Weekly vegetable update 9/10/2020

Author: Natalie Hoidal, UMN Extension Educator, Local Foods and Vegetable Production

Crop report

It's been another intense week of harvesting. While the cold has slowed things down a bit, farmers are now harvesting both summer and fall crops. Growers in far northern Minnesota experienced some frost on Tuesday night, but it looks like the week ahead will be warmer.

Cucurbits: Melon and squash harvest is ongoing. Some pumpkin growers have begun to harvest as well. Continue to treat powdery mildew up to 7-10 days or so before harvest if it is serious enough to reduce canopy cover. If you've already lost substantial canopy cover and you're seeing sunscald, consider harvesting if fruits are at least 50% orange and moving them to the shade to cure.
Tomatoes and peppers: Tomato and pepper harvest has slowed down with the cold, though high tunnel tomatoes are still looking great. See the photo below for a seriously impressive tunnel of tomatoes. Take time this fall to remove all residue from tunnels and to really clean up your tomato fields where you had disease pressure.
Cole crops: Most parts of the state either already had rain in the last couple of days or will get more in the days to come. While cool weather is less favorable to cole crop pathogens like black rot and Alternaria, do keep an eye out for disease pressure and avoid these fields until they are completely dry. See last week's article for an overview of treatment options.
Sweet corn: Sweet corn harvest is wrapping up for most growers. Corn earworm flights remain relatively high in Blue Earth County, and we've heard reports of problems from growers around the Twin Cities.
Carrots and beets: Farmers have been harvesting successions of carrots and beets all summer, but now is when they really start to get good. Many of the carrot farmers I work with are erring towards earlier and earlier harvests at the expense of really sweet carrots. With increasingly unpredictable fall weather, many growers are harvesting early to avoid situations where the ground freezes early or where fall rains prevent access to fields.
Potatoes: Farmers have also been harvesting early potatoes all year, but we're now reaching the fall storage potato harvest. It's been a tough potato year, so congrats on making it this far! As always, be vigilant with throwing out bruised or scraped potatoes to avoid soft rot contamination of your storage area.
Garlic: Planting season is almost upon us!! Garlic should be planted 1-2 weeks after the first killing frost. In Northern MN planting is typically done the 3rd to 4th week of September, and in Southern MN it's done in the first or second week of October. Make sure you have your seed in order and that you've reviewed the Growing Garlic in Minnesota guide.
A tunnel so long you can't see the other side! And some very very happy tomatoes at Untiedt's.

Problems in the field

Internal white tissue in tomatoes

This is a relatively common issue in tomatoes, particularly in larger slicer tomatoes, and sometimes in romas. We've been getting a lot of reports from gardeners who have perfect, beautiful looking tomatoes, but when they cut them open the tissue is hard, white, and tasteless. Internal white tissue disorder is primarily a heat stress response; the vascular tissue in the fruit can become damaged when daytime temperatures exceed 90F and nighttime temperatures are consistently in the high 60s and 70s. While it is cooling down now, we are seeing the residual effects of heat stress in weeks past.

In some cases it has to do with potassium uptake, but just like blossom end rot, yellow shoulder, etc. the problem is not necessarily a lack of potassium, but an inability to transport it quickly enough. When it's very hot outside, cell division progresses rapidly. Nutrients like calcium and potassium have limited mobility, so the plant isn't able to transport these nutrients quickly enough when cell division speeds up. If you're seeing widespread issues, it is worth testing for some of these additional nutrients in a soil test just to make sure they're not lacking in the soil, but it is typically a heat issue. Consistent moisture is key for nutrient mobility during really hot summer periods.

Here's a nice little variety trial from Purude looking at susceptibility to internal white tissue disorder.

(more) Cucurbit viruses

This has been a good year for viruses. With the early arrival of migratory insects like aphids and leafhoppers and the long, hot summer, conditions were perfect for virus-carrying insects. The most recent round of viral issues is showing up in pumpkins. At the point that you're seeing warty-structures on your fruit, it's too late to do much. But, it's worth getting it diagnosed. There's a whole complex of mosaic viruses that affect cucurbits, and some can overwinter in residues or nearby perennial plants. Resistant varieties do exist, but you have to know which specific virus you're dealing with.