Author: Natalie Hoidal, UMN Extension educator, local foods and vegetable crops
What a week! You all made it though another week of temperatures in the high 90's, and despite a bit of heat stress, many farms now have strawberries, broccoli, cauliflower, zucchini, garlic scapes, and high tunnel cucumbers. As expected, most of the summer insects are out and about, but I'm not yet seeing too many farms that have reached economic damage thresholds. The week ahead is projected to be much more reasonable temperature wise, and we're even supposed to get some rain, giving both you and your plants some respite.
Crop updates
- Cole crops: Growers are harvesting their first broccoli and cauliflower this week. So far disease has not really been an issue - we actively tried to inoculate a field with black rot and have so far failed because the environmental conditions are just not ideal for disease spread. This is good news for farmers. Insects however, are out and active. I've seen quite a few imported cabbage worm adults and their eggs, as well as diamondback moth feeding damage and pupae. Just a reminder that these are the economic damage thresholds:
- Pre-cupping: 50% of plants have at least 5 diamondback moth larvae per plant, or 20-30% of plants have 1 or more imported cabbage worm or cabbage looper eggs or larvaa.
- Cupping to harvest: 10% of plants infested with any caterpillar larvae or eggs.
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| Diamondback moth pupa and characteristic windowpane feeding. Photo: Natalie Hoidal |
- Potatoes: Pretty much the same update as last week: Some growers already have flowers on their potatoes, and for others, the potatoes are just emerging. Potato beetles have been out for a while now, but this is the first week that I saw first generation nymphs (the first development stage after hatching from eggs). If you're planning to use insecticides, particularly preventative ones like Bt, neem, and pythrethrins, this is the best time to do so, 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! A new potato update is that we're seeing quite a few potato leafhoppers. These insects are small and their damage can look like a nutrient issue, so they often slide under the radar. Learn about how to monitor for them and treat them here.
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| Potato leafhopper. Frank Peairs, Colorado State University, Bugwood.org |
- Peas harvest is upon us. Most growers have very healthy looking peas this year that made it through to harvest with pretty much no disease issues thanks to the dry weather.
- Carrots and beets
are looking great. If you've not done so already, start scouting for aster leafhoppers. They tend to do very well in this hot, dry weather, and nearby states are having problems.
- Onions: Onions are starting to form bulbs - I'm seeing some farmers start to sell immature onions at markets this week. Irrigation is critical at this bulb formation stage, so make sure your soil is staying moist, even with rain in the forecast. Continue to keep an eye out for onion thrips as the weather stays warm and dry.
- Tomatoes: I got to eat my first MN tomatoes this week from a deep winter greenhouse in Pillager! Most farmers are still a few weeks out from tomatoes, but for the most part tomato plants seem to be responding fairly well to the heat. I got a few questions this week about curling leaves, which is 100% normal when temperatures are so high. Just keep your plants irrigated, and they should unfurl as temperatures drop. There are a couple of viruses that cause leaf curling, but due to the high heat, the leaf curling you're seeing in the field is most likely just a heat response. If your leaves stay curled in the coming week, consider reaching out or seeking a diagnosis.
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| Physiological leaf curl. Photo: Dr. Joey Williamson, Clemson University |
- Garlic: More farmers are harvesting garlic scapes this week. The Ontario vegetable update from last week had some important advice about scape harvest, and recommended that scape harvest be done by hand to avoid damage: "Past research has shown that by accidentally removing one leaf when the
scape was removed, bulb sizes were reduced by 13% and the yield was
reduced by an average of 17.5%. The same trial showed that yield was
greatly impacted as the number of leaves cut during mowing increased. If
the top two leaves were cut, the yield was reduced by approximately
25%, almost outweighing any potential gains you would expect by removing
the scape in the first place." Additionally, look for leek moth feeding damage on garlic scapes as you harvest, and squish any larvae or cocoons that you see on your garlic plants.
- Asparagus: As asparagus harvest wraps up, keep an eye out for asparagus beetle (as well as eggs) and various diseases on the ferns. Right after harvest is a good time to manage asparagus beetle to ensure that your plants can continue to develop healthy and robust root systems for a good harvest next year. You can read more about post-harvest asparagus management in the U of M asparagus guide.
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| Asparagus beetle eggs. Photo: Jeff Hahn |
- Cucurbits: Cucurbits are coming along nicely; many growers are harvesting their first zucchini from the field, and cucumbers from the high tunnel this week.
Vegetable weather report
Over the next week we can expect highs in the mid to high 80's, with a few cooler days with highs in the low 70's. Most parts of the state are expected to get some rain on Thursday or Friday, and again on Sunday, but it's unclear how much rain we will actually get. The 7 day precipitation forecast from weather.gov is projecting very little rain in the northwest (up to half an inch or so), but the southeast corner of the state will likely get over an inch of rain.
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| 7 day precipitation forecast, weather.gov |
Problems in the field and things to anticipate this week
What insect is this?
In hot, dry years we tend to see more insects, and so it makes sense that I'm getting a lot of calls and emails from folks who are seeing insects they've never seen before. You are always welcome to submit questions directly to our team (you can submit questions and requests for diagnostic help here), there are a couple of tools to be aware of as well:
- VegEdge insect profiles - click on your crop, and you'll see a list of insects that tend to feed on said crop. Some are insects we see every year, and some are more sporadic.
- What insect is this? - this is a photo based guide to help you ID insects.
In particular I've had quite a few questions about the Three Lined Potato Beetle. This insect has always been around, but with more farmers growing tomatillos and ground cherries, we're starting to see it more often.
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| Three lined potato beetle larvae look a bit like slugs, and they carry their feces on their backs to deter predators. Photo: Natalie Hoidal |
Turtles!
I realize a vegetable update is a weird place to talk about turtles, but I have seen turtles laying eggs at almost every farm I have visited this week! Since many vegetable farms have open sandy areas, farms within a mile or so of wetlands can end up looking like ideal egg laying habitat. Watch out for turtles as you're dong field work, and if you see them laying eggs, mark the spot so that you can try to avoid running over it with heavy machinery. Most turtle eggs hatch within 2-2 months, so starting in mid-August, start to watch for baby turtles.
Parasitic bees
There is a team of researchers at Penn State who are interested in collecting a particular parasitic bee, Triepeolus remigatus, which parasitizes the nests of squash bees. Squash bees are very important pollinators of cucurbits, and so this research may help us to better understand the pollination systems of cucurbits. If you see these bees on your farm, please reach out to Stephania Sandoval at
sfs5975@psu.edu, phone: 814-441-6102.
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| Triepeolus remigatus bee. Photo: Stephania Sandoval |
Educational opportunities
The Vegetable Beet: join us during your lunch break on Wednesdays for a
30 minute discussion about vegetables. Next week's topic will be about organic certification 101.
If you're seeing interesting things in
your fields, need help identifying problems, or just want to share
photos, we'd love to hear from you! Growers can reach out directly to me
any time at hoida016@umn.edu, and you can submit questions and requests for diagnostic help here.
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