West central Michigan vegetable update – May 3, 2017

Be on the lookout for early-season pests like cutworms and true armyworms in coming weeks.

An asparagus spear with its tip nicked by the mower. Nicks can look similar to white cutworm damage, but will all be at a similar height. Image courtesy of Ben Werling, MSU Extension.

An asparagus spear with its tip nicked by the mower. Nicks can look similar to white cutworm damage, but will all be at a similar height. Image courtesy of Ben Werling, MSU Extension.

Weather

There could be a risk of frost and freezing temperatures late Sunday and Monday morning, May 7-8, and again late Monday and Tuesday morning, May 8-9.

For all vegetables, be on the lookout for black cutworm this spring, especially in fields that had heavy winter annual weed cover. These spots are favored for egglaying, and a flight was detected in other parts of the state this week. It takes roughly 300 degree-days base 50 degrees Fahrenheit from a significant flight for caterpillars to hatch and grow to their most damaging size.

Crops

Widespread asparagus harvest had not started in Oceana County farms I visited early this week. Cool temperatures held harvest back and some farms just finished their final mowing Monday, May 1. Cool weather that slows spear growth can elevate the risk of white cutworm damage, though this pest is typically very sporadic and does not cause widespread damage. Note that fields where spears were up when they were mowed can have their tips nicked, which looks similar to white cutworm damage, but damage will all be at a similar height (mower height).

Processing carrot planting has progressed well at some locations up until our recent rainy weather. Fresh-market carrots were just emerging last week in barley windbreaks. In past years, some growers observed spotty cutworm damage in carrots, so it may pay to scout for this pest in fields that had a good cover of winter annual weeds like chickweed. Cutworms can feed on these weeds and then move to the main crop after they are killed by herbicides. A variety of pyrethroids are labelled for control, including esfenvalerate (e.g., Asana XL), β-cyfluthrin (e.g., Baythroid), bifenthrin (e.g., Brigade) and zeta-cypermethrin (e.g., Mustang Maxx).

For cole crops, in the past Michigan State University Extension determined crucifer flea beetle larvae can cause damage to root crops like turnips and radishes. However, this damage is distinct and different from that caused by cabbage maggot. The observed damage consisted of “pin-prick”-like, tiny holes in the root surface, while cabbage maggot larvae produce extensive tunneling. Foliar insecticides will not help prevent cabbage maggot damage.

Flea beetle holes on radish Maggot tunneling on turnip

The picture on the left/top shows pin-prick-like holes on a radish from flea beetle larvae. Damage from this pest looks very different from tunneling caused by cabbage maggot, as seen on this turnip in the picture to the right/bottom. Images courtesy of Ed Grafius (left, radish) and Bern Werling (right, turnip).

For sweet corn, a true armyworm trap in Oceana County detected significant numbers this spring, so this moth could be active and laying eggs in grassy areas. It could be worth scouting for this pest in young sweet corn this year, as damage is easily prevented once an infestation is detected. Also, consider scouting for black cutworm at the same time (see note above).

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