Authors: Marissa Schuh and Natalie Hoidal
Growers are bringing a gorgeous variety of vegetables to markets and CSA boxes around the state.
Parts of the state received some extreme winds that damaged crops earlier this week. Looking ahead, the NOAA 8-14 day forecast is calling for above normal temperatures and below average precipitation. Read on for information on aster yellows and late blight, as well as other crop considerations at this point in the growing season.
Late Blight found in Madison, WI area
This morning (8/28), late blight was confirmed on tomatoes in Dane County, Wisconsin (think Madison). While we are approaching the final month of the growing season, this disease can still kill tomato and potato plants quickly.
This disease is easiest to spot when humidity is high, and leaves in the center of a dense canopy are often the first to get infected. Leaf spots are a brown-gray, sometimes described as greasy. You may see white spores on the underside of the leaf. As spots grow, they turn darker brown with a grey-green edges, they will also move into the petiole and stem (stems will appear brown).
See this page for a refresher on this disease and more pictures of what to look for.
If you suspect you’ve found late blight, reach out and we can work on diagnosis. This disease can be very destructive, so if the pathogen is in Minnesota, it is important for all growers to know.
Late blight products are most effective before infection is present. Products for this disease are specific – as late blight isn’t a fungus (is is most closely related to phytophthora). Check for effective products in the Midwest Vegetable Production Guide. Infected plants should be removed and destroyed.
What is going on with aster yellows this year?
Minnesota growers are reporting losses from aster yellows in garlic, onions, carrots, and potatoes. States around the region are reporting more aster yellows than we might expect with our cool, wet growing season. In Michigan, researchers run a program where they track what percent of leafhoppers parts of the state are infected with aster yellows, and are finding generally high levels of aster yellows infectivity in the population there. What is going on?
While we know the basics of aster yellows and the leafhoppers that spread it, drilling down into what exactly is happening in a given year is difficult. Leafhoppers move to Minnesota on winds from the south, and they may or may not arrive carrying aster yellows. Aster yellows is a disease that can infect and survive in many other species of plants, so uninfected aster leafhoppers can pick up the pathogen once they are in MN. Some theories and thoughts.
Crop Updates
Carrots: Carrots are being harvested. Some farms are experiencing large losses for aster yellows. Managing this disease, especially organically, is tricky. There aren’t any known effective organic products. This leaves us with variety selection as our main tool, as aster yellows biology makes a lot of the cultural practices organic growers rely on ineffective or impractical. Depending on how your planting is set up, row covers can protect fall carrots, but will make weed control difficult.
Different carrot varieties susceptibility to aster yellows, from Commercial Vegetable Production in Wisconsin.
Garlic: Growers from across the state continue to report aster yellows, with many expressing they haven’t seen Aster Yellows like this since 2012. Garlic with aster yellow will have discolored wrappers (often presenting as purple streaks). These cloves can be eaten, but should not be saved or sold as seed. Some cloves look like they have aster yellows, while others look fine? If they have aster yellows, you will likely know if you have germination issues in the spring..jpg)
Let us know what you thought of this year's vegetable updates
We are nearing the end of the part of the season where issues that arise can be addressed. Let us know below if these updates helped you out this growing season. If they missed the mark, we want to know that too! Share your thoughts below.
Growers are bringing a gorgeous variety of vegetables to markets and CSA boxes around the state.
Parts of the state received some extreme winds that damaged crops earlier this week. Looking ahead, the NOAA 8-14 day forecast is calling for above normal temperatures and below average precipitation. Read on for information on aster yellows and late blight, as well as other crop considerations at this point in the growing season.
Late Blight found in Madison, WI area
This morning (8/28), late blight was confirmed on tomatoes in Dane County, Wisconsin (think Madison). While we are approaching the final month of the growing season, this disease can still kill tomato and potato plants quickly.
This disease is easiest to spot when humidity is high, and leaves in the center of a dense canopy are often the first to get infected. Leaf spots are a brown-gray, sometimes described as greasy. You may see white spores on the underside of the leaf. As spots grow, they turn darker brown with a grey-green edges, they will also move into the petiole and stem (stems will appear brown).
Late blight causes distinct hard, brown areas on unripe tomatoes. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Late blight on a potato leaf. Pathogen causes brown areas with diffuse edges, almost like watercolor. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
See this page for a refresher on this disease and more pictures of what to look for.
If you suspect you’ve found late blight, reach out and we can work on diagnosis. This disease can be very destructive, so if the pathogen is in Minnesota, it is important for all growers to know.
Late blight products are most effective before infection is present. Products for this disease are specific – as late blight isn’t a fungus (is is most closely related to phytophthora). Check for effective products in the Midwest Vegetable Production Guide. Infected plants should be removed and destroyed.
What is going on with aster yellows this year?
Minnesota growers are reporting losses from aster yellows in garlic, onions, carrots, and potatoes. States around the region are reporting more aster yellows than we might expect with our cool, wet growing season. In Michigan, researchers run a program where they track what percent of leafhoppers parts of the state are infected with aster yellows, and are finding generally high levels of aster yellows infectivity in the population there. What is going on?
While we know the basics of aster yellows and the leafhoppers that spread it, drilling down into what exactly is happening in a given year is difficult. Leafhoppers move to Minnesota on winds from the south, and they may or may not arrive carrying aster yellows. Aster yellows is a disease that can infect and survive in many other species of plants, so uninfected aster leafhoppers can pick up the pathogen once they are in MN. Some theories and thoughts.
- Did aster leafhopper have an easy time overwintering? There has been some theorizing that aster leafhopper potentially had more success overwintering further north (though probably not as far North as Minnesota). This could mean that the aster leafhopper arrived in Minnesota earlier than in previous years, meaning this season had a longer window for aster yellows infection.
- Did weeds infected last year have an easier time surviving the winter? The phytoplasm that causes aster yellows only lives in plant material and inside vectors. Maybe this year we have more infected weeds/landscape plants surviving the winter and providing a local reservoir of aster yellows that uninfected leafhoppers picked up when they get here. Research in Manitoba, our northerly neighbor, suggested that, at least in canola, there was higher than typical aster yellows in 2023. The weeds I am seeing commonly on farms that host aster yellows can infect include sowthistle, wild lettuce, and horseweed.
- Did intense weed pressure make aster leafhoppers life easier? Leafhoppers do well when they have a diversity of plants to feed on, and a large, diverse weed population could give the leafhoppers a boost once they land here.
- What was going on in neighboring fields? Aster yellows is a super mobile insect (one of the reasons that insecticides – organic and conventional – don’t do a good job controlling it), so what is going on in neighboring fields can have a huge impact on local aster yellows dynamic. Fields that border pastures, ditches, and weedy fallow fields are more likely to run into aster yellows issues. When these areas dry out or are mowed, aster leafhoppers move on to something nearby.
Crop Updates
Carrots: Carrots are being harvested. Some farms are experiencing large losses for aster yellows. Managing this disease, especially organically, is tricky. There aren’t any known effective organic products. This leaves us with variety selection as our main tool, as aster yellows biology makes a lot of the cultural practices organic growers rely on ineffective or impractical. Depending on how your planting is set up, row covers can protect fall carrots, but will make weed control difficult.
Different carrot varieties susceptibility to aster yellows, from Commercial Vegetable Production in Wisconsin.
Garlic: Growers from across the state continue to report aster yellows, with many expressing they haven’t seen Aster Yellows like this since 2012. Garlic with aster yellow will have discolored wrappers (often presenting as purple streaks). These cloves can be eaten, but should not be saved or sold as seed. Some cloves look like they have aster yellows, while others look fine? If they have aster yellows, you will likely know if you have germination issues in the spring.
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Discolored wrappers and small bulbs. Photo: UMN Extension.
Tomatoes: Leaf spots and fruit spots continue to pop up. Look out for late blight.
We’re nearing the point where the first frost of the season is typically just a few weeks away (hooray/gulp). The idea of topping plants - a practice most commonly done with tomatoes and Brussels sprouts - is to remove the apical meristem(s) (growing points) of the plant, which encourages the plant to shift its resources into ripening its existing fruit vs. investing in new vegetative growth. Topping tomatoes about 1 month before the first frost (or in a high tunnel, 1 month before you plan to pull your tomatoes) helps the plants put their energy into existing fruit. It's only recommended for indeterminate tomatoes, and only if you've pruned them to a single or double leader. If you have determinate tomatoes, their ripening physiology is very different and you won't see much of a benefit. Removing flowers results in a similar response, but is much more time consuming than simply topping the plant at the growing point.
Vine crops: Powdery mildew continues to spread. We are also seeing a couple of other foliar disease. Anthracnose is out. This disease is characterized by spots that turn yellow, then tan and crispy. These spots are not bound by the veins, and as the leaf spots dry out, the tissue may fall out, leaving a hole.
We’re nearing the point where the first frost of the season is typically just a few weeks away (hooray/gulp). The idea of topping plants - a practice most commonly done with tomatoes and Brussels sprouts - is to remove the apical meristem(s) (growing points) of the plant, which encourages the plant to shift its resources into ripening its existing fruit vs. investing in new vegetative growth. Topping tomatoes about 1 month before the first frost (or in a high tunnel, 1 month before you plan to pull your tomatoes) helps the plants put their energy into existing fruit. It's only recommended for indeterminate tomatoes, and only if you've pruned them to a single or double leader. If you have determinate tomatoes, their ripening physiology is very different and you won't see much of a benefit. Removing flowers results in a similar response, but is much more time consuming than simply topping the plant at the growing point.
Vine crops: Powdery mildew continues to spread. We are also seeing a couple of other foliar disease. Anthracnose is out. This disease is characterized by spots that turn yellow, then tan and crispy. These spots are not bound by the veins, and as the leaf spots dry out, the tissue may fall out, leaving a hole.
Anthracnose in cucumber. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
We are nearing the end of the part of the season where issues that arise can be addressed. Let us know below if these updates helped you out this growing season. If they missed the mark, we want to know that too! Share your thoughts below.
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