Managing Late-Season Drought Stressed Corn

Categories: GROWING, CORN
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The chance of drought somewhere across the U.S. exists every year. Understanding drought severity, duration, and stage of crop growth while under drought can be helpful in setting proper yield expectations, as well as for determining if harvesting early as silage will provide more value than previously intended grain. Monitoring conditions and yield potential of the crop throughout the season can help assess options for harvest.

Effects of Drought Stress to Corn

Timing and duration of drought stress determine severity of yield loss. Early season drought often shortens plant height and limits the number of ovules (potential kernels) in developing ear shoots, but typically has minimal impact on yield if precipitation is received prior to pollination. The impact of drought on yield is much greater in the weeks just prior to and after pollination. Drought occurring throughout reproductive stages can cause 10-50% yield losses depending upon what specific reproductive stage the crop is in when stress occurs (Table 1). Drought stress just prior to silking can delay silk exertion from husks resulting in poor pollination. Asynchronization between pollen shed and silking is one of the main reasons peak yield reductions (40-50%) occur from drought stress at this timing. Drought stress occurring closer to the end of pollination commonly results in ovules not being pollinated, causing barren ear tips, or aborting kernels after pollination.

Drought stress occurring after a successful pollination can still cause premature death of leaf tissue and kernels, resulting in a shortened grain fill period and lighter kernel weights. It can also cause ear shanks to prematurely collapse resulting in drooping ears and discontinuing movement of sugars to the ear before physiological maturity (black layer) is reached. Additional drought stress after black layer will have no impact on grain yield.

Drought Influence on Nutrient Availability

In addition to drought limiting the biological processes that require water, it can also limit nutrient availability from the  soil. Uptake of all nutrients can be lessened due to reduced root development under severe drought. However, of the main 3 nutrients, potassium (K), is the most likely to become deficient. Positively charged K cations in the soil solution become tightly bound to negatively charged soil particles. The lack of an actively growing root system and less diffusion of K into soil solution can often cause K deficiency symptoms in soils with medium to high soil K test results.

Drought Influence on Disease and Insects

In addition to nutrient deficiency, corn plants can be more susceptible to a different set of insects and disease from moisture stress. Spider mites and grasshoppers thrive in hot, dry weather causing a need to monitor crops closely for pest development in these conditions. Disease complexes are most often associated with wet conditions that are not present in a drought year. However, there are pathogens such as charcoal rot, Fusarium root rots, and rusts that favor droughty conditions and can cause significant damage. Drought conditions can also promote certain types of ear mold development which can potentially lead to the presence of specific mycotoxins in grain. Aspergillus and Fusarium molds are more likely to occur in hot, dry years. Aspergillus is responsible for the production of aflatoxins and Fusarium molds have the potential to develop into fumonisins. Risk of grain infection will increase if grain was previously damaged by insect feeding. Mycotoxins can impact livestock milk production, reproduction and immunity and should be tested for if suspected prior to feeding.

Harvest Decisions for Drought Affected Corn
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Under severe drought conditions, where ears are developing limited grain, it may be better to salvage the crop as silage. ​​​​​​​Evaluating ears 7-10 days after pollen shed for developing kernels helps indicate potential grain production. Elongating silks that remain green and continue to grow after pollen shed are a good indicator of poor pollination. If the plants receive water, fertilized kernels will continue to grow and develop. If pollination is poor, or if kernels are not growing, the field could be considered for silage harvest.

Harvest management decisions depend on the remaining yield potential in the field. It is important to observe the estimated yield of each individual drought stressed field since each has unique conditions that impact yield. Also be mindful of the development of stalk rots that may influence the standability of the field if choosing to harvest as grain.

Please contact your local Golden Harvest Seed Advisor or Agronomist with any questions.

References:

1Classen, M.M., and R.H. Shaw. 1970. Water deficit effects on corn. II. Grain components. Agron. J. 62:652

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