West central Michigan vegetable update – May 17, 2017
Asparagus harvest has started fast and furious, carrot and onion stands are developing and early-season cole crop pests are active.
For all crops, remember not all bugs are bad or good, some are just around. This week, I have seen large numbers of what are likely March flies or “lovebugs.” The larvae live in the soil doing their own thing and are not known to damage plants, then adults emerge in large numbers and mate. They are not pests and their flight should be over soon.
Warm temperatures sped the arrival of full-on asparagus harvest in Oceana County this week. Degree-day totals are sufficient for common asparagus beetle to be active and laying eggs, and I did observe beetles active and laying eggs last Friday, May 12, in Newaygo County. Products with one-day pre-harvest intervals include those with the active ingredients carbaryl (e.g., Sevin), permethrin (e.g., Perm-Up), acetamiprid (Assail) and methomyl (Lannate).
Carrot stands are developing in Oceana and Newaygo counties. The recent light rain some areas received should be helpful.
For leafy cole crops, cabbage white butterflies were active in Oceana and Ottawa counties this week. I did observe some egglaying, though eggs were not common on plants. This points to the importance of scouting: The presence of butterflies or moths does not mean there are caterpillar populations warranting control. It does suggest scouting is important. If you are using Bt products, research at Ohio State University did not find any advantage of evening versus daytime applications in one trial. Timely application is likely the most important goal when using Bt.
Maggot activity was readily observable at one location as well, and degree-day models suggest fly activity should start peaking over the next 1.5 weeks at the Hudsonville, Hart at Standale/Walker Enviroweather stations. Currently, there are no known, effective rescue treatments for cabbage maggot. For leafy brassicas, plants can tolerate more maggot damage as they grow, and early spring populations are typically the most damaging. This means plants that survive until after the early spring peak of activity have been through the worst pressure. Leaving row covers on until after peak activity subsides can help plants weather this first generation. View Enviro-weather’s cabbage maggot model that predicts cabbage maggot activity based on degree-days activity.
Some onion growers were applying graminicides to kill barley nurse crops this week. Terminating barley when it is about 4–5 inches high will help ensure it does not cause yield reductions in onions. Use the highest labeled rate of a graminicide, such as clethodim (e.g., Select Max and generics), sethoxydim (e.g., Poast) or fluazipop-P (e.g., Fusilade DX).
For root crops, cabbage maggot activity could be peaking over the next few weeks (see above). Radishes and turnips are susceptible to this pest. If you are using row covers, leaving them on until after peak activity subsides can help plants weather this first generation. View Enviro-weather’s cabbage maggot model that predicts cabbage maggot activity based on degree-days activity.
Sweet corn is up and more was being planted this week, with some plantings recovering from frost damage early last week.