Michigan spotted wing Drosophila update – July 10, 2018

Julianna Wilson<jkwilson@msu.edu>, Rufus Isaacs<isaacsr@msu.edu> - July 10, 2018

Cooler weather last week coincided with a big jump in the number of SWD caught in traps; ripening fruit must be protected against infestation.

Ripening tart cherries are just one of the many fruits grown in Michigan that are vulnerable to spotted wing Drosophila infestation if not protected. Photo by Julianna Wilson, MSU Extension.

Spotted wing Drosophila (SWD) were caught in significantly higher numbers last week in all regions over the previous week, with an average of 11 flies per trap in southern and central counties, and just over nine flies per trap in northern counties in Michigan. This is likely due to the cooler weather we had, since we know SWD are not as active when average temperatures are above 90 degrees Fahrenheit.

By now, if you grow a susceptible crop at a vulnerable stage, you should have begun a management program for this pest. All thin-skinned berries and cherries become vulnerable when they start to color, including blueberries, cherries, raspberries, gooseberries, currents and saskatoons. Wild hosts include blackberries, honeysuckle and buckthorn, so susceptible crop plantings next to these are expected to have higher pressure from SWD. However, so far, fruit samples from crops being actively managed for SWD have not been infested with larvae. Since plums and other larger stone fruit can be fully ripened off the tree, simply not letting them get to the 3.5 pounds of pressure stage before harvest will prevent SWD infestation.

For blueberry growers harvesting early varieties, below is a table that was developed to compare insecticides for SWD control in this crop. This lists most of the registered options for controlling this pest in Michigan, along with the many restrictions (re-entry, re-application, etc.) that need to be taken into account when developing a program to protect blueberries from SWD infestation. As harvest continues, monitoring should also continue as new fields come into ripeness. Note also that some high catches of blueberry maggot have been recorded this past week in blueberry fields where no pest management has been used over multiple years. This is a reminder to beware of this potential fruit pest even though attention has been so focused on SWD.

Insecticides for SWD control in blueberries
Trade name	Class	Active ingredient	Rate	Season max.	Max. apps	Days btn spray	*PHI (d)**	REI (h)**	Resid. (d)	Rank
Imidan	Org. phos.	phosmet	1.33 lb	7.13 lb	5	0	3	24	7-10	****
Malathion 8F^a	Org. phos.	malathion	2.5 pt	5 pt	2	5	1	12	5	***
Mustang Max	Pyrethroid	z-cypermeth.	4 oz	24 oz	6	7	1	12	5-7	****
Danitol		fenpropathrin	10.6-16 oz	32 oz	2	14	3	12	5-7	****
Brigade/ Bifenture^b		bifenthrin	5.3-16 oz	80 oz	-	7	1	12	5-7	***
Hero		z-cyp + bifenth.	4-10.3 oz	46.35 oz	-	7	1	12	5-7	***
Lannate SP	Carbamate	methomyl	0.5-1 lb	4 lb	4	3	3	48	7	****
Exirel	Diamide	cyazypyr	13-20.5 oz	60 oz	-	5	3	12	7	****
Delegate	Spin.	spinetoram	3-6 oz	19.5 oz	6	3	3	4	7	***
Entrust WP^c		spinosad	1.25-2 oz	9 oz	6	6	3	4	3-5	**
Entrust 2SC^c		spinosad	4-6 oz	29 oz	6	6	3	4	3-5	**
Cormoran	Neonic + IGR	acetamiprid + novaluron	20 oz	35 oz	-	7	8	12	7	***
Assail	Neonic	acetamiprid	5.3 oz	26.6 oz	5	7	1	12	5-7	**
Pyganic^c	Pyrethrum	pyrethrum	32-64 oz	59 oz	-	3	0.5	0	2	*
Grandevo WDG^c	Biological	Chromobacterium	3 lb	-	-	-	0	4	3-5	**
Azera^c	Biological	Neem + pyrethrum	32-56 pt	58 oz	10	3	0	12	2-5	*

^a Malathion 8F (Gowan) has a 24c label for Michigan blueberries.
^b Bifenthrin pyrethroids may be more effective in hot temperatures (90s) than other pyrethroids.
^c Use in organic production.

For tart cherry growers, there is a 24C label for Mustang Maxx to be able to use this product up to three days prior to harvest. Contact your local Michigan State University Extension educator if you need a copy of this special use label for controlling SWD in tart cherries. For more information on managing SWD in cherries, download the free SWD management guide for cherries available from MSU.

For best results in controlling this pest, use materials and methods that are rated excellent against SWD to protect fruit. As always, be sure to calibrate your sprayer to maximize coverage and rotate insecticide chemistries to prevent the risk of developing insecticide-resistant populations of SWD on your farm.

We will continue to monitor SWD as the season progresses. Our general regional reports provide an overview of the regional situation, but monitoring flies on your own farm provides a more relevant source of information on SWD activity. We are also recommending growers check their fruit for infestation through the season.

For the recently released guide to SWD management in organic systems, see “Management Recommendations for Spotted Wing Drosophila in Organic Berry Crops.”

For more information on effective insecticides registered for use to control SWD, refer to the MSU Extension Michigan Fruit Management Guide for 2018 (E154).

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).