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After Hail Storm, Be Sure to Estimate Crop Growth Stage

After Hail Storm, Be Sure to Estimate Crop Growth Stage
UNL has a number of resources available about decision to replant.

Hail storms with up to baseball-sized hail hit corn and soybean fields across portions of central and eastern Nebraska last week. Corn in the affected area ranged between V2 and V7 and soybeans ranged between VE and V2. Forecasts for good weather conditions in the next few days will allow the crops to recover more rapidly than they would if the storms occurred earlier in the season.

However, some crops at this point will have some yield loss associated with stand reductions and defoliation. In addition, if replanting is necessary, yield penalties for both crops will be significant, according to Roger Elmore, University of Nebraska-Lincoln Extension cropping system agronomist.

Hail-damaged corn in northern Dodge County between Scribner and Uehling as a result of severe thunderstorms on June 3. (Photo by Nathan Mueller for CropWatch)

It is important to estimate the crop growth stage at the time of the hail event since a crop's ability to recover from hail damage depends on its growth stage. Several UNL Extension resources will help you assess crop damage at various growth stages and determine your management options. Yield loss data in these publications is based on information from the National Crop Insurance Service (NCIS).

Evaluating Hail Damage to Corn, UNL EC126, discusses the three types of hail damage affecting corn--plant stand reduction, direct damage, and leaf defoliation. It also discusses how to estimate yield loss and describes remedial actions for hailed fields. It can be found at www.ianrpubs.unl.edu/sendit/ec126.pdf. Knowing the development stage and accurately estimating the amount of defoliation are essential to accurately assessing hail loss, Elmore says.

During vegetative growth stages, NCIS uses a horizontal leaf method for staging corn growth instead of the leaf collar method. As a result, there are two more horizontal leaves than visible collars. Corn at the V5 growth stage (5 visible collars) is at the 6- to 7-leaf stage when adjustors determine loss on their tables. Before V5 (6- to 7-leaf stage), losses from leaf defoliation are usually minor with most losses occurring from stand reduction.

At the V6 growth stage the growing point emerges above the soil surface and the potential for stand losses and defoliation losses increases.

With a typical hybrid, it takes about 620 growing degree days (GDD) to reach V6. Accumulated GDD at several Nebraska sites indicates that fields in some areas that were planted in April are likely near V6. See GDD tables, in the CropWatch Weather section at cropwatch.unl.edu/gdd-etdata. Corn planted much later is not likely to be at the V6 growth stage at this time.

Hailed corn plants at these early development stages can look very poor, but the long-term damage and potential yield loss may be less than would occur from replanting now. Even at the 7-leaf to 9-leaf stages, 50% of leaf area can be destroyed and cause only 5% yield loss.

Be careful when assessing plant survival. It is difficult to distinguish living from dead tissue immediately after a storm, so delaying your assessment a week or so provides a more accurate assessment of viability. Another reason for delaying assessment is that some plants initially surviving a storm may soon die because of disease infection entering at the sites of plant or stalk damage. Warm dry weather following the storm will promote faster recovery.

The June 2011 CropWatch article, Assessing Flood/Hail Damage to Crops and Remedial Actions, discusses why it's also important to consider weed, disease, and insect pressures and includes a table of yields from a research study looking at the agronomic performance of short-season corn hybrids planted mid- to late-June. Go the cropwatch.unl.edu and click on archives.

Evaluating Hail Damage to Soybeans, at www.ianrpubs.unl.edu/sendit/ec128.pfd describes procedures used to assess soybean hail damage. It may be useful in estimating crop yields from stand reduction, leaf defoliation, stem damage, and pod damage and includes a guide to determining crop growth stage. Fortunately, leaf loss and defoliation during the vegetative development stages have little effect on soybean yield.

Stand losses impact final yields more than defoliation during vegetative stages. For example, if the pre-storm plant population was 120,000 plants per acre and half the stand was destroyed, yield potential would be 77% of normal --a 23% reduction. In contrast to corn, soybeans have multiple aboveground growing points, any of which can generate a stem during vegetative growth stages, Elmore says. For example, a soybean plant at V1 or one trifoliate leaf growth stage has two axillary buds at the cotyledons, two at the unifoliate leaves and one at the trifoliate leaf, plus the one terminal bud, for a total of six buds available for growth. Therefore, soybean plants that were cut above the cotyledons have at least two axillary buds for regrowth.

Replant considerations
Yields of both corn and soybean are significantly reduced when planting in early June.

For corn, see Table 2 in the May 9, 2014 CropWatch article. For example, if you replanted between June 5 and June 15 and achieved a stand of 35,000 plants per acre, yield could be about 54% of a similar stand planted in late April to early May. On the other hand, if you planted in late April to early May and hail reduced plant populations to 20,000 plants per acre, yield potential would be around 89%.

For soybean, yield potentials decrease 1/4 to 5/8 bushel per acre per day when planting after May 1. Yield starts to drop when plant stands are reduced below 100,000 plants per acre and yield really drops when stands get below 75,000 plants per acre. Current recommendations are not to replant earlier planted soybeans with at least 75,000 plants per acre and a fairly uniform stand across the fields. Soybeans have multiple growing points and can add branches to compensate for fewer plants per acre.

Contact your insurance agent and have fields visited by an adjustor prior to replanting.

Source: UNL CropWatch

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