This past week was a tough one on some crops. We’ve seen crusting, hail, wind, and frost cause damage to crops throughout the State. The following are considerations for plant recovery and replant.
Recovery: For any situation, while it’s hard to wait, waiting 3-5 days does help when assessing any regrowth potential. We may need closer to 5 days with the rain and cool nights forecasted. Some may have experienced plants in your field that have burnt leaves and appear to be very dry. When you dig up the plants, check the roots and see if they appear white and healthy. If they appear stunted or burnt back, that may still be ammonia burn occurring. Most of what I’ve seen this week was due to wind damage from the amount of soil moving, ridges of dirt, and plants ultimately being ‘sand-blasted’ minus the sand. In cutting open plants, look to see if the growing point is white/cream in color and firm. That would indicate it is healthy and should survive. Often one can see the newer green leaves under the dying brown ones that were exposed to wind. The brown, drying leaves may do some wrapping. Often the wrapped leaves are removed by wind as regrowth pushes through, depending on severity of wrapping.
Similarly, if the corn experienced hail and/or freeze damage, digging plants and splitting stems to check for healthy growing points are part of the assessment.
For soybean, the growing point is above ground. The most critical point for new soybeans is when they’re emerging with hypocotyl hook exposed. Anytime the hypocotyl gets pinched (whether from crusting, frost at soil surface, some PPO inhibitor damage), the soybean won’t survive. Soybeans can survive the cotyledons being stripped and/or burnt off. Soybeans at the true VC stage (unifoliolates unfurled) can have 4 growing points below the main growing point (due to the axillary buds) which can shoot new petioles. What was cool for me was watching this in an organic field where the farmers flame for weed control. The soybeans after flaming can look similar to frost damage, yet a few days later, new shoots formed from the axillary buds. I haven’t experienced frost damage past the true cotyledon (VC) stage so I can’t say for sure how they will recover in fields that were hit hard. I’m hoping they could react similar to the flaming situation, depending on how badly the hypocotyl was damaged. The hypocotyl is the stem portion below the cotyledons.
Replant Considerations: For corn, the following chart from Iowa State University by Roger Elmore and Lori Abendroth, is the standard for consideration regarding populations.
For soybean, I have left stands as low as 50,000 plants/acre, particularly the closer to mid-June we get. I realize that’s hard, especially when one considers weed control. University of Wisconsin found only a 2 bu/ac yield increase when replanting early soybeans between 50,000 and their optimum stand of 100,000-135,000 plants/acre. A York County irrigated field in 2018 comparing 90K, 120K, and 150K became final plant stands of 60,875, 88,125, and 121,750 plants/acre with yields of 93, 94, and 97 bu/ac respectively.
As you assess plant stands, keep in mind that a gap in one plant row will be compensated by plants in the adjacent flanking rows. They will form extra branches to take advantage of the sunlight. Thus single-row gaps may not be as yield-reducing as you might think, especially in narrower row spacings.
If one replants at this time of year, it’s best to use a similar maturity as what one started with. We can still use full season maturities to mid-June. For stands less than 50,000 plants per acre, plant a similar maturity into the existing stand; don’t tear out or kill an existing stand as early planted soybeans have a higher yield potential. And, you can also test this for yourself via an on-farm research study! Simply leave a planter pass of your existing stand, plant into your existing stand for a planter pass, and alternate this across your field. Please see this protocol for more information.