Authors: Natalie Hoidal & Marissa Schuh
It’s really starting to look like summer out there. Most CSAs are starting this week, we’re seeing more produce at farmers markets, and strawberries will start to be picked soon. There’s been a dramatic expansion of drought conditions over the last week, but with widespread rain across most of the state and cooler conditions forecasted, hopefully we’ll get some relief. This week is a good time to get caught up on pruning, and to squeeze in as much weeding as possible between the rains that will inevitably bring big flushes of weeds.
Tomatoes: In fields, the basket weave (otherwise known as Florida weave, or any number of names including “weave”) is the most common system on commercial farms. In high tunnels, the big decision is whether to use a single or double leader. Just based on personal experiences and talking to growers, we really like the single leader system. It’s just cleaner and easier, and makes lowering and leaning a bit simpler. The main reason we can see for using a double leader system is cost. If you have super expensive seed, or you're paying for grafted tomatoes, a double leader system allows you to use half the number of plants.
People who really try to optimize tomatoes (like companies selling tomato management software) often promote cluster pruning for optimal yields. Is it really worth it? The debate is out. Our colleague Becky Sideman in New Hampshire studied cluster pruning a few years ago, and found mixed results (click here to read the full report).
Cucumbers: Overall, using a net system is less labor intensive than pruning, and may allow for more beneficial insects and a longer crop lifespan. However, it can also promote more foliar disease if you have a history of foliar disease problems in your tunnel or if you’re not using powdery mildew resistant varieties. The main downside is that you end up with a total mess of plastic netting + cucumber vegetation at the end of the year that is hard to separate. We’ve been following along on Instagram this year as Clay Bottom Farm tries a number of burlap and jute products to replace plastic, and were especially intrigued by their jute cucumber net, which would allow you to simply compost everything. We’re excited to see how it works for them.
In general: Pruning can make plants vulnerable to disease spread. Sanitize your pruning shears after every few plants (we know, easier said than done), and ideally use a cart to drop pruned leaves into as you go. Pruning tomato suckers before they reach a pencil-diameter will help to reduce the size of the wounds left behind; a smaller wound can scab over more quickly, which is important for disease prevention.
Are you looking for more hands-on practice with pruning and trellising? Join us on the St. Paul campus next week for a high tunnel pruning field day!
Asparagus: Harvest is winding down for many farmers. When the spears you are seeing are pencil sized, it is time to let the plants fern out and build energy for next year.
The time of the final pick is a key time for asparagus weed management. For conventional growers, synthetic auxin herbicides can be applied in the day-of or day-after final harvest (this helps limit damage to spears or fern). Another option for emerged weeds is glyphosate — to use this, remove all spears so that the patch is totally picked. You can mix glyphosate and a synthetic auxin. This is a helpful combo if you have tricky perennial weeds in your space. For more information on herbicides, see the Midwest Vegetable Production Guide.
For organic growers, after a final, clean pick is a good time for shallow cultivation between rows. This will work best on small, recently emerged annual weeds and won’t do much to control perennials like Canada thistle. Other organic options include flaming and, of course, hand weeding. For more information on weed management in asparagus, see “Weed Management Options for Asparagus.”
Beans: Seeing bean plants with holes? Check for bean leaf beetle – it is out and about right now. At passing glance this can look like a cucumber beetle, but is a relative. More ID and management info on the UMN page “Bean leaf beetle.”
Brassicas: Crops are sizing up, and pests are out. Flea beetles are present – management options are limited in organic production. A treatment threshold is 10-20% of leaf area damaged. Organic insecticides don’t do a great job against this pest, conventional growers have options.
The cole crop caterpillars are also out. I heard from one grower that they had seen very little diamondback moth, but cabbage loopers had appeared almost a month earlier than usual. There is a tendency to call any caterpillar on brassicas a looper, while looper is one of three species. If you are trying to hone in on your management, learning to tell the three different species apart can help you better evaluate risk, as each species is capable of different levels of damage. Learn more about these caterpillars at “Caterpillars on cole crops.”
We also got a report of zebra caterpillar. This is a species we see sporadically, but it is a real attention grabber – it is colorful (the name zebra is earned), and feeds in large groups, which can cause patches of heavy defoliation. If you are seeing these, they can be managed with physical removal (they are often clustered on only a few plants in limited areas) or by spot sprays of a product labelled for caterpillars.
Carrots and beets: The first successions of carrots and beets will be reopening in a couple of weeks. The recent rains and humidity will create conditions for foliar disease, such as cercospora and alternaria leaf blights. Unfortunately, we don't have effective organic products for these diseases (though there are conventional options, see the Midwest Vegetable Production Guide).
Corn: Corn is all over the place. In northern MN people are still planting their first successions of corn, whereas in southern MN, corn is two feet tall. Our colleague Charlie Rohwer in Waseca has been trying to plant sweet corn earlier and earlier. This year he transplanted corn into plastic mulch on April 7th, and used row cover during the cold stretches of April. Some of it died in an early May frost, but most of it survived and is already silking (though the plants are really quite small to be silking, so we’ll see what the yields look like).
Cucurbits: This week is a critical time for cucumber beetle management. Early June is when we see them start to come out in full force, and when your plants are small is when they are most susceptible to damage. For a review on management options, see “Managing tricky vegetable pests: Cucumber beetle.”
Garlic: Garlic is scaping in the southern part of the state. Earlier harvest of scapes means bigger bulbs, but often it’s hard to get to them in time in early summer. The most important thing is to avoid clipping leaves, which can significantly decrease garlic yields. Taking the time to remove scapes carefully, by hand, is worth it in the long run.
If you’re planning to save and sell garlic seed this year, it’s time to think about garlic bloat nematode testing. Nematodes can be carried on garlic bulbs and once established, are very difficult to get rid of, so starting with seed that’s been tested is important. Jerry Ford from Sustainable Farming Association has developed a garlic bloat nematode testing guide.
Strawberry: Harvest is beginning across the state. Iowa growers have reported low yields, potentially due to dry winters that have made winter survival hard for many perennials. We’ll see whether we see the same trend in Minnesota this year.
Tomatoes: Tomatoes are growing quickly. Field grown cherry tomatoes are already setting fruit, though they won’t ripen for a while. We’re seeing plenty of foliar pathogens start to show up on lower leaves, so pruning will be critical for good air flow, especially as we see high humidity in the forecast.
It’s really starting to look like summer out there. Most CSAs are starting this week, we’re seeing more produce at farmers markets, and strawberries will start to be picked soon. There’s been a dramatic expansion of drought conditions over the last week, but with widespread rain across most of the state and cooler conditions forecasted, hopefully we’ll get some relief. This week is a good time to get caught up on pruning, and to squeeze in as much weeding as possible between the rains that will inevitably bring big flushes of weeds.
Pruning time
If you haven’t already started pruning, now is the time to get started. It’s best to prune plants early and often. This helps avoid wasted energy (plants producing large amounts of foliage that will just get removed), and stress (removing too much at once). We have two favorite go-to guides for pruning if you need an in-depth overview of how to do it:- Cornell’s guide to pruning tomatoes
- Purdue’s high tunnel cucumber guide, which has a nice comparison of a net system to a single leader system on pages 6 & 9.
Tomatoes: In fields, the basket weave (otherwise known as Florida weave, or any number of names including “weave”) is the most common system on commercial farms. In high tunnels, the big decision is whether to use a single or double leader. Just based on personal experiences and talking to growers, we really like the single leader system. It’s just cleaner and easier, and makes lowering and leaning a bit simpler. The main reason we can see for using a double leader system is cost. If you have super expensive seed, or you're paying for grafted tomatoes, a double leader system allows you to use half the number of plants.
People who really try to optimize tomatoes (like companies selling tomato management software) often promote cluster pruning for optimal yields. Is it really worth it? The debate is out. Our colleague Becky Sideman in New Hampshire studied cluster pruning a few years ago, and found mixed results (click here to read the full report).
Cucumbers: Overall, using a net system is less labor intensive than pruning, and may allow for more beneficial insects and a longer crop lifespan. However, it can also promote more foliar disease if you have a history of foliar disease problems in your tunnel or if you’re not using powdery mildew resistant varieties. The main downside is that you end up with a total mess of plastic netting + cucumber vegetation at the end of the year that is hard to separate. We’ve been following along on Instagram this year as Clay Bottom Farm tries a number of burlap and jute products to replace plastic, and were especially intrigued by their jute cucumber net, which would allow you to simply compost everything. We’re excited to see how it works for them.
In general: Pruning can make plants vulnerable to disease spread. Sanitize your pruning shears after every few plants (we know, easier said than done), and ideally use a cart to drop pruned leaves into as you go. Pruning tomato suckers before they reach a pencil-diameter will help to reduce the size of the wounds left behind; a smaller wound can scab over more quickly, which is important for disease prevention.
Are you looking for more hands-on practice with pruning and trellising? Join us on the St. Paul campus next week for a high tunnel pruning field day!
Crop reports
Living in the southern half of the state, it’s always humbling to spend some time in northern Minnesota in early June and see how different the growing season is just a couple of hours north. Lilacs are still blooming as far south as Cloquet, and we realize some of these updates that come primarily from the southern half of the state may feel out of touch from what you’re experiencing up north. Think of these as things to look forward to in 2-3 weeks.Asparagus: Harvest is winding down for many farmers. When the spears you are seeing are pencil sized, it is time to let the plants fern out and build energy for next year.
The time of the final pick is a key time for asparagus weed management. For conventional growers, synthetic auxin herbicides can be applied in the day-of or day-after final harvest (this helps limit damage to spears or fern). Another option for emerged weeds is glyphosate — to use this, remove all spears so that the patch is totally picked. You can mix glyphosate and a synthetic auxin. This is a helpful combo if you have tricky perennial weeds in your space. For more information on herbicides, see the Midwest Vegetable Production Guide.
For organic growers, after a final, clean pick is a good time for shallow cultivation between rows. This will work best on small, recently emerged annual weeds and won’t do much to control perennials like Canada thistle. Other organic options include flaming and, of course, hand weeding. For more information on weed management in asparagus, see “Weed Management Options for Asparagus.”
Beans: Seeing bean plants with holes? Check for bean leaf beetle – it is out and about right now. At passing glance this can look like a cucumber beetle, but is a relative. More ID and management info on the UMN page “Bean leaf beetle.”
 |
| Bean leaf beetle is a yellow to orange to red with black spots. Photo: Ward Upham, Kansas State University, Bugwood.org. |
Brassicas: Crops are sizing up, and pests are out. Flea beetles are present – management options are limited in organic production. A treatment threshold is 10-20% of leaf area damaged. Organic insecticides don’t do a great job against this pest, conventional growers have options.
The cole crop caterpillars are also out. I heard from one grower that they had seen very little diamondback moth, but cabbage loopers had appeared almost a month earlier than usual. There is a tendency to call any caterpillar on brassicas a looper, while looper is one of three species. If you are trying to hone in on your management, learning to tell the three different species apart can help you better evaluate risk, as each species is capable of different levels of damage. Learn more about these caterpillars at “Caterpillars on cole crops.”
We also got a report of zebra caterpillar. This is a species we see sporadically, but it is a real attention grabber – it is colorful (the name zebra is earned), and feeds in large groups, which can cause patches of heavy defoliation. If you are seeing these, they can be managed with physical removal (they are often clustered on only a few plants in limited areas) or by spot sprays of a product labelled for caterpillars.
 |
| Zebra caterpillars are colorful and feed in groups. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org |
Carrots and beets: The first successions of carrots and beets will be reopening in a couple of weeks. The recent rains and humidity will create conditions for foliar disease, such as cercospora and alternaria leaf blights. Unfortunately, we don't have effective organic products for these diseases (though there are conventional options, see the Midwest Vegetable Production Guide).
Corn: Corn is all over the place. In northern MN people are still planting their first successions of corn, whereas in southern MN, corn is two feet tall. Our colleague Charlie Rohwer in Waseca has been trying to plant sweet corn earlier and earlier. This year he transplanted corn into plastic mulch on April 7th, and used row cover during the cold stretches of April. Some of it died in an early May frost, but most of it survived and is already silking (though the plants are really quite small to be silking, so we’ll see what the yields look like).
 |
| Corn silking in Waseca, Photo by Charlie Rohwer |
Cucurbits: This week is a critical time for cucumber beetle management. Early June is when we see them start to come out in full force, and when your plants are small is when they are most susceptible to damage. For a review on management options, see “Managing tricky vegetable pests: Cucumber beetle.”
Garlic: Garlic is scaping in the southern part of the state. Earlier harvest of scapes means bigger bulbs, but often it’s hard to get to them in time in early summer. The most important thing is to avoid clipping leaves, which can significantly decrease garlic yields. Taking the time to remove scapes carefully, by hand, is worth it in the long run.
If you’re planning to save and sell garlic seed this year, it’s time to think about garlic bloat nematode testing. Nematodes can be carried on garlic bulbs and once established, are very difficult to get rid of, so starting with seed that’s been tested is important. Jerry Ford from Sustainable Farming Association has developed a garlic bloat nematode testing guide.
Strawberry: Harvest is beginning across the state. Iowa growers have reported low yields, potentially due to dry winters that have made winter survival hard for many perennials. We’ll see whether we see the same trend in Minnesota this year.
Tomatoes: Tomatoes are growing quickly. Field grown cherry tomatoes are already setting fruit, though they won’t ripen for a while. We’re seeing plenty of foliar pathogens start to show up on lower leaves, so pruning will be critical for good air flow, especially as we see high humidity in the forecast.
Irrigation tip for early summer in high tunnels
We’re seeing people using more drip lines in high tunnels lately. Overall, this is probably a good thing; watering a larger root zone allows plant roots to spread out over a wider area and access nutrients from a larger volume of soil. At this point in the season, roots are spreading quickly as our plants take off from seedlings into larger, more mature plants. One strategy for high tunnels is to lay four lines of drip per bed, but start with just two lines per bed while plants are small. This helps to prevent nitrate leaching when the root system as small. As we get further into June and plants get bigger, turning on the other two lines allows the plants to spread out and access more water and nutrients.
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