- Author: Mark Bolda
As any grower knows, vinegar flies, Drosophila spp., have been a major deal in strawberries the last few years. It seems the slightest delay in picking (especially in the fall) is met with an onslaught of vinegar flies followed by a huge loss of fruit.
I have the good fortune to be funded this year by the North American Strawberry Growers Association (NASGA) on a study looking at predaceous nematodes as a way of controlling vinegar flies. More on that at a later date, but having my research assistant Monise Sheehan and I spend some time looking closely at vinegar flies in strawberry brings up some observations that I would like to share here.
First of all, regular vinegar flies, as opposed to the spotted wing drosophila, Drosophila suzukii, do not oviposit in fruit, rather they oviposit on the surface. I am going to underline that this doesn't at all mean they won't damage the fruit, since it is only 24 hours each one spends in the egg stage before becoming an active larva fully capable of penetrating into the fruit.
It is interesting to see where the egg laying is taking place. It's uncommon to see eggs just deposited on a healthy fruit (Photo 2); it is rather in wounds (Photo 3) and cracks (Photo 4), bruises and any other kind of damage which softens and compromises the integrity of the fruit where the bulk of the eggs are found.
I think the take home message for strawberry growers and supporting professionals is to know how very fast the life cycle of vinegar flies goes and the big role that damage, be it wounds, cracking, bruising or general softness has in promoting their development.
- Author: Mark Bolda
In some of the first literature written in Japan in 1939 (Kanzawa, T.) about spotted wing drosophila, Drosophila suzukii, (SWD), experiments were made regarding the sensitivity of the egg and larval stages of spotted wing drosophila to periods of temperatures above and below freezing (32o F).
As is noted in the two graphs below, at constant temperatures of up to 35o F, 96 hours or more of cooling resulted in total mortality of spotted wing drosophila eggs and larvae. This was also anecdotally confirmed in tests conducted in 2009 in California.
While temperatures below freezing are not useful to fruit shippers, temperatures in the area of 35o F are. However, it is important to note that for success the constancy of the temperature is critical. So, while in an ideal situation constant temperatures of 35o F or a little below are effective in SWD egg and larvae suppression when extended for periods longer than 96 hours, the reality can vary significantly from the ideal. Shipped fruit ordinarily do not experience lengthy regimes of constant temperature as they are moved from place to place. Temperatures of a refrigerator truck can vary by location inside and placement of the produce (ie on the side, towards the bottom etc.), and certainly the temperatures at the point of sale can vary from the ideal to room temperature to even warmer.
Additionally, while initial damage from SWD on raspberries, blackberries and strawberries can be difficult to detect, this is not the case for other fruits such as cherries or blueberries, where the activity of SWD will leave an unsightly blemish.
The take home message from this information is that while extended cooling can be suppressive of SWD, growers should not rely on cooling alone. It will still be important to manage SWD in field.
Thanks to Shinji Kawai for making the information from the 1939 Kanzawa paper available.
- Author: Mark Bolda
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:
|
Chemical |
Treatment Rate per acre |
Water Carrier Rate per acre |
|
Malathion |
64 fl oz |
179 gallons |
|
Delegate (spinetoram) |
6 oz |
179 gallons |
|
HGW86 (Cyantraniliprole) Not Registered in Caneberry |
398.6 ml |
179 gallons |
|
Altacor (Chlorantraniliprole) |
64 fl oz |
179 gallons |
|
Actara (Thiamethoxam) |
129.6 g |
179 gallons |
|
Untreated Control |
- |
- |
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
|
|
Pre-application |
Post One Day |
Post One Week |
Post Two Weeks |
Post Three Weeks |
|
|
12/3/2009 |
12/4/2009 |
12/9/2009 |
12/16/2009 |
12/23/2009 |
|
Altacor |
8.0 a |
28.7 a |
3.3 bc |
49.3 a |
6.3 a |
|
Actara |
13.0 a |
38.0 a |
6.0 abc |
48.7 a |
6.0 a |
|
UTC |
17.7 a |
38.0 a |
7.3 ab |
62.3 a |
4.7 a |
|
Delegate |
8.3 a |
18.0 a |
2.3 bc |
18.7 a |
4.7 a |
|
Malathion |
12.7 a |
10.3 a |
1.7 c |
14.3 a |
1.0 a |
|
HGW86 |
12.0 a |
33.0 a |
9.0 a |
46.7 a |
2.3 a |
Means followed by the same letter do not significantly differ (P=0.05, Student-Newman Keuls)
Table 2: Infested fruit
|
|
Pre-Application |
Post 1Week |
Post 2 Weeks |
Post 3 Weeks |
|
|
12/3/2009 |
12/9/2009 |
12/16/2009 |
12/23/2009 |
|
Altacor |
10.3 a |
2.7 b |
0.3 b |
4.3 ab |
|
Actara |
4.7 ab |
3.0 b |
1.7 b |
2.3 ab |
|
UTC |
8.7 ab |
9.0 a |
0.7 b |
6.3 a |
|
Delegate |
3.3 b |
0.3 b |
0.0 b |
0.0 b |
|
Malathion |
8.7 ab |
2.0 b |
0.7 b |
0.3 b |
|
HGW86 |
6.0 ab |
1.7 b |
0.7 b |
3.3 ab |
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.
- Author: Mark Bolda
