sp.
2
, Kruskal-Wallis test was used.

Mr Sau’s orchard


18
The average damage level on flushing shoots by shoot borers and tea mosquito bugs
was 2.4% and 1.4%, respectively, on trees with weaver ants, and these damage levels
were significantly lower than those on trees without weaver ants (Table 11).

Table 11. The mean % flushing shoots damaged by the main insect pests in trees with
and without weaver ants at Mr Sau’s orchard, Dong Nai province, Vietnam.
Mann-Whitney U test
Survey
date

Pest
name
Trees
with
1

No.
of
trees
Mean %
damage /tree
+
SD
Rank sum Statistic
No WA 45 8.3 + 8.2 1321.0 Shoot
borers
WA 8 2.4 +
3.8 110.0
U = 286.0; df =
1; P = 0.008
No WA 45 5.5 + 4.7 1337.0
July
2006
Mosquito
bugs
WA 8 1.4 +
2.8 94.0
U = 302.0; df =
1; P = 0.002

Field observations and laboratory rearing


The Branch borer

According to our field observations, the branch borer lived in cashew orchards
throughout the year. Eggs were laid singly predominantly at the tip of mature leaf
shoots. After hatching, a larva started to bore into the shoot, and fed on materials
inside. With feeding progress, the larva bore downward to the thick twig and branch,
resulting in a hollow tunnel in the centre of the branch. At a regular distance, the larva
made a hole to the branch surface to get rid of the waste from the tunnel (Fig. 7). The
branch borer had only one generation per year. Adults lived 20 +
5 days, and they
usually emerged between mid March and early June, and they were active in early
evening. The egg laying lasted 25 +
5 days, which took place from April to July. The
initial damage symptom by young larvae was dark brown excreta sticking on the skin
of a mature shoot (about 10 – 15 cm long from the tip; Fig 7), and these damaged
shoots were mostly and easily seen on trees between July and August. The
development of the second instar larvae to a mature stage (which stops eating) was
270 +
10 days, which was from late April to January the following year. Pupation
took place in the branch and lasted 45 +
5 days, which was from February to March.
The life cycle of the borer in a year is summarised in Table 12.

Fig. 7. The excreta holes (7 holes circled in red)
of a branch borer larva and the initial damage
symptom.

A magnified hole
after removal of
excreta






19
Table 12. The life cycle of the branch borer in southern Vietnam.
Stage Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Adult | |
Egg | |
Larvae | |
Pupae | |

In a field survey at Mr Sau’s orchard in Dong Nai provinve, every tree was
affected by the branch borer, but the damage symptoms were lower on trees with
abundant weaver ants than trees without the ants. In our evening observations, weaver
ants chased a female branch borer from fresh shoots to a dry flower shoot.

The stem-root borer

Our field observations showed that the stem-root borer lived in cashew orchards
throughout the year, and it had only one generation per year. The adults emerged
between mid January and May, and they were active during evening for mating and
ovipositing. Adults prefer to oviposit
• on old trees (> 5 years old) that have thick bark with more cracks,
• on wounded trees either caused by stem borers during the previous season or

by physical actions like pruning,
• in the cracks between the conjunctions of the trunk and the main branches and
wounded places, and the most eggs were found within one meter from the
ground.
Eggs are elongate in light yellow, and 4.1 mm long and 1.4 mm broad. After hatching,
the larvae bore through the inner bark and feed on sapwood, resulting in the small
patch of exudation of a reddish brown liquid with some fine frass on the tree trunk
between the tree base and up to one meter height (Fig 8). The newly hatched larva
was about 3.5 mm long, which was easily removed (Fig 8), and grew up to about 58
mm long. Later in the year (November to December), mature larvae bored into the
heartwood at the tree base, and each larva excavated a chamber in which the
calcareous pupal cell was formed from the excretions of the larva. Pupation took place
late in the year. The pupa is about 35 mm long, creamy-white, robust and protected by
the grey coloured cocoon. The adult usually remains in the cocoon until January. The
life cycle of the stem-root borer is summarised in Table 13.




Fig. 8. The initial damage symptoms of the stem-
root borer on tree trunk.

20

Trees over 10 years old are more infested than young trees. In our field observations,
a pupa in cocoon was parasited by a fungus.

Table 13. The life cycle of the stem-root borer in southern Vietnam.
Stage Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Adult | |

Egg | |
Larvae | |
Pupae | |

Selection of soft chemicals to control thrips

Two small scale experiments showed that Abamectine was more effective in
controlling chilli thrips than Applaud and D.C. Tron oils, and it did not show any
effect on weaver ants two weeks after spraying.

Natural enemies of aphids and mealy bugs

In our rearing trials, a total of 12 species of natural enemies of aphids and 9 species of
natural enemies of mealy bugs were determined (Table 14). These natural enemies
were more frequently seen in the IPM plot than in the farmer’s plot at Hong Loc
Centre orchard.

Table 14. The number of species of natural enemy reared from aphids and mealy
bugs, Hong Loc Centre, Dong Nai province, Vietnam.
Aphids Mealy bugs
Name of natural
enemy
No. of species Name of natural
enemy
No. of species
Ladybirds 4 Ladybirds 2
Hoverflies 4 Midge 1
Lacewings 2 Butterfly 1
Parasitic wasp 1 Parasitic wasp 5
Dipteran fly 1

21
Discussion

In cashew orchards, the common insect pests that damage flushing terminals, cashew
apples and nuts were tea mosquito bugs, shoot borers, coreid bugs, apple-nut borers,
leaf rollers, leaf miners, aphids and mealy bugs (Tables 2, 3, 7, 9, 10 and 11; Figs 2 –
5). The major insect pests during the flower and fruiting periods were tea mosquito
bugs, shoot borers, leaf rollers and apple-nut borers. The common insect pests that fed
on inside branches and stems were branch borers and stem-root borers.

Weaver ants are effective in controlling a range of common insect pests. From field
experiments in our demonstration orchards, weaver ants were similar to insecticides
for controlling tea mosquito bugs, shoot borers, the apple-nut borer, leaf rollers, leaf
miners and aphids during the flowering and fruiting periods (Tables 2 and 7; Figs 2 –
5). In field surveys, at different types of orchards, flushing terminals or nuts were
significantly less damaged by tea mosquito bugs, shoot borers, leaf rollers, the apple-
nut borer and coreid bugs on trees with weaver ants than on trees without the ants
(Tables 9 – 11). The branch borer was one of the main pests in the demonstration
orchards, its damage in the two plots was not assessed. This is because our monitoring
was based on fresh damage on flushing terminals, but this pest damaged cashew trees
by boring into mature terminals. However, a field survey at Mr Sau’s orchard
suggested that the damage symptoms were lower on trees with abundant weaver ants
than trees without the ants. Also, in our evening observations, weaver ants were
observed chasing a female branch borer from mature shoots to a dry flower shoot.
This suggests that weaver ants can catch or deter some branch borer adults from trees.
Based on larvae damage behaviour and adult oviposition, to control this pest, some
other methods will have to be used apart from weaver ants (see below).

Weaver ants create higher quality nuts and similar yield compared to insecticides. Due
to the control efficiency of the insect pests by weaver ants, trees protected by the ants
produced higher or similar numbers of flushing terminals than trees protected by
insecticides (Tables 1 and 6). With abundant weaver ants, the nut yield in the IPM
plot was similar to the farmer’s plot (Tables 5 and 8), but the nut quality was higher in
the IPM plots than in the farmer’s plots. The nuts were cleaner and shinier in the IPM
plot than in the farmer’s plot. This is because in the nut developmental stage, young
nuts continuously secrete extrafloral nectar, particularly on the inside curve of nuts,
which is a good food source for weaver ants. With insecticide spray, the nectar is
continuously deposited on the inside curve of nuts, resulting in a black residue on the
nuts due to fungus invasion. The nuts in the farmer’s plots have sooty mould, and
look dull. However, this nectar is continuously taken away by weaver ants, and thus,
trees in the IPM plot produce clean and shining nuts. Although we did not measure
insecticide residue of nuts, the residue level should be much lower in nuts produced in
IPM plots than those in farmer’s plots because no insecticides were used in the IPM
plots.

Keeping weaver ant populations high and stable is a key for success in controlling
insect pests and achieving high yield and nut quality. In this study, two major factors
responsible for the reduction of weaver ant populations were fights between weaver
ant colonies and competition between weaver ants and other ant species. Due to
boundary fighting between weaver ant colonies, the ant abundance was greatly
reduced from 80% in July 2007 to 28% in January 2008 at Mr Ty’s orchard (Fig 1),

22
resulting in the significant reduction of yield in the IPM plot (Table 4). However, in
the IPM plot, there were 20 trees on which the ant abundance was > 35%, and the
yield from these trees was similar to that in the farmer’s plot (Table 5).
At Hong Loc Centre orchard, the ant populations were high (between 60% and 80%)
and stable (Fig 6), which resulted in a yield similar to that produced by the farmer’s

plot (Table 8). In contrast, at Mr Bi’s orchard in 2007, because of weaver ant
boundary fights, the abundance of weaver ants was < 40% in the IPM plot, which was
low. The average damage level for each of the main pests was greater in the IPM plot
than in the farmer’s plot, resulting in the significantly lower yield and nut quality
compared to the farmer’s plot. Also, in 2008 at the same orchard, due to the side-
effect of ghost ant baiting, weaver ant abundance was greatly reduced from 65% in
early January to below 15% late January. As a result, the main insect pest damage was
much higher and the yield was much lower in the IPM plot than in the farmer’s plot.

A complete failure of insect pest control by weaver ants at Mr Bi’s orchard was due to
the boundary fighting between weaver ant colonies and the strong competition
between weaver ants and ghost ants in 2006 – 2007, and the strong competition
between weaver ants and ghost ants in 2007 – 2008. With detailed instruction in the
cashew IPM curriculum together with field practice, the boundary fighting between
weaver ant colonies can be easily resolved. Having followed this instruction, the
experimentalist successfully managed weaver ant colonies in the block 2 of Mr Bi’s
orchard in 2007 - 2008. For the competition between weaver ants and ghost ants, we
found that grass and weeds in orchards play an important role. At Mr Bi’s orchard, the
orchard owner kept this orchard cleared of any weeds, especially during the period of
flowering and nut setting. Therefore, apart from cashew trees, no other plants could be
used by ghost ants. In order to survive, they were forced to forage on cashew trees,
resulting in the serious fighting with weaver ants for food. However, at Hong Loc
Centre orchard, which is 25 km away from Mr Bi’s orchard, ghost ants were
commonly seen in the IPM plot, but no such competition was observed. Weaver ants
foraged on flower panicles and young nuts actively and peacefully. Ghost ants were
hardly seen on trees with abundant weaver ants, but actively foraged on weeds, grass
and cashew coppice, which were kept at about 30 – 40 cm high, between tree rows.
This suggested that weeds provided alternative food source for ghost ants. Therefore,
to use weaver ants in cashew orchards, especially in the areas with abundant ghost
ants, weeds should be kept at around 30 – 40 cm height, and they should be managed

by mechanically cutting, but not by herbicides.

Minor pests like mealy bugs and aphids are unlikely to become the main pests after
weaver ants are used in cashew orchards. It is well known that weaver ants have a
mutual relationship with some homopteran pests, such as mealy bugs, aphids and
scales. This is because scales, mealy bugs and aphids contain sugar in their excreta,
and this is desirable food for weaver ants. To get a rich sugar solution, weaver ants
farm these insects. Therefore, whether mealy bugs and aphids, that are currently
considered minor pests in cashew orchards, will become major ones after the main
pests are controlled by weaver ants is a major concern. Our regular monitoring
demonstrated that the average level of flushing terminals with aphids or mealy bugs
was similar between the IPM plot and the farmer’s plot at Mr Ty’s orchard and the
Hong Loc Centre orchard during the period of flowering and fruiting (Tables 2 and 7).
In the field observations and lab rearing, at least 20 species of predators and
parasitoids were found to feed on or parasitise aphids and mealy bugs (Table 14). This

23
demonstrates that when weaver ants were present, the minor pest insects of mealy
bugs and aphids were present, and predators and parasitoids of these pests were also
present, resulting in very little damage to the cashew crop. It is worthwhile
mentioning that during the wet season (cashew tree dormancy or leaf flush), the mean
level of flushing shoots with aphids was higher in the IPM plot than in the farmer’s
plot (Table 3). This is because at this time of year, trees had very low numbers of
flushing shoots which were fully patrolled by weaver ants, especially shoots with
aphids. Therefore, the natural enemy activity was reduced. On the other hand, during
the wet season, aphids cannot do much damage to trees and should not affect cashew
yield the following year. Instead, they provide food for weaver ants, keeping the ant
population stable.

The control strategies for thrips, branch borers and stem-root borers can fit the cashew

IPM program well. The key component of the cashew IPM program is weaver ants.
This ant is very susceptible to many kinds of toxic insecticides, such as trichlorfon,
dimethoate, carbaryl, etc. Therefore, when weaver ants are used in cashew orchards,
no toxic insecticides can be use. Although weaver ants can manage a lot of insect
pests, they have limited ability to control thrips on developing apples and nuts and the
larvae of branch borers and stem-root borers. Hence, the methods developed for
controlling these pests should not be detrimental to weaver ants.
To control thrips, abamectine seemed to be effective, and it was not harmful to
weaver ants in the laboratory experiments. In our plan, abamectine will be tested in
field experiments in late 2008 before it can be recommended to cashew farmers.
For branch borer control, the initial damage symptoms caused by young larvae
is easy to recognize on mature shoots (Fig 7) between July and August, which is the
cashew tree dormant period and is also a good time for tree pruning. Therefore, July is
a good time to start the monitoring based on the damage symptoms and to control the
pest. For young trees (2-3 years old) that are initially infested by the borer, shoots
with the damage symptoms (Fig 7) should be cut, and this work can be combined with
general tree pruning practice. The cut material should be taken out of the orchards for
making compost or burying underground. For production trees that are repeatedly
infested by branch borers, apart from the removal of the shoots with initial damage
symptoms, the branches that are heavily damaged should be removed. For branches
that clearly show dark brown larvae excreta at regular intervals along the branch (Fig
7), the lowest larvae excreta should be located and removed, and BT or a contact
killing insecticide solution should be injected into the tunnel with a syringe, and then
the hole should be plugged with a cotton swab containing the same material. Such
methods were used in Mr Bi’s orchard.
July is also a good time for the stem-root borer’s control. Based on the
oviposition behaviour of adults, the initial damage symptoms (Fig 8) can be easily
identified on the tree trunk between the base and one meter above the ground, and
young larvae can be easily found and killed with a knife (Fig 8). This is particularly
effective protection for young trees from stem-root borers. For orchards with old trees

(> 10 years old), due to the fact that stem-root borer adults prefer to oviposit on
infested trees, the heavily-infested trees or major branches should be cut down and
removed out of the orchards to reduce ovipisition cue. Once the wood has dried out
sufficiently, it should be burned to kill all the remaining larvae and eggs. Painting tree
trunks up to one meter high from the ground with whitewash materials should also
reduce adult oviposition. It is evident that trees with severe or moderate infestation
may not be saved, and so, the control at early infestation stage is critical. Trees

24
repeatedly damaged for 2-3 years should be injected with BT or a contact killing
insecticide solution into the tunnel with a syringe to kill the larvae after removal of the
bark with excretion materials. The hole should be plugged with a cotton swab soaked
in a mixture of carbon disulfide, naphthalene and creosote. Finally, the wound should
be sealed with clay or cattle dung.
In summary, the control of branch borers and stem-root borers involves the
monitoring, the removal of young larvae and the chemical injection. This strategy
should have no negative effect on weaver ants so that it can be integrated into the
cashew IPM program.

Based on the results and general farming practice from the IPM plots, a cashew IPM
program which is suitable for cashew growing conditions in Vietnam has been
developed and briefly summarised in Appendix 1.


25
Appendix 1

The Integrated Pest Management Program for
Cashew Growers in Vietnam

Based on characteristics of cashew tree development in Vietnam, a year is divided
into four periods:
(1) dormancy or leaf flush, which is the wet season (June – September);
(2) pre-flowering flush, which is the beginning of the dry season (September –
mid October);
(3) flowering, nut setting and fruiting, which is the dry season (November – Early
February); and
(4) harvest and post harvest, which is the late dry season and beginning of the wet
season (February - April).

For each period, Table 1 lists a number of farming activities together with Chapter
references of the Cashew Manual in brackets. This is for farmers to understand when
to do what, and how to do it. An empty box is provided at the beginning of each
farming activity (Table 1). Put a tick in each empty box when you complete an
activity. This is for mature orchards. For either young or old orchards, this program
can be modified accordingly.

Table 1. Farming activities in each cashew phenological period for cashew
growers in Vietnam.

Cashew
phenology
Month IPM activities
Dormancy or
leaf flush (the
wet season)
June -
September
□ Monitoring and managing weaver ant colonies
for pest control (see 7.2.1.5 for details);

□ Controlling stem and branch borers (4.9, 4.10);
□ Pruning (3.5.1.1);
□ Fertilizing (3.5.1.2);
□
Weeding (3.5.1.3);
□
Compost making or mulching (3.3.2 and 3.5.1.3);

□ Intercropping (
3.5.1.3)
;
□ Transplanting young trees, if needed (3.5.1.5); and
□

Propagation, if needed.
Pre-flowering
flush
(beginning of
the dry season)
September
–mid
October
□ Managing weaver ants for pest control;
□ Monitoring the main insect pests and diseases
(Part 4 and Part 5);
□ Fertilizing and/or Micro-nutrient application; and
□ Bush fire prevention (3.5.2).

Flowering, nut

setting and
fruiting (the
November
– January
□ Managing weaver ants for pest control;
□ Monitoring the main insect pests and diseases;