Can you believe it? It was like winning the Triple Crown in a way this week. Sorry horse fans, you weren’t so lucky. We got heat, sunshine and dry weather. Writing this column midweek I am hopeful that when you read this we have continued staying dry so our farmers can finally get a lot of field work done and maybe get us somewhat caught back up. The outlook did not look perfect at all. Fingers crossed.
If you were the lucky ones that had some crops planted, the frost that came last week may or may not have over impact. On the downside, soybeans in low areas of the field are most likely to be affected. Plants should be assessed for damage at least five days after suspected injury to inspect for regrowth.
If damage occurred above the cotyledons, the plant will likely recover. If damaged occurred below the cotyledons, the plant will not recover. Look for a discolored hypocotyl (the “crook” of the soybean that first emerges from the ground) which indicates that damage occurred below the cotyledons. If soybeans were not yet emerged at the time of the freeze, they should be fine.
On the upside, although early planted corn has been severely damaged by recent frosts in some areas, the effects of the low temperatures on corn survival will probably be negligible for the most part.
Peter Thomison, Ohio State corn specialist, notes that in past years, we have observed that corn that was in the process of germinating or as far along as the V1 stage (one leaf collar visible) survived freezing soil temperatures in April with little impact on crop performance or plant stand.
Agronomists generally downplay the impact of low temperature injury in corn because the growing point is at or below the soil surface until V6 (six leaf collars visible), and thereby relatively safe from freezing air temperatures. Moreover, the cell contents of corn plants can sometimes act as an “antifreeze” to allow temperatures to drop below 32 degrees F before tissue freezes, but injury to corn is often fatal when temperatures drop to 28 degrees F or lower for even a few minutes.
Effects of low temperatures on germination are far more serious when combined with snow and freezing rain. When dry corn seed absorbs cold water as a result of a cold rain or melting snow, “imbibitional chilling injury” may result. However these conditions were largely absent following the recent frosts.
If assessing fields, something else to keep a watchful eye out for will be the Black cutworm. Ohio State entomologists report that they have started to see cutworm damage in Ohio corn. Black cutworm (BCW) is the prime offender, though other species exist. Adult BCW (moths) are migrants from the south that start moving into Ohio in April, and lay eggs that hatch into the cutworm caterpillars.
Although there are some hotspots for egg laying, these predictions are far from exact. Moths tend to seek out fields with a lot of weeds, especially winter annuals such as chickweed, to lay their eggs. The eggs are laid in the weeds and the tiny larvae feed on the weeds until the weeds are killed by herbicide or tillage at which time the larvae will move onto the corn planted in the fields.
An additional concern related to corn is that most of the crop is being planted relatively late this spring. Corn will be rather small when larvae of these pests begin their heavier feeding. Thus, the potential for plant injury and subsequent economic losses will be much higher than normal because of the size of the corn. Black cutworms go through seven instars, with only the last four producing the greatest amount of injury.
Insecticidal seed treatments do not offer much protection. Some Bt corn train packages provide BCW protection and some do not. Early detection of cutworm infestations and timely application of rescue treatments are the keys to achieving effective stand protection.
Producers should start scouting for BCW as soon as the corn begins emerge. Rescue treatments can then be applied if necessary. If cutting is above ground, cut plants will likely recover if a timely rescue treatment is applied. In contrast, below ground feeding is generally characterized by wilting plants that have been cut below the growing point, or plants cut off before emergence, and is harder to recover from.
Soil moisture conditions can sometimes dictate where you might expect to find cutting with above ground cutting occurring under moist soil conditions and below ground cutting occurring under dry soil conditions. Treatment is warranted when visible cutworm injury is observed on 3 percent to 5 percent or more of a stand.
If a significant cutworm infestation is detected too late, cutting has occurred below ground and below the growing point, then a rescue treatment may achieve only marginal results.
Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for 28 years, currently serving Clinton County and the Miami Valley EERA.