Fields dried out enough for a very productive week of planting. This update includes reminders about early season insect management, an overview of quackgrass and crabgrass management, reminders about herbicide drift, and some miscellaneous observations about snakes and ants in vegetable fields.
Crop updates
Asparagus: Hot weather is really going to push spears to grow quickly. Keep up with irrigation if possible, and remember to stop harvest when spears are pencil sized. If you’re seeing asparagus beetle pressure, review When and How to Use Insecticides for Asparagus Beetles.Tomatoes: Some tomatoes are looking great and some are looking pretty rough. Many people had to hold their tomatoes a bit longer than expected, leading to rootbound plants that were light stressed, and prone to water stress. Paired with high temperatures and limited water last week, we’re seeing some sunburnt tomatoes, and plants that are generally struggling to recover from being wilted.
Brassicas: This may be an obvious reminder, but it’s worth taking the time to check your Brassica transplants for aphids. Early season management of Brassica crops often includes row cover to help prevent damage from flea beetles, cabbage maggot, and cabbage caterpillars. Row cover also creates ideal conditions for an aphid outbreak since beneficial insects are excluded. A few aphids can very quickly become a few thousand.
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| Aphids on kale seedlings. Photo: Natalie Hoidal |
Cucurbits: Cucumbers, melons, and squash are most susceptible to cucumber beetles when they are small, and good management now can help to keep populations low throughout the season. Here’s a refresher about cucumber beetle management for those of you who would like to review your management plans.
Sweet corn: So far this has been a good year for sweet corn. Seedcorn maggot does not thrive in hot conditions, and early planted sweet corn tends to silk before earworm becomes a problem. If you’ve struggled with birds in the past and are thinking about trying some bird management/scare tactics, place your order early enough to receive what you’re going to try before corn silks.
Strawberries: Strawberries are about a week away in most of the southern and central parts of the state! Strawberries are particularly susceptible to pathogens when they are blooming. The dry weather ahead will be beneficial for keeping disease pressure low.
What’s on our radar this week
Herbicide drift
During the week or so of dry weather, some corn and soybean farmers may have been applying products on herbicide resistant crops. One active ingredient commonly associated with off-target damage, dicamba, has important cutoff dates specific to Minnesota. South of Interstate 94, certain dicamba containing products (XtendiMax®, Engenia®, and Tavium®) cannot be applied after June 12. North of Interstate 94 they cannot be applied after June 30. There are also additional restrictions on air temperature with no application allowed above 85 degrees F. Applicators are required by law to follow these restrictions along with any that may be on their product’s label. You can read more about dicamba regulation in the state at the Minnesota Department of Agriculture’s dicamba page.
Note that there are a lot of things happening this year that can make
transplants look bad, be it being held in the greenhouse longer than
planned to being transplanted in hot weather. The University of California has a tool you
can use to look at what damage caused by different herbicides looks
like. Dicamba and 2 4-D are two of the most common active ingredients
being used and are prone to drift. They both are auxin herbicides,
meaning they impact plant hormones and the way a plant grows.
Susceptible plants that have been exposed to these types of herbicides
often have twisted and distorted leaves and stems, as well as stunted
growth.
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| A pepper plant with 2, 4-D herbicide injury. Note stunted, cupped leaves, wiggly veins, and curving stems. Photo: David B. Langston, University of Georgia, Bugwood.org |
Another clue in deciphering if what you see is herbicide drift is to look at neighboring vegetation, such as trees or weeds. They can display the same types of cupping, twisting, and distortion that vegetables do.
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| Sumacs are a common tree in Minnesota, this one is displaying symptoms of dicamba drift. Photo: William Jacobi, Colorado State University, Bugwood.org. |
If you suspect dicamba related damage to your vegetables or fruits, there is a specific complaint process you can access here. For an unknown or non-dicamba product, you can pursue the process at this link. These processes are the main way to get the testing done to confirm herbicide drift. Also, consider listing your farm on DriftWatch registries and communicating with neighbors beforehand to help avoid possible issues.
Quackgrass & crabgrass at field edges
Two grass weeds have come up in our conversations with growers – quackgrass and crabgrass. A couple of growers are worried about looming patches on field edges.
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| Quackgrass and it’s spreading rhizomes. Photo: Steve Dewey, Utah State University, Bugwood.org |
While these are both grasses, they have different biology with different potential management options
Quackgrass
- Lifecycle: Perennial
- Importance of seeds: Not very - many populations are clones with sterile seeds
- Importance of vegetative growth: Very - mostly spreads through rhizomes
- Drought tolerance: Moderate – Rhizomes left on soil surface during hot, dry weather may dry enough to be killed.
- Shade tolerance: Moderately shade tolerant – will form fewer rhizomes in shade. Rhizome formation stops at 97% shade.
- Tilling: Rhizomes typically in top 4 inches of soil. Tillage increases the number of shoots but each shoot is weaker. Shoots that survive produce new rhizomes are 3-4 leaf stage. Tillage that keep rhizomes in tact and exposes they to hot sun most effective.
- Mowing : Repeated mowing reduces energy stores in rhizomes. Reduces energy rhizomes have for spreading.
- Key times for management: Three leaf stage- energy reserves lowest.
Large Crabgrass
- Lifecycle: Summer annual
- Importance of seeds: Very - Seeds are often common in soil and move easily with soil stuck shoes, tools, and machines. Also move with water.
- Importance of vegetative growth: Somewhat - plants expand out from nodes, allowing crabgrass to spread over large areas
- Drought tolerance: High - Has a deep root system that it grows very quickly. Does well in conditions where other plants struggle.
- Shade tolerance:Partially shade tolerant (around 60% shade).
- Tilling: Seedlings are easy to till. Large plants have roots up to 6 ft deep. Medium to large plants readily reroot. Soil on the lower portion of stems encourages rooting of stems.
- Mowing: Can reduce and prevent seed set if done regularly
- Key times for management: Seedling - easy to kill with cultivation.
Much of the concern is around these grasses creeping into the field, and both these grasses have it in their biology to creep. Tilling these guys at this point in the season probably isn’t going to take them out, though there is some potential to shade them out. For example, cover crops can shade out quackgrass, but the cover needs around 900 lbs of biomass/acre to do so. Note that both crabgrass and quackgrass have pretty high shade tolerance – a straw mulch or cover crop stands that isn’t dense isn’t going to stop them. A tarp is mostly like to do the trick.
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| Large crabgrass with its distinctive seed head. Photo: Steve Dewey, Utah State University, Bugwood.org |
Wireworms vs Cutworms
As if this spring hasn’t put young plants through enough, both wireworms and cutworms continue to be reported on farms.Wireworms
Wireworms are the immature forms of a couple of species of beetles. Wireworms have a broad range of roots and tubers they feed on, which can include weeds and many crops. Adult beetles like to lay eggs on grasses and small grains. Wireworms feed on roots for anywhere from 1 to 7 years before becoming adults, meaning that places where you see damage this year could have damage again next year. Wireworms also are most likely to be found in cool, moist soils that were previously in sod, pasture, small grains, and other grasses (potentially including cover crops sorghum sudangrass).Wireworm damage can look a couple of different ways. Above ground plant parts may be stunted and showing signs of stress or nutrient deficiency. Root crops will have shallow holes in them. Extreme feeding might cause plants to tip over, but you won’t see a distinct, at- or above-ground cut like a cutworm would do. Digging around impacted plants will often lead to wireworm discovery if they are the cause of what you’re seeing.
As for treatment, there isn’t really much available. They do not like heat, so this week will likely drive many deeper into the soil and away from transplants.
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| Wireworm feeding on a cabbage transplant. Above ground this plant was showing symptoms of nutrient deficiency, digging at its base revealed wireworm root feeding to be the root issue. Photo: Marissa Schuh, UMN Extension. |
Cutworms
Cutworms continue to be a problem this year, and more cutworms are likely on tap. Some Minnesota counties had significant black cutworm flights. Depending on where you are in the state, these guys may still be small and just doing foliar feeding, or may be getting big and strong enough to cut plants.
Snakes & ants
During the last two years of drought, we saw ants building nests in fields, and in some cases saw significant crop damage from ants. While the drought is over for most of the state, the ant hills may still be present in fields. In the last couple of weeks, we’ve noticed more snakes in fields than usual, particularly red belly snakes. It turns out red belly snakes inhabit old ant mounds during the winters, which may explain their increased presence in fields. These snakes are completely harmless to people, and may even provide a benefit to your crops by eating insects and slugs. |
| Redbelly snake. Photo: Chris Falt, Wikmedia commons |
Vegetable Weather Report
Rain has been spotty across the state. Most fields dried out enough to require irrigation before the showers this week. While some area will receive nearly an inch of cumulative rainfall in the scattered storms starting yesterday (Wednesday May 30th) and ending tomorrow, the week ahead looks mostly dry. Parts of North Central MN may receive an inch or so of rain over the next 7 days, but most growers should plan to continue irrigating regularly. Pay close attention to recent transplants, which are likely to experience some heat stress. |
| 7 day precipitation forecast, weather.gov |
Missing the fruit update?
We know many of you are missing the weekly fruit updates this summer. We are in the process of hiring a new fruit educator to join our team and hope to have more fruit content for you soon. In the meantime, the Midwest Fruit Pest Management Guide is an excellent resource.
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