The month of August has been especially noteworthy in 2000 because of the number of storms that have had hail and high winds. Some fields in western Wisconsin have been hailed and flattened up to four times this season. Also, we have observed in our plots less brace root formation and smaller stalk diameters. With the exception of the most recent storms, corn has recovered quickly (within 2 days), but there is significant lower stalk curvature. As the season progresses less recovery will take place. I have received a number of questions asking about the yield consequences of hail loss and lodging after silking.

Hail Damage

The effect of hail damage on corn yield is well documented in agronomic literature. Hail adjusters use standard tables to calculate compensation for yield loss associated with hail. The amount of yield loss due to stand reduction is estimated about 7-10 days after a hail event. Four assessments are made on corn when hail occurs after silking (Vorst, 1990) including:

Determining yield loss due to stand reduction,
Determining yield loss due to defoliation,
Determining direct ear damage, and
Bruising and stalk damage.

Determining yield loss due to stand reduction is made by comparing yield potential of the field at its original population with yield potential at its now-reduced population. Yield loss after silking is adjusted directly by determining the percentage of killed plants. Likewise ear damage yield losses are adjusted directly by determining the percentage of damaged kernels on ears.

In corn, most yield reduction due to hail damage is a result of leaf loss. To determine yield loss due to defoliation, both the growth stage of the field and the percent leaf area removed from the plant must be determined. Significant yield damage due to defoliation occurs immediately after silking and decreases as the plant matures (Table 1).

Table 1. Estimated percent corn yield loss due to defoliation occurring at various stages of growth.
	Percent leaf area destroyed
	20	40	60	80	100
Tassel	7	21	42	68	100
Silked	7	20	39	65	97
Blister	5	16	30	50	73
Milk	3	12	24	41	59
Dough	2	8	17	29	41
Dent	0	4	10	17	23
Black layer	0	0	0	0	0
derived from National Crop Insurance Service Bulletin

Damage due to bruising is determined at harvest by counting the number of lodged plants. Bruising may allow an avenue of infection for stalk rots and molds that cause mycotoxin problems. Weather conditions during the remainder of the season affect disease severity.

Lodging Damage

The time from silking to maturity is the time kernels are filled. Sugars are needed to simultaneously support the developing kernels and maintain stalk strength. Anything that restricts production or movement of sugars or competes with the stalk or kernels will decrease yield and increase death of root and stalk cells. Rotting organisms more easily enter the stalk reducing stalk strength. Numerous factors restrict or compete for sugars during grain fill including high grain yield, cloudy weather, drought stress, high temperatures, hail, early frost, leaf diseases, and European corn borer. The effect of lodging on various plant physiological processes such as energy required for altering stalk growth, nutrient uptake, water uptake, and light penetration and how these processes influence subsequent yield is not well studied.

The most sensitive stage for lodging to occur is during late vegetative growth stages when the stalk is at full height and brace roots have not yet formed. In a Wisconsin study, lodging occurring at V10 caused little damage, while lodging events that occurred near silking caused 15 to 30 percent yield loss in hand harvested plots (Carter and Hudelson, 1988). The upper regions of the plants straightened to vertical within 2 days following lodging. Lodging during vegetative growth stages did not affect plant development, as silk dates were identical for all treatments and lodging did not influence harvest grain moisture. Later lodging events lowered ear height more than 24 inches due to pronounced lower-stalk curvature.

No research has documented yield loss damage from specific lodging events after silking. Defoliation (Afuakwa and Crookston, 1984) effects on yield may provide some insight (Tables 1 and 2). Much will depend upon the ability of the plant to recover to an upright stature.

Table 2. Grain yield loss after plants killed or defoliated.
Corn Development Stage	Plants Killed	Plants Defoliated
	percent yield loss
R4 (Soft dough)	55	35
R5 (Dent)	40	25
R5.5 (50% kernel milk)	12	5
R6 (Black layer)	0	0
derived from Afuakwa and Crookston, 1984

Guidelines for Managing Fields after Late-Season Hail and Lodging Events

The types of options available to farmers vary from farm-to-farm and field-to-field. On a farm basis, the decision hinges on availability of other corn handling systems involving drying capacity, silage storage facilities, high moisture corn handling equipment, snaplage equipment, etc. On a field basis, things to consider are plant recovery, mold development, moisture levels for ensiling, effects on maturation rate, and yield and quality. Safer storage of corn predisposed to mold causing organisms can be achieved by drying grain to 15.5% moisture, ensiling at the proper moisture for the storage structure, or treating high moisture corn with propionic or acetic acid.

Silage: Consider chopping a hailed or lodged field for silage, especially if grain prices are low. If ensiling, damaged corn should be stored separately from other silage already put up. Damaged corn may have lower quality, and by storing separately, there is an option of mixing poor and good silages to obtain a satisfactory ration, or feeding the damaged silage to animals that do not have high quality forage requirements. Rotary cutter heads for silage chopping may not be useable in lodged corn (Greg Andrews, UWEX Pierce County Agent, Personal communication).

Grain: The amount of stalk straightening decreases when lodging occurs at VT or later. Harvest speed will likely need to be reduced, especially for lodging occurring later. Test weight will likely be reduced.

Weather has a strong influence on harvesting. It not only influences harvest timing, but also rate of stalk degradation and whether plants will be able to stand until you get to them. Temperature, rain, snow and wind all play key roles in the amount of lodging. Assessing the severity of lodging in fields will help in scheduling grain harvest later. Watch closely fields that were severely lodged and adjust timing of harvest if required.

Literature Cited

Afuakwa, J. J. and R. K. Crookston. 1984. Using the kernel milk line to visually monitor grain maturity in maize. Cop Science 24:687-691.

Carter, P. R. and K. D. Hudelson. 1988. Influence of simulated wind lodging on corn growth and grain yield. J. Prod. Agric. 1:295-299.

Vorst, J. V. 1990. Assessing Hail Damage to Corn. National Corn Handbook NCH-1:4 pp.