FROM THE FARM REPORT: ASSESSING STORM DAMAGE IN CORN

Thunderstorms are the primary source of moisture for our non-irrigated crops in July. While the rain is often needed by our crops this time of year, these powerful convective storms have the potential to do plenty of damage to them under the right conditions.

Storms almost always move in with a large outburst of wind. Even without a tornado or microburst, these winds can be strong enough to snap corn plants off at the base if they are at a vulnerable stage. Then, there is the hail, which can shred both leaves and stalks in addition to giving the hood of your truck a new look.

Whenever a nasty, hail-slinging storm damages a field, the natural response is to go inspect the damage. This is one of the rare times when I advise farmers not to look at their crops. Why? That’s because storm damage almost always looks way worse than it really is. Looking at a field right away only serves to dampen your spirit, use up your precious time, and get your boots muddy. If you do need to assess the field for insurance or decision-making purposes, I suggest waiting several days before doing so to get a more accurate picture of what’s gone and what’s not.

The proper way to estimate yield loss is to use a hail damage chart. These can be found online through various university and extension sites. Hail charts show the estimated grain loss from both plant population reduction and defoliation of the remaining plants. All you have to do is look at the column corresponding to the proper stage of development and match that with what you observe in the field. For example, a 10% stand loss at the V11 stage corresponds to a 19% yield loss with 65% defoliation.

Corn plants are the most vulnerable to storm damage during the early reproductive phase and the least vulnerable during the early vegetative stages. A plant can be completely defoliated while the growing point is below the ground with less than 10% yield loss if it survives (which it most likely will). Furthermore, surviving plants can compensate somewhat for missing plants by producing a second ear in some cases. Stand loss in the later stages of development is more of a direct, 1:1 reduction.

Once you know the estimated yield loss, the next question is what are you going to do with that information. It is very rare that estimated yield losses will be justified by re-planting. Re-planting is not only costly, but it always results in a crop with reduced yield potential due to the shorter growing season – even if you get a perfect stand. Leaving the damaged corn alone is often the best option, although weed and disease pressure will likely be higher under this scenario. On the flip side, defoliated corn represents a great opportunity to try interseeding a cover crop. The additional light in the canopy will allow for excellent establishment of a species like annual ryegrass while having a negligible impact on the remaining crop. It’s better to have a cover crop growing between your corn than a bunch of late-emerging weeds.

— Allen Wilder

wilder@whminer.com