Weekly Vegetable Update 7/23/2020

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

Precipitation was wildly inconsistent this week. Some growers experienced downpours, and even tornadoes and hail. Other expected rain, but received none at all. For everyone, it's been hot except for a lovely cool day yesterday thanks to winds coming from Lake Superior. We can expect another hot week ahead with high dewpoints and relative humidity. This means crops are growing quickly and keeping you all very busy. It also means the potential for disease spread and heat stress is high.

Crop report

• Tomatoes and peppers: Thanks to some very warm weather over the last couple of weeks, tomatoes and peppers are maturing more evenly this week. With high humidity in the forecast, preventative sprays (of either biocontrol agents or fungicides, or both) will be important. Continuing to monitor soil moisture closely will also be important for preventing physiological issues related to soil moisture inconsistency. Check out our recent podcast with Dr. Inga Meadows from NC State University about spray programs in organic tomatoes.
• Cole crops: The heat this week and last resulted in some weird brassica developments, mainly things like uneven or lumpy heads, and leaves growing out of broccoli heads. Cole crops that have experienced heat stress in the critical period just prior to head formation tend to be more susceptible to diseases, so keep a close eye on disease pressure. While we typically see flea beetle pressure drop off in mid-June, I've received multiple reports of flea beetle damage this week. 
• Cucurbits: with the hot weather, farmers are having to pick cucumbers and zucchini almost constantly. Leaving fruit on the vines too long is problematic for many reasons like unmarketable fruit and soft rot susceptibility. Melons are coming along, but most farmers are at least a week out, in some cases many weeks out from harvest. 
• Asparagus: as fern canopies become more dense, keep an eye out for rust and other diseases. 
• Garlic harvest is mostly complete.  
• Potatoes: some farms have started to harvest early potatoes. I visited a field this week with 100% defoliation from potato beetles. Leafhopper populations are still very high. 
• Beans and peas: green bean harvest is in full swing. For dry beans or beans that will not be harvested for a while, leafhopper damage remains high. Peas are being planted for fall harvest; this year was a bad year for pea diseases, so make sure you're planting fall peas in a different field from your spring peas if you had any issues. 

Leafhopper damage in beans, NH

Problems in the field

Onion problems

This year's onion crop was off to a great start, but I've started to hear reports of problems from around the state, primarily related to soft rot and thrips. Soft rot tends to develop in bulbs around the time of harvest, and is difficult to detect before harvest since most symptoms are underground. It is especially prevalent in fields that are irrigated continuously in hot weather (sound familiar??), and when onion maggots are present. Waiting until onions are completely mature to harvest, allowing the leaves to dessicate after lifting and before topping, and culling any onions exhibiting soft tissues at harvest will help to reduce the spread of soft rot. Once the bulb is infected, onions will not store.

Thrips populations have also increased, especially in areas that received less rainfall this week. The threshold for onion thrips is 1 thrip per leaf; scout about 10 onions, pulling the leaves back to count thrips. Since thrips have a very short lifecycle, treatments should be repeated every 5-7 days. For conventional growers, see recommendations from the Great Lakes Vegetable Production Guide. For organic growers, Spinosad is your best bet, but take care to avoid resistance issues.

Bacterial Soft Rot
Howard F. Schwartz, Colorado State University, Bugwood.org

Heat-related deformities

Many farmers are in peak broccoli and cabbage harvesting season for the summer, but the high temperatures have caused deformities ranging from lumpy heads to leaves growing out of heads to brown bead. In fact, these problems are so widespread that grocers and wholesalers with mostly local contracts for broccoli at this time of year have had to start importing from California and other states.

Oddly shaped cucumbers

Plants have been growing very quickly this week due to the high temperatures. With cucumbers forming over the span of only a few days, they need very consistent moisture to be able to develop normally. Misshapen cucumbers are likely a result of soil moisture inconsistency. Additionally, oddly shaped fruit can be a result of pollination issues. While some cucumbers are parthenocarpic (produce fruit without pollination), many varieties still require pollination. If a flower is incompletely pollinated, or if there are pollen deformities related to high temeratures, your cucumbers may have a crooked shape or may be bulbous on one end and pinched on the other.

Misshapen cucumbers, NH

Insect and disease forecast

Diseases

We continue to see high humidity and a high dew point, creating excellent conditions for disease spread. Scout regularly, send samples to the disease clinic for identification, and removed diseased tissue if possible (only when conditions are relatively dry and your hands / tools are clean). Most growers should be implementing preventative spray programs (including organic growers) on crops that consistently have disease issues. 

Insects

Flea beetles: We typically think of flea beetles in cole crops as being a spring problem, but I've heard numerous reports this week of flea beetles reaching damaging levels, particularly for new plantings of spring brassicas. Here's a review of flea beetle management strategies.

Tomato hornworm: This insect is rarely problematic or present in large numbers, but their impressive size is often surprising to growers who see them for the first time.

Squash bugs: We've been seeing squash bugs here and there for a while now, but nymphs are now emerging and developing. While we typically don't see damage until later in the season, squash bugs are much easeir to manage when they are at the nymph stage.

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.