East Michigan vegetable update – May 8, 2019

Planting is going along, but field prep is delayed in soils in low laying areas and soils with more clay.

Potassium and magnesium deficient tomato plants
Potassium and magnesium nutrient deficiencies show up in lower tomato leaves at the onset of fruiting. Manganese toxicity looks a lot like this and can occur if it is foliar applied and not needed, or if soil pH is lower than 6.0. Photo by Ben Phillips, MSU Extension.


Some weather is coming up from the southwest today, May 8, bringing rain tomorrow and a good chance of black cutworm moths with it. Wet soils and weedy fields are a perfect place for black cutworm moths to lay eggs and thrive. Timely herbicide application, or tillage to bury weed residue, is typically the key to avoiding a black cutworm infestation. If weeds or a cover crop are killed 10-14 days before crop emergence or transplanting, most existing and hatching larvae die from the tillage or starve out from the lack of healthy weeds instead of moving to the new crop buffet.

We are getting into seed and root maggot times. Here is a table that summarizes the maggots of concern and the degree days that signify when they will be laying eggs in the areas around seedlings. I used the Lapeer Enviroweather station as an example. The onion maggot model is from NEWA.


Seed corn maggot emergence - base 39 F

Onion maggot emergence – base 40 F

Cabbage maggot emergence - base 43 F

Current degree days (Lapeer)




Overwintering flies start to emerge and lay eggs

201 (occurred 18 April)

390 (forecasted to emerge by May 14)

298 (forecasted to emerge by May 14)

Peak flight and egg laying of overwintering flies

342 (occurred on 4 May)



Peak flight and egg laying of first generation flies




Peak flight and egg laying of second generation flies




You can find more detailed weather information for your area by visiting the Enviroweather station closest to you

Vegetable crops

Greenhouse management. I visited a grower with a set of AcuRite sensors that transmit temperature and humidity information from the tomato hoophouse every 16 seconds to a base station in the house. That’s a nice way to keep an eye on things. Their website advertises that a phone app can be used as the base station as well, at a similar cost.

Field preparation is on-going as conditions allow.

Asparagus is holding tight. Not much harvest taking place, though some folks have taken a first picking.

Garlic is the most hopeful thing to see in a slow spring. They do not seem to mind.

Onion and carrot nurse crops are being sprayed off in the oldest plantings. Some weeds are coming through before the onion two-leaf stage. If the weeds get larger than 0.125 inch, they can be harder to control. The best option may be to wait until the two-leaf stage rather than risking damaging plants with an early application.

Heated hoophouse tomatoes are coloring. Some of the most common nutrient issues in hoophouse tomatoes are calcium acetate (Ca), potassium (K) and magnesium (Mg) deficiencies as the plant sets fruit. Leaf symptoms of potassium and magnesium will show up on the oldest leaves as those nutrients are pulled from them to fuel the growing fruits. Magnesium-deficient leaves take on a chlorotic yellow marbling between the leaf veins, which can become brown speckled and necrotic. Potassium-deficient leaves will turn yellow along the edges and up between the veins and eventually burn up starting at the edge, leaving bright green veins. Potassium deficiencies also show up in the fruit at yellow-shoulders disorder, and calcium acetate deficiencies show in the fruit as blossom end rot.

Further, lower soil pH (under 6.0) can increase manganese (Mn) to toxic levels that can cause leaf symptoms that resemble a deficiency of magnesium or potassium. So, it is worth knowing your soil pH when diagnosing issues. Foliar nutrients mixed with insecticides and fungicides can also create toxicity symptoms, especially if the pesticide has an oil carrier.

It is important to maintain a fertigation schedule of potassium in a roughly 2:1 or 3:1 ratio with nitrogen (N) as fruit sets and through harvest. Calcium is not often lacking, especially in soils with higher pH or water with higher alkalinity, and is supplied to the plants most effectively through regular irrigation. Magnesium can be supplied with Epsom salts as a corrective treatment at 2 pounds per 100 gallons of water or as a monthly application of 1 pound per 100 gallons of water through the drip irrigation system metered at 1:100.

It is worth noting all of these nutrients compete for space on roots with phosphorus (P). Over fertilization with phosphorus will result in fewer calcium acetate, potassium and magnesium ions getting into the plant and will result in deficiencies even if you are supplying enough. For in-soil tomatoes, the Hartz ratio is a good place to start when considering your fertility plan. Get your soils tested and plug in the values in the Hartz ratio calculator for phosphorus, potassium, magnesium, calcium acetate and the Cation Exchange Capacity (CEC). The calculator will show you how your soils compare to soils with a low risk for yellow-shoulders disorder, (a good indicator that something is off).

Brassica transplants are in. Some is on plastic. Irrigation headers were being hooked up in Tuscola County plasticulture rows.

Early sweet corn on or under plastic appears to be gaining popularity. Many growers have not had a chance to plant their main season varieties, while a few early birds have 4-inch plants.

Vine crops are up in the trays. Some watermelons are getting leggy. Plastic is being laid in preparation for early melons and watermelons under hotcaps or low tunnels.


It is never too early to make accommodations to attend the Great Lakes Fruit, Vegetable and Greenhouse Growers EXPO, Dec. 10-12 in Grand Rapids, Michigan. Hotel blocks are open and tend to go fast. The combination of grower-focused, research-backed presentations and an exhibit hall featuring a diverse set of vendors make it a can’t-miss event.

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.

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