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.

Strawberry and caneberry growers should be reminded that the CDFA-USDA regulatory program for light brown apple moth is still regnant in Santa Cruz and north Monterey counties this year and we should all be taking steps to reduce numbers of this pest in the production fields.  I communicated with Rick McKay, head of the USDA-APHIS regulatory effort for this area, and he assured me the program will be active again in 2013 in the same way it was active last year, at least until September 30.    

Pheromone based twist ties are a good way to reduce LBAM numbers in fields, especially in raspberries and blackberries since the ties are attached to the trellis with very little effort and time.  The twist ties are still available through the Santa Cruz County Agricultural Commissioner at 763-8080.  There are still quite a few left, and a quick call to the distributor Pacific Biocontrol Corporation reassured me that these ties, which were received in 2010, are still viable since they are being stored in a cooler and are in their original packaging.  These twist ties cost nothing and give growers a good measure of protection against LBAM infestation and the accompanying regulation.

For those who may have missed the February 5 Annual Strawberry Production Research meeting, the Powerpoints of most of the presentations are now available on our county website.  The presentations will be found just under the Current News link:

http://cesantacruz.ucdavis.edu/

The cold weather we have been experiencing over the past few days has prompted a lot of talk and even articles in the popular press over what the effect of this cold would be to local berry growers.  Beyond the damage that very cold temperatures could cause tender plant parts such as flowers and emerging vegetative parts (of which we fortunately don’t have very many right now), the question worth exploring is what benefit this weather could be bringing to our berry crops.

Many of our cultivated fruiting plants originate from temperate regions, including many berry species and tree fruits, and as such go dormant in response to oncoming cold weather in the autumn.  This adaptation of dormancy protects the plant buds from injury when temperatures fall below freezing and the buds stay this way until enough cold has been accumulated over time.

This accumulation of cold over time, known as chilling requirement and measured in hours as chill units, is the minimum amount of cold after which many fruit trees, caneberries and strawberries need to be exposed to in order to grow properly in the following spring.  The total number of hours of chill needed to establish proper flowering and vegetative growth vary substantially for plant types and even between varieties of the same plant species.

If plants requiring a certain amount of chill hours do not receive it, they may end up blooming or leafing out late in the spring or in an spread out, uneven fashion. Additionally, they may subsequently experience reduced fruit production and quality.

Another complication of calculating chill units in California, as compared to much colder regions of the country, for example Wisconsin where temperatures can be below freezing for weeks at a time (go Badgers!), is that our region tends to have a cycling of warm and cold weather throughout the winter.  How then do we as agriculturalists in California calculate chill accumulation in this back and forth between cold and warm?

To calculate chill hours, there are three common models all based on the principle that plants accumulate chill between 45 degrees F and freezing (32 degrees F and not below).   One model ignores the below freezing threshold and simply calculates total number of hours under 45 degrees F, another calculates number of hours between 32 degrees and 45 degrees, and another, called the Utah model, is bounded by 34 degrees and 45 degrees but also accounts for negative chill accumulation, being the understanding that temperatures above 61 degrees detract from chill hours already accumulated.  It is worth pointing out that in the Utah model, temperatures under 34 degrees do not accumulate chill, nor do they detract from it.

Yet, the fluctuating temperatures of California still are a challenge to some degree for these models, and the University of California is engaged in research to get a better handle on these conditions, and is has been testing a “Dynamic Chill Model” and a “Chill Portion Model”.   Both of these are beyond the scope of this blog, but Central Coast agriculturalists seeking to further their understanding about chill and how to manage it, will find an excellent resource at :

http://fruitsandnuts.ucdavis.edu/Weather_Services/chilling_accumulation_models/