Weekly vegetable update – May 22, 2024

Authors: Marissa Schuh, Shane Bugeja, and Natalie Hoidal

Much of the state got over an inch of rain Tuesday, with reports of over 2 inches of rain common across much of the state.

General Crop Notes

With ample moisture and moderate temperatures this spring, cool season grasses are having a blast. As cover crops such as cereal rye start to enter reproductive stages, the options for effective termination narrow. Roll-crimping is typically done after the boot stage, and is popular with some no-till organic producers. You can tell if your plant is in the boot stage by feeling the top of the stem for a bulge. That bulge contains the seed head of the plant. Later growth stages after boot are similar to wheat’s. Roll-crimping is not perfect. For example, a 2012 Iowa State University study needed 2 to 3 passes with the roll crimper to kill a hairy vetch/rye cover crop mix. Extra passes in the field are not ideal or cheap, especially with a busy season ahead.

The upper half of a wheat plant in boot stage. Photo: University of Minnesota.

If you do not have a roll-crimper then mowing can be a back up. Typically mow timing is at the boot stage, early heading, or pollen shed. Exactly what type of mower is best depends on how you want the residue to lay, what is available, and how quickly you want the rye residue to “disappear”. Tillage and/or herbicide treatments can follow depending on how well the rye survives that initial mow. A follow up treatment might be needed if mowing is your only control measure. In 2022, a University of Minnesota experiment showed glyphosate application or tillage being effective for killing heading cereal rye, but mowing only had a 45% success rate. For more information, Penn State Extension and SARE also have good write ups that dive into the pros and cons of different mowers, rye termination methods, and/or general tips.

We often get questions in May from growers who are doing bed prep about how fertility calculations should change in a raised bed system. If you're growing on raised beds vs. open fields, there's often an assumption that the actual area in production is less, and therefore you can use less fertilizer (e.g. on a 5 foot bed system, 2 of the 5 feet are rows vs. actual beds where plants are growing, so we can use 3/5 of the fertilizer recommended in the nutrient management guide, right?). Unfortunately, this isn't quite accurate. Plants grown in open fields also have open rows, and often the yields in raised bed systems are a bit higher, which means the plants grown in these systems require the same amount of fertilizer, if not more to reach the same yield. It’s best to stick to the fertility guidelines outlined in the UMN Nutrient Management Guide, or those outlined on your soil test.

Depending on how quickly your area dries out from yesterday’s rains, transplants may get held for longer than intended. Make sure to keep an eye on them for disease, and take steps if they are starting to get leggy.

• Reduce over temperature – Bring transplants outside, or open up the greenhouse as much as possible.
• Beyond reducing the overall temperature, a commonly used strategy in the floriculture industry is the DIF method, in which you keep your greenhouse warmer at night than during the day, which limits stem elongation. One adaptation to the DIF method that may be easier for growers trying it for the first time is the “cool morning pulse”. With this approach, you would reduce the greenhouse temperature for 2-3 hours at dawn, bringing the temperature 5-10 degrees (F) lower than the nighttime temperature (Cox, 2007).
• Another method for reducing plant growth is to use physical agitation. Agitation should gently bend the plant stems; too much force can lead to breakage. When plants are agitated a couple of times each day using physical brushing, running a stick or pipe over the tops, adding fans, or even brushing your hands through your plants, they slow their growth and put energy towards reinforcing the stem and building up their waxy cuticle layer. Take care to only do this when plants are dry, and with clean hands or sanitized equipment to prevent disease spread.

Another note for anything that is outside, more predicted dates of blackworm cutting arrive in the next week. Continue to look out for leaf edge feeding that indicates you have a local populations of cutworms who are growing into the plant snipping part of their lifecycle.

Crop updates

Asparagus harvest is ongoing. While most growers have no problem selling their asparagus promptly, make sure you’re following best post-harvest practices if you need to store your asparagus more than a few days before you sell it. The optimal storage temperature for asparagus is 32 degrees fahrenheit with 95% humidity. Asparagus with looser tips will go bad faster, so try to sell these spears towards the beginning of the day at farmers markets, and save the spears with tighter tips for later since they keep longer.

Brassica planting in the field and harvest from hoophouses continues. We've seen cabbage white butterflies out and about, and diamondback moth also likely present as well. Remember that cole crops tucked under row covers may be protected from these pests and flea beetles, but these spaces can also be an aphid oasis.

As vine crops get planted, keep an eye out for cucumber beetles. The window for trap cropping has passed once crops are in the ground, an organic grower’s next best bet is row cover. If managing with insecticides, the threshold for treatment is an average of .5 beetles per seedling for cucumbers and muskmelons, and 1 beetle per plant for pumpkins, winter squash, and watermelons.

When vine crops enter a field, cucumber beetles follow. This seedling is at threshold. Photo: UMN Extension.