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Weekly vegetable update 9/7/23

Authors: Natalie Hoidal and Marissa Schuh

Following one final heatwave that brought a flush of ripe tomatoes, there’s a distinct fall feeling in the air. We know you’re all still as busy as ever, but fall tends to bring a feeling that the home stretch is near, and field work becomes more pleasant as temperatures drop. We’re gearing up for fall programming and nearing the end of our weekly updates. This update includes a couple of unique things we’re seeing on farms this week, and some reminders for fall.

Water in peppers

We received a unique report this week of water accumulating in bell peppers. The peppers looked completely normal with no obvious lesions, but they were filled with water despite limited rainfall and the grower using drip irrigation. As peppers ripen, the calyx (the area where the fruit attaches to the stem) becomes thinner, reducing the amount of nutrients and water that the plant can transplant to the fruit. However, in some cases, and seemingly in some varieties in particular, this thin layer ends up letting in water. This is especially common if the fruit is especially lobed on top since rain water can accumulate in the tops of peppers. It can also happen if peppers are washed in a dunk tank. In this particular case, seeing water inside of peppers was unexpected due to the drought and lack of overheat irrigation. If you see this in your fields, keep in mind that a pepper with water inside the fruit cavity will likely have a reduced shelf life. (We’re also curious to hear from you if you’ve seen this - hearing from growers helps us track trends and develop better advice).

Crop cleanup – a slog, but for some pests it matters

Many crops are running out of steam – it's been a long, stressful year, and the fruit they produce are ready for harvest. It's been a long, stressful growing season for us too, but we can reduce pest problems next year if we take the time to remove plants after harvest. Many insect pests spend the winter in crop residue, so the sooner we remove the residue they want to bunk down in, the fewer easy spots there are for them to overwinter.

Squash bugs hanging out in the soil near old summer squash vines, and on fruit that was left in the field. Photo: Natalie Hoidal

Residue removal is an important cultural control for the following pests…
  • Squash bug - removing/tilling vine crop residue reduces overwintering spots
  • Flea beetles - destruction of roots kills larva feeding under soil
  • Swede midge - removal of above ground parts of brassica stops reproduction
  • Cabbage aphids - eggs for overwintering are laid on brassicas, residue destruction can destroy eggs and egg-laying spots
  • Cabbage Maggot - the generation that builds the overwintering population is still out in some parts of the state, residue destruction reduces this population’s numbers
  • Imported cabbage worm - overwinters as pupa in crop debris, destroying debris can destroy pupa
  • Diamondback moth- overwinters as adults in crop debris, destruction of residues reduces overwinter sites
For the pests mentioned above that are seeking overwintering sites, mowing around the crop perimeter will also make it harder for them to find a place to hunker down. A bonus benefit is that mice don’t like scurrying across wide open spaces, so if you are seeing nibbles in things like squash and pumpkins, cleaning up can be a two-fer pest management-wise.

Residue management is also important in the management of many plant diseases. For diseases that require host tissue to survive, for example bacterial canker and black rot, finely chopping crop residue and burying it will speed up how quickly the crop material is broken down, which will in turn mean fewer pathogens in the future.

Gearing up for garlic

We’re just a few weeks away from garlic planting, so we thought we’d share some reminders about best practices for garlic planting:
  • The ideal planting window is mid to late September in northern Minnesota, and early October for the southern part of the state. While the window for planting is longer than originally thought, it’s still best to aim for a couple of weeks before the first hard frost in your area. This allows the root system to begin developing before winter, but prevents the bulbs from developing too much vegetative growth, which is susceptible to frost.
  • Choose a well-drained site, ideally sandy loam or loam, as garlic is sensitive to sitting in wet soil. The idea of wet soil seems far off right now, but our spring weather has become wetter and wetter, so choosing a spot with good drainage will likely benefit you next year.
  • If you’re using quickly available nitrogen sources like urea, apply ⅓ - ½ the recommended nitrogen rate in the fall at the time of planting.
  • If you’re using a slow-release form of nitrogen like compost or composted manure, you can apply most of your nitrogen in the fall when you plant. Ideally, test your compost and manure. Testing is valuable because it helps you understand how much fertility you’re providing and helps you to avoid issues like salt contamination. Read more here about understanding compost analysis results, and read more here about understanding manure analysis results.
  • Make sure to purchase seed from a reputable source, and from someone who has tested for disease and nematodes in their seed garlic. The Sustainable Farming Association maintains a garlic directory with garlic sellers who have tested their seed for garlic bloat nematode:
  • Spacing: closer spacing tends to produce higher yields with smaller bulbs, whereas wider spacing tends to produce lower yields with larger bulbs. Common spacing for Minnesota growers is 6-8 inches between bulbs, and 8-40 inches between rows. The between row distance has such a huge range because between row spacing is usually dictated by your approach to weed management. If you plan to hand-weed, closer spacing works. If your existing cultivation equipment needs to fit between rows, adapt your row spacing accordingly.
  • Finally, make sure to mulch. Mulching helps to prevent frost damage, provides weed control, and helps with moisture retention.
  • Read more about garlic management in the Growing Garlic in Minnesota guide.

Fall soil testing

This is your annual reminder that fall is a great time to test your soil. The UMN soil lab tends to be overwhelmed with samples in the spring, and so the turnaround time can be too short to make good nutrient management decisions for spring crops if you wait. Testing in the fall is reliable for spring nutrient management decisions, as organic matter, phosphorus and potassium levels tend to stay fairly consistent throughout the winter. It also gives you time to make a detailed fertility plan and seek support with nutrient management decisions.

The video embedded below provides an overview of fall soil testing on diversified vegetable farms, addressing questions like “how may separate samples should I take?”, “how should I handle soil testing when I have multiple crops?” and “how often should I test?”

Has this newsletter helped you this growing season? Let us know!

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