The 2024 outlook for spotted wing drosophila in Michigan cherry orchards
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EmailWarm and wet conditions have sparked early detection of spotted wing drosophila, which is likely to mean 2024 will be a challenging year for protecting fruit against this pest.
As cherries get closer to harvest, the number one insect pest on the minds of growers each year is spotted wing drosophila (SWD), Drosophila suzukii. Every season the question is whether or by how much this pest will overlap with fruit ripening, because as cherries ripen they become increasingly vulnerable to infestation by SWD. So far, the 2024 season has been warm and with higher rainfall and humidity compared to the past few years. This has resulted in earlier detections of SWD in Michigan, by about one to two weeks.
Additionally, the 2023-24 winter was also relatively mild, and we hypothesize that more SWD likely overwintered with the warmer winter conditions. Fruit ripening is also earlier than average. Michigan State University Extension recommends growers use trapping and fruit sampling in their weekly monitoring to assess fly activity, determine how populations may be increasing on your farm, and whether your management program is working to protect fruit.
For more information of the origins and biology SWD, see Spotted Wing Drosophila Biology and Identification from Michigan State University (MSU).
Trapping for adults
Trapping for adults to determine whether they are presently active in an orchard requires a trap baited with an attractant, hung in the shade of the canopy near the orchard edge. An inexpensive option is a 32-ounce cup with 3/8-inch holes near the lip, with a yeast-sugar bait solution (1 tablespoon of active dry yeast with 4 tablespoon of sugar, a drop of dish soap, 12 ounces of water) and a sticky card suspended from the lid. Alternatively, you can bait the same trap with a commercial lure over an inch of soapy water to drown any captured flies (Photo 2).
Another option is to use a commercial lure with a dry sticky trap, such as a red panel trap. It is important to look at overall incidence across multiple traps on the farm, as well as noting the current stage of fruit development in each block to determine whether a management program targeting this pest needs to start.
Interpreting trap catch
The most conservative approach to SWD management in cherries is to begin protecting fruit when fruit starts to turn color and you have captured an SWD fly in one of your traps. Other MSU research has indicated management can be initiated when 5–10% of the traps in your region are reporting fly catches and fruit are ripe enough to be at risk.
The MSU Enviroweather model for SWD in cherries can help you determine when your fruit are ripe enough to be vulnerable to SWD egglaying. The model is based on accumulated degree-days since full bloom in tart cherries.
Sampling fruit for larvae
Sampling fruit for larvae, also known as the filter test, is an important scouting method to determine whether fruit infestation is occurring to aid with choosing protectants and harvest timing decisions, and to confirm that control measures have been successful.
- When fruit starts to color, collect samples from multiple blocks at each farm and high pressure locations (near wooded edges, etc.) and low-pressure locations (interiors).
- Each sample should consist of about 2 pints (16 ounces) of fruit with stems removed.
- Soak fruit in water for at least 30 minutes; this allows time for larvae to exit fruit.
- Pour fruit and liquid into a course strainer or piece of hardware cloth shaped into a funnel placed over a coffee filter.
- Examine coffee filter for larvae (easiest with a hand lens or microscope).
The following video contains more details on this larval sampling method. Note: Methods for cherry are similar to those used in blueberries, with the exception that instead of lightly squishing the fruit, just the stems are removed.
Interpreting larvae in fruit
Given how quickly this pest can reproduce and how devastating infestation can be, if larvae is detected in your fruit, a cover spray of an insecticide that is rated excellent against this pest should be applied to protect fruit and maintain populations at current low levels.
Managing SWD
Managing SWD is challenging because populations can grow rapidly under warm summer conditions, especially after rain events. Frequent rain events will require shorter spray intervals. High heat conditions will make some pesticides less effective (for example, pyrethroids). Based on our experience in Michigan, SWD control will likely require a seven-day spray interval under dry conditions with tighter intervals following rain or other wetting events, alternating with different materials.
Since publication of the Tart Cherry Management Guide, fruit entomologists in the Department of Entomology at Michigan State University have tested some new materials; these include Leverage, Spear T and Cormoran. It is also important to note that the label for Mustang Maxx now includes the three-day preharvest interval for cherries. Table 1 includes these new materials and label changes, as well as their relative efficacy.
Table 1. Insecticides registered for use in Michigan CHERRIES and their expected efficacy against SWD, cherry fruit flies and leafrollers, the main late season targets. Materials are listed alphabetically.
|
Trade Name† |
PHI |
REI |
Days bet trts |
Rate/acre |
Max AI/acre per season |
Relative efficacy against: |
||
|---|---|---|---|---|---|---|---|---|
|
SWD |
CFF |
LR |
||||||
|
Apta 15SC |
14 |
12 |
10 |
21-27 fl oz |
0.56 |
E |
||
|
Baythroid XL |
7 |
12 |
14 |
2.4-2.8 oz (0.019-0.022) |
0.044 |
G |
G |
G |
|
Cormoran DC |
8 |
12 |
10 |
20-28 oz |
0.97 lb (novaluron) |
G |
||
|
Danitol 2.4 EC |
3 |
24 |
10 |
21.3 fl oz (0.4) |
0.8 |
E |
G |
G |
|
Delegate 25 WG |
7 |
4 |
7 |
6-7 oz (0.071-0.109) |
0.438 |
G |
G |
E |
|
Entrust 2 SC†† |
7 |
4 |
7 |
4-8 oz (0.062-0.124) |
0.45 |
E |
G |
E |
|
Exirel 10 SE |
3 |
4 |
7 |
13.5-20.5 fl oz (0.09-0.13) |
0.4 |
E |
E |
E |
|
Grandevo WDG†† |
0 |
4 |
NS |
3 lb (0.9) |
NS |
G |
G |
|
|
Imidan 70W* |
7 |
72 |
NS |
2.125 lb (1.5) |
5.25 |
E |
E |
E |
|
Leverage 360 SE |
7 |
12 |
14 |
2.4- 2.8 oz |
0.088 (imida-cloprid) 0.044 (beta-cyfluthrin) |
G |
G |
G |
|
Movento 2SC |
7 |
24 |
14 |
6-8 fl oz (0.09-0.12) |
0.24 |
G |
||
|
Mustang Maxx 0.8 EC |
3 |
12 |
7 |
4 fl oz (0.025) |
0.15 |
E |
F |
G |
|
Rimon 0.83 EC1 |
8 |
12 |
7 |
20-40 fl oz (0.13-0.26) |
0.97 |
G |
G |
E |
|
Spear-T |
0 |
4 |
3 |
2-3 gal |
NS |
G |
||
|
Verdepryn 100 SL |
7 |
4 |
7 |
11 oz (0.072) |
0.22 |
E |
E |
E |
|
Warrior II 2 CS |
14 |
24 |
5 |
2.56 fl oz (0.04) |
0.2 |
E |
G |
G |
Pest abbreviations: SWD = spotted wing drosophila, CFF = cherry fruit fly, LR = leafrollers.
Efficacy rating codes: F = Fair, G = Good, E = Excellent, based on MSU field/lab bioassays.
† This is not meant to be an exhaustive list. For more pest and disease ratings on materials registered for use in cherries, please refer to the Michigan Fruit Management Guide E-154. If there is no efficacy rating listed for a given product/pest combination, efficacy should be considered unknown for that particular pest. For more information on the proper use of individual insecticides, please refer to the specimen label for each material.
†† This material is OMRI approved.
*Imidan is not labeled for use in sweet cherries due to phytotoxicity issues.
1 While not having contact toxicity to adults, sublethal effects following adult exposure leads to nonviable eggs.
Keys to success
- Use on-farm monitoring to know when SWD flies are active.
- When SWD flies are present, protect ripening cherries through harvest using effective, registered insecticides.
- Use the filter test to look for larvae in ripening fruit to check whether management programs are working.
- Minimize any delay in harvest – the longer ripe fruit remain on trees, the more likely they are to be infested.
- Remember to rotate chemical classes (modes of action) to prevent the development of insecticide resistance.
See more details on SWD management in cherries from MSU.
This article contains pesticide recommendations based on research and pesticide regulations relevant to Michigan. However, changes in pesticide regulations occur constantly. Some pesticides mentioned may no longer be available, and some uses may no longer be legal. Contact your local county Extension office if you have questions about particular materials.
The information contained within this article does not supersede pesticide label directions, nor is it meant to be exhaustive in terms of available materials registered for use against insect pests of cherries. To protect yourself, others, and the environment, always read the label before applying any pesticide.
For more information regarding pest management in commercial orchards, refer to the current version of the MSU Extension Michigan Fruit Management Guide, E-154.
