Natalie Hoidal
After a week of cooler days and a lot of smoke, we’re seeing some more typical summer conditions. Crops are responding well to the heat; our heat loving crops like tomatoes and peppers are finally ripening in fields as planting for fall harvested crops slows down. This week’s update includes late season fertility adjustments, a few new (to us) plant mysteries, and some notes about diseases.
This is the time of year when we really start to see which fields have too much nitrogen. If you’re seeing healthy plants with tons of leaves but no flowers or fruit, too much nitrogen is the likely culprit. Peppers have a distinct lifecycle shift from vegetative to reproductive growth (i.e. green leafy growth to flowers and fruit), and nitrogen tells the plant to keep producing green leaves. This is especially problematic for specialty hot peppers like habaneros, which need an especially long growing season. Unfortunately, there’s not much we can do at this point to remove nitrogen from the soil. Instead, take note and reduce your fertility rates next year.
On the other hand, this is also the time of year when we start to see a lot of nutrient deficiencies, especially in high tunnels. Plants are working overtime in the summer heat and long days to grow as fast as possible and produce fruit, and so they are using a lot of nutrients. As plants shift from vegetative growth (leaves) to reproductive growth (fruit), they tend to start using more potassium. If you’re noticing deficiency symptoms, it’s always helpful to submit a foliar sample to the soil lab.
The photos below show three common deficiency symptoms:
Photos: Tomato potassium deficiency: Wikimedia Commons, Goldlocki; nitrogen deficient cucumbers: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org; magnesium deficient tomato: Bruce Watt, University of Maine, Bugwood.org
Many growers like to use liquid products this time of year like fish emulsion. Some quick tips for figuring out how much of a liquid product you need (sorry for starting this week’s newsletter with math equations!!):
Educators across the country have been describing a phenomenon of cucumbers that get soft and shriveled at the blossom end after harvest. The shriveled ends become spongy and whitish inside. I noticed this in a large box of cucumbers I bought in southeast Minnesota last week, where about half the cucumbers in the box started to look like this after about 2 days in the fridge. We ruled out cold injury (though cold injury can be a big deal with cucumbers! They are sensitive to cold and should be stored at around 50 degrees F). Instead, we settled on a diagnosis of a mix of heat stress, and potentially calcium uptake issues related to inconsistent soil moisture, very similar to blossom end rot in tomatoes.
After a week of cooler days and a lot of smoke, we’re seeing some more typical summer conditions. Crops are responding well to the heat; our heat loving crops like tomatoes and peppers are finally ripening in fields as planting for fall harvested crops slows down. This week’s update includes late season fertility adjustments, a few new (to us) plant mysteries, and some notes about diseases.
Late season fertility adjustments
This is the time of year when we really start to see which fields have too much nitrogen. If you’re seeing healthy plants with tons of leaves but no flowers or fruit, too much nitrogen is the likely culprit. Peppers have a distinct lifecycle shift from vegetative to reproductive growth (i.e. green leafy growth to flowers and fruit), and nitrogen tells the plant to keep producing green leaves. This is especially problematic for specialty hot peppers like habaneros, which need an especially long growing season. Unfortunately, there’s not much we can do at this point to remove nitrogen from the soil. Instead, take note and reduce your fertility rates next year.
On the other hand, this is also the time of year when we start to see a lot of nutrient deficiencies, especially in high tunnels. Plants are working overtime in the summer heat and long days to grow as fast as possible and produce fruit, and so they are using a lot of nutrients. As plants shift from vegetative growth (leaves) to reproductive growth (fruit), they tend to start using more potassium. If you’re noticing deficiency symptoms, it’s always helpful to submit a foliar sample to the soil lab.
The photos below show three common deficiency symptoms:
- Tomato with potassium deficiency: leaf edges of the older leaves turn yellow and then brown and crispy
- Cucumber with nitrogen deficiency: Older leaves turn light yellow. Generally the whole leaf turns yellow.
- Tomato with magnesium deficiency: Older leaves get yellow blotches between the leaf veins, while the veins remain bright green
Photos: Tomato potassium deficiency: Wikimedia Commons, Goldlocki; nitrogen deficient cucumbers: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org; magnesium deficient tomato: Bruce Watt, University of Maine, Bugwood.org
Many growers like to use liquid products this time of year like fish emulsion. Some quick tips for figuring out how much of a liquid product you need (sorry for starting this week’s newsletter with math equations!!):
- First, figure out how much of a nutrient you want to apply per acre. Let’s say your goal is to add 10 pounds of nitrogen per acre per week to supplement the fertility products you applied this spring.
- Then, figure out how many pounds of that nutrient are needed for your space. Let’s say your high tunnel is 30’ x 96’, and about 25' x 90' are in production once you’ve accounted for the end spaces. That’s 2250 square feet, or .05 acres. If we need 10 pounds of nitrogen per acre, we only need (2250 sq ft * 10 lbs/A / 43560 sq ft per acre) = 0.52 lbs of nitrogen for your high tunnel per week.
- Here’s the step people often miss: When you’re using a liquid product, you need to figure out the weight per gallon. Let’s say you’re using a fish emulsion product that’s labeled 5-1-1 (5% N, 1% P, 1% K). You read the fine print on the label to see that it’s 9.6 lbs per gallon. We can multiply the weight per gallon by the % nutrient, since nutrients are listed as % of the product by weight. So, if we were looking at nitrogen, 9.6 lbs * 0.05 = 0.48 pounds of nitrogen per gallon. With this example, you would be adding about 1 gallon of 5-1-1 fish emulsion per week to your high tunnel to provide 10 pounds of nitrogen per acre.
Crop updates
Cucumbers
We continue to hear reports of poor pollination in high tunnel cucumbers. This looks like tiny cucumbers (an inch or less long) shriveling up and drying out, while the plants continue to look healthy. This is a classic sign of heat stress. The best ways to deal with this are 1. 30% shade cloth stating in mid-July, and 2. Consistent irrigation.Educators across the country have been describing a phenomenon of cucumbers that get soft and shriveled at the blossom end after harvest. The shriveled ends become spongy and whitish inside. I noticed this in a large box of cucumbers I bought in southeast Minnesota last week, where about half the cucumbers in the box started to look like this after about 2 days in the fridge. We ruled out cold injury (though cold injury can be a big deal with cucumbers! They are sensitive to cold and should be stored at around 50 degrees F). Instead, we settled on a diagnosis of a mix of heat stress, and potentially calcium uptake issues related to inconsistent soil moisture, very similar to blossom end rot in tomatoes.
Melons
As we near melon ripening season, we’re hearing from colleagues to the southeast of us (Indiana, Illinois) that they’re seeing a lot of fruit cracking. This is mostly happening as a result of heavy rains right around harvest time. As melon harvest approaches, this will be a good year to evaluate which melon varieties do well in a summer with a lot of rain.Pepper problems
In addition to very leafy peppers with no fruit, we’re seeing bacterial spot around the state. This disease thrives in warm, humid conditions. Some strains affect just peppers, others affect just tomatoes, and others affect both. It can be worth getting your peppers tested to confirm the strain, but in general, it’s good practice to use really good sanitation when this disease pops up. If it’s in your pepper field, don’t work in your tomato field after you’ve been in the pepper field. Clean your tools, boots, and clothes well to avoid spreading it from one crop to the other. For organic growers, there are some pesticide options listed in the Midwest Veg Guide. In addition to copper, which is the go-to for bacterial diseases, there are some products listed that work by boosting the plant’s own immune system. Often growers will combine a copper product with one of these other products to boost effectiveness.
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| Image: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org |
Onions
Onions are maturing and being harvested. I heard one report of purple blotch last week. Purple spot (Alternaria porri) tends to develop in wet weather, and often infects onion leaves that have been previously damaged by other pathogens, insects (e.g. onion thrips), or hail. If your farm was hit by hail in the last few weeks, this is definitely something to scout for. If you are seeing purple blotch, harvest your onions as you normally would, allow them to cure, and remove the leaves after the onions are fully cured.Tomatoes
Tomatoes are finally starting to ripen in earnest in the field. I’ve noticed an odd phenomenon in two different places, one outdoor and one in a high tunnel: one tomato will start to wilt from the top, but the others around it seem fine. This wilting pattern occurs throughout the field in every 10th or so plant. In both cases the wilted parts of the tomatoes had some gray mold (Botritis). Initially I thought this might be the culprit, but after reviewing the symptoms with colleagues, we came up with the following:- Gray mold is really good at colonizing already damaged or stressed tissues, and in both cases was likely not causing the initial wilt. Either way, it’s worth treating the gray mold or pruning out gray mold infected tissues before they produce spores, as these spores can spread quickly throughout the planting and cause more problems.
- Vegetable colleagues in New York shared that they see these symptoms frequently with white mold. It tends to be sporadic (every 10th plant or so) and long before you see obvious signs of white mold, you see plants starting to wilt like this. In other crops like beans or lettuce, white mold is fuzzy, white, and hard to miss. But the New York educators who see this often said they usually don't see the fuzzy white fungus until it's extremely advanced. Instead they just see wilting plants, and when they cut open the stems at the base of the soil, they see the sclerotia which look like mouse poop inside the stem. White mold can quickly build up in high tunnel soils, and is more common in soils that are saturated (wet). If your plants are showing these symptoms, consider cutting the stem open right at the soil line to look for evidence of white mold.
The photo below isn’t great, but it’s the best one I took showing the wilting symptoms from the top. The leaves also had some standard foliar pathogens including early blight and septoria.
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| A wilty tomato plant surrounded by healthier plants. Photo: Natalie Hoidal |
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