West central Michigan vegetable regional report – June 22, 2016

Asparagus harvest is at the finish line, insect activity continues.

Shutdown of many west Michigan asparagus fields should be complete today, June 22, or by the end of this week. This is the last main chance for growers to apply herbicides after a clean picking or mowing. Powell amaranth continues to be a challenge, as resistance to standby PSII inhibitors such as diuron was documented in Michigan in 2001.

For post-emergence control, dicamba can be applied with glyphosate; this combination can also be helpful for suppression of field bindweed, a problem perennial. As a hormonal herbicide, dicamba can cause crop injury and epinasty (twisted growth). Applying it after a clean picking or mowing is critical for limiting the extent of injury. Alternatively, 2,4-D also has post-emergence activity against pigweeds and is often used in combination with glyphosate.

For pre-emergence control, Chateau has good efficacy in addition to some burndown activity. Always apply products according to the label. Michigan State University research suggests this product should not be applied more than once in every two years at lay-by due to the potential for herbicide-related crop injury and yield decline. Fungicides for prevention of foliar diseases should continue to be applied to young fields that were shut down earlier and have expanded leaves. A first fungicide application can be made to mature fields once shoots develop and leaves, or “cladophylls,” expand.

Carrot scouts continue capturing low aster leafhopper numbers. Infectivity from an Oceana County sample taken June 19 was 1.8 percent, yielding a threshold of 28 leafhoppers per 100 sweeps.

Striped cucumber beetle activity continues in cucurbits. In some cases, beetle populations are still being noticed past the three-week period of insecticidal activity of FarMore FI400 seed treatments. A variety of foliar insecticides are labelled for control after seed treatments wear off, including bifenthrin (e.g., Brigade, Capture), carbaryl (e.g., Sevin XLR), esfenvalerate (e.g., Asana XL), beta-cyfluthrin (e.g., Baythroid XL) and permethrin (e.g., Perm-Up).

Thresholds can help serve as a guide to help determine if insecticide application is critical. Too time-strapped to scout all your fields? Consider focusing on fields with less than five true leaves, as these are most susceptible to beetle feeding and bacterial wilt. Different vine crops also vary in susceptibility to bacterial wilt, with cantaloupes and cucumbers most susceptible. To scout, count the number of beetles on five plants at five locations per field. Take an average of your counts across these 25 plants, and compare them to the recommendations below to get a feel for how critical is the treatment.

Treatment threshold for striped cucumber beetle

Plant stage

Threshold

Cotyledon and 1 leaf

0.5 beetles per plant

2-4 true leaves

1 beetle per plant

More than 4 true leaves

3 beetles per plant

Weather continues to be good for thrips population growth in onions. If you have made your first Movento application, this week you could make your second application if thrips populations moderately exceed the 1 thrips per leaf threshold. If you have already made two back-to-back applications, or two weeks have passed since your first application, you can switch to an alternative product such as Agri-Mek or Lannate. Consider reserving Radiant for later in the season, as this product is most effective at knocking down high populations.

In potatoes, all life stages of Colorado potato beetle were present to our east in Montcalm County, but summer adults have not been observed to date. According to the Michigan Late Blight Risk Monitoring website, the weather forecast will be favorable for late blight development for two to three out of the next five days from June 22-26, with risk higher to the southwest. To date, the most northerly report of late blight on USAblight is from Virginia.

Note that some sweet corn growers are using slow-release nitrogen or a mix of slow-release nitrogen and urea early in the season. MSU Extension vegetable educator Ron Goldy found that about 150 pounds per acre actual nitrogen applied all up front as slow-release, or with about 20-30 percent of total nitrogen applied as urea with the remainder as slow release, supported yields comparable to pre-plant plus sidedress applications, though it may or may not be as economical depending on the relative price of these nitrogen formulations. See his report for more information, “Poly-Coated Urea as a Season-Long Nitrogen Source for Sweet Corn” (page 8).

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