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First weekly vegetable update of 2024 - May 15, 2024

A rainy spring has delivered much needed moisture, with the amount of the state in drought going from a majority of the state to limited areas in the Northwest/central and Southeast corners. What might we be in for the rest of this growing season? NOAA Climate Prediction Center's models for the summer call for hotter than normal temperatures and average precipitation. There are also predictions that we will have wildfire smoke on-and-off this summer, though for fewer days than last year.

The Minnesota draught monitor at the end of 2023 (left) to May 7th. The darker the color, the more severe the draught in that area. Images: US Draught Monitor

General crop notes

Every spring we receive some photos of transplants that indicate over-watering. While some questions from beginning growers who are just getting the hang of things, some came from experienced growers as well. One of the most common causes is that a grower will try a new potting mix, or in some cases they'll use the same product, but the texture seems different from bag to bag. 

During cold weather, your plants will not be actively growing much, and will thus not take up much water. If you stick to a scheduled watering regime in your greenhouse (or wherever you start your seeds), you're likely to end up over or under watering. Rather than sticking to a preordained schedule, keep an eye on the weather and your plants, and water accordingly.  Some telltale signs of overwatering are: green algae-like growth, brownish or soaked perlite, and soils that are visibly wet.

Cutworms can cause problems in many crops. We continue to have black cutworm flights making their way into the state.  The first bunch of these caterpillars large enough to cut plant stems are predicted to start cutting plants in Brown County later this week. Cutting dates (calculated based on when a large moths were caught and the degree days needed for caterpillars to grow) are arriving across southwest and south central Minnesota, see the linked article from the field crops team to learn about what cutworm predictions exist for your area. See last week’s article about cutworms for tips for ID and management.

For conventional growers wondering about their herbicide options, check out the interactive Midwest Vegetable Control Guide.  You can plug in the crops you grow, what kind of herbicide you’re looking for (Grasses or broadleaf or both? Pre- or post-emergent?) and get the info you need to see if the product is a good match for your growing situation.  Pumpkin growers can look to this article and flowchart.

Finally, Mid-May is the point in the season where we start to see herbicide drift cases. Take preventative measures to protect your farm: these can include signing up for DriftWatch, and talking to your neighbors and calling your local co-ops to make sure they know about your farm.

Crop updates

Brassica planting continues, as does the arrival of pests. Cabbage maggot emergence continues across the state.  Make moves to protect transplant brassicas if you have a history of this pest. For organic growers, row covers are a great option that will also give you flea beetle protection. For conventional growers, the chlorpyrifos saga is ongoing, with the product temporarily legal to use this year (though unlikely to have a brassica label in the future).  

Most growers don't have their cucumbers, melons, and pumpkins in the field yet, but the week ahead of planting is a great time to start thinking about cucumber beetle management. Managing this pest is complicated and requires a multi-faceted approach. One of those approaches is to use an attractive trap crop BEFORE you plant your main cucurbit crop. If you have some quiet time while you work this week, check out the Vegetable Beet podcast episode titled "Ugh Bugs! Organic Cucumber Beetle Management". 

Ideally, garlic should receive about 1/3 of its nitrogen requirements in the fall at planting, and the rest in late April or early May. Applications should be made when plants are between 4 and 6 inches tall.  Don’t hold off too long, as excess nitrogen late in development can delay bulb set. More info on garlic management here. If you missed the window, make a note in your calendar for next year.

This garlic is showing signs of N deficiency, make application long before you see this. Photo: Natalie Hoidal.

Customers often expect green beans early in the season, so it's tempting to get your green beans planted early. However, similar to sweet corn, green beans are susceptible to seedcorn maggot during cold and wet spring conditions. By either transplanting or waiting until your soil warms up, you'll reduce the risk of seedcorn maggot (whose flight activity is peaking right now in the lower 2/3rds of the state).  Seed corn maggot soil activity is minimal once soil temperatures reach a consistent 70°F.

Before you plant your potatoes, make sure you have a Colorado potato beetle management plan in place. Organic growers should review our video from two years of trials with farmers at Clover Bee Farm, Shepherd Moon Farm, and Big River Farms to test non-chemical management strategies for potato beetles. Check out the video from the trials to see what the farmers thought of strategies including trenches, row cover, straw mulch, trap crops, and flaming. 

The mild winter seems to have helped out Japanese beetle grubs, as more extension educators around the state are getting flooded with calls about white grub feeding.  Adult beetles lay eggs in well-watered grassy areas, so if you are planting in ground that was in pasture, turf, or fallow last year, you may run into issues with white grubs, especially in root vegetables.  There isn’t a lot you can do once you realize your planting area has white grubs doing damage, so if you are concerned, plant something in these spots where the roots aren’t the thing you harvest.

For sweet corn, use soil temperature to pick when you plant. Check the soil temperature maps in your area and wait until temperatures get closer to 60°/65°F consistently to plant your sweet corn. Planting too early can result in root rot pathogens, or greater susceptibility to seedcorn maggot (who is flying right now in the southern 2/3rds of the state).

Another thing to have on your radar with sweet corn is that potential for winter rye to provide a green bridge for true armyworm, as well as an egg laying site for black cutworm. Make time to scout for leaf edge feeding, especially if you’re in a county that has had black cutworm flights.

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