This past week was beautiful! We saw more recovery on frost-damaged plants and it allowed for a lot of post-herbicide spraying. A question I kept receiving was how long to wait to spray crops that were frost damaged. Some labels will say to wait 48-72 hours before applying a herbicide while others don’t give a time, they just mention that injury to the crop can occur under specific temperatures or when plants are under stress. How I answered based on what we have recommended in the past is for any type of adverse weather event impacting crops (hail, frost, etc.), wait at least 3-5 days based on the label or until one starts to see plant regrowth of both the crop and the weeds. We would say the same for anyone who unfortunately experienced hail damage this weekend.

Interseeded Cover Crops: This past week was also a busy one for our team interseeding cover crops into V3-V4 corn. We are currently in the third year of a partnership between our farmer cooperators, The Nature Conservancy, Nebraska Extension, UBBNRD, and Kellogg’s. A couple cooperators are in the 4^th year. The goals for planting cover crops into early season corn and soybean include reducing nitrogen inputs, weed control, improving soil health, increasing diversity, and providing forage for livestock. We’ve successfully achieved cover crop establishment and season long growth, covers that survived after harvest and survived into the spring to various extents in all years of the study. In the on-farm research locations from 2019-2021, the interseeded cover crop yielded less in 5 of the 12 site-years but yield was not impacted in the others. In 2021, there was no yield difference between the interseeded cover crop and check strips when seeded into soybean at two locations. Yields in 2020 and 2021 were impacted in some fields due to the July 9^th windstorm in both years which opened up the canopy producing greater cover crop biomass.

Biomass samples taken in late September pre-harvest and pre-frost has ranged from 97 lb/ac to 2192 lb/ac. These are field averages as individual reps were over 4000 lb/ac in severely wind damaged fields. Additional growth was achieved after harvest but not collected. Biomass samples for nitrogen content taken in 2021 ranged from 5-200 lb N /ac. Beginning soil health assessments were taken the first year of the study and will be completed in September of 2022 for comparison.

We’ve also learned a lot about herbicide interactions with cover crops; they are fairly resilient. For the corn locations, we’ve went with a full PRE herbicide (generic Lexar, Callisto, Acuron…have not used Resicore) and then for POST, within 3 days either direction of interseeding using Roundup, Liberty, and sometimes dicamba with no impacts to the covers that we interseed. We have also had success using ½ rate of Lexar or Callisto at least 1.5 weeks prior to interseeding. The covers were scraggly, but they did come through it. We have never used a residual on the corn we interseed, but using a Group 15 was an option once the covers emerged and got up about an inch to provide residual if the guys wanted it.

For the soybeans, if a full PRE was applied at least 3 weeks prior to interseeding, we didn’t worry about it (which was the case in 2021). For POST, we just used Roundup and either Liberty or Dicamba within 3 days either direction of interseeding with again, the thought of a Group 15 if needed for residual once the covers were 1″ tall. In soybean, we interseeded 10 lb/ac red clover with 20 lb/ac of wheat. The field we interseeded at emergence had red clover survive the entire growing season, through harvest, and was growing this spring for the successive corn crop. It was unexpected and gave us insight into another way of potentially establishing a perennial crop for nitrogen. It ended up being killed out by the corn herbicide, but is something we’re repeating in different ways in 2022.

Regarding species that we feel are most successful in the corn, we like buckwheat, iron and clay cowpeas, clovers (red and sweet), brassicas such as collards and radishes, forage soybean, annual and Italian ryegrass. We’ve consistently seen sweetclover and the ryegrasses survive the winter into the spring. Depending on the year, we’ve also seen red clover and hairy vetch survive the winter. We’ve learned much more that I don’t have room for here. If you’re interested in learning more, be watching for our articles at cropwatch.unl.edu. Also, save June 30^th for a potential Interseeding Cover Crop Driving Tour.