A Guide for Hail Damaged Crops

By Gary W. Hergert, Extension Soil and nutrient management specialist
Robert Harveson, Extension Plant Pathologist
Robert Wilson, Extension Weed Specialist
Jim Schild, Extension Educator
University of Nebraska Panhandle Research and Extension Center

Many areas of the Panhandle have received moderate to severe hail, and hail season isn’t over yet. Evaluating hail damage for the different crops is specific to the crop, stage of growth, hail severity and what has already been done for the crop in terms of weed control, fertilizer and any plant protection products. This article will attempt to discuss the major management decisions and factors that should be considered following hail.

A grower’s first reaction is to do something that will benefit the crop; however, many corrective actions may or may not improve growing conditions or improve yield potential. Adding ‘something’ may only increase costs and reduce potential profits. Often making sure that you have adequate weed control or providing cultivation for aeration and weed control is all that is needed. Deciding what to do can be complicated, but the steps you should follow before doing anything are:

1. Wait and allow regrowth for 7 to 10 days.
2. Determine remaining population and yield potential (see hail effects discussion).
3. Check your weed control and the remaining residual value of applied herbicide and determine whether additional herbicide and/or cultivation is needed (see weeds discussion).
4. Check your fertilizer N rate based on projected new yield potential (corn and sugar beets). If you have plenty of N for the new yield potential, additional N or S or micronutrients will not increase yield potential (see fertilizer discussion).
5. Determine plant health status and consider plant protection options (see plant health discussion).

The discussion will be by crop and by practice.

• Hail and Corn

• Hail and Dry Edible Beans

• Hail and Sugarbeets

• Hail and Herbicide

HAIL AND CORN

Hail Effects: Hail damage to corn has three major effects: plant stand reduction, direct damage (breakage, bruising), and defoliation. Any crop damage reduces the plant’s ability to compete with weeds. Loss of leaf area opens the canopy, allowing more sun for weeds. For this time of year, replanting is probably not a good option, so you must consider what the remaining stand will yield.
Much of the information below is a condensed version of UNL Extension Circular 126.

The extent of hail damage is related to stage of crop development, so accurately determining corn growth stage is essential. An excellent resource for stages of corn development can be found in Iowa State Extension publication PMR 1009 (A link to this publication is at the Cropwatch corn web page. Until the V6 growth stage, leaf defoliation is usually a minor concern compared to stand reduction. At V6, the growing point is near the soil surface. The crop insurance industry (NCIS) uses a slightly different method to determine growth stage, be sure to know which system your consultant, insurance person or agrichemical dealer is using.

Growth and development of the crop can be estimated by calculating growing degree days (GDD). Information on GDD is in UNL Extension Circular 126, or information can also be taken from the UNL CropWatch site (cropwatch.unl.edu, then click on corn) that has a table based on area of the state and crop emergence date. At this point much of the Panhandle is running 6 to 10 days behind long-term normal GDD accumulation.

Approximate growing degree days to reach different stages for a hybrid requiring 2450 GDD:

Yield Loss Due to Stand Reduction: After a hail you need to wait several days to determine the extent of damage. Plants need to begin regrowing, allowing time for damaged plants to die from damage and disease. This usually takes 7 to 10 days. To accurately estimate damage, count different areas of the field that represent different hail severities, soil types, varieties, etc. Only count plants that have normal expanding leaves in the leaf whorl. Some plants may be twisted, “tied,” or show “buggy whipping” and because you cannot determine how much later they will develop normally, they should not be counted as viable plants.

Number of feet in 1/1000 of an acre for different row widths.

Most producers today are planting seed corn at populations from 28,000 to 35,000 per acre, hoping for a 95percent stand, which would range from 26,600 to 33,259 plants per acre. Percent yield loss due to plant population reduction below your target population can be estimated by comparing yield potential of the original population to the new lower population. Yield reductions due to stand reduction only are shown in Table 3. The values may seem low, however, this is only part of the yield loss. You must also estimate yield loss due to defoliation and direct loss (hail damage to developed ear and kernels).

Table 3: Estimated percent corn yield loss due to stand reduction through the 10th leaf stage

Next, you need to determine yield loss due to defoliation and direct loss. Most hail adjustment charts do not assign yield loss to defoliation until after the 7 leaf stage. A condensed version of defoliation loss from EC126 is printed below in Table 4.

Table 4: Estimated percent corn yield loss due to defoliation at different growth stages

Yield losses can be roughly estimated by adding losses from table 3 plus those in table 4 for a given growth stage. This value will be the percentage reduction of your original yield potential and will give you an estimate of your yield potential. As an example, say you have a hail at V10 at an original population of 32,000 with 60% of the leaf area destroyed. You assume an original yield potential of 185 bushels per acre. You now have 22,000 plants left giving you a loss of 11% (Table 3). From Table 4, the loss would be about 10% for a total of 21% making your new yield potential 79% of 185 bushels which is 146 bushels per acre.

Remedial Actions: Moderate defoliation and plant stand will also result in reduced water use because of reduce leaf area. To avoid over-irrigating, it is a good idea to check soil moisture instead of relying on general evapotranspiration (ET) estimates from established sources (such as NebGuides or CropWatch).

Nitrogen Fertilizer Needs: Yield potential and N need are closely related. One of the best tools to use is the N recommendation spreadsheet that can be downloaded from cropwatch.unl.edu. It is an Excel spreadsheet. You can use initial soil test information if you assume there has been little change. Be sure to include added fertilizer already applied when calculating a new N recommendation based on a new yield goal.
Generally, no extra N will be needed if most of the N has already been applied. Extra nitrogen or sulfur usually does not improve crop growth or recovery unless there has been major leaching on sandy soils. If yield potential has been reduced, nitrogen need has also been reduced.

Other Nutrient Needs: Other nutrient needs including extra potassium or micronutrients will not enhance yield unless they were deficient and were not applied as part of your normal fertilizer program.

Corn diseases: Hail damage can reduce yields by a number of ways, depending upon crop growth stage when the event occurs. Foliar diseases, both fungal and bacterial, have been observed to be more prevalent and damaging following thunder and hailstorms.

Some fungal diseases like grey leaf spot have been reduced with fungicide applications after storms. However, we do not see this disease often in this region due to our more arid climate. Research trials in Illinois have further indicated that foliar fungicides provided very little benefit to corn injured by simulated hail in the absence of disease.

Corn damage is similar to that of dry beans, providing entry points for bacterial pathogens. Thus bacterial diseases such as Goss’ wilt can also be problematic after hail damage. Keep in mind that fungicides WILL NOT PROVIDE PROTECTION from Goss’s wilt, as they are only active against fungal pathogens. Applications of copper have been demonstrated in some cases to be beneficial for reducing bacterial infections after hailstorms, but this is not consistent.

HAIL AND DRY EDIBLE BEANS

Effects: Following a storm, the first decision is how much of the stand is left and how healthy are the plants. A stand of 45,000 to 50,000 plants per acre is enough to have near-normal yields, given normal growing conditions for the rest of the year.

Growers should evaluate the crop 5 to 7 days after the damage to determine if the plant is healthy to count in the stand or should be considered dead. Look for new trifoliate leaf growth to determine healthy plants. Plants that have no or only one unifoliate leaves and no sign of trifoliate growth should also be considered dead or not able to produce seed. Flag out 24 feet of row in 22-inch rows and 17.5 feet of row in 30-inch rows. Fifty plants or more are needed in both these row spacings.

Damage to the crop early in the growing season, if the plants survive, has little effect on harvest yield. The following graph is from two years of data showing percent defoliation at different plant growth stages. As with most crops the most severe yield reductions occur when the crop is damaged in the reproductive growth stages.

Replanting: If replanting is the decision, choose a short season dry bean variety such as Ivory or Gemini, in Great Northerns. Pinto varieties would be Othello, Bill Z, or Buckskin. Contact your insurance carrier to see what is the last date to replant beans under your policy. Replanting dry beans past June 25 increases the likelihood that the crop will not mature in the fall, especially if we experience a mid September freeze.

Disease management: In Nebraska there are four major diseases: common blight, halo blight, and brown spot, and wilt. Each disease is favored by high moisture conditions and any factor that wounds bean plants, such as storms, hail, or any other physical damage from humans or farm equipment. Storms are the perfect opportunity for bacteria to become established, as they can cause wounding and will also move the pathogen and/or infected plant residues between and within fields.

Bacteria are also highly capable of surviving in crop residues until environmental conditions may occur that favor infection. Daily temperatures favoring development of each disease vary: halo blight - less than 80 F; brown spot – less than 85 degrees F; common blight and wilt – greater than 85 degrees F. Unfortunately, bacterial diseases once begun are not easy to manage. The most important method of control initially is a correct diagnosis. Because the efficacy of several control measures depends on the specific pathogen, the most important method of control initially is a correct diagnosis of pathogen in order to make the right decision on management.

Chemical control is variable depending on pathogen, weather and disease pressure. Increased economic returns have been realized for infections with halo blight and brown spot with copper-based applications 40 days after emergence and then repeated every 7-10 days for a total of 3 applications. However, control of common blight with copper sprays has not been as successful as with halo blight and brown spot, and currently it is unknown how copper sprays affect wilt.

Genetic tolerance is available in a few cultivars, but complete disease resistance packages are difficult to obtain. Several popular cultivars have good levels of resistance to common and halo blights, but are more prone to infection by rust or white mold.

Other practices that may be useful are avoiding the planting of infected seed or beans in close proximity to infected fields from the previous year.
For any questions or problems with bacterial disease in beans please contact Bob Harveson at 308-632-1239 or rharveso@unlnotes.unl.edu

HAIL AND SUGARBEETS

Disease management: Hail can result in plant damage that is virtually undetectable to complete defoliation of the leaf material. Unless the hail occurs when plants are in the seedling stage of growth, the beets will almost always recover and continue growing. However, both root yield and sucrose concentration can be significantly reduced.

Moderate damage from hail will be seen as holes in the leaves or tears along the leaf edges. Severe damage occurs when the intensity or size of hailstones increases, and it is not uncommon to reach a point where complete defoliation of plants may occur. The defoliation may be similar to that of a defoliator used during harvest, leaving root crowns standing in fields.

Few disease problems are specifically favored by hail, unlike those of corn and dry beans, however, any pathogen can still be potentially problematic when introduce into plants that have undergone mechanical damage of any kind.

HAIL AND HERBICIDES

Hail, wind damage, and pounding rain can all have severe effects on crops and weeds. Following weather related crop damage the grower often ponders if herbicide should be applied for weed control to maintain a spraying schedule.

There are several reasons for caution:

• First, if the crop is damaged can it safely metabolize the herbicide to avoid further crop damage?
• Second, if weed foliage is damaged will the weed have enough leaf area to absorb the herbicide for control?

The answer may rely on patience. Allow the crop plant to develop several normal healthy leaves that are actively photosynthesizing. This will enhance the crop’s ability to degrade the herbicide.
New leaf growth on weeds will facilitate absorption of herbicides, which will result in improved weed control. Usually with warm temperatures plants will begin to regrow new leaves within a week and the weed control program can be resumed.

Spraying too early after a hail storm can result in poor weed control and consequently in having to retreat at a later date. If after a week crops have not responded with new growth they may need to be replanted and if herbicides were applied too quickly after the storm the herbicide may limit replant options.