Weekly vegetable update 6/23/2021

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

We are still in a drought, but this week has been much more manageable. Most farmers got a little bit of rain, and temperatures have been much more forgiving. Crops are growing quickly, and we're just about at peak summer where most of our crops have started to mature.

Crop updates

• Cole crops: I've been seeing some very healthy broccoli, cauliflower, bok choy, radishes, and kale this week. As always the Lacinato kale seems to be struggling the most from flea beetle damage. Cole crop caterpillars are very active right now, so keep scouting to make sure populations do not reach economic threshold levels:
  
• Pre-cupping:  50% of plants have at least 5 diamondback moth larvae per plant, or 20-30% of plants have 1 or more imported cabbage worm or cabbage looper eggs or larvaa.
  
• Cupping to harvest: 10% of plants infested with any caterpillar larvae or eggs.

• Potatoes: We are now seeing all four stages of potato beetle larvae in the field, and expect to see a second generation of adults soon. Many potatoes are flowering across the state, which means tubers are forming, and will begin to bulk soon. Irrigation is especially important during this period to prevent hollow heart, which is a result of inconsistent moisture. Continue to keep an eye out for potato leafhoppers, and either continue to remove potato beetles, or use a preventative spray program if populations are increasing.  

 

Potato beetle larvae. Photo: Natalie Hoidal

• Pea harvest continues with no major problems.  
• Carrots and beets are looking good. I haven't actually had any reports of aster yellows yet, but leafhoppers are out and about, and this is the time of year we start to see aster yellows symptoms. Scout your carrots for any discolored or distorted leaves, and remove carrots with symptoms.
  
• Onions: Continue to keep an eye out for onion thrips as the weather stays warm and dry. Bulb formation is underway, so keep your onions irrigated!
  
• Tomatoes: Some farmers are harvesting their first tunnel tomatoes this week. The weather has cooled down just in time for flower formation in field tomatoes. Tomatoes seem to have recovered well from the heat, but we're starting to see a little bit of disease pressure, particularly in tunnels where humidity is starting to build up. Start scouting your tomatoes regularly, and identify all potential pathogens so that you can address them early.

High tunnel tomato scouting diagram from Michelle Grabowski and Angela Orshinsky

• Garlic: Most farmers are now harvesting garlic scapes. As per last week's update, make sure to do so carefully, ideally by hand, so that you do not damage the leaves. In these final weeks until garlic harvest, keep irrigating regularly so that the soil maintains consistent moisture, and keep an eye out for insects like thrips and leek moths.
  
• Asparagus: As you finish your asparagus harvest for the season, take some time to focus on weed control and asparagus beetle management. Read about weed management options in the U of M asparagus guide.  
• Cucurbits: Cucurbits are flowering and setting fruit at this point; many growers are harvesting zucchini and high tunnel cucumbers. The heat may have caused some early flower abortion or odd fruit, but this week's temperatures are much better for healthy flowering and fruit formation. Cucumber beetles have been terrible this year. See Marissa's article from this week for mid-season cucumber beetle management tips, with pollinators in mind. 

  

  Keep pollinators in mind when managing cucumber beetles. Photo: Natalie Hoidal
  

 

Vegetable weather report

Over the next week we can expect highs in the 70's and 80's. The Twin Cities and southeastern parts of the state may get some scattered showers over the weekend, with an inch or more of rain projected over the next 7 days. The northern and western parts of the state are expected to stay dry. 

7 day precipitation forecast, weather.gov

Problems in the field and things to anticipate this week

Summer fertilizing tips

I've received a few photos of nutrient deficient plants, and some more general questions about foliar feeding at this point in the season, so I thought I'd share some general considerations for summer fertilizer applications:

• Soil-applied fertilizer should be incorporated to reduce losses - at this point in the season, you could achieve this by adding fertilizer to a trench a few inches from your crop, or using a water soluble fertilizer with your irrigation.
• The soil has to be moist for fertilizer to be accessible to plants, so make sure you're irrigating consistently before and after an applicaiton.
• We've reached the point in the summer where certain crops become quite sensitive to nitrogen. This is particularly true for cucurbits and peppers - at this point in the season when plants are getting ready to flower, a late nitrogen application can delay flowering and fruiting, instead encouraging the plant to invest in vegetative growth. 
• Foliar applications can burn plants if they are too concentrated. It's better to stick to less concentrated applications more frequently. But, keep in mind that foliar feeding should be supplemental rather than your primary fertilizer source. Foliar samples can tell you whether your plants are on track nutrient-wise, and what they are lacking. Read more about foliar testing here. 
  

Anticipating squash and pumpkin insects

The cucumber beetles have already been a struggle this year, and cucurbit growers (particularly pumpkin and squash growers) should anticipate more insect pressure in the near future. Now is the time in the season when we start to see squash vine borers and squash bugs. Yellow bowls of soapy water can work as traps to detect squash vine borer arrival (and provide degree of of control). Begin scouting the undersides of the leaves for clusters of squash bug eggs and nymphs. 

Squash bug eggs. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

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 cucumber beetle management.

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.