Washington Tree Fruit Research Commission

Research Reports

Lygus Bug and Thrips Ecology in Washington State Stonefruit Orchards Final Report 2001-2003 (2004)

FINAL PROJECT REPORT
WTFRC Project #
YEAR 0/0
Organization Project #
Title:Lygus Bug and Thrips Ecology in Washington State Stonefruit Orchards Final Report 2001-2003
PI:D.B. Walsh
Organization:Agrichem/Environ. Educ. Spec, WSU-Prosser
 PDF version of report

Co-PIs

M. Bush, Coop. Ext. Agent, Yakima, County

R. Wight, Field Research Dir., IR4 Project, WSU-Prosser

 

Objectives

Objectives:  Lygus

1.        Compare Lygus sampling techniques for Lygus on the orchard floor.
2.        Establish damage thresholds for Lygus on stone fruits in the Yakima Valley and Columbia Basin.
3.        Attempt to fine tune the UC Lygus phenology model to fit eastern Washington Lygus populations.
4.        Develop riparian habitats that will not serve as a point source for Lygus infestations.
5.        (New for 2003) Evaluate the role of cover crop and orchard floor management on pest and beneficial abundance.
Objectives:  Thrips
1.       Screen candidate compounds for their ability to suppress thrips populations that are infesting stone fruit orchards. Candidate compounds include spinosyns, insect growth regulators, synthetic pyrethroids, and neonicotinyls.
2         Evaluate several sampling techniques to determine thrips abundance.
3         Develop a relationship between thrips feeding and fruit injury.
4         (New for 2003) Evaluate orchard floor insecticide/ herbicide treatments on thrips abundance

Significant findings

SIGNIFICANT FINDINGS- LYGUS
Orchard Sampling. In 2001, 2002 and 2003 several Lygus abundance sampling techniques were investigated. Techniques tested included sweep net samples of the orchard floor, beat sampling of trees, and colored sticky cards. Sweep net sampling of the orchard floor was the only technique tested that caught substantial numbers of Lygus. The use of colored sticky cards in measuring abundance of Lygus was not efficient at capturing Lygus.
Phenology Model. A phenology model currently used in California proved effective at predicting the first generation hatch of Lygus in late-May in Eastern Washington and the subsequent peak hatch event in mid-July. However, the model lost predictive accuracy as the season progressed and would provide little predictive value for when adult migration into orchards might occur in April or May.
Biological Control. A parasite Peristenus spp. attacks the nymph stages of Lygus and keeps individuals from reaching sexual maturity by emerging in the late instar nymph or early adult stage. 
Extensive surveys conducted by Walsh in 2002 and 2003 determined the presence of Lygus parasitism by Persitenus spp. in several important fruit production regions in Washington State. However, the results of the survey were disappointing in that levels of parasitism were low or not detected in several important stone fruit growing areas

SIGNIFICANT FINDINGS-THRIPS
Flight monitoring. Thrips flight activities were monitored in stonefruit orchards with yellow and blue sticky card traps in 2001 and 2002. Blue cards are proving to be significantly (P<0.01) more effective then yellow cards at catching western flower in stone fruit orchards. We have observed a definite orchard edge effect with the orchard floors bordering riparian buffers having significantly (p<0.01) greater populations of thrips then the orchard floor 92 meters inside the orchard. There were also significant (P<0.05) differences in abundance of thrips as measured by blue sticky card with the orchard floor having a greater abundance of thrips then cards placed in the canopy on both the orchard edge and 92 meters in.
Cover Crops. Replicated plots of 14 cover crop blends were established on the Roza unit at WSU IAREC in May 2003. We have documented significant differences among cover crop blends in their potential to build populations of western flower thrips.
Orchard floor treatments. Post-harvest orchard floor insecticide and herbicide treatments were inconclusive in their effect on the distribution of thrips population within the tree canopy.

SIGNIFICANT FINDINGS-RIPARIAN BUFFERS. We have developed considerable evidence that riparian areas are confirmed sources of hemipteran and thrips pests. These include both stinkbugs, (Jay Brunner, personal com), Lygus bugs and flower thrips (Walsh unpl. data). We have also documented an increase in the populations of several beneficial arthropods in riparian buffers. We have also identified host plant on which Lygus can complete development and feral plants around which the abundance of flower thrips are greater then plants that appear to be non-hosts for flower thrips

Methods

Methods:  - Lygus
1.       Lygus sampling. We compared several sampling techniques to assess Lygus populations in the riparian sites and nearby orchard floors in early spring to assess when adults became active and to determine when the first generation egg hatch takes place. Sampling techniques tested included sweepnet, colored sticky cards, whole plant quadrants, and insect vacuums.
2.       Lygus damage thresholds. Sleeve cages were sewn in 2001 that covered 1 meter lengths of tree branch. Fruit was thinned so that constant ratios of Lygus to fruit can be maintained. Adult Lygus were introduced into the sleeve cages on apricot trees on May 21 at ratios of 0.8, 0.4, 0.2, 0.1, 0.067, 0.05 and 0 Lygus per fruit. Each cage treatment was replicated 4 times on apricot trees on May 21, 2001 and April 30, June 25, 2002. Cages were left on the trees for 2 weeks and when they were removed the branches
were treated with acephate. A damage assessment was taken just prior to commercial harvest.
Phenology Model. A phenology model currently used in California proved effective at predicting the first generation and subsequent hatch of Lygus in late-May in Eastern Washington and the subsequent peak hatch event in mid-July. This model has little predictive value for when adult migration into orchards might occur
in April or May.
Biological Control. A parasite Peristenus spp. attacks the nymph stages of Lygus and keeps individuals from reaching sexual maturity by emerging in the late instar nymph or early adult stage.  Extensive surveys conducted by Walsh in 2002 and 2003 determined the presence of Lygus parasitism by Persitenus spp. in several important fruit production regions in Washington State. However, the results of the survey were disappointing in that levels of parasitism were low or not detected in several important stone fruit growing areas.
Orchard floor cover crops. Replicated plots of 14 cover crop blends were established on the Roza unit at WSU IAREC in May 2003. Irrigation was applied by handline sprinklers and irrigation was applied to mimic recommended orchard management practices. Sweep net surveys were conducted every 2 weeks and the number of Lygus, thrips and spiders captured was quantified and calculated.

 

Methods- Thrips
1.   Insecticide efficacy. An insecticide efficacy trial was established in a nectarine orchard in the lower Yakima Valley to test the post fruit set efficacy of registered and candidate compounds on flower thrips. Registered compounds that will be screened include endosulfan, carzol, and spinosad. Candidate compounds tested include lamda-cyhalothrin, pyriproxifen, thiamethoxam, and novoluron. Insecticides were applied by hand wand at 100 gallons per acre to 6 one tree replicates. Shake samples were taken taken prior to and at timed intervals following insecticide application.
      Orchard floor insecticides and herbicides were applied post harvest to determine their effect on the distribution of thrips in the tree canopy.
2    Insecticide residual. A primary constraint for efficacy studies on thrips on tree fruits is inconsistency in pest distribution. Following insecticide application we caged 4 individual fruit per tree/replicate in the orchard. Into these cages we placed approximately 10 immature thrips. These individual treated fruit were collected several days prior to commercial harvest. The fruit was evaluated and graded for thrips damage.
3.       We have tested several techniques for evaluating thrips population abundance in stone fruits and other crops. Techniques tested have included several colors of sticky card traps, a beating sample, a water shake sample, and an alcohol shake sample. We will adapt these techniques to provide recommendations for sampling thrips abundance in stonefruit orchards.

Results and discussion

RESULTS/ DISCUSSION LYGUS-2001-2003
Lygus have an extensive host range of both native and exotic plants. In extensive field surveys conducted during summer of 2001, 2002, and 2003 we have observed a greater abundance of Lygus in riparian field sites directly adjacent to orchards with established stands of exotic flowering weedy plants then in sites comprised mainly of bunch grasses or native shrubbery. This research has enabled us to develop a list identifying which introduced and native plants are serving as alternate hosts for Lygus.

 

Lygus feeding has been likened to chemical injury. Lygus feeding damage in stonefruit orchards is a significant concern after fruit set Branch cage studies in 2001 and 2002 have helped quantify proportional Lygus abundance to fruit damage. Sleeve cages were sewn in 2001 that covered 1 meter lengths of tree branch. Fruit was thinned so that constant ratios of Lygus to fruit can be maintained. Adult Lygus were introduced into the sleeve cages on apricot trees on May 21 and April 30, June 25, 2002 at ratios of 0.8, 0.4, 0.2, 0.1, 0.067, 0.05 and 0 Lygus per fruit. Each cage treatment was replicated 4 times on apricot trees on each date. Cages were left on the trees for 2 weeks and when they were removed the branches were treated with acephate. A damage assessment was taken just prior to commercial harvest. Lygus damage was noted if necrotic feeding spots were present below
the fruit surface.

Lygus feeding injury results of regression analysis between the ratio of adult Lygus bugs per fruit to the percent of fruit observed to have sustained feeding damage.




Biolgical control.  A parasite attacking Lygus spp. was discovered in 1995 in Washington State and subsequent collections in Parma, Idaho in 1996 and 1997 showed that the parasite was present (Mayer unpublished data).  The parasite has been described as Peristenus howardi Shaw (Hymenoptera: Braconidae), a new species . Previously, Peristenus pallipes Curtis was reported from Idaho. However, recent taxonomic work on the genus indicates that these may have been misidentified.  Peristenus spp. attacks the nymph stages of Lygus and keeps individuals from reaching sexual maturity by emerging in the late instar nymph or early adult stage.

 

Collections made in 2000 (Mayer, unpublished data) did not document  the parasite’s presence beyond the Touchet, Washington and Parma, ID regions. Extensive surveys conducted by Walsh (AE News 2003) in 2002 and 2003 determined the presence of Lygus parasitism by Persitenus spp. in several important fruit production regions in Washington State. However, the results of the survey were disappointing in that levels of parasitism were low or not detected in several important fruit growing areas Extensive surveys in 2002 and 2003 determined the presence of Lygus parasitism by Persitenus spp. In total over 75 sites were surveyed and over 8,000 Lygus were dissected to determine if Peristenus spp were present. Parasitism by of Lygus by Peristenus was greatest in areas that were less disturbed by human activity.

 

Phenology Model. A phenology model Walsh helped develop in 1990 (www.ipm.ucdavis.edu) proved effective at predicting the first generation hatch of Lygus in spring in Eastern Washington (Table 1) and the subsequent peak hatch periods for the 2nd and 3rd generations of Lygus in 2001, 2002, and 2003. In running this model degree days are accumulated starting on March 1 with 54° Fahrenheit serving as a horizontal lower-cutoff for development. Eggs laid by adult Lygus in late- winter will require approximately 252 degree days in order to hatch. This corresponded well with when we observed our 1st generation of nymphs in both orchards and in our riparian survey sites (Table 1) in mid to late May.  Although this model proved fairly effective at predicting hatch periods for Lygus during the summer months it has been our observation that the majority of feeding injury on tree fruits is caused by adult Lygus and that this model does little towards predecting when adult Lygus will migrate into tree fruit orchards. Rather rainfall patterns and the subsequent dry-down of the over-wintering hosts of Lygus is a prime cause of spring movement of adult Lygus. During the summer months harvest of field and forage crops (primarily alfalfa) also contributes to movement of adult Lygus.

 

Table 1. Cumulative degree day accumulations 54°,  predicted dates of peak hatch for the 1st, 2nd, and 3rd generations of Lygus and the actual average number of Lygus caught per sweep among all of the samples taken bi-weekly at our riparian survey sites (n=72) for 2001 and 2002.
                                                2001                                                                2002
                        Cumulative        Model Nymphs            Cumulative        Model Nymphs
Date                  DD                  Prediction         /sweep   DD                 Prediction         / sweep
March 1                0                                          n/a                      9                                            n/a
April 1                 35                  (1st adult 4/2)     n/a                     27                    (1st adult 4/9)     n/a
April 15               39                                          n/a                     69                                            n/a
May 1               109                  1st hatch            0                      119                    1st hatch            0
May 15              198                  (May 23)          0                      166                    (May 27)          0
June 1               384                                          1.6                  307                                            0.6
June 15              484                                          1.2                   473                                            1.3
July 1                675                                          0.8                   713                                            1.5
July 15               961                  2nd hatch           1.3                   991                    2nd hatch           3.2
August 1          1196                  (July 23)           3.0                 1351                    (July 17)           0.3
August 15        1513                                          1.6                 1573                                            1.2
September 1     1784                  3rd hatch           0.7                 1870                    3rd hatch           3.4
September 15   1984                  (Sept. 8)           2.4                 2052                    (Sept. 8)           1.3
October 1        2153                                          1.2                 2173                                            1.3
October 15       2215                                          0                    2235                                            0
November 1     2237                                          0                    2272                                            0
2003
March 1                0                                          n/a                       
April 1                 50                  (1st adult 4/2)     n/a                       
April 15               84                                          n/a                       
May 1               131                  1st hatch            0                          
May 15              194                  (May 25)          0                          
June 1               360                                          1.3                       
June 15              555                                          1.5                       
July 1                758                                          0.6
July 15               987                  2nd hatch           0.9
August 1          1370                  (July 22)           0.8
August 15        1619                  3rd hatch           2.1
September 1     1900                  (Aug 22)           3.2
September 15   2074                                          6.1                                                                   .
                                               
Orchard floor cover crops. Replicated plots of 14 cover crop blends were established on the Roza unit at WSU IAREC in May 2003. Cover crop blends included perennial rygrass, buckwheat, buckwheat/ryegrass, alfalfa, crimson clover, hairy vetch, alfalfa/ryegrass, clover/ryegrass, vetch/ryegrass, Austrian winter pea, pea/ryegrass, Bug n Breakfast, and naturalized and endemic weeds. Irrigation was applied by handline sprinklers and irrigation was applied to mimic recommended orchard management practices. Sweep net surveys were conducted every 2 weeks and the number of Lygus, thrips and spiders captured was quantified and calculated. In total the cover crop plots were sampled 6 times on 30 June, 14 July, 29 July, 12 August, 9, September and 22 September respectively. Analysis of variance demonstrated that there were no significant differences in Lygus populations among the sample dates so all the dates were pooled.

In 2003, the “Ambient” and “Endemic weedy plants consisted primarily of pigweeds and barnyard grass. These plots are essentially the same but have extra plots will prove helpful in the future as we expand these studies. We can conclude that all of the cover crops were superior to no weed control in reducing populations of Lygus bugs as estimated by sweep net samples.

 

RESULTS/ DISCUSSION- Thrips 2001, 2002, and 2003
2001.    An efficacy trial was established in a nectarine orchard in the Columbia Basin at which 9 insecticides were evaluated for their ability to suppress thrips on nectarines. Insecticides were applied on July 27, 2001 with a handgun sprayer to runoff.
Insecticide efficacy was measured in 3 ways. (1) shake samples of branches were taken 3 days after insecticide application. (2) To measure insecticide residual sleeve cages made of floating row crop cover were placed over 4 individual fruit per replicate tree 3 days following insecticide application. Approximately 10 western flower thrips were then placed into each individual cage. The cages were then left on for 1 week. After which the individual fruit were picked, transported to IAREC and evaluated for thrips feeding damage.  (3) An equivalent number of representative non-caged fruit were harvested at the same and transported to IAREC and evaluated for the presence of thrips feeding injury. 
Formulated product                            Active ingredient                    lb ai/Acre
Novaluron 0.83 EC                                novaluron                                  0.039
Esteem 0.86 EC                                                pyriproxyfen                              0.11
Success                                                spinosad                                    0.156
Success + Omni oil 0.5%                       spinosad                                    0.156
Asana L                                               esfenvalerate                            0.075
Provado + Silwet                                   imidacloprid                               0.10
Surround                                               kaolin                                        50 (product)
Actara                                                  thiamethoxam                            5.5 oz (product)
Pyrimite                                                pyribaden                                  0.3
Untreated control

 

 

Results for thrips shake samples 3 days after insecticide application on July 30, 2001. Actara, Asana, Esteem, Provado, both Success treatments and Surround provided significant control (p<0.01) of thrips compared the untreated control in pairwise t-tests.


 

 

Results of damage assessment of caged fruit. Approximately 10 thrips were placed w/i individidual fruit cages for 1 week. No insecticide treatment provided effective residual and prevented thrips feeding injury compared to the no treated control in this study


Results of damage assessment of non-caged fruit..All of the insecticides provided significant (p<0.01) control of thrips and prevented thrips feeding injury compared to the non treated control in pairwise t-tests in this study.


Insecticide Efficacy 2002
Two insecticide trials were established in 2002. The first was established in early April in the Mesa, WA area. A late frost devastated the orchard about 3 days after we made the applications. A second trial was established in Sunnyside, WA on 4/26/02 and the following insecticides were applied
Formulated product                            Active ingredient                    lb ai/Acre
Success + Omni oil 0.5%                       spinosad                                    0.156
Carzol                                                   Formetanate-hydrochloride         2 # product
Actara                                                  thiamethoxam                            5.5 oz (product)
Fujimite                                     fenpyroximate                           0.15
Asana L                                               esfenvalerate                            0.075
Untreated control

 

Shake samples of branches were taken 3 days after insecticide application and sticky cards were placed in the tree canopy. No differences in thrips populations were observed within this trial
Temporal Thrips feeding injury. In 2002 we designed a sequential sample experiment in which we established cages weekly from July 1, 2002 through August 5, 2002. Cages were placed over individual fruit on control trees. Fifteen to 20 thrips were placed into 10 per tree to total 40 cages each week. On August 8, 2002 the fruit were removed from each cage site and rated for thrips feeding injury.  Damage from thrips feeding in these no choice tests increased with fruit maturity though the month of July and demonstrates that late-season suppression of thrips is important at high population densities.

Orchard floor treatments. The orchard floor of a late bearing cherry orchard was treated post harvest with some candidate compounds, roundup and mowing to determine if these treatments changed the distribution of thrips within the canopy. The treatments included Carzol, Asana, Mustang-Max, Roundup, and mowing. Pretreatment samples determined that populations were fairly low as measured with yellow sicky cards place at 5 inches above the soil surface and 5 feet in the canopy. Cards were placed out on 2 August, 2003 and were removed on 5 August. Subsequently all of the treatments and mowing were applied on 5 August 2003. A post-treatment 3 day sticky card samples were taken on 12 August.

 


 


 

These treatments were inconclusive and will require repeating.

 

Thrips Sampling. Thrips flight activities were monitored in a peach orchard in the Yakima Valley near Wapato and at a peach and a nectarine orchards near Mesa. This study was run in conjunction with other projects that we had ongoing on thrips management on several other crops comparing blue or yellow sticky cards as a monitoring tool. At present thrips abundance has been counted on 320 blue cards and 320 yellow cards in or near stonefruit orchards. Blue cards are proving to be significantly (P<0.01) more effective then yellow cards at catching western flower thrips in or near stonefruit orchards.


At each orchard site blue and yellow sticky cards were placed weekly in weeds near the orchards edge, on the orchard floor and canopy on edge of the orchard and on the floor and canopy of trees 160 feet in the orchard. At each site the blue cards consistently caught more thrips then the yellow cards and the greatest abundance of thrips was observed in nearby “weeds” followed by cards placed on the edge of the orchard floor.

Results from sticky card traps collected weekly from a peach orchard near Wapato, WA. The counts are the number of thrips captured per 5” by 3” sticky card in the 72 hours prior to the day listed. There is a definite edge effect with utilizing sticky cards to estimate thrips populations in this orchard


Results from sticky card traps collected weekly from a peach orchard near Mesa, WA. The counts are the number of thrips captured per 5” by 3” sticky card in the 72 hours prior to the day listed.

 


Results from sticky card traps collected weekly from a nectarine orchard near Mesa, WA. The counts are the number of thrips captured per 5” by 3” sticky card in the 72 hours prior to the day listed.


 

Orchard floor cover crops. Replicated plots of 14 cover crop blends were established on the Roza unit at WSU IAREC in May 2003. Cover crop blends included perennial rygrass, buckwheat, buckwheat/ryegrass, alfalfa, crimson clover, hairy vetch, alfalfa/ryegrass, clover/ryegrass, vetch/ryegrass, Austrian winter pea, pea/ryegrass, Bug n Breakfast, and naturalized and endemic weeds. Irrigation was applied by handline sprinklers and irrigation was applied to mimic recommended orchard management practices. Sweep net and yellow sticky card surveys were conducted every 2 weeks and the number of thrips and captured was quantified and calculated. In total the cover crop plots were sampled 5 times on 30 June, 14 July, 29 July, 12 August, and 9, September respectively. Population estimates on sticky cards varied across dates and within plots. However, thrips populations tended to be reduced in buckwheat/ buckwheat combination plot. Since this was the establishment year for these plots we will have to see how things change as the cover crops mature over the next several years.

 

 

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