Weekly vegetable update 8/13/2020

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

Many of you were hit by the storm this week. For most, it meant very heavy rainfall. For some, it meant devastating hail. Others were not hit at all, and instead had a busy and productive week of harvesting. For those of you who did see damage, please reach out to our team if there is any way we can support you. 

We have some stormy weather predicted across most of the state this weekend (unfortunately with some more hail potentially predicted in certain regions), followed by a very reasonable week of high temperatures in the upper seventies, which should be great for harvesting.

Crop report

• Cucurbits: Cantaloupe production is in full swing, and watermelon production is ramping up. Pumpkin and squash growers should continue to be proactive about powdery mildew and squash bugs. 
• Tomatoes and peppers: Tomatoes are at peak summer production, and peppers are getting there. I continue to see blossom end rot issues. Now is the time to start removing flowers if you have not done so already. Flower production is energy intensive, and current flowers won't have enough time to become ripe fruit.
  
• Cole crops: I received numerous reports about flea beetles this week; it's unusual, but not unheard of to see flea beetle problems this late in the season. I also got a couple of reports of brown bead (see more info below). Temperatures have been more moderate for the last week, and are expected to stay that way, which bodes well for crops that are just entering their head formation phase.
  
• Onion Harvest is ongoing. Soft rots do well in hot weather, so take extra precautions this year during harvest to avoid bruises and scrapes, which allow soft rots to enter the bulbs. Take some extra time with your storage onions to sort out anything that is bruised or scraped. The rain storms have helped to reduce onion thrip populations, but they remain high on some farms.
  
• Potatoes: While most potatoes are looking pretty good this year, I have received a slow trickle of questions about soft rot and scab. Potatoes with soft rot should be discarded immediately. Potatoes with scab are technically edible if peeled, but take extra care if you choose to store these potatoes, as they are more susceptible to secondary rots.
  
• Beans: Despite all of the leafhoppers and some spider mites, most farmers seem to be harvesting a pretty healthy and consistent crop of green beans. 
• Garlic: It's time to start purchasing garlic seed! See last week's post for guidance. 
  
  

Problems in the field

Hail

While some fields were irreparably damaged this week, we received a few questions from farmers whose pumpkins and melons were hit with hail, but still seemed relatively in-tact. This damage ranged from foliar damage to pocked fruit depending on the size, shape, duration, and velocity of the hail. After being hit by a mild to moderate hail storm, there are a few things to consider as you move forward with management decisions.

If you've suffered substantial leaf damage, but the growing points are still in-tact (this is likely since the growing points are fairly protected), your plants will likely recover. However, they will be more susceptible to bacterial and fungal infection. Consider a preventative fungicide application, such as a copper containing product. If you've already been seeing a specific issue like powdery mildew, use a product specifically tailored to that pathogen.

If you do a quick online search about responding to hail damage, you might find articles recommending a nitrogen application. However, these articles are mostly written with early season damage in mind. I checked with our nutrient management specialist Carl Rosen to clarify these recommendations, and here's what he said: I honestly think it is too late to do much of anything about hail damage for pumpkins right now.  Probably one of the worst times it could hit because there is only about a month of good growing season left.  The decision to add N might depend on the amount of damage. If there is light damage - less than 25% defoliation then a small amount of N as a foliar or with irrigation might be beneficial (5-10 lbs/A as a foliar or 15-20 lbs in the drip).  With severe defoliation, adding N might eventually produce more foliage but by the time new leaves form there will not be enough time to produce marketable pumpkins. 

 

Howard F. Schwartz, Colorado State University, Bugwood.org

Brown bead and hollow stem

Multiple farmers sent me photos this week of brown bead in their broccoli. Portions of the head become necrotic (they turn yellow, then brown and stop growing), giving the head a mottled appearance that almost looks like diseased spots. Brown bead is a bit like yellow shoulder or blossom end rot, in that it's not caused by a specific thing, but rather a combination of environmental variables. High heat during head formation can cause brown bead, as can inconsistent moisture. While low nitrogen levels alone will not cause brown bead, not having enough access to nitrogen can exacerbate the problem. Like blossom end rot, brown bead is often associated with low calcium levels in the head tissues, but this has less to do with total Ca in the soil, and more to do with the difficulty of transporting calcium. While you cannot control temperatures, you can control your soil moisture. Keep soil moisture as consistent as possible during these hot summer days. 

I also got a photo of hollow stem, which we often start to see around this time of year. If you're seeing BOTH brown bead and hollow stem, you might have a boron deficiency, but make sure to base any boron applications on a soil test since too much can be toxic. Both conditions are also more prevalent in very fast growing varieties, so take that into consideration when choosing varieties for next year. Additional factors involved in hollow stem are plant spacing and too much nitrogen; here's a nice overview from Iowa State. 

Hollow stem, Photo from Waxwing Farm

Insects: Despite the heavy rains I continue to see spider mite issues, as well as surprisingly high flea beetle populations in late season broccoli. See last week's update for more info about mites, and this week's flea beetle article for more info about flea beetles.

Technical Assistance

If you're seeing interesting things in your fields, insects and diseases, or just want to share photos, we'd love to hear from you! As always, don't hesitate to reach out with questions and pictures. We're still here for technical assistance over the phone, via text, or via email.

Vegetable questions go to me (Natalie): hoida016@umn.edu

Fruit questions go to Annie: kloddann@umn.edu

Food safety questions go to Annalisa: hultb006@umn.edu

Educational opportunities: things to listen to in the field

Great Lakes Vegetable Producers Network: join us during your lunch break on Wednesdays for a 30 minute discussion about vegetables. All previous episodes can be downloaded as podcasts, and are available on Apple Podcasts. Next week's episode will be about cover crops; our most recent episode was about irrigation. You can also visit the network page for recordings of all previous episodes, and listen along to the mp3 recordings while you work.

Also remember that What's Killing my Kale is ongoing, with recent episodes about flowering and fruit set in cucurbits, apple crop load management, measuring soil health, nutrient management in wet soils, Spotted Wing Drosophila updates, and climate change adaptation. These episodes are also available through the Apple Podcasts app, or can be downloaded directly online.