University of Vermont

The Impact of Summer Thunderstorms on Corn Yield The Impact of Summer Thunderstorms on Corn Yield

Heather Darby and Sid Bosworth, Extension Assistant Professor, UVM Extension - Northwest Region and Extension Associate Professor, Department of Plant and Soil Science, University of Vermont

During mid-summer, we often will have strong thunderstorms that pass through the area.  Strong winds and hail that often accompany thunderstorms can cause considerable damage to corn.  The stage of development of the corn crop will strongly determine the extent to which strong wind and hail will damage the corn.  There has been very little research conducted on the impact of wind and hail on silage yields.  Therefore the information in this article pertains to grain yield loss studies.

Strong winds can damage corn by snapping or lodging plants (plants laying nearly flat to the ground), especially if the corn’s root system is not fully developed.  This is a common problem in corn plants just prior to the rapid stalk elongation phase of development.  In addition, corn growing rapidly under high temperature and excessive soil moisture conditions has increased vulnerability to snapping and lodging.

Corn is most vulnerable to snapping when it has 5 to 8 leaves (10-24 inches in height) and from the time it has 12 leaves through tasseling.  Snapping problems generally disappear once tasseling begins.  Hybrids will vary in their brittleness and hence their vulnerability to snap.  However, all hybrids are at risk from wind injury when they are growing rapidly prior to tasseling.  Growth regulator herbicides, such as 2,4-D or Banvel, applied late in the season or during hot humid conditions have been associated with an increased risk of plant brittleness.  Yield loss from snapping will depend on the percentage of field affected and whether the stalk breakage occurs above or below the ear.  Stalks that break off below the ear results in zero yield for that plant (if harvested for grain).  If the stalk breaks above the ear yield losses will be due to the loss of energy producing leaves above the ear.

Lodged corn will recover or straighten up to varying degrees depending on the growth stage of the crop. Generally, younger corn has a greater ability to straighten up with minimal “goose-necking” than older corn.  After plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery (providing you are not chopping up the lodged corn).  Yield effects of lodging will primarily depend on whether or not there is adequate soil moisture for roots to regrow and anchor the plant.    In addition, yield loss can occur if goose-necked plants cause the crop to become unharvestable.  In a Wisconsin Study, lodging that occurred when the plants had 10 leaves caused little damage while lodging events near silking caused 15 to 20 percent yield loss.  Yield loss from later lodging events was due to difficulty at harvest because of lowered ear height due to goose necking at the lower portion of the stalk.  Lodging during earlier growth stages did not affect plant development as silk dates were identical to non-lodged plants and lodging did not influence harvest.  Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as proper maturity is reached.

Hail can cause corn yield loss by reducing stands (plants killed outright) and defoliating plants.  If hail damage occurs during early corn development, the number of plants killed will not be directly proportional to yield loss.  This is because the surviving plants around a killed plant will compensate by increasing their potential ear size or by developing a second ear.  For example, a 25 percent reduction in plant population should reduce yield by less than 10 percent.  Defoliation of plants will usually result in most of the damage.  When corn has less than 6 leaves, it is minimally affected by hail because the growing point is below the soil surface.  However, once the growing point is above the soil surface (more than 6 leaves) the plant becomes increasingly vulnerable to hail damage.  Plants are the most susceptible to yield loss from hail at the tasseling stage.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth.   Shredded leaves that remain green and connected to the plant will continue to be functional.  The effect of leaf death on grain yield will increase as the plants approach silking, and then decreases throughout grain fill.  If damage occurs prior to tasseling, plants usually show new growth within 3 to 5 days after injury occurs.  For this reason, estimates of hail damage (for crop insurance reporting) should be delayed several days to allow for this period of regrowth.  Estimates of grain yield loss in corn due to leaf defoliation are shown in Table 1.  Keep in mind that these are grain yield reductions not silage yield reductions.  At this time there are no studies reporting the impact of leaf defoliation on silage yield and quality.  However, since the leaf portion of the plant makes up a proportion of the total yield of silage one would imagine that leaf defoliation would have a greater impact on silage yields than just grain yields.

Often, when damage from wind and hail occur- such as stand loss, lodging, and defoliation, other hidden stalk and ear damage may also occur.  These plants are often more susceptible to infection by pests which may further reduce yields.  Lodged plants may also be more susceptible to mycotoxin producing fungi. Assessment of these types of damage must be done later usually closer to harvest.

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Last modified May 26 2004 01:29 PM

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