Authors: Natalie Hoidal & Marissa Schuh
It's been hot - remarkably so. Crops are responding accordingly with slow fruit production and aborted flowers. Most of the state should get some rain tomorrow, but in some cases it may be too much rain at once, leading to splitting. Powdery mildew and corn earworm are showing up on schedule.
When we look at data from around the state, we can see that in southern MN (based on Waseca data), we are just a little bit ahead in terms of growing degree days (basically - units of accumulated heat that drive plant and insect growth), and pretty much on par with cumulative precipitation. In theory that should mean our produce should be on track, even a little ahead of schedule.
In reality, the precipitation has been really uneven, with stretches of many days without water, and then huge rainfall events. High temperatures both during the day (90+ degrees F) and night (70+ degrees F) limit pollination and flower development. In Crookston MN, temperatures have reached 100 degrees for the past 5 days straight, and we set 43 maximum daily temperature records and 60 record warm minimum temperatures during the heat wave in early to mid July. Drought continues to expand, with 95% of the state now classified at least “very dry”, with 75% under moderate drought, and 35% under severe drought.
For the most part, this hasn’t resulted in devastating losses to vegetable crops, just a general delay and reduction in fruit production, more reliance on irrigation, and hot, tired farmers. And… as a result of more limited field work time this year due to wet soils after large rainfall events, extreme heat, and smoky conditions, the weeds are thriving.
Sugar cube melons are reaching maturity, as are tomatoes (cantaloupe and melon are are two primary climacteric vegetables). Harvesting melons and tomatoes that are *almost* ripe and letting them fully mature off the vine may save you a lot of split fruit. Other things to consider harvesting early: radishes, carrots, potatoes. These root crops are not climacteric, but they are prone to splitting and to all kinds of issues when they sit in waterlogged soil. Harvesting a little early will result in smaller produce, but helps to alleviate the risk of splitting.
Summer field days are hard for farmers to attend, but if you are indeed experiencing a bit of a quieter week after the chaos of mid July, consider joining us for a field day next Friday, August 7th at 10th Street Farm. We’ll learn about leaning into fall and winter harvests in high tunnels, and maintaining high tunnel soil health. Ashley and Chris do such a good job of managing their tunnels for nearly year-round production, even really experienced growers will learn something.
Powdery mildew continues to pop up. If in the past you have ended up with sunburned squash or handle-less pumpkin, this is the disease to manage. It can defoliate plants, leading to smaller yields and fruit exposed to the sun. It is also the main reason stems become dry and fall off – which is a real headache in pumpkins. The time to treat this disease is when you first start to see it, so scout and see if you are finding it. This disease starts in the oldest leaves in the densest part of the canopy, you will see these leaves develop yellow spots, and if you flip them over, you will see the distinctive powdery white spots.
If you are thinking of treating this disease, make sure to check current product recommendations from the Midwest Vegetable Production Guide. FRAC groups 1 and 11 don’t always perform reliably, and there are a lot of products in those groups. Rotate between FRAC groups, and you can stop applications 21 days before your last harvest.
Potatoes: What do we do about a problem like Colorado Potato beetle? We had a couple of interesting conversations with growers this week about physical management strategies, like vacuums and machines designed to knock beetles off plants while collecting them for disposal. University of Vermont has an interesting rundown of different Colorado Potato Beetle removal devices throughout history. Have you built something? Marissa wants to hear about it, please drop me a note.
Sweet corn: As we enter August, we approach the window of consistent corn earworm pressure. We did get some flights at the tail end of June that got into early sweet corn, but as we enter August and September, there will likely be a pretty consistent risk of corn earworm. The last week has had some conducive conditions for corn earworm movement, but your farm's risk will still be localized.
Some notes on corn earworm:
How does this growing season compare?
The USDA tracks crop progress in a variety of commodity crops. Overall, commodity crops appear to be doing really well this year. And yet, it feels like everything is chugging along just a little bit more slowly this year. The tomatoes (in fields) have been producing, but have been slow to really put on a lot of fruit. We’re seeing cucumbers with hundreds of flowers, but only a handful of fruit. We don’t really have concrete data to support this observation, it’s just what we’re seeing as we visit farms. |
| Aborted tomato flowers due to heat. Photo: Natalie Hoidal |
When we look at data from around the state, we can see that in southern MN (based on Waseca data), we are just a little bit ahead in terms of growing degree days (basically - units of accumulated heat that drive plant and insect growth), and pretty much on par with cumulative precipitation. In theory that should mean our produce should be on track, even a little ahead of schedule.
In reality, the precipitation has been really uneven, with stretches of many days without water, and then huge rainfall events. High temperatures both during the day (90+ degrees F) and night (70+ degrees F) limit pollination and flower development. In Crookston MN, temperatures have reached 100 degrees for the past 5 days straight, and we set 43 maximum daily temperature records and 60 record warm minimum temperatures during the heat wave in early to mid July. Drought continues to expand, with 95% of the state now classified at least “very dry”, with 75% under moderate drought, and 35% under severe drought.
For the most part, this hasn’t resulted in devastating losses to vegetable crops, just a general delay and reduction in fruit production, more reliance on irrigation, and hot, tired farmers. And… as a result of more limited field work time this year due to wet soils after large rainfall events, extreme heat, and smoky conditions, the weeds are thriving.
Harvesting early
A few weeks ago we wrote about climacteric (will ripen off the vine) vs. non-climacteric (will not ripen off the vine) fruits and vegetables. This week’s weather brings a perfect example of why you may want to harvest climacteric crops early. We are looking at potentially 2.5+ inches of rainfall tomorrow in some parts of Minnesota, following hot, dry weather. A 2-inch rainfall delivers perfect conditions for splitting.Sugar cube melons are reaching maturity, as are tomatoes (cantaloupe and melon are are two primary climacteric vegetables). Harvesting melons and tomatoes that are *almost* ripe and letting them fully mature off the vine may save you a lot of split fruit. Other things to consider harvesting early: radishes, carrots, potatoes. These root crops are not climacteric, but they are prone to splitting and to all kinds of issues when they sit in waterlogged soil. Harvesting a little early will result in smaller produce, but helps to alleviate the risk of splitting.
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| An early-developing watermelon fruit that split, likely due to temperature fluctuations. Photo: Natalie Hoidal |
Fall crops + field day
We’re reaching the point in the growing season where there’s a little lull. Crop canopies have filled in quite a bit, which helps with weeds. Most fall crops like beets, carrots, and broccoli have been planted at this point. There is still time to plant the quicker crops that can tolerate a bit of cold like lettuce, spinach, and radishes.Summer field days are hard for farmers to attend, but if you are indeed experiencing a bit of a quieter week after the chaos of mid July, consider joining us for a field day next Friday, August 7th at 10th Street Farm. We’ll learn about leaning into fall and winter harvests in high tunnels, and maintaining high tunnel soil health. Ashley and Chris do such a good job of managing their tunnels for nearly year-round production, even really experienced growers will learn something.
Crop updates
Vine Crops: Sugarcube melons grown from transplants are beginning to ripen, and winter squash are sizing up. It’s a good time to review our guide to harvesting and storing melons and squash. The very quick summary: cantaloupe style melons will generally ripen off the vine, and can therefore be harvested early. Watermelons, most honeydew, pumpkins, and squash will not ripen off the vine, and therefore you’ll need to wait until they are fully mature.Powdery mildew continues to pop up. If in the past you have ended up with sunburned squash or handle-less pumpkin, this is the disease to manage. It can defoliate plants, leading to smaller yields and fruit exposed to the sun. It is also the main reason stems become dry and fall off – which is a real headache in pumpkins. The time to treat this disease is when you first start to see it, so scout and see if you are finding it. This disease starts in the oldest leaves in the densest part of the canopy, you will see these leaves develop yellow spots, and if you flip them over, you will see the distinctive powdery white spots.
If you are thinking of treating this disease, make sure to check current product recommendations from the Midwest Vegetable Production Guide. FRAC groups 1 and 11 don’t always perform reliably, and there are a lot of products in those groups. Rotate between FRAC groups, and you can stop applications 21 days before your last harvest.
Strawberries: We don’t usually write about fruit, but strawberries fall somewhere in between since they are grown more like a vegetable than a woody perennial (and we also happen to think they make a great, logical addition to a vegetable farm). While June bearing strawberry season is long over, day neutral strawberries are beginning to meaningfully produce fruit. We’ve seen a lot of tiny, “catfaced” berries that are suffering from poor pollination. We think this is mostly heat related, but Madeline wrote about it more extensively in this week’s fruit update.
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| Albion day neutral strawberries with small, cat-faced fruit. Photo: Natalie Hoidal |
Potatoes: What do we do about a problem like Colorado Potato beetle? We had a couple of interesting conversations with growers this week about physical management strategies, like vacuums and machines designed to knock beetles off plants while collecting them for disposal. University of Vermont has an interesting rundown of different Colorado Potato Beetle removal devices throughout history. Have you built something? Marissa wants to hear about it, please drop me a note.
Sweet corn: As we enter August, we approach the window of consistent corn earworm pressure. We did get some flights at the tail end of June that got into early sweet corn, but as we enter August and September, there will likely be a pretty consistent risk of corn earworm. The last week has had some conducive conditions for corn earworm movement, but your farm's risk will still be localized.
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| Corn earworm. Jack Dykinga, USDA Agricultural Research Service, Bugwood.org |
Some notes on corn earworm:
- Corn earworm moths are carried to Minnesota on weather fronts from Southern states, then get dropped by the fronts. These drops can be somewhat localized – when I’ve trapped corn earworm, I could get a hundred moths at one farm and a dozen at a farm ten miles away.
- Once they are dropped, they are attracted to corn with green silks, which is where the moths lay their eggs. If field corn is silking in your neck of the woods, the corn earworm will be diluted and there will be less pressure on your sweet corn. If neighboring field corn is not silking, moths will be laser focused on any sweet corn plantings with green silks. They will lay eggs there, and after one to eight days the eggs will hatch (the warmer it is, the faster the hatch), the caterpillar will march into the ear, where it is protected from our control measures. We can’t do anything to manage the adults or the eggs – all our controls are focused on the caterpillar.
- The window we have for control of corn earworm is when the tiny caterpillar hatches from the eggs and climbs the silks. This window is small – both in physical space, and in time. So, what are the key things to think about so we can manage this destructive pest effectively?
- Get products in the right place – onto green silks. This might be using a drop nozzle, and will also mean repeat applications as moths can lay many eggs. The silks themselves grow, sometimes up to 1.5 inches per day for around a week and a half. This means one application isn’t likely enough, as the ear will produce new lengths of green silks that aren’t protected, and the eggs may be laid upon. Once 90% of the silks are brown in a field, we can stop treatment.
- Choosing the right product – there is documentation of pyrethroid resistance in corn earworm. If you are using pyrethroids and still having corn earworm problems, use the highest labelled rate, and if that isn’t giving satisfactory results, use a different chemistry. We are entering the time of year when corn earworm populations are consistently very high – this means more risk of there being pyrethroid resistance. Diamides (which are available alone and with pyrethroids) and spinetoram are the other active ingredients to try. For organic growers, Bt (applied with a horticultural oil), Entrust, and Helicovex are options.
- Applying products at the right time – this is the hardest thing to nail, as this is a migratory insect whose populations can fluctuate with the weather. In August and September, populations tend to be consistently high, but local trapping data can help fine tune when applications should be made. Applications may also be needed more frequently if it's hot – this means the silks grow continuously, and eggs hatch quickly.
Feel like you are nailing this and still having problems? The best way to fine tune a program is to trap for corn earworm in your own fields. The number of moths you catch can inform when you start a spray program, as well as how often you make applications. This video series from Michigan State covers the different components of trapping, from set-up to making spray decisions on what you catch. You can also reach out for advice, Marissa has direct experience trapping for corn earworm and interpreting what you do with your trap catches.
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