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9 Aug 2017
URL: http://www.kingcorn.org/news/articles_17/CornyUpdate_0809.html

Brief Update on Indiana Corn Crop Conditions

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen at purdue.edu
Twitter: @PurdueCornGuy


A rough start to the growing season put Indiana's corn crop behind the proverbial 8-ball from the beginning, due to the weather- and disease-driven challenges to germination, emergence, and early establishment of the young plants. Many fields were replanted, fully or partially, in an attempt to get out from behind the 8-ball. However, frequent and excessive rains on poorly drained soils "put the damper" on many of those attempts and many fields remain rife with blank "wet holes" or stunted, uneven corn plant development throughout.

Consequently, the percentage of the 2017 Indiana corn crop rated as good to excellent (the highest two crop condition categories) hovered in the high 40's for nine straight weeks (Fig. 1) and only recently "improved" up to the low 50's with the most recent USDA-NASS crop progress report. Nine straight weeks of such low statewide crop condition is not without precedent, but you have to go back 21 years (1996) to find a similar early-season stretch of poor crop condition ratings. Statewide corn yields that year subsequently averaged about 7% below the historical trend yield.

Fortunately, the 2017 weather conditions during the important pollination and early kernel set period were mostly favorable and kernel numbers per ear in fields I have walked recently appear to be generally acceptable. Plant health relative to diseases is relatively good, though common rust is indeed common this year and reports have trickled in regarding early onset of southern corn rust in the southern third of the state. Weather conditions from here forward will determine whether these foliar diseases become pervasive and serious. Some fields exhibit noticeable late-season nitrogen deficiency, though often primarily in areas of fields that are also severely stunted by earlier periods of excessive water.

As of Sunday, 6 Aug, nearly 50% of the state's corn crop had reached the dough stage of kernel development or beyond and some was reported to be in the dent stage (USDA-NASS, 2017). At dough stage of development, only 40 to 50 percent of the final grain yield has been determined and so the next 30 to 45 days are important for determining the remainder of the final grain yield. Moderate rainfall and slightly cooler than normal temperatures from here on out would be beneficial for improving the yield prospects of the 2017 corn crop.

Given the current, somewhat average, pace of crop development, the bulk of the state corn crop will likely reach physiological maturity and be safe from fall freeze events from mid-Sept through early October. Such timing of maturity would be about on par with the most recent 5-year average and well ahead of usual occurrences of fall frosts or killing freezes.

Once kernel development reaches the dent stage (Nielsen, 2016b), growers can begin to sample ears, count kernels, and estimate grain yield (Nielsen, 2016a). The accuracy of such yield estimates rely on number of ear samples collected and areas of field sampled. While sampling, be on the lookout for the potential development of ear rots (Woloshuk, 2009, 2010. Frequent rains during pollination tend to favor the infection of silks by many of the causal ear rot fungi. Send samples of infested ears to Purdue's Plant and Pest Diagnostic Laboratory to confirm the specific ear rot disease (PPDL, 2017).

Between now and harvest, growers should continue to walk fields and scout for the onset of stalk rot diseases (Freije et al., 2016), especially in those fields that experience severe stress during these next 30 to 45 days. Send samples of stalk rot to Purdue's Plant and Pest Diagnostic Laboratory to confirm the specific ear rot disease (PPDL, 2017). Access to aerial imagery can aid the identification of problem areas within fields and help target areas to inspect more closely. Fields that develop significant levels of stalk rot should be targeted for earlier harvest to avoid the headaches of harvesting "weak-knee'd" corn plants that could be lying on the ground.

Current Indiana Corn Crop Conditions
Fig. 1. Seasonal Indiana Corn Crop Condition Ratings (percent "good" to "excellent") for Select Years.

Related references

Freije, Anna, Bob Nielsen, Kiersten Wise. 2016. Stalk Rots of Corn. Purdue Extension Pub. #BP-89-W, Purdue Univ, West Lafayette, IN. https://www.extension.purdue.edu/extmedia/BP/BP-89-W.pdf [URL accessed Aug 2017].

Nielsen, R.L. (Bob). 2016a. Estimating Corn Grain Yield Prior to Harvest. Corny News Network, Purdue Univ. Extension. https://www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html. [URL accessed Aug 2017].

Nielsen, R.L. (Bob). 2016b. Grain Fill Stages in Corn. Corny News Network, Purdue Univ. Extension. https://www.agry.purdue.edu/ext/corn/news/timeless/GrainFill.html. [URL accessed Aug 2017].

PPDL. 2017. Submit-A-Sample. Purdue Plant and Pest Diagnostic Laboratory. https://ag.purdue.edu/btny/ppdl/Pages/Submit-A-Sample.aspx. [URL accessed Aug 2017].

USDA-NASS. 2017. Crop Progress. USDA Nat'l Agricultural Statistics Service. http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1048 [URL accessed Aug 2017].

Wise, Kiersten. 2010. Common and Southern Rusts (Corn). Purdue Extension Pub. #BP-82-W, Purdue Univ, West Lafayette, IN. https://www.extension.purdue.edu/extmedia/BP/BP-82-W.pdf [URL accessed Aug 2017].

Woloshuk, Charles and Kiersten Wise. 2009. Diplodia Ear Rot of Corn. Purdue Extension Pub. #BP-75-W, Purdue Univ, West Lafayette, IN. http://www.extension.purdue.edu/extmedia/BP/BP-75-W.pdf. [URL accessed Aug 2017].

Woloshuk, Charles and Kiersten Wise. 2010. Gebberella Ear Rot of Corn. Purdue Extension Pub. #BP-77-W, Purdue Univ, West Lafayette, IN. http://www.extension.purdue.edu/extmedia/BP/BP-77-W.pdf. [URL accessed Aug 2017].