Michigan vegetable crop report – June 19, 2024

The heat wave is accelerating crop growth and pest activity.

A large field with growing tomatoes.
Field of processing tomatoes in southeast Michigan. Photo by Chris Galbraith, MSU Extension.


Irrigation demand is high this week.

This week’s forecast features:

  • Variably cloudy, hot and humid to the south through early weekend with scattered showers and thunderstorms possible daily. Cloudy and cooler to the north with scattered showers and thunderstorms each day into the weekend. Heavy rainfall totals possible this week to the north. Fair, cooler and less humid early next week.
  • High temperatures from the upper 60s to the north to low 90s to the south through Saturday, June 22, with heat indices into the 90s possible to the south. Low temperatures from the 50s north to 70s south Wednesday through Saturday. Temperatures cooling statewide to highs in the low 80s and lows in the 50s by early next week.
  • Above normal daily potential evapotranspiration rates expected again this week (daily values from 0.17–0.24 inches).
  • Medium range outlooks generally call for warmer than normal temperatures and near to above normal precipitation totals.

Produce Food Safety On-Farm Readiness Reviews 

On May 2, the U.S. Food and Drug Administration (FDA) released their final revisions to the Food Safety Modernization Act Produce Safety Rule Pre-Harvest Agricultural Water Rule. If you are a grower in Michigan, this is a great time to schedule an On-Farm Readiness Review (OFRR). Not only can our team help you assess your on-farm produce safety risks, we can help you assess your water system in light of the updated water rule. If you have already had an OFRR on your farm, no problem, we are happy to come back out to help you assess your water system based on the new parts of the water rule. 

An On-Farm Readiness Review (OFRR) is an opportunity for a grower to walk around their farm with their local conservation district produce safety technician and a produce safety specialist from Michigan State University Extension. These 2-hour educational visits take place during the harvest season and are meant to be casual and low stress. Everything discussed during an OFRR is confidential and focused on ways a grower can reduce their own risks in relation to produce safety. There is no pressure to take our advice either, we are just here to support you in your produce safety efforts!  

Heat considerations

With hotter temperatures comes greater risk of volatilization and spray drift. Volatilization depends not only on air temperature but also relative humidity—the less water vapor in the air, the more potential for evaporation. This article on applying pesticides during hot weather can help with determining what combinations of air temperature and relative humidity are appropriate for applying pesticides during a heat wave.

The following safety reminder comes courtesy of Laurel Harduar Morano with the Michigan State University (MSU) College of Human Medicine:

With a hot Michigan summer upon us, it is important to be mindful that hot weather can be dangerous while working outside. The heat produced by your body while working plus high outdoor temperatures makes it more likely for your body to overheat. To prevent overheating, do the following: drink plenty of fluids; take frequent breaks in the shade, and if possible, reschedule high energy tasks for earlier or later in the day.
Call 911 immediately if severe symptoms of overheating occur such as confusion, slurred speech, fainting, nausea/vomiting, rapid pulse, seizures, hot dry skin, or heavy sweating. Move the person to a cool place and help lower their temperature with a cool wet cloth and/or cool bath. Do not leave the person alone. Death can occur if the body does not cool down, so it is essential to have a plan before such symptoms occur.

Thinking outside the crop

If farming were easy… what would Extension educators do? Farming brings new things each year, including confusing patterns of damage. Growers and educators can spin their wheels searching for possible explanations. In these situations, it is nice to at least rule some causes out, leaving others to investigate. One place to look is “outside the crop.” This is true in two ways. First, check outside the crop species by looking at weeds growing amongst the symptomatic vegetables. Do they share the same symptoms? If yes, it suggests the ultimate cause is probably not a disease or insect. Most insects and diseases specialize on a handful of related species. There are likely a few weed species in your field that are from completely different plant families than the crop. So, if the weeds look sick just like the crop, it’s worth investigating another cause, such as fertility, spray injury, drift or weather related injury.

It’s also helpful to look outside the crop literally, seeing if plants along field edges share similar symptoms. This can be especially helpful in determining if spray drift might be an explanation; if an injurious spray arrived from another place, it may injure plants outside the field too. This type of evidence gathering can at least help you rule out some causes to pull at more profitable threads!

Crop updates 


We are experiencing July weather in early June. As harvest winds down, make sure to protect fern in fields that were shut down earlier. This extremely warm, humid stretch of weather will be very favorable for purple spot development.

Continue to exercise care if applying 2,4-D as part of your burndown component, especially given the high temperatures this week. Hot conditions can evaporate the water in the spray droplet, volatilizing it, creating drifting particles that can move quite long distances. There is a formulation of 2,4-D called Embed Extra that may help to some degree, and using a bit more water volume and coarse droplets can also help.

Brassicas and greens

Transplanting continues and cabbage harvest has begun in southeast Michigan. Caterpillars are feeding and scouts in southwest Michigan are trapping diamondback moth and cabbage looper. Imported cabbage worm adults (cabbage white butterflies) are flying. Thrips damage can also be found on leaves. Refer to this article by Zsofia Szendrei on how heat waves can exacerbate populations of thrips and other pests.

Cabbage plants that have been eaten by deer or groundhogs emerging from a field
Groundhog or deer damage in cabbage. Wildlife damage tends to be most severe around field edges. Photo by Chris Galbraith, MSU Extension.

Carrots and celery 

For information on aster leafhopper thresholds and aster yellow infectivity risk, check out this recent article from Zsofia Szendrei and consider signing up for the text alert system.



All types of vine crops are being planted. Field-planted cucumbers and zucchini have started going to market in southwest Michigan. Angular leaf spot has been found in at least one farm, which can look like downy mildew.

Cucurbit downy mildew spores have been detected in a spore trap in Saginaw County. No crop infection has been reported yet. Read the Michigan State University Extension article, “First 2024 cucurbit downy mildew spores identified in air samples in Saginaw County” for more information. Keep up to date on the development of this vegetable disease at the Hausbeck Lab Downy Mildew News website.

Fruiting vegetables

Early plantings are flowering and more plastic is being laid for later plantings. For indeterminate tomatoes in high tunnels, vertical trellising is most popular while determinate tomatoes grown out in the field are usually supported by the horizontal “basket weave” (also known as Florida weave) trellis system. Check out this video from University of Maine for an introduction to this method.

An issue of concern during heat waves is blossom drop in tomatoes, peppers and related crops. As temperatures climb to 90 degrees Fahrenheit or higher for multiple days, plants become stressed and abort flowers in order to prioritize survival in hot and dry conditions. Too high of temperatures also reduce the quantity and quality of pollen produced—pollen grains have an overly gummy texture and lower success in fertilization. Certain tomato varieties are more heat-tolerant than others and show lower incidence of blossom drop during warm spells.

Close-up of tomatillo blossom.
Close-up of tomatillo blossom. Unlike tomatoes, tomatillos cannot self-pollinate despite having complete flowers (flowers that contain both male and female parts). This means at least two tomatillo plants must be grown together for fruit set to occur. Photo by Chris Galbraith, MSU Extension.

Boron toxicity was reported in tomato plants this past week. Boron is an essential micronutrient and is taken up via roots, mostly in the form of boric acid. The range between boron deficiency and toxicity is extremely narrow—narrower than any other element. Generally, soils with less than 0.5 parts per million (ppm) boron are considered deficient, while only a few ppm more may result in toxicity.

Boron toxicity can occur in plants when they are exposed to higher concentrations of boron than they can tolerate. Symptoms of boron toxicity on tomato leaves include yellowing, browning, dry tips, necrotic lesions, chlorosis and necrosis on the margin of the leaves. Fruit may appear misshapen and plants may be stunted and show less productivity. Stems can also crack or become corky. Severely affected plants can die.

Irrigation can be used to help flush excessive boron out of the soil. Some biological agents have been shown to alleviate boron toxicity in tomato plants. The good news is that if you used a higher concentration of boron this year, it will not stay in the soil since it is highly mobile and may not affect the crop next season.

Wilted and brown tomato plants and leaves.
Symptoms of boron toxicity in tomato leaves and plants. Photo by Salta Mambetova MSU Extension. 


Herbicide applications and mechanical cultivations continue in direct-seeded onions. We are reaching the longest day of the year (June 20), and the long days of the year that surround this date are cues for our long-day onions to initiate bulbing. The primary goal for onion growers is to have large enough plants by now so that they can begin to use their leaves as sunlight accumulators for their bulbs. Shrimpy plants will only support shrimpy bulbs. This is especially important for growers targeting the colossal sizes of the sweet onion market. Many varieties of sweet onions are actually intermediate-day onions, which start bulbing even earlier than long-day types. This is why they are most typically transplanted in April from bareroot plants grown down south or from greenhouse grown starts that begin their life from seeds in January and early February.

Garlic scapes and actual bulb harvest has begun on some farms, and it’s earlier than usual. If you plan to grow garlic next year, you must begin sounding out your seed sources now, as the seedstock goes fast between July and August, with slim pickings in September and October.

Peas and beans

Peas are being harvested and beans are flowering. Japanese beetles are out and active.

Root crops and potatoes

Radishes and turnips are ready in many areas. Colorado potato beetles can be found in all life stages now, and it may be worth a foliar application of insecticide if you did not use an at-plant treatment. For organic growers, the insecticide spinosad can provide control of early life stages of Colorado potato beetles. The foliar browning and curl from leafhopper feeding, called hopperburn, can be found in some areas.


Strawberry harvest is ongoing. The strawberry season started two weeks earlier this year due to the warm temperature. Strawberry root rots caused by various pathogens have been trickling into MSU Plant and Pest Diagnostics.

Sweet corn

It is almost time to start setting traps for sweet corn moths and bookmarking weblinks that provide pest updates:



This work is supported by the Crop Protection and Pest Management Program [grant no. 2021-70006-35450] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. 

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