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Extension Update from Jenny Rees

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Jenny’s REESources-October 16, 2016

Harvest is rapidly progressing with some pleased with yields and others not so much.  The past week, I’ve answered a number of calls and looked at samples of ear rot in addition to a few corn plant carcasses.  It’s really hard to determine causes for lower yields from samples provided this time of year.  This year was another challenging one regarding the environmental conditions and various biological factors that also affected our crops.  The following are some factors for consideration on a field by field basis.  The full article with photos and weather graphs can be viewed at http://cropwatch.unl.edu.

As we review planting and early season conditions, variability in precipitation with excess moisture in some locations led to variable planting dates with some replanting.  It also led to variable emergence and plant growth within fields. Damping off and other seedling diseases were a problem in some fields and in some hybrids, resulting in stand losses.

Excess moisture may have resulted in denitrification and/or leaching of nitrogen in some fields where nitrogen was applied pre-plant. If rescue treatments or the majority of nitrogen could not be applied in-season, nitrogen stress may have occurred.  Excess moisture also affected some post-herbicide applications which may have resulted in weed pressure in some fields, potentially impacting yield.

As June rolled around, growers may recall plants appearing yellow from lack of root development from April/May rainfall. We also had high heat and high winds in June which made the soil hard and increased plant stress from lack of root development. Some corn plants were in a critical growth stage (V5-V8) during this time. Irrigation was recommended to help reduce plant stress.

Rapid plant growth continued to occur. A cold snap over the July 4 weekend followed by a July 7 windstorm with hail affected pockets throughout the state. Plants most affected by greensnap were between V10 and V14 growth stage at this time. By the end of July there was a period of high nighttime temperatures which may have affected kernel setting. By late summer, portions of the state were in drought due to limited rainfall from early June through August. Solar radiation was good for both corn and soybean yields; however, the high relative humidity resulted in reduced evapotranspiration (ET). The high humidity did appear to help plants in drought-stricken areas hang on longer. Ear formation concerns were also observed on racehorse hybrids and determined to be the loss of the primary ear node although exact reasons for this are still being determined.  Insects such as western bean cutworms and grasshoppers were an issue throughout the state. Spider mite flare-ups occurred during milk to early dent growth stages with some farmers questioning additional pesticide applications given current economics.

Bacterial leaf streak was observed in plants as early as V7 and appeared in a more wide-spread area after the July 7th wind storm.  Gray leaf spot was often confused with bacterial leaf streak, eventually with both occurring on the same plants as the season progressed.  Southern rust showed up with some growers surprised at the rapid increase late season that may have impacted yield and standability.

September resulted in corn appearing to rapidly lose health and we didn’t see the long period of drying husks on green stalks as is often observed. Weather data shows a period with very low solar radiation during this time, which may have impacted corn plants physiologically.  Several stalk rot diseases can cause early plant death and potentially impact yield if they infect and develop early. These diseases are caused by fungi that survive in the soil and infect and develop in plants that may have been grown under crop stress, such as nutrient deficiency, moisture imbalance (too wet or too dry), wounding, and loss of leaf area, such as caused by leaf diseases, among others. Hybrid selection may help to reduce the incidence of stalk rot diseases. Anthracnose stalk rot (and top dieback), as well as Fusarium stalk rot have been observed, and others, such as charcoal rot, which is more common in dry growing conditions, also could be possible.

Ear rot diseases have been observed somewhat in the past few weeks.  Dr. Tamra Jackson-Ziems and I wrote another article regarding this in this week’s CropWatch at http://cropwatch.unl.edu with photos and detailed information on what to look for.  Everything I’ve seen thus far has been Fusarium/Gibberella, Diplodia, or Penicillium.  Some have complained about ear shanks being fragile with ears dropping easily and what some are calling ‘cob rot’.  Most of what I’m seeing is limited to where insect damage, ear formation, or tight husks occurred.  It’s important to scout high risk fields and to know whether they’re a problem to help make informed decisions about storage and feeding.

Not affecting yield, but something I’m also hearing reports about is “black dust” on combines and augers during harvest.  This is most likely due to secondary fungi feeding on dead/decaying plant tissue and these fungi release copious amounts of spores.  More information on this can also be seen in this week’s CropWatch at http://cropwatch.unl.edu.

In summary, a number of factors across this production season may be affecting yields. If you are experiencing lower than expected yields, consider the factors listed in this article to help determine what might have affected your crop on a field-by-field basis.