Weekly Vegetable Update 7/21/2021

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

The drought continues across most of the state with no obvious end in sight. It seems like many people are really starting to feel burnout this season, with continual weather-related discouragement, and overall exhaustion. But, as summer crops start to come in more consistently, there's some encouragement on the horizon.  

Crop updates

• Garlic: Garlic harvest continues across the state, with most peoples' garlic crop looking very good. You have a few options for curing garlic. With the hot dry weather, field curing might actually be a good option this year if you have limited tunnel or rafter space. Read more about curing options on our postharvest handling page. 
• Tomatoes: High tunnel tomatoes are beginning their peak production period, and field tomatoes will be soon. Despite the drought we have started to get a few more reports of common foliar diseases, but these are mostly from gardeners who may not be pruning sufficiently or tend to overwater. It seems like certain varieties that were peoples' go-to varieties sold out and so folks are trying new things this year, sometimes with less than ideal results.
  
• Peppers: I'm seeing quite a few photos of sunscald on peppers.  This is fairly normal, especially for peppers in edge rows or with less developed canopies. Sunscald spots can be more vulnerable to secondary infections, so remove these peppers as soon as you see them. 

 

Pepper with sunscald, Photo: Natalie Hoidal

• Cucurbits: We have fully entered cucumber and zucchini season, and many people have more than they can handle. Take note and adjust your planting size accordingly next year. Our crops colleagues are starting to see increasing two spotted spider mite populations in southern Minnesota, and these mites tend to be attracted to cucumbers, particularly in tunnels. Keep an eye out for mites - predatory mites can be effective for suppression, and there are some sprays that can be used if populations build. 

Spider mites up close, Natalie Hummel, Louisiana State University AgCenter, Bugwood.org

Speckling on leaves from spider mite feeding, Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

• Cole crops: Early June plantings of broccoli and cabbage are maturing now. We're seeing some major differences in days to maturity as well as head size in our broccoli trials this summer. Young transplants seem to be doing well, with less flea beetle damage than last year, though this can vary significantly by location. We're seeing some significant differences in earliness, head shape and size, lumpiness, and flowering tendencies in our broccoli trials that we're excited to share with you for next year.
  
• Potatoes: Some potato growers are already harvesting, and others are weeks to over a month out. In the first early potatoes I've seen, I've noticed some scab. Unlike most pathogens, potato scab actually does well in dry soils. Potatoes with scab are still safe to eat, but may be unappealing to customers. Second generation adult potato beetles are emerging - spraying adults is less effective than spraying larvae.  
• Carrots: I'm getting more reports of Aster Yellows in carrots, particularly in Western Minnesota. It is totally normal to see aster leafhoppers and some aster yellows, so do not panic if you're seeing them. Rather, try to remove infected plants and bury or burn them, and conduct regular scouting of leafhoppers to monitor populations. The treatment threshold is based on the number of leafhoppers you catch using an insect sweep net (click link for video tutorial of how to use a sweep net). Wisconsin has a nice table breaking down the thresholds. Since we don't know the infectivity rate in Minnesota (aka the % of leafhoppers that are infected), we assume 2.5%. This means that means if you do 100 sweeps through your field, the threshold would be 20 leafhoppers if you have susceptible varieties, and 40 leafhoppers if you have resistant varieties. Do not spray until you have reached this threshold. 

Subtle foliar symptoms of aster yellows include leaf color turning a purplish brown. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

• Sweet corn: We're seeing more ripe sweet corn this week, with much more on the way. Review Marissa's article from last week to learn more about monitoring for corn earworm.
  

Vegetable weather report

There is no rain in sight, and temperatures are projected to stay fairly high (highs of 90, nighttime lows around 70). This is an improvement from prior weeks heat-wise, but still pretty warm. With projected dewpoints in the 60s for the next week or so, we can expect conditions to remain fairly humid.

7 day precipitation forecast, weather.gov

Southern Minnesota is unlikely to receive rain at all this week. Northern Minnesota is projected to receive an inch or more of rain, which should mostly come on Friday night, but local meteorologists are predicting that this storm system will be spotty. Some good weather news is that the smoke seems to be thinning, so should have better air quality in the next few days. 

 

Problems in the field and things to anticipate this week

Talking to your customers about funky vegetables

The prolonged heat and drought are causing all kinds of weird issues in vegetables from hollow heart in potatoes, to bolting, curdy heads in Brassicas, to misshapen cucurbits (this is a pollination issue, but heat impacts pollination). You may find yourselves having to explain these issues to your customers this year, and reassuring folks that their funky looking vegetables are indeed safe to eat. 

One question I have for you, readers, is whether or not  you would like me / our team to develop some consumer-facing fact sheets that you can use to educate customers at the farmers market, in your CSAs, etc.

Japanese beetles everywhere?!

We typically don't think of Japanese beetles as a major pest of vegetables - they tend to go for landscape ornamentals and fruit crops. However,  they seem to be eating everything in sight this year. Farmers have sent reports of them feasting on a wide range of crops from potatoes to kale to herbal plants like hibiscus. While we discourage home gardeners from spraying, there are a few things that farmers can apply to repel them, and if necessary to treat them. 

• Kaolin clay - can be an effective repellent, but doesn't work well for crops where the leaf is the part of the plant that's eaten / used since it leaves a sticky white residue.
  
• Neem - can also be an effective repellent / feeding anti-stimulant, but should not be used as a knock-down product.
  
• Row cover - works great if you get it on early enough, or if you're able to physically remove most of the beetles before applying.
  
• Bacillus thuringiensis galleriae - Bt is typically reserved for larvae, but this specific strain (galleriae) has been shown to be effective on adult Japanese Beetles. The most common formulation is called BeetleGone (this is not an endorsement of a specific product).

Japanese beetle feeding on hibiscus leaves. Photo: Natalie Hoidal

Educational opportunities

The Vegetable Beet: join us during your lunch break on Wednesdays for a 30 minute discussion about vegetables. Next week's topic will be about oomycetes / water molds.

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.