West central Michigan vegetable regional report – June 9, 2015

There have been reports of damaging populations of early-season, migratory moth pests, including true armyworms and cutworms. Be on the lookout for their activity.

Rust aeciospore lesions (bottom of plant) and purple spot (top of plant) on the base of asparagus fern. Controlling rust at this stage can reduce problems with the later, more rapidly reproducing uredospore stage.

Rust aeciospore lesions (bottom of plant) and purple spot (top of plant) on the base of asparagus fern. Controlling rust at this stage can reduce problems with the later, more rapidly reproducing uredospore stage.

Crop report

Asparagus rust aeciospore lesions and purple spot were readily visible in a research plot gone to fern in Oceana County this week, providing a nice example of the different appearances of these two diseases at this point in the season. Prompt treatment with Tebuconazole can help prevent later-season problems. Field shutdown has been starting in some locations for young fields.

Cole crops and other vegetables can be attacked by cutworms. These larvae are nocturnal, going down into the soil during the day and leaving behind clipped plants after feeding. A variety of pyrethroids are labelled for conventional treatment. The insecticidal bait Seduce is also available for organic growers.

Cucurbit growers should be on the lookout for striped cucumber beetles.

Onions continue to develop with stands varying between onion growing locations in Michigan, in part due to early season variation in weather. Michigan State University Extension weed specialist Bernie Zandstra has received reports of injury due to Goal applications, which may be due to cloudy weather that kept onions from developing a thick, waxy cuticle. Lambsquarter populations are high this year and could be difficult to control given wet weather ahead.

Potato and tomato growers should be vigilant about killing and removing volunteer potatoes. These are the single most important early-season source of late blight, which can overwinter in tubers.

Sweet corn growers should be on the lookout for true armyworm damage. This pest migrates to Michigan in spring. Females prefer to lay eggs on grasses, making fields that have weedy grasses a good spot to scout. Look for chunks cut out of the leaf margins and frass in the corn whorl. Larvae are active at night and hide in the whorl or in the soil during the day, making early morning a good time to detect this pest. Large infestations can seemingly defoliate fields overnight, but problems have their root earlier on. This sporadically important pest can be monitored for with pheromone traps; once moths are detected, field scouting should begin.

corn armyworm damage 
True armyworm damage to corn this week. Caterpillars feed on the margins of leaves, leaving a distinct pattern of damage. Scouting for this sporadic but damaging pest is important. It will help avoid unhappy surprises, but also allow you to conserve beneficials by not treating if pests are not present at damaging levels.

Scouting is key. Applying insecticides for a sporadically important pest can unnecessarily kill beneficials. For example, I spotted a good number of spined solider bugs in a sweet corn field this week, a voracious predator of insect pest larvae, including caterpillars and beetles.

spined soldier bug 1 spined soldier bug 2
A spined soldier bug on a sweet corn plant. This insect is a voracious predator of pests. It can be distinguished from herbivorous stink bugs by a black dot on its posterior plus spined shoulders.

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