Weekly Vegetable Update - July 24, 2024

Authors: Marissa Schuh and Natalie Hoidal

General Notes
Some areas continue to get heavy rainfall, other parts of the state are drying out. The NOAA forecast for August is calling for a slight chance of above normal temperatures, and a normal amount of rain.

Plants on some farms, and maybe in every farm’s low spots, are struggling. The below picture from Purdue University highlights how different crops are affected by waterlogging. The crops on the left side were submerged in water for three days, while the three on the right were grown in optimal conditions.

Waterlogging in vegetable crops. Photo: Wenjing Guan, Purdue University.

Crop Updates
Bean: Harvest continues. I have gotten pictures of some leaves with yellowing and scorched edges. A potential culprit is leafhoppers, particularly potato leafhopper. This leafhopper makes it’s way up to Minnesota each summer, and uses it’s straw-like mouthpart to feed on plant juices. While they don’t spread disease, their feeding produces disease-like symptoms. When the leafhoppers feed, they not only hurt that plants through feeding, but through a toxin in their saliva. This toxin plugs the plant's vascular system up, causing v-shaped yellow areas on the edges of leaves. Over time, these area’s turn brown, crispy, and die. You can monitor populations using a sweep net, and use what you find to make spray decisions. See the Midwest Vegetable Production Guide for thresholds and products.

 Hopper burn in snap beans. Photo: F. Becker, The Ohio State University Extension

Carrots: We 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.
• Hairy carrots may have aster yellows. There are many carrot varieties with tolerance to aster yellows, so consider planting more tolerant fall carrot varieties.  See the below table from Commercial Vegetable Production in Wisconsin for more information on varieties, as well as more details on their Aster Yellows Index.

Different carrot varieties susceptibility to aster yellows, from Commercial Vegetable Production in Wisconsin 
 

Pepper: Around July we start to get reports of deformed pepper plants with curled, puckered leaves. This can happen for a variety of reasons, and sometimes it's difficult to distinguish symptoms from one another. There are three main things that can cause peppers to look this way:

• Herbicide drift: Usually if you're experiencing drift, you will see similar symptoms across the farm, with various crop families impacted.
• Thrips, mites, and aphid feeding: These small insects are often difficult to see because of their size, and because they often spend time on the lower sides of leaves, or in plant crevices. They have straw-like mouthparts, allowing them to feed on plants without causing obvious large holes (like insects with chewing mouthparts would). Instead, their feeding can cause leaf deformations, and a general chlorotic appearance (yellowing leaves). Scout carefully for these insects if your pepper plants look deformed, as they may not be immediately obvious. They are especially common in tunnels. Sometimes we see heavy feeding damage on transplants early in the season, and even if insect pressure decreases in the field, the foliage can remain deformed. Thrips, mites, and aphids can also transmit viruses, so it's important to scout for them often.
• Variety: Some peppers are honestly just odd looking. In our pepper trials over the years, we've found that habanero peppers and other very hot peppers like ghost peppers tend to have a more mottled appearance overall with curlier leaves.

Sweet corn: Harvest is ongoing. I got a report from a grower in Southeastern Minnesota of corn earworm. Looking at weather models, there was a potential drop of Corn Earworm moths with the weather front that moved in on July 14th. Occasionally this pest sneaks up to Minnesota and does early damage, but typically in Minnesota it is a pest we battle from August onwards. For more information on sweet corn pests to look out for from this point out, see this article.