Introduction: As noted previously in this blog, lygus bugs are a major pest in strawberries since they cause mis-shaping of fruit from their feeding on the early forming fruit.  This pest has been a real challenge to California strawberry growers, one reason being that the populations in the Central Coast production regions have become quite tolerant or even resistant to many of the pesticides used for it. 

Fortunately several promising insecticide chemistries for control of lygus bugs have become available for field trials over the past few years.

Please note that sulfoxaflor and tolfenpyrad are still NOT REGISTERED (flonicamid is) for use in strawberries.

Three large scale trials of up to a third of an acre per treatment were conducted this past year to test these three novel insecticides under real field conditions. 

Application: One trial in a second year strawberry field in Salinas testing three materials (plus one grower standard) was conducted with a standard research backpack sprayer (applied 5/3/2012), another (overseen by the California Strawberry Commission) in a first year field in Guadalupe with a tractor mounted spray rig (applied 8/28/2012 and 9/12/2012), and a third in Watsonville with another tractor mounted spray rig (applied 10/5/2012 and 10/12/2012).  Refer to the table below for rates of test material and water carrier.

¹ Note that these materials were added with the surfactant Natural Wet at the rate of 8 fl oz/A.

Insect and Fruit Sampling:  Lygus bugs were sampled by beating 20 strawberry plants (3 times each) in a row into an open plastic container and counting small nymphs, large nymphs and adults.  Lygus bugs were sampled weekly for 6 weeks following the first spray application in Guadalupe, weekly for three weeks following the first application in Watsonville and weekly for four weeks following the application in Salinas.  Fruit evaluation took place on 9/26/2012 and 10/10/2012 in Guadalupe and 10/19/2012 and 10/26/2012 in Watsonville.   Fruit sampling consisted of randomly picking 50 fruit from the center two furrows of each trial.  These picked fruit were graded into three categories; marketable, unmarketable due to lygus feeding (“catfacing”) and unmarketable due to other causes (mainly rots and small size). 

Statistical analysis is a standard analysis of variance (ANOVA), using a square root or a logarithmic transformation in some instances in order to closer meet the assumptions of the statistical analysis .

Results and Discussion:The experimental sprays worked, especially the sulfoxaflor.  Analysis by date show that sulfoxaflor treated plots in the Guadalupe and Watsonville trial were associated with lower numbers of adults, large nymphs and small nymphs on multiple dates after the initial application, and treated plots in Watsonville.  Tolfenpyrad also did result in significant reduction in numbers of nymphs and adults on certain evaluation dates, particularly two weeks after the first application. 

See Graphics 2-4 below for visual demonstration of evaluation results of lygus nymphs and adults 14 days after first pesticide application at each trial site.

The use of sulfoxaflor resulted in significantly higher amounts of marketable fruit than the untreated control on three sampling dates at both evaluation sites, while the use of tolfenpyrad resulted in significantly higher amounts of marketable fruit than the untreated control on two sampling dates at the trial site in Watsonville.  Refer to Table 1 below for a summary of these results.

Table 1: Average marketable fruit yield for each sampling pick date for insecticide trials in Guadalupe and Watsonville, CA

*Letters indicate significant differences by post hoc analysis at p<0.05

Outside of malathion and flonicamid, the sulfoxaflor and tolfenpyrad are still NOT REGISTERED for use in strawberries.  Before using any insecticide products, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.