West central Michigan vegetable regional report – June 8, 2016
Crop progress continues despite cool and dry weather.
For asparagus, once cladophylls have emerged after fields are shutdown, apply your first fungicide application to protect against purple spot and asparagus rust. Remember, a preventive program is always more effective than a reactive program. Chlorthalonil (e.g., Bravo WeatherStik) and mancozeb (e.g., Penncozeb) have proven equally effective at preventing purple spot in recent trials and have some activity against asparagus rust. Tebuconazole (e.g., Onset, Tebustar, Orius) has proven more effective at preventing rust outbreaks than chlorothalonil or mancozeb in Michigan State University trials and can be included with these products as part of an overall disease prevention program.
Spotted asparagus beetle was active at one location last week. Unlike common asparagus beetles, this insect is not a major pest as beetle larvae feed on berries, not fern. Read more about asparagus beetles in the MSU Extension fact sheet, “Common and spotted asparagus beetle as pests of asparagus.”
Carrot growers were applying linuron over the past week in west Michigan processing carrots. Ladybug pupae were visible in multiple carrot fields this week. These predatory insects were likely feeding on aphids on wheat nurse crops and are beneficial.
For celery, leafhopper numbers were reported to be lower this week with cool weather. To date, only two leafhoppers out of many tested were carrying aster yellows. Activity could pick up once warm weather returns.
Cucurbit consultants report striped cucumber beetle activity started soon after plant emergence. Note, fungicides can be used to help protect against Phytophthora capsici fruit rot. However, these need to be applied to the fruit. Soil applications will not be helpful for fruit rot.
Onion thrips were present in west Michigan onions this week. Scouting should begin now. In small onions, thrips can be difficult to detect in leaf crevices. Remember that thresholds for spray decisions are based on the number of thrips per leaf. The threshold for Movento (active ingredient spirotetramat) is one thrip per leaf. This means, for example, that onions with five true leaves could have an average of four thrips per plant without requiring treatment. If thrips are below threshold the week you’d normally first apply Movento, skip that week and reevaluate populations again. For more on surfactants, products, thresholds and scouting, see “Cost-effective onion thrips control program 1: Choose good products, add the right surfactant” and “Cost-effective onion thrips control program 2: Apply at right time based on scouting and thresholds” by MSU Extension.
For potatoes, Colorado potato beetle adults were active last week in Ottawa County.
Sweet corn consultants report true armyworms were active last week in west Michigan field corn that bordered wheat. This very spotty pest is typically not a widespread problem, but can be locally damaging if not detected promptly. Scouts should look for telltale damage caused when caterpillars feed along leaf edges. Female moths of this migratory pest prefer laying eggs in grassy areas, including rye covers that precede corn or neighboring crops like wheat. Examine 20 plants at five locations to scout for this and other early season pests. Treatment is justified if more than 35 percent of seedling or early whorl-stage corn is infested.
Consultants also reported cutworm activity last week in field corn, so continue looking for clipped plants on young corn. Chickweed has been very abundant in some areas this spring, and fields with this weed are highly attractive to black cutworm moths. Scouting corn or other vegetables planted into fields that had chickweed could be helpful. Pyrethroid insecticides are effective for both these pests. For organic growers, the spinosad bait Seduce is available for cutworms, while Entrust (active ingredient spinosad) and Dipel DF (Bacillus thuringiensis subsp. kurstaki) are labelled for armyworms. Note, Dipel is most effective when armyworms are small. A nice guide to sweet corn scouting is North Central IPM Center’s “Sweet Corn Pest Identification and Management.”