Weekly Vegetable Update 9/3/2020

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

Crop report

Following a few weeks of intense summer heat, we've had a beautiful week with perfect harvesting weather. Most farmers are harvesting non-stop right now, but it's still worth making time for ongoing management in fall crops.

Cucurbits: Melon and squash harvest is ongoing, and pumpkin harvest will soon be upon us. I'm seeing a lot of diseased cantaloupes in the field, and every cantaloupe I've purchased at a farmers market or grocery store this year (from multiple MN farms with fairly diverse geography) has had disease problems, mostly Anthracnose. It may be worth treating for powdery mildew for another week or so in pumpkins you plan to harvest in late September and October. Pumpkin growers should continue to monitor squash bugs, cucumber beetles, and aphids.
Tomatoes and peppers: Tomatoes and pepper production are quite variable around the state. I've seen quite a few tomatoes that are about ready to pull due to disease issues. High tunnel tomatoes are mostly looking great. I saw a lot of bell peppers with sunscald this week. Fruit with sunscald are more susceptible to secondary pathogen infection, so it's a good idea to harvest and remove these fruits if possible.
Cole crops: We're finally getting some nice cool fall weather, perfect for head formation. As expected, I'm seeing a lot of Alternaria and black rot pressure. See last week's article for an overview of treatment options.
Sweet corn: Corn earworm flights were high in Blue Earth County this week, but were generally low further north.
Onions: Harvest is ongoing. Take care to avoid harvesting before onions are fully mature; the necks should as dry as possible before topping. I'm seeing a lot of soft rot in onions from farmer's markets. More on onion soft rot.

Tissues with sunscald are more susceptible to secondary rots. Photo: NH

Problems in the field

Anthracnose

I've been seeing a lot of Anthracnose this year, particularly in cantaloupe and bell peppers. A question I often get from growers who are seeing the same pathogen group (e.g. Alternaria, Anthracnose, Cercospera) affect multiple crops is whether it's the same pathogen affecting them all. Thankfully, for rotation purposes, they are typically separate species of the same genus, meaning they only affect one or a couple of plant families. The reason we sometimes see multiple species of the same pathogen group in the same field is that since they are related, they have similar optimal conditions.

In the case of Anthracnose, various Colletotrichum species including Colletotrichum coccodes, Colletotrichum gloeosporioides, and Colletotrichum acutatum affects peppers and tomatoes. A separate species, Colletotrichum orbiculare, commonly affects cucurbits in the Midwest, particularly melons and cucumbers. So, from a rotation perspective, you could plant a solanaceous crop following a cucurbit and vice versa, even if you had Anthracnose in that field. In all cases, it's a best practice to remove or till-under infected residues as quickly as possible after harvest.

Post-harvest issues

Post-harvest issues are, in my opinion, some of the worst issues to manage for vegetable farmers. You've worked incredibly hard all season to produce a healthy crop, and to have it go bad in storage can be devastating. I've noticed quite a few post-harvest issues already this year, in particular soft rot in onions and various pathogens in melons.

While the harvest season is extremely busy and many farmers are starting to get pretty tired at this point in the year, it's worth taking the time to inspect fruit / bulbs / roots, etc. for scars, soft spots, and bruises, and discard those with issues. The saying that a single bad apple can spoil the lot is unfortunately sometimes true for various vegetables.

Second, make sure you're storing produce at the proper temperature and humidity. There are three general types of storage conditions that vegetables need:

Cool and dry (50-60°F and 60% relative humidity),
Cold and dry (32-40°F and 65% relative humidity), and
Cold and moist (32-40°F and 95% relative humidity)

For a list of optimal conditions for each vegetable, see the full guide here. (The title is targeted to gardeners, but the info is still very useful to farmers of all scales).