- Author: Mark Bolda
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.
Table 1: Treatment list.
Treatment |
Rate |
Adjusted pH |
Pestout |
1% v/v |
pH 5.8 |
Pyganic 1.4 |
64 oz |
pH 7.5 |
Pyganic 1.4 |
64 oz |
pH 5.5 |
Untreated control |
- |
- |
Results:
Table 2: Efficacy of various organically registered pesticides.
|
"Females" |
Males |
Total |
"Females" |
Males |
Total |
|
11/17/2009 |
11/17/2009 |
11/17/2009 |
11/19/2009 |
11/19/2009 |
11/19/09 |
PestOut @ 1% 5.8 pH |
9.33 a |
4.67 a |
14.00 a |
0.67 a |
1.33 a |
2.00 b |
Pyganic 64 oz/A 7.5 pH |
9.33 a |
7.33 a |
16.67 a |
0.33 a |
0.33 a |
0.67 b |
Pyganic 64 oz/A 5.5 pH |
15.67 a |
6.67 a |
22.33 a |
0.67 a |
0.00 a |
0.67 b |
Untreated control |
11.67 a |
6.33 a |
18.00 a |
3.67 a |
5.00 a |
8.67 a |
|
"Females" |
Males |
Total |
|
11/20/2009 |
11/20/2009 |
11/20/09 |
PestOut @ 1% 5.8 pH |
15.67 a |
7.67 a |
23.33 a |
Pyganic 64 oz/A 7.5 pH |
13.67 a |
5.33 a |
19.00 a |
Pyganic 64 oz/A 5.5 pH |
4.33 a |
6.33 a |
10.67 a |
Untreated control |
8.67 a |
13.33 a |
22.00 a |
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.