MSU Extension Vegetables

Weather

We are three to seven days ahead of our normal degree day accumulations. The heat and dryness has been having impacts on all of our crops. Some warm season crops are growing faster than they can move potassium or calcium, resulting in some false deficiency symptoms.

Thrips and spiders mite populations are growing quickly on many crops. Treating them with broad-spectrum insecticides will kill important biocontrol bugs and can actually increase mite and thrips population after treatment. Michigan State University Extension entomologist Zsofia Szendrei wrote a great article summarizing ways to manage thrips and spider mites while preventing flare-ups through the use of more selective insecticides which are systemic. These can kill the plant feeding thrips and mites without harming the beneficial bugs.

Click the links below to view maximum and minimum air temperatures, as well as degree-day and rainfall accumulations from Jan.1 through the last 14 days:

• Emmett
• Fairgrove
• Flint
• Frankenmuth
• Freeland
• Kinde
• Lapeer
• Linwood
• Munger
• Pigeon
• Romeo
• Sandusky
• Verona

Crops

All brassicas except Brussels sprouts are now starting to go to market, with fall crops being transplanted. Scouts have found all of the caterpillars are out in most fields. Onion thrips numbers have been a increasing due to the hot dry weather. Swede midge trap catches deployed by Michigan State University Extension remain low.

Zucchini and yellow squash are being picked. Pumpkins and winter squash are vining out. In both crops, thrips are becoming an issue with the hot dry weather. According to Elaine Roddy in Ontario, damage to older leaves may not be a concern, but stunting of new growth indicates the need to treat. Thrips can scar and deform fruits as well.

I have seen some symptoms that resemble bacterial wilt transferred by cucumber beetles. Isolated plants independent of soil moisture? Roots are healthy? No squash borer in the vine? If yes to all three, then it is probably bacterial wilt. Young plants can quickly melt down in the high heat and low moisture conditions we are experiencing.

Some crown rots have shown up in patchy patterns in plasticulture pumpkins. I suspect some of this is due to wind and hot plastic damaging stems and opening an infection point. Otherwise, the dry weather has kept most root and crown rots at bay in dryland pumpkins.

Cantaloupe plants are supporting fruits that are beginning to net, and some growers are moving their first loads. I have seen some low-level gummy stem blight symptoms in some fields, as well as thrips and two-spotted spider mites.

Pickling cucumber plantings are continuing. Downy mildew has not been confirmed in the Midwest yet. Last confirmed outbreak was in Maryland on July 6. Harvests have begun. The extended dry weather has had, and will continue to have an impact on new plantings. In my variety trial I witnessed what appeared to be three separate germination periods following a single planting, as limited soil moisture allowed germination to occur during small rain events between dry spells.

Some tomatoes are exhibiting blossom drop in hoophouses due to heat stress.

Both the hoophouses and in field tomatoes in our area have been confirmed with impatiens necrotic spot virus (INSV) and also tomato spotted wilt vrus (TSWV). Both diseases are transferred by thrips. They get on tomatoes in the hoophouse when shared with untreated ornamental flowers. Symptoms are hard to see when plants are young. Once planted, leaf necrosis and severe stunting will make a field look twiggy and bare. Plants that are infected when they are older will begin to decline with leaf death and wilting. Plants that live long enough will make fruit that is misshapen and mottled. Infected plants are a total loss. Replanting with leftover plants from the greenhouse could be a waste of time if they are also infected.

If infected plants and uninfected plants are sharing a field, then culling plants or treating for thrips will be important to slow the spread. Greenhouses that grow flowers and vegetables must monitor for thrips with blue sticky traps to guide preventative treatments. Especially when buying in flowers to resell. Great Lakes IPM is a good source.

Tomato spotted wilt virus (TSWV) symptoms include black circular specks on leaves like they were dotted with a permanent marker that eventually coalesce into entire charred looking leaves that fall off. Infected transplants will fail to thrive, seen here. Older plants will produce misshapen and discolored fruit. 

Late blight in potatoes and tomatoes has not yet been detected in Michigan, and most areas remain forecasted at low to medium risk.

If you are a commercial pepper grower who regularly uses copper and are detecting leaf spot, please let us know (email me at phill406@msu.edu). The Hausbeck vegetable pathology lab is testing isolates for copper sensitivity.

Sweet corn is silking and insecticide applications have begun. A Tuscola County trapper has caught three corn earworm moths in eight days (0.375 moths per night). The Midwest Vegetable Production Guide recommends treatment is justified when green silks are present and moths are being caught. If less than five moths are caught per night, then a five-day spray interval is adequate. As moth catches approach 50 to 100 per night, a two- to three-day interval would be more appropriate. Treatments can cease when 90 percent of silks are brown. Pyrethroids (mode of action 3A) still work, but Rick Weinzierl, from Illinois, recommends growers should consider tank mixing different modes of action, including Lannate (methomyl 1A), Coragen (chlorantraniliprole 28), or Radiant (spinetoram 5). Besiege is a premix of chlorantraniliprole (28) and lambda-cyhalothrin (3A).

Meetings

• July 19, 6 – 8 p.m. Southern Michigan Pheasant and Monarch Recovery Workshop at Fish Point State Wildlife Area DNR Office. 7750 Pringle Rd, Unionville, MI 48767. John Bauer, 989.673.8174 x 107, john_bauer3@mi.nacdnet.net
• July 20, 6 – 8 p.m. Southern Michigan Pheasant and Monarch Recovery Workshop at Ubly Fox Hunter’s Club. 2351 Ubly Rd, Bad Axe, MI 48413. John Bauer, 989.673.8174 x 107, john_bauer3@mi.nacdnet.net
• July 21, 6 – 8 p.m. Southern Michigan Pheasant and Monarch Recovery Workshop at Richville Conservation Club. 3270 Sanilac Rd, Vassar, MI 48768. John Bauer, 989.673.8174 x 107, john_bauer3@mi.nacdnet.net
• Sept. 26, 9:30 a.m. – 4 pm. The Midwest Mechanical Weed Control Field Day. PrairiErth Farm. 2073 2000 Ave, Atlanta, IL 61723. See in-row cultivation tools demonstrated on vegetable crops, with a trade show, and grower experiences with mechanical cultivation. Event registration is $20 (lunch included). Check it out on Facebook: facebook.com/mechanicalweedcontrol

Need your water tested for the Food Safety Modernization Act (FSMA)? Check out the Michigan Ag Water Lab Map.

Please contact me at phill406@msu.edu or 616-901-7513 with questions, concerns, or to schedule a farm visit. You can also send plant materials to MSU Diagnostic Services.