West central Michigan vegetable regional report – May 8, 2013

West central Michigan has seen warmer than average weather in the last week, speeding plant and insect development in vegetables. Cooler weather with a frost risk will arrive this weekend.

Mid-week weather summary

Overall, growing degree day (GDD) accumulations since March 1 (GDD base 50 degrees Fahrenheit) have sped since last Wednesday (May 1) with average temperatures roughly 7 to 13 F above 30-year normals. As a result, most of west central Michigan is only behind normal GDD accumulations by a few days. By comparison, the region was over one week behind last Wednesday.

Weather outlook

Michigan State University state meteorologist Jeff Andresen forecasted that this Thursday (May 9) will be the last day with highs in the 70s, with significantly cooler weather on the way. Given changes in the upper atmosphere, a drop in temperatures to a few degrees below normal is forecast for this Friday (May 10) with highs cooling to the low 50s and upper 40s this Sunday (May 12) with the arrival of a Canadian air mass. Given lows may be in the mid- to upper 30s this weekend, there is a risk of frost late Sunday night through Monday morning (May 13). The best chance for rain will occur this Thursday, although precipitation above 0.1 to 0.2 inches is not expected north of I-94.

The National Weather Service’s 6-10 day forecast for next Sunday, May 13, through Friday, May 17, which will cover the start of major asparagus harvest operations, calls for normal temperatures and a chance of above-normal precipitation. Andresen does not have high confidence in this forecast and would expect temperatures and precipitation to be slightly below normal. The 8-14 day outlook, which covers May 15-21, calls for normal temperatures with above-normal precipitation. Again, Andresen does not have high confidence in this forecast.

Crop updates

General update. Despite our cool weather in early April, we have made up significant growing degree days recently, so insect development is likely only a few days behind average. As a result, expect insect activity to pick up with little delay. For example, growing degree day models suggest that seed corn maggot activity and egglaying have peaked in Hudsonville, Mich., and Fremont, Mich., and will peak within a week in Hart, Mich., and Ludington, Mich. Similarly, growing degree day models predict that cabbage maggot will become active this week in Hudsonville, Mich., and Sparta, Mich.

Asparagus has emerged throughout Oceana County with harvest commencing on younger fields this week, and some growers are expecting to begin harvesting the majority of their fields by the end of this week. By next week, well-established fields and those that have lagged behind will catch up and harvesting should become the major focus in asparagus. (Note, in southwest Michigan harvest began last week.)

In some locations, rye has not been mowed off. If significant spear emergence has occurred through the rye, this could lead to loss of harvestable spears when rye is mowed. Given our recent warm temperatures, glyphosate applied up to this Tuesday (May 14) should kill rye within roughly three days so that rye can be mowed without significant risk of growing back.

In terms of insects, yesterday (May 7) I observed both adults and eggs of common asparagus beetle in northern Oceana County, suggesting they are active and laying eggs in our area. Based on past experience, pre-harvest applications of Lorsban (one day pre-harvest and restricted entry intervals) made for cutworms provide roughly three to four days of control for asparagus beetles. For the harvest period, generic carbaryl, Sevin 80S and Sevin XLR are available for control (one day pre-harvest interval). Showing pickers what asparagus beetle eggs look like can allow them to detect it during harvest and alert you to the need to apply these insecticides.

Two species of cutworms are active early in the season and can damage asparagus. White cutworm caterpillars overwinter as larvae and are ready to feed once it warms in the spring. They emerge first and damage the tips of spears. Dark-sided cutworms overwinter as eggs and do not reach damaging size until two weeks after hatching (i.e., later than white cutworms). Dark-sided cutworms feed on the bottom 2 inches of spears, causing the damaged side to grow slower than the undamaged side which results in bent spears. Both cutworms feed at night and spend the day below the soil surface.

For both species, a threshold of 5 percent damaged spears can be used to decide whether or not to apply an insecticide, although most growers spray regardless as a preventive measure. Michigan State University Extension recommends scouting 20 spears at five locations within a field; if more than five spears show evidence of cutworm damage, treat immediately.

Carrot planting has progressed and is now mostly finished in Oceana County on mineral soils. The most immediate pest concern is damping off, or Pythium, which can kill emerging seedlings and reduce plant stands.

As of last Wednesday, May 1, onion planting was in full force in Newaygo County. Growers are typically finished with onion planting in the Grant, Mich., area by this time, but many were just starting. Seed corn maggots are likely now active in both Newaygo and Ottawa counties. During control failures, seed corn maggot larvae can kill seedlings and reduce onion stands. Because this insect prefers laying eggs on soils with high organic matter, it almost always poses a threat for muck vegetable growers. Note that stands could be especially at risk if Trigard-treated seed was planted without an additional Lorsban drench; recent experience suggests that Trigard alone, while often effective for onion maggot, does not provide consistent control for seed corn maggots.

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