Introduction:  An August 2009 field trial demonstrated the efficacy of  malathion and zeta-cypermethrin (Mustang) against the spotted winged drosophila (SWD), Drosophila suzukii in raspberries.  The following summary reports efficacy of additional materials trialed against SWD in December 2009.

Materials and Methods:

Treatments:

Products were applied on December 3, 2009 with a Maruyama 056 gas powered back pack sprayer at maximum labeled rates in 179 gallons water per acre and 150 psi.  Each plot was 1,173 sq ft of a proprietary raspberry variety under polyethylene-covered tunnels.

Pre- and post-treatment estimations of SWD were made with a D-Vac Model 122 (hand carry) gas-powered insect sampling device operated at an airflow capacity of 280 cu ft per minute per square foot at the opening of the collecting head.  Each side of a 36-ft section of 4-ft high hedge row was sampled.  Collected samples were transferred from the D-Vac into Ziploc bags for transport back to the lab where they were frozen for approximately an hour prior to counting.

Because male SWD (easily distinguished by the black spot on their forewings) comprised over half the total Drosophila captured in most samples, we assumed the remaining fraction of Drosophila to be female SWD (which do not have spotted wings).  However, since the species of the females was not confirmed, they will be given in results as "females". Results are reported as total (male + female) SWD.

In order to evaluate the impact of treatments on incidence of fruit infestation by larval SWD, thirty marketable fruit were collected from the center of each treatment replicate prior to treatment and then 7-, 14-, 21- and 28-days post-application.  Fruit samples were placed in 4x6x12-inch plastic bags fixed with a 1x ¾-inch PVC screened vent tube sealing the open ended of the rearing bag (see photo below).  After two weeks, the numbers of larvae, pupae and adults were enumerated.

Results:

Table 1: Total numbers of male + "female" SWD captured in D-Vac samples

Means followed by the same letter do not significantly differ (P=0.05, Student-Newman Keuls)

Table 2: Infested fruit

Means followed by the same letter do not significantly differ (P=0.05, Student-Newman Keuls)

The effect of Delegate and Malathion was most notable in the evaluation of infested fruit (Table 2).  Although all treated fruit collected one week after application demonstrated significantly lower levels of infestation than the untreated control, Delegate and Malathion treatments continued to show significant levels of control up to three weeks after application.

Conclusion: This study demonstrates that Delegate is as effective as malathion in controlling SWD at relatively low population levels as those encountered during December 2009.

There are several insecticides mentioned for control of vinegar flies in this article.  Before using any insecticides, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.

We are very grateful for the cooperation of Dutra Farms and Chris Hogan for providing the test site.

Fruit infestation study

Previous posts have outlined several pesticides which are very effective in controlling spotted wing drosophila in berry crops.  Unfortunately, similar levels of success have not yet been achieved in organic production systems.

As it is well known that many pesticides such as pyrethrins, pyrethroids and some organophosphates (but definitely NOT spinosyns for which the opposite is true) are more active when applied in relatively acidic tank mixes.  The following study addresses this hypothesis in controlling spotted wing drosophila, Drosophila suzukii, in organically managed raspberries.

Table 1 below describes the treatments which were made.  Applications were made on November 18, 2009.  Tank mix was acidified with Mixwell water conditioner and adjusted using a hand held pH meter.  It is notable that it did not take much MixWell to acidify the six gallon tank mix, a mere 10 ml brought a pH 7.8 mix down to 5.8.

Water carrier rate was the equivalent of 180 gallons per acre, and applications were made with a backpack sprayer.  

Samples were taken one day prior to application, one day and two days after treatment application.  Sampling was done differently in this study than in others.  Owing to the relatively low numbers of flies in the plots, a “buc vac” (depicted in the photograph below) was utilized.  A 36 foot section of hedgerow was sampled on both sides, and these sections were not sampled again in the course of the study.  Flies and other insects caught in the net were emptied into a large, labeled Ziploc bag, frozen and counted in the lab later on.  Male spotted wing drosophila are easily recognized by the black spot on the back of each wing, other vinegar flies without spots were grouped together as female spotted wing drosophila. 

Continuing work with the “bug vac” shows that this machine quite effective in removing and sampling flies.  Resampling an infested area that has just been vacuumed with the "bug vac" yields very few flies, meaning that most have been removed the first time around.  In the lack of a heavy infestion, the "bug vac" is probably the better choice for researchers.

Results:

 Table 2: Efficacy of various organically registered pesticides.

Means followed by the same letter do not significantly differ (P=0.05, Student Neuman Keuls).

Spraying with Pyganic or Pestout with either tank mix pH modification arrived at the same result.  Numbers of total flies fell significantly one day after application, but two days after application no statistical differences were found between any of the treatments and the untreated control.

It is apparent from this study that acidification of the tank mix makes no difference in the efficacy of Pyganic.  Additionally, this work adds to the conclusion that the efficacy against vinegar flies of Pyganic or the horticultural oil PestOut is limited to one day.

There are several insecticides mentioned for control of vinegar flies in this article.  Before using any insecticides, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.

Motorized bug vac for sampling spotted wing drosophila

The following is a summary of further comparisons of baiting techniques for the spotted wing drosophila Drosophila suzukii.  Previous posts have evaluated the use of various fruit purees and other mixes and these have determined that a mixture of one 2.5 oz packet of yeast + 4 teaspoons sugar + 12 ounces of water distributed in four or five Mason jars were very effective in monitoring and evaluating infestation levels of spotted wing drosophila.

Another test of baits was run last week.  Traps (a 500 ml Nalgene bottle with 4 holes in the lid) containing one pellet torula yeast (see photo below) dissolved in 100 ml water, the yeast + water + sugar bait mixture mentioned above and finally a commercial “filth fly mix” called Yellow Muse (AgBio Corporation) allowed to cure for several weeks (the fermentation process of this material may be important) were placed November 3, evaluated November 6 and then again evaluated November 9.

The results are shown below (numbers in columns refer to average numbers of flies captured in each trap):

“Females” means that they are vinegar flies without spots on the wings and assumed to be spotted wing drosophila (SWD), while males were readily identifiable with spots on the wings.

Means followed by same letter do not significantly differ (P=.05, Student-Newman-Keuls)

From the chart above, it is apparent that the torula yeast is not very attractive to spotted wing drosophila, while yeast + sugar + water continues to be, along with well cured Yellow Muse filth fly mix, the most useful.

Dry, "torula" yeast

Packet of Yellow Muse fly bait

One of the most obvious manifestations of calcium deficiency in strawberry is “tip burn” of the rapidly growing new leaves in the center of the plant.  Some varieties tend to manifest this symptom more than others.  

Calcium is an important structural of component of cell walls and cell membranes in plants.  A deficiency of calcium in the plant leads to a general collapse of membrane and cell wall structure, and the resulting leakage of polyphenols concludes with necrosis in the affected areas.  Since there is broken down and dead tissue in these areas, microbial infection frequently results, but this is a secondary effect.

The scientific literature says that in strawberry, leaves containing less than 0.9 percent calcium are deficient, with a significant percentage of plants showing tip burn symptoms.   Furthermore, calcium sufficiency is said to be in the area of 1.5% of dry leaf tissue.

Calcium deficiency in plants is not necessarily a direct result of a lack of calcium in the soil and as such might not easily be addressed simply by increasing the amount of calcium fertilizer applied.  Calcium is moved from the roots to the rest of the plant via evapotranspiration by the water conducting elements of the plant, also known as the xylem.  If there is a lot of evapotranspiration, such as on a hot, dry day, calcium will be moved from the roots and up through the plant.  Conversely, lengthy spells of cool, humid (read fog) weather will not facilitate evapotranspiration and subsequently calcium movement can be restricted.  Plant organs such as the fruit and developing leaves do not transpire as much as a fully mature, expanded leaf, and therefore would tend to be the first to express calcium deficiency.

Photo Mark Bolda, UCCE

Photo Mark Bolda, UCCE