East Michigan vegetable regional report – June 24, 2015

Ben Phillips<benp@msu.edu>, Michigan State University Extension - June 24, 2015

Diseases are mounting their assault on multiple Michigan vegetable crops.

Weather

Many growers in a northeast band sweeping across the I-69 corridor received 3 inches of rain Monday evening, June 22, and growers in the Bay area received some major precipitation last Thursday, June 18. This has caused some fervor to pump fields across roads into adjacent ditches. Other growers got the perfect amount of rain. However, all of this rapid precipitation, mild temperatures and warm nights have created the perfect disease environment.

Here are the rainfall and growing degree day (GDD) base 50 degrees Fahrenheit accumulations to date from Michigan State University Enviro-weather stations.

Rainfall and GDD summary
Location	GDD (50 F, March 1)	Rainfall (inches, April 1)
Linwood	732	7.67-7.15 (0.52 since last week)
Frankenmuth	824	7.49-7.3 (0.19 since last week)
Lapeer	843	10.24-7.9 (2.34 since last week)
Romeo	837	9.78-9.38 (0.4 since last week)

Crops

Sugar snap peas are being picked.

Early potatoes are being harvested. Late blight has been found in North Carolina and we should be extra observant for late blight to show up in Michigan this year. Michigan State University Extension plant pathologist Willie Kirk has been recommending some alternatives to chlorothalonil for protective fungicides, as some growers have found it difficult to obtain pure formulations this year.

Many field-planted vine crops are flowering and vining, including watermelon, cantaloupes and cucumbers. Cucurbit downy mildew has been confirmed in Michigan, and commercial growers are encouraged to start preventative applications of fungicides. MSU Extension plant pathologist Mary Hausbeck has crafted an example spray program that is based on spore counts, Enviro-weather conditions and confirmed downy mildew samples.

Greenhouse tomatoes are being harvested. Some fields are showing bacterial diseases and require copper applications to prevent their spread in this high precipitation trend we are going through. Rotating with products containing chlorothalonil will help protect plants from late blight, which could be moving our way in these weather conditions. Both of these diseases should be high priority for growers this year.

Onions on the muck are getting lots of precipitation and should be scouted for bacterial diseases as well. There is a new bacterial pathogen on Michigan onions that the Hausbeck Lab is conducting research on. Any samples of yellow, water-soaked leaves should be directed to the nearest MSU Extension county office or scout to be brought to campus.

Sweet corn is just starting to tassel and silk, and growers should be on the lookout for corn earworm moths. The current trapping methods call for a threshold of one moth per trap per night to begin insecticide treatments. Once your spray program has begun, the threshold changes to direct scheduled sprays. If you find less than 10 moths per night per trap, then spray every seven days. If you find more than 10 moths per night per trap, then you need to tighten up your spray schedule.

Please contact me at phill406@msu.edu or 989-758-2502 to pick up any suspected disease samples, or send the diseased plant parts to MSU Diagnostic Services.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).