Many corn fields across Ohio are experiencing exceptionally dry conditions. Rain early this week will bring some relief but forecasts call for more dry weather later. Moisture stress during the early-mid vegetative stages of corn development is atypical in Ohio. Based on observations made at the end of last week, most corn across the state ranged from about V5 (the five leaf collar stage) to V10 or slightly beyond. Ear formation is probably well underway in fields at the more advanced stages of development. However, as early as the V4/V5 stage, ear shoot initiation is completed and the tassel is initiated on the top of the growing point. During the rapid phase of corn vegetative growth (which generally starts by V7), ear yield components are being determined. Kernel row numbers per ear are generally established by about V7.

Will the recent moisture stress impact ear formation and yield potential? It takes fairly severe stress conditions during the early vegetative growth stages to impact kernel row numbers per ear. Kernel row numbers are usually less affected by environmental conditions than by genetic background. Therefore, in most cornfields, it’s unlikely that kernel row numbers have been impacted significantly by recent dry conditions. However, unlike kernel rows per ear, kernels per row can be strongly influenced by environmental conditions. Determination of kernels per row (ear length) is not usually complete until V12 to V15. Severe drought stress during the two weeks prior to pollination can reduce kernels per row and lead to a reduction in grain yield.

Iowa research by Claassen and Shaw on effects of drought on grain yields in corn is widely used in assessing the potential impact of water stress on yield potential. According to this Iowa research, drought stress during early vegetative growth usually has a negligible impact on grain yield. Some corn agronomists contend that mild drought during June may even be beneficial because roots generally grow downward more strongly as surface soils dry, and the crop benefits from the greater amount of sunlight that accompanies dry weather. However, during later vegetative stages, when kernel numbers per ear are determined, plants become more sensitive to stress. According to Claassen and Shaw's findings, four days of stress (i.e. corn wilted for four consecutive days) at the 12th-14th leaf stage has the potential of reducing yields by 5 to 10 percent.

References:

Claassen, M.M., and R.H. Shaw. 1970. Water deficit effects on corn. II. Grain components. Agron. J. 62:652-655.

Nielsen, R.L. 2012. Hot & Dry; More of the Same Not Good for Corn Yield. Corny News Network, Purdue Univ. http://www.agry.purdue.edu/ext/corn/news/articles.12/HotDryMoreSame-0528.html [URL accessed June 11 2012].