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Learning from ‘plagues’ of 2011

Sundry plagues affected Iowa’s corn this year. Yet, the season started well, even considering slightly late planting dates. Early in the growing season many thought Iowa was a “garden spot’”; conditions were so good. The coffee-shop talk and news stories changed in July.

Learning from ‘plagues’ of 2011

Sundry plagues affected Iowa’s corn this year. Yet, the season started well, even considering slightly late planting dates. Early in the growing season many thought Iowa was a “garden spot’”; conditions were so good. The coffee-shop talk and news stories changed in July.

Abiotic plagues. First, fierce winds flattened a 100-mile stretch across central Iowa like a steam roller right before tasseling, reducing yield through fewer ears and kernels, and possibly lighter kernel weights. Then high temperatures during pollen shed and silking followed across nearly the entire state, reducing yield through fewer kernels and lighter kernel weights, and hastening development.

Wind struck later in the season, too. Even through late August, storms lodged entire fields and undoubtedly pulverized other fields with hail, reducing yield through reduced kernel weights. And then, perhaps the last issue for the season, at least as I write this, frost scraped off yield potential in scattered fields across northern Iowa in mid-September, a week or more before maturity, again reducing yield through kernel weight reductions.

Biotic plagues. Biotic menaces prevailed, too, with insects and diseases.

Japanese beetles aggressively clipped silks at precisely the wrong time in some fields, preventing pollination and no doubt reducing kernel numbers. Then beginning in mid-August, aphids assaulted cornfields resulting in not only a sticky mess, but also likely reducing yield through reduced kernel weights. The culprits: corn leaf aphid and bird cherry oat aphid.

Gray leaf spot and northern leaf blight were among other foliar fungal diseases that displayed their damage during seed fill. And to top the season off with a different flare, Goss’s wilt hit our fields in late July and made the headlines as potentially the “Disease of the Year.” Despite our hot July, this bacterial disease progressed rapidly within and between fields across northern and central Iowa. All of these diseases reduce yield through reductions in kernel weights.

Yield forecasts decline

September yield forecasts are below trendline. With all of these issues, it shouldn’t surprise anyone that Iowa corn forecasts are down. As of September, the USDA National Agricultural Statistics Service’s forecast for Iowa’s state average yield was 167 bushels per acre, 2 bushels above last year and 10 bushels below the 30-year trend.

By the time you read this, you will have seen the October forecast. Will it change from the September forecast? No one knows, but certainly we do know the plagues of 2011 reduced Iowa corn yields.

Lessons learned

What can we learn from 2011 to prepare us for 2012? Let’s address both of these categories of plagues.

Abiotic plagues. First, planting fields in different row orientations — some planted north-south, and others east-west if possible — may, in some cases, reduce the impacts of a specific wind from one direction lodging or breaking plants (greensnap) in multiple fields in the storm’s path.

Second, the rapid pace of planting (over 1.2 million acres per day) has an up and a downside. The developmental stage of the majority of our crop was similar at any given time during the 2011 growing season.

On the upside, the July 11 windstorm that hit during late-vegetative growth would have caused far more damage to yield if it had occurred a week later when the majority of our corn was tasseling and silking. The downside is, of course, that since developmental stages differed little, the majority of our crop was susceptible to the same abiotic stresses.

This isn’t the way to spread risk. But in 2011 when planting was delayed into early May, getting the crop into the ground quickly was more important to maximize yield potential than reducing risk by spreading out planting dates.

Biotic plagues. Good scouting is the best approach to handling both the insect pests and fungal diseases we saw in 2011 based on information from ISU Extension entomologist Erin Hodgson and ISU Extension plant pathologist Alison Robertson. Economic thresholds exist for some of these pests and diseases.

Hybrids differ in their tolerance of both major fungal diseases that plagued us in 2011 — gray leaf spot and northern corn leaf blight. Appropriately timed insecticide and fungicide applications can provide a quick knockdown and protection of yield as well.

Hybrid tolerance/resistance to the bacterial disease Goss’s wilt also exists. If you had a problem with this bacterial disease in 2011, here are two strategies for defense in 2012:

Screen Goss’s wilt resistant/tolerant hybrids carefully for planting in 2012. Hybrid differences in 2011 were striking, according to Robertson. Since it is a bacterial disease, spraying a fungicide won’t help.

Rotate to a crop other than corn since the bacteria can overwinter on crop residue. Continuous corn increases the chance for the bacteria’s survival. Conserve the soil by relying on these two strategies rather than tilling excessively.

Learn well from 2011 to maximize yield potential in 2012!

Elmore is the Iowa State University Extension corn agronomist.

This article published in the October, 2011 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.

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