West central Michigan vegetable update – May 23, 2018

Ben Werling<werlingb@msu.edu>, Michigan State University Extension - May 23, 2018

Pest activity has increased over the past few weeks and growers are looking forward to a stretch of dryer weather.

Asparagus harvest accelerated up until cool weather this weekend. There have been reports of problems with common asparagus beetle this year. Below is information repeated from last week on beetle control in case it is helpful.

In the past, carbaryl has been an effective choice for controlling adult beetles during harvest. Experience suggests there is little advantage to using XLR formulations of Sevin during harvest as spears with residue are being rapidly removed, so longer residual activity may not be a big benefit prior to the fern season. Assail has also proven effective in trials in the southeast for killing adults and preventing egglaying on spears and is a different mode of action compared to other available products.

A list of products with one-day pre-harvest intervals (PHI) that are labelled for control of asparagus beetle (and other pests) is below.

Product (active ingredient)	Labelled for pest?			Use patterns
Product (active ingredient)	Asparagus beetle	Tarnished plant bug	Japanese beetle	No. applications per season at full rate	Minimum retreatment interval	REI/PHI
Assail (acetamiprid)	Yes	Yes	Yes	2	10 days	REI = 12 hr PHI = 1 day
Carbaryl 4F (carbaryl)	Yes	No	No^a	5 (3 in harvest and 5 total for harvest + fern)	3 days	REI = 12 hr PHI = 1 day
Lannate (methomyl)	Yes	No	No	5	None	REI = 2 days PHI = 1 day
Lorsban (chlorpyrifos)	Yes	No	No	3 (1 pre-harvest + 2 post-harvest)	10 days	REI = 2 days PHI = 1 day
Perm-Up (permethrin)	Yes^b	Yes	Yes	4	7 days	REI = 12 hr PHI = 1 day

^aJapanese beetle is not listed under asparagus as a target pest, but is listed under other crops as controlled by carbaryl.
^bExperience suggests permethrin is not as effective as carbaryl for controlling adult beetles.

For cole crops, cabbage planting got a late start but was progressing at Ottawa and Kent County farms and will resume again once fields dry out. Cabbage maggots were present in a turnip trial Zsofia Szendrei, Michigan State University Extension entomologist, and I are conducting with a collaborator.

Diamondback moths were active at one location yesterday, May 22; in the coming weeks, caterpillar populations will start developing. This is a tiny moth whose caterpillars are small and wiggle and drop from a thread when disturbed. These caterpillars are smaller, and do less damage, than imported cabbageworm and cabbage looper. This means early in the season it is possible for plants to tolerate some caterpillars without major damage. This is reflected in the below thresholds from the “Midwest Vegetable Production Guide,” which can be used with scouting data to make treatment decisions.

Crop	Stage	% plants with infested
Crop	Stage	Diamondback moth	Imported cabbageworm and cabbage looper
Cabbage	Transplant to cupping	50% with ≥ 5 larvae/plant	30% with ≥ 1 larvae/plant
	Cupping to early head	50% with ≥ 5 larvae/plant	20% with ≥ 1 larvae/plant
	Early head to harvest	10% with ≥ 1 larvae/plant	10% with ≥ 1 larvae/plant
Broccoli, cauliflower	Transplant to first curd	40% with ≥ 1 larvae/plant	20% with ≥ 5 larvae/plant
Broccoli, cauliflower	First curd to harvest	10% with ≥ 1 larvae/plant	10% with ≥ 5 larvae/plant

For cucurbits, if you are worried about Phytophthora capsici causing damping off and stand loss, remember that the FarMore FI400 seed treatment includes the fungicide Apron, which has the same active ingredient (mefenoxam) as Ridomil. Note, some areas of Michigan with a history of mefenoxam use may have mefenoxam insensitive Phytophthora capsici.

As the season progresses, remember that good fruit coverage is essential for protecting cucurbits from Phytophthora fruit rot. Unfortunately, soil applications made at planting will not be helpful for fruit protection.

For hops, potato leafhopper was detected in a hopyard in mid-Michigan this week. Basal spikes with infection are starting to show downy mildew sporulation. Growers are out removing spikes before sporulation and making their second fungicide application. As things dry out, growers are trying to make nitrogen applications.

For sweet corn, planting schedules are off to our east in Montcalm County and behind other places, too. Some seedling corn is looking yellow, but should do better with increased sunshine on the way. You may consider adding slightly more nitrogen than normal at sidedress time if you have had heavy rains on light soil that could have leached planting-time fertilizer. Overall, true armyworm and black cutworm captures have occurred, but have not been very high to our east in Montcalm County. Reports from Indiana also suggest black cutworm flights have been low as of last week.

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).