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Weekly Vegetable Update: 6/26/2024

Authors: Marissa Schuh, Shane Bugeja, and Natalie Hoidal

General Notes
This was the week where plant diseases made themselves known across Minnesota. Specifics will be discussed below, but key things across all crops is…
  • Stay out of fields when leaves are wet
  • Prune and stake relevant crops to improve airflow so leaves dry out
  • Manage weeds within and on field borders to increase airflow
  • Scout regularly – the earlier you catch the disease, the more effective your management can b
Drowned out areas in fields need to be closely watched for weeds as the water recedes. Pre-emergent herbicides may have been degraded or washed out, and their performance can be subpar. Late emerging pigweeds, such as waterhemp, can make a quick deposit into your weed seed bank if not caught soon enough. Cultivation is also an option to control these plants, but be mindful of the risks to your farm’s soil health from repeated passes.

If the land is not going back into vegetable production, consider sowing a summer cover crop. We can get several important bases covered at once. Keep the soil in place, fight weeds, and prevent fallow syndrome from affecting a future cash crop. Sorghum sudangrass, buckwheat, lacy phacelia, pearl or Japanese millet each have their strengths and weaknesses, and much depends on your goals. This UMN Extension article from 2020 was written for field crops, but sums up a similar wet weather situation and how grasses fared when sown around July.

Most summer covers also double as forage. If you do not have grazing animals on your farm, consider listing on the Minnesota Cropland Grazing Exchange. Leasing a small area to sheep, cattle, or goats can keep the biomass manageable and help cycle nutrients on-farm. Also, check out the Midwest Cover Crop Council to check out seeding rates and timing for your specific county in Minnesota. (Note: the row crop selector tool on their website works fine for horticultural setups, as you are just looking for sowing windows and species information.) .

Crop Updates
For high tunnel vegetables, we are starting to get reports of the small, soft-bodied insects. For pests like aphids, thrips, whiteflies, and spider mites, before you have major outbreaks is the time to introduce biological control organisms. They do more to keep smaller populations from exploding than reigning in already high populations.

Cucumbers: Take some time this week to prune high tunnel cucumbers if you have not done so already. Pruning is critical for good airflow, disease prevention, and easy harvesting. Ideally, use shears rather than doing this by hand, and make sure to sanitize your pruning shears after every few plants to avoid spreading diseases.

Pepper: The wet start to the season has created perfect conditions for bacterial spot. This disease is cause by bacteria, meaning the pathogen moves with and infects plants in the presence of water. If you've had the disease in the last few years, the pathogen may have hung out on decaying pepper plant matter or tools and surfaces. If this is your first time seeing this disease, it may have come in on seeds or transplants.
Bacterial spot causes brown, irregularly sized spots on leaves. It can also infect fruit. Photo: Paul Bachi, University of Kentucky Research and Education Center,

Anything you can do to increase air flow will help.  There are both organic and conventional treatment options available. See the Midwest Vegetable Production Guide for options.

Potatoes: Early blight is cropping up across the state. This disease is kind of a fact of life when it comes to growing in Minnesota. See the Midwest Vegetable Production Guide for fungicide options.
Early blight on potato. Photo: Howard F. Schwartz, Colorado State University,

Potato beetle larvae are starting to emerge. If you're planning to use insecticides, particularly neem or pyrethrins,the best time to use them is when larvae are small, as they become more tolerant as they become more mature. If you're growing on a small scale and rely on physical removal, taking some time to squish eggs now can save you quite a bit of time later!

Making this all a little more tricky is the appearance of potato leafhopper. Potato leafhoppers sometimes emerge around this time & alfalfa fields get cut around mid to late June, which can drive leafhoppers into neighboring fields. Their feeding can give plants a scorched appearance.

Sweet corn:
Some sweet corn stands are uneven, likely because of moisture. Root systems have had a hard time developing and nitrogen may have leached. Premergent herbicides might have also been washed out of the zones where they effectively combat germinating weeds. Take time to check in on stand emergence and weeds this week, and cultivate and make applications of fertilizer as needed.

Tomatoes: Leaf spot diseases are showing up. See this article for more information.

Vine crops: Cucurbits continue to size up, though planting was delayed on many farms. The first set of fruit are starting to set in field zucchini.. Remember that this first flush of fruit can be poorly pollinated as sometimes it takes bees a minute to find the flowers. More female flowers are on the way and fruit will hopefully be pollinated more thoroughly in the future.

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