Authors: Marissa Schuh and Natalie Hoidal
Minnesota has had pretty minimal days under 90 until the tail end of last week, when heat and humidity moved in. UMN Extension has developed guidelines around how often to rest and drink water, you can find those here. For how this heatwave may affect some of our vegetable crops, you can read a refresher here.
We are on tap for some extreme winds. If you are seeing plant damage, timely applications of copper and fungicides can help protect the plants from pathogens. For more information on how strong winds can impact vegetables at this point in the season, see this article from Iowa State.
Some generalist diseases
In the last week we have gotten reports of a couple of moisture-loving pathogens that affect a wide range of vegetable crops. Both of these diseases can survive for a long time in our soil, so quick detection and removal of infected plants can help reduce the amount of the pathogen you have going forward.
Phytophthora
This long-lived, water-loving disease is a problem in vine crops, tomato, peppers, and eggplant (though winter squash and peppers get it the worst). The disease often starts in low spots, with all plants in the low spot permanently wilting. Closer looks at these plants will reveal phytophthora's calling card – coating infected plant materials in a blanket of white spores, almost as if the dead plant was coated in powdered sugar. The pathogen can infect all parts of the plant, from root to steam to leaves to fruit.
Phytophthora often first causes plant wilting in low spots. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Key things if you are seeing this disease is to remove infected plants, as this disease will continue to infect new plants and make new resting structures all summer long. Next, think about water, as this pathogen moves with and thrives in water. Think about how mater moves out of infected areas, and make sure to clean shoes and equipment that go through the area. Work in this area last, and remember that this pathogen can infect pumpkin and winter squash in a way where they look fine at harvest, but melt down on their way to customers. Managing this one is long-term and tricky, feel free to reach out (612.460.7462) for help with diagnosis and management if you think you’re seeing this disease on your farm.
Infected leaves and cucumbers, showing the white spores. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
For more information on phytophthora, visit the UMN’s webpage on this disease.
White Mold
White mold is a long-lived soilborne disease that can infect beans, cabbage, tomato, and potato.
This disease can infect all parts of the plant. The first symptom of infection in these plant parts is pale, water-soaked areas that will eventually become covered with a fuzzy white mold. Infected areas eventually produce things that look like mouse droppings. These structures are like a spore bunker, surviving in the soil for 5-8 years until a period of prolonged moisture triggers it to open and start another round of white mold infection.
Minnesota has had pretty minimal days under 90 until the tail end of last week, when heat and humidity moved in. UMN Extension has developed guidelines around how often to rest and drink water, you can find those here. For how this heatwave may affect some of our vegetable crops, you can read a refresher here.
We are on tap for some extreme winds. If you are seeing plant damage, timely applications of copper and fungicides can help protect the plants from pathogens. For more information on how strong winds can impact vegetables at this point in the season, see this article from Iowa State.
Some generalist diseases
In the last week we have gotten reports of a couple of moisture-loving pathogens that affect a wide range of vegetable crops. Both of these diseases can survive for a long time in our soil, so quick detection and removal of infected plants can help reduce the amount of the pathogen you have going forward.
Phytophthora
This long-lived, water-loving disease is a problem in vine crops, tomato, peppers, and eggplant (though winter squash and peppers get it the worst). The disease often starts in low spots, with all plants in the low spot permanently wilting. Closer looks at these plants will reveal phytophthora's calling card – coating infected plant materials in a blanket of white spores, almost as if the dead plant was coated in powdered sugar. The pathogen can infect all parts of the plant, from root to steam to leaves to fruit.
White Mold
White mold is a long-lived soilborne disease that can infect beans, cabbage, tomato, and potato.
This disease can infect all parts of the plant. The first symptom of infection in these plant parts is pale, water-soaked areas that will eventually become covered with a fuzzy white mold. Infected areas eventually produce things that look like mouse droppings. These structures are like a spore bunker, surviving in the soil for 5-8 years until a period of prolonged moisture triggers it to open and start another round of white mold infection.
In some ways white mold hangs around and infects plants like a weed seed – future white mold infection happens when these bunkers are buried in the top few inches of the soil and sense the right conditions to release spores. The spores that come out infect that plants they touch, and there is one round of infection and spore-bunker setting per spore (like a weed with an annual lifecycle).
Moisture management is the basis of white mold management. This starts at the time of field selection and planting layout (keeping susceptible crops out of fields with poor wind flow, and orienting rows for ease of drying), and continues when making decisions about varieties and planting density (less dense canopy = more drying).
Crop Updates
Onions: Onions are humongous on some farms thanks to all the rain. Soft rots do well in hot weather, so take extra precautions this year during harvest to avoid bruises and scrapes, which allow soft rots to enter the bulbs. Take some extra time with your storage onions to sort out anything that is bruised or scraped.
Remember as you finish curing onions and garlic that these crops have somewhat unique storage requirements. They prefer cool conditions (~40 degrees F) and lower humidity (50-60% relative humidity). If possible, they should be stored separately from most other vegetables, which tend to prefer high humidity. Review our postharvest guide for crop-specific instructions.
Melons: Knowing exactly when to harvest melons can be extremely tricky. Harvesting too early can result in tasteless fruit, whereas harvesting too late makes melons spoil more quickly, and opens up doors for disease problems. To help you harvest at the right moment, we’ve developed a handy to harvesting and storing melons, squash and pumpkins.https://extension.umn.edu/commercial-fruit-growing-guides/harvesting-and-storing-melons-squash-and-pumpkins
Vine Crops: Start scouting for powdery mildew on a regular basis, as preventative treatments are much more effective, and this is the time of year we start to see symptoms. This is a pathogen that quickly evolves resistances to different fungicides, so check in with the Midwest Vegetable Guide to see how the products in your program stack up.
Green beans with white fuzz and black spores-bunkers. Howard F. Schwartz, Colorado State University, Bugwood.org
Moisture management is the basis of white mold management. This starts at the time of field selection and planting layout (keeping susceptible crops out of fields with poor wind flow, and orienting rows for ease of drying), and continues when making decisions about varieties and planting density (less dense canopy = more drying).
Crop Updates
Onions: Onions are humongous on some farms thanks to all the rain. Soft rots do well in hot weather, so take extra precautions this year during harvest to avoid bruises and scrapes, which allow soft rots to enter the bulbs. Take some extra time with your storage onions to sort out anything that is bruised or scraped.
Remember as you finish curing onions and garlic that these crops have somewhat unique storage requirements. They prefer cool conditions (~40 degrees F) and lower humidity (50-60% relative humidity). If possible, they should be stored separately from most other vegetables, which tend to prefer high humidity. Review our postharvest guide for crop-specific instructions.
Melons: Knowing exactly when to harvest melons can be extremely tricky. Harvesting too early can result in tasteless fruit, whereas harvesting too late makes melons spoil more quickly, and opens up doors for disease problems. To help you harvest at the right moment, we’ve developed a handy to harvesting and storing melons, squash and pumpkins.https://extension.umn.edu/commercial-fruit-growing-guides/harvesting-and-storing-melons-squash-and-pumpkins
Vine Crops: Start scouting for powdery mildew on a regular basis, as preventative treatments are much more effective, and this is the time of year we start to see symptoms. This is a pathogen that quickly evolves resistances to different fungicides, so check in with the Midwest Vegetable Guide to see how the products in your program stack up.
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