Weekly vegetable update 9/8/2021

Author: Natalie Hoidal, UMN Extension educator, local foods and vegetable crops 

It's really starting to feel like fall. Many farmers are harvesting a flush of carrots and beets, and cool season crops like lettuce, chard, and Brassicas are coming along nicely. The drought is still persistent, but a few weeks of steadier rainfall has made it a bit more manageable. 

I looked at the vegetable update I wrote this week last year, and I was wearing a heavy fall jacket, noting that tomatoes and peppers had slowed down substantially due to the cold. What a different set of conditions than we're experiencing right now!

Crop updates 

• Cucurbits: Melon harvest is still strong, but many farmers are reaching the end of the melon season and transitioning focus to winter squash and pumpkins. I've noticed that stores around the state have embraced fall decor early this year, and people seem to be buying pumpkins a bit ahead of schedule. The most ideal scenario from a pumpkin storage standpoint is to harvest pumpkins as soon as they are ripe. The forecast for the next week is good for pumpkin field curing (warm and dry). After curing for 10 days or so, move them into storage.  If you need to leave pumpkins in the field for pick-your-own markets, try to leave the healthiest pumpkins with the least amount of powdery mildew (which is abundant this year), or other diseases. If you have vines that are heavily infected with powdery mildew, or that have died back substantially, consider cutting the stems and moving your pumpkins to the shade to prevent sunburn and infection into the handle.  

 

Pumpkins in fields with powdery mildew should be removed when ripe to prevent infection of the stem. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

• Cole crops: Last week we hosted our last episode of the Vegetable Beet, and it was all about broccoli. When I started my job in 2019, I was consistently told by farmers that black rot was the #1 priority on their farms, but since that time Alternaria seems to have rapidly replaced it as the primary disease threat. I learned in our conversation last week that this is true across the country, and that more virulent strains of Alternaria have become prominent from Georgia to New York. Check out our final episode if you'd like to learn more about research projects going on around the country related to broccoli.  
• Tomatoes: Field grown Romas and heirloom slicer tomatoes are coming in strong this week, and many farmers are offering bulk orders for canning and preserving. If you haven't yet topped your indeterminate tomatoes, this is a good time to do so - read more about topping in last week's update.  
• Potatoes: Harvest for fresh markets is starting to wrap up, and farmers are starting to focus on storage potatoes.  We've seen a lot of post-harvest potato problems in the last couple of years, so make sure you're putting some extra attention towards sorting out bruised or scraped potatoes, and any potatoes with soft spots. Avoid washing them too vigorously prior to storage, as they can get nicked in the process, creating susceptible wounds.

Bacterial soft rot has been a challenge for growers in recent years. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

• Garlic: Garlic planting is right around the corner. Growers in northern Minnesota should plan to plant in mid to late September, while growers in the southern part of the state can wait until early October. Planting too early can cause shoots to emerge above the soil line and freeze (ideally shoots should emerge from the clove before winter, but not break the soil line). Now is a good time to start preparing beds for garlic planting to allow residues from your previous crop or cover crop to break down. It's also a great time to get a soil test (turnaround time is about 2 weeks right now) so that you have time to amend your soil.  
• Sweet corn: Corn earworm trap counts remain above the threshold across the state, though they have dropped a bit from last week. 

 

Corn earworm counts remain high across the state. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

• Carrots: For the most part, carrots are looking great this year. I always receive a few questions at this time of year from folks with very misshapen carrots. There are a few causes, and it's important to figure out which one (or ones) is causing deformations so you can make changes next year.
  • If your soil is very rocky or compact, carrots can fork - growing on raised beds can reduce compaction and provide better drainage. 
    
  • Too much nitrogen can cause carrots to branch. If you're seeing a lot of branching and your soil isn't especially compact or rocky, think back to the amount of nitrogen you applied (this is especially relevant for faster release sources). Carrots need about 120 lbs N on low organic matter soil, 100 lbs on medium organic matter soil, and 80 lbs on high organic matter soil.
    
  • Pythium is a soil borne disease that can cause excessive branching and stubbiness. This is typically an issue in fields without good drainage that receive excess water - while we are in a drought, there have been cases of farmers receiving 3-5 inches of rainfall in a single rain event. Pythium is often accompanied by cavity spot symptoms.
    
  • Root knot nematode also causes branching, but it's typically accompanied by nubs all over the roots, and often excessive hairiness. Hairiness is also a symptom of aster yellows, but carrots with aster yellows should not have distinct nubs. 

   

  

  Forked carrots are often simply a result of compaction, but it's worth investigating other potential causes. M.E. Bartolo, Bugwood.org

  
  

Vegetable weather report

The US drought monitor has not yet been updated from 8/31 at the time I'm writing this, but from 8/24 to 8/31, there were significant shifts from extreme drought to severe drought, and also from areas experiencing severe drought to now only moderate drought. That said, rainfall will be quite limited this week. Parts of northeastern Minnesota might receive up to a half inch, but most of us will get closer to 0.1 to 0.25 inches or so. 

 

We're reaching the time of year when nighttime temperatures in northern MN could soon drop to freezing temperatures (not likely, but not out of the question). But, it looks like nighttime temps will hover in the 40s and even 50s for the next 10 days or so across the northern portion of the state. 

 

7 day cumulative precipitation forecast, weather.gov

Problems in the field and things to anticipate this week

Fall manure applications

For growers who rely on fresh manure as a source of fertility, fall is usually the best time to apply it for food safety reasons. If you're starting to shop around for manure, make sure you're following some basic best practices:

• Get it tested. Many MN soils have excess phosphorus, which is harmful to freshwater ecosystems. A manure test will help you understand the nutrient profile of the manure you're applying, and will allow you to make responsible nutrient management decisions. 
• If you're grazing animals directly rather than applying manure from another source, test your soil directly on a regular basis. 
  
• Wait until soils are cooler to avoid nitrate losses.
• Consider planting a winter hardy cover crop to retain nutrients in the soil in early spring as the ground thaws. 
• Pay attention to food safety -  To reduce the risk of contaminating fresh produce, follow the 90/120 day rule from the National Organic Program guidelines for applying animal manure.Read more about safe and responsible manure management in the link below.
  
• Read more about fall manure applications in this article that our manure management team put together last year for fruit and vegetable growers.

Grazing chickens through vegetable fields in the fall after harvest is relatively common. Make sure you're doing so safely. Photo: KRiemer, Pixabay

Saving seed

If you're saving seed for your farm, make sure you're saving seed from enough plants to maintain the genetic diversity and integrity of your population. Additionally, seed should only be saved from healthy plants. Hot water treatment can help to reduce disease carry-over from year to year, but it is not a substitute for starting with clean, healthy seed.

Seed Savers Exchange has an excellent guide to seed saving that tells you how many individual plants you should save seed from in order to maintain a variety, and how far apart your plants need to be from similar plants (such as the distance between two separate varieties of sweet corn).

 

 Fagiolina del Trasimeno cowpeas, Photo: Natalie Hoidal

Technical assistance

 If you're seeing interesting things in your fields, need help identifying problems, or just want to share photos, we'd love to hear from you! Growers can reach out directly to me any time at hoida016@umn.edu, and you can submit questions and requests for diagnostic help here.