East Michigan vegetable update – August 12, 2020

A beautiful week ahead for harvesting. Many crops are high yielding this season.

Sap beetles in a severely cracked heirloom tomato.
Sap beetles in a severely cracked heirloom tomato. Photo by Blair Neifert.


Our region received between 0 – 0.5 inches of rain over the last week. We were lucky that the derecho storm system weakened over Lake Michigan. The corn belt was hit badly by strong winds up to 100 mph and endured significant crop damage.

The medium range forecast suggests warmer than normal, with normal or below-normal precipitation, dew points in the 50’s, and low temperatures in the 60’s. This means many places should have mornings free of dew and rain splash, which is good for limiting disease movement.

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

Here is a table that summarizes European corn borer activity, based on Growing Degree Day models. I used Lapeer as an example.


European Corn Borer emergence – Base 50 F

Current degree days (Lapeer)


Overwintering generation start to emerge and lay eggs

450 (occurred 11 June)

Peak flight and egg laying of overwintering generation

700 (occurred 28 June)

Peak flight and egg laying of 1st generation

1,700 (occurred 31 July)

Peak flight and egg laying of 2nd generation


 Phytophthora Phthought

This disease is kind of like diabetes of the farm. If diagnosed, you will be living with it and will need to change certain practices and behaviors to reduce its effects on the long-term productivity of your business. It can be overwhelming to read about this plant destoyer. So, here is just one thought at a time for anyone going through this.

Following extended wet periods, keep an eye on fields for sustained wilting coming from a soft root crown or fruit rots with white powdery mold after soils drain. Tomatoes and watermelon are less likely to wilt from phytophthora, but the fruits will. Peppers and squash are more likely to show both soft root crowns/wilting and fruit rots. Consider leaving these sections alone until everything is done or destroying them. Either way, wash soil off of the equipment used to do it before moving to a clean area. Note these hot spots for crop rotation and drainage improvement purposes for the next several years.

Crop progress and pests

Cole crop harvest continues. Brussels sprouts are waist high, and some topping took place this week for early crops. The rest of the “main season” Brussels sprouts will be topped in early September.  The very last of the fall-harvested broccoli, cabbage and cauliflower varieties were going this week on farms I visited.

One farm called me out to inspect a runaway Alternaria infection, as the grower was seeing lots of black spores. Turns out, most of the “spores” were insect poop. Can you tell which is which in this little 3-part quiz? https://forms.gle/wfS34cFRTxsmyDcJ7 

Sweet corn harvest has been great. Through the first week of August, most of the corn earworm migration has been apparently deposited west of us in southern Wisconsin and Minnesota, and northern Illinois and Iowa. But, with the strong west-to-east derecho on Monday that came across that same area I would not be surprised if we got some more moths showing up in traps this week.

Cucumber harvest has stopped on some farms and plants have been pulled. Since downy mildew has become such a regular and expensive disease to control, some farms have just stopped growing later cucumber crops. Mechanically-harvested pickling cukes are yielding very well this week, and growers will be maintaining a fungicide program through to last harvest in September.

Melon and watermelon picking has been strong. Some melons over the last week were cracking with the rain. Some farms received a high volume that caused the splits.

Pumpkins and most winter squashes are looking very healthy on most farms, with a strong fruit set. Some are orange already. The only powdery mildew I could find this week was on spaghetti squash and on one butternut planting where there were a lot of weed escapes. Acorns and delicatas are being harvested, with some butternuts, buttercups, kuri ready as well.

Atlas is an amazing butternut variety. Butternuts, as a class of squash, are disease and insect resistant already. In a variety trial from 2017, in a weedy strip till system, I observed Atlas to be relatively bushy, yielding one to two marketable fruit per plant with a large neck portion that is all meat and no seeds. They would have probably yielded more if I had waited another two weeks (or planted two weeks earlier, or controlled weeds better or used black plastic). The plants ripened about 40% of their large fruit after 130 days in a weedy strip-tilled field, 20 days longer than advertised. Another 40% were still green. Because of the efficiency of its fruit shape and size, it is classified as a “processing squash.” That might turn you off from trying it if you grow for fresh market. But, I think it’s worth it. Customers need to process it at home anyway and will quickly see the advantages of it. The crops I saw this week on plastic were looking great.

Field tomatoes, peppers, and eggplants are being picked. It has been a good bell pepper year. A lot of people are growing Aristotle, and the plants are yielding 4 large peppers at each harvest. Blossom End Rot is tough to distinguish from sunscald and Anthracnose sometimes. All three cause a flattened, thin or bleached out appearance to parts of the fruit at first. BER and sunscald is rapidly followed by colonization of the black-spored Alternaria. Anthracnose has a lighter sporulation color. BER tends to be on the end of the fruit, and on the first fruit lowest to the ground, but not always. Sunscald and anthracnose is more common on the sides and shoulders of most fruit. Some varieties hold the fruit with their blossom ends up, which can scald too. If you are maintaining a fungicide program, it’s more likely BER or sunscald. If your irrigation scheduling has not been good, it’s more likely BER.

Blossom end rot, sunscald, and Anthracnose in bell peppers are confusing to tell apart.

Blossom end rot, sunscald, and Anthracnose in bell peppers are confusing to tell apart. Photo by Ben Phillips, MSU Extension.

 I have gotten reports of sap beetles infesting tomatoes. These beetles are largely attracted to easily accessible juices from fruits that have already cracked, or have been pitched in the row middles because of BER or something. They might then move to fruits on the plant with small cracks, and proceed to lay eggs in there and widen those cracks with burrowing larvae. The best course of action is to remove the cull fruit from the row middles and try to pick fruit as they are blushing to ripen them indoors. They are much less likely to crack open this way. Especially heirloom varieties.

I have seen bacterial canker show up in tomatoes on multiple farms, reported to me with pictures and from visits. The easiest diagnostic character is the birds eye spotting on the fruit. Foliar symptoms are harder to ID visually. This disease was most likely hanging on from the transplant house. It is seed borne, and if plants are badly infected at transplant time they will fail to thrive or set much fruit. These young plant infections will frequently show discoloration of the vascular tissue when you cut the stems open.

Sometimes the infections stay at a low level until midsummer and then start to build. I think that is what we are seeing this year. In these scenarios you tend to find fewer stem symptoms and more fruit symptoms, but not a quite as much yield loss as a young plant infection.

Either way, managing bacterial diseases in the greenhouse is the best option with a rotation of copper and streptomycin. Once in the field, a regular treatment with copper + mancozeb rotated with Tanos can help reduce spread of the diseases from rain splash.

Summer plantings of beans and beets for fall harvest are looking strong.

Transplanted onions have been going to market over the last few weeks. I visited one farm that uses black plastic mulch for their onions. They were experiencing high rates of soft rots on the outer sheath of the bulb. Upon cutting and closer examination, we found no internal ring discoloration, softening or bad odors, like you might expect from some foliar diseases that move into the bulb. In fact, the smell made me hungry. These onions were cooking. This does not happen all the time, but enough that some growers have switched to using white plastic for their onions.

Great Lakes Vegetable Producer’s Network

MSU is participating in a live weekly roundtable discussion during the growing season for commercial vegetable producers in the Great Lakes and Midwest region. Join us! We broadcast live via Zoom at 12:30 ET/11:30 CT every Wednesday from the first week of May to the first week of September. Listen live or later here: www.glveg.net/listen. If you have a pressing vegetable production issue that you would like discussed, simply email it, along with your phone number, to greatlakesvegwg@gmail.com

Next week: World Without Lorsban

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.

Did you find this article useful?