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Watch for Diplodia ear, stalk rot

Agriculture.com Staff 09/28/2009 @ 2:04pm

Could one corn fungal disease be behind the latest swings in the market?

Monday's Agriculture.com Marketeye report indicates the growing instances of diplodia ear rot in parts of the eastern Corn Belt amounted to "one of the main factors that rallied corn prices in mid-week" last week.

So, what's so bad about Diplodia ear rot that it can singlehandedly move the corn market with a just a few reported cases?

Diplodia ear rot thrives in cool, wet conditions during the grain fill period for corn, making the summer of 2009 an almost ideal time for the fungal disease to thrive, specialists say. It's caused by the same fungus that leads to Diplodia stalk rot, both of which can be a lingering problem, especially if you grow continuous corn. The rot begins as "black fruiting bodies" on husks, cob tissues and kernels, according to Iowa State University (ISU) Extension plant pathologist Alison Robertson. Left unchecked, it can create difficult harvest conditions by breaking down stalks, but more importantly, can cut yields by as much as 15% to 20% by lightening kernel weights and reducing nutritional value, Robertson says.

"Diplodia ear rot is first noticeable in the field by a bleached appearance of the husk. When you peel back the husk, you see a white, fluffy fungus," adds University of Illinois Extension Integrated Pest Management specialist Suzanne Bissonnette. "The good news is that the Diplodia fungus will not produce toxins in the grain; the bad news is that kernels will be very lightweight, shriveled, and of very poor quality. Diplodia is starting to be observed and will likely be our most common ear rot this season."

Though it doesn't produce toxins in grain, the Diplodia rot can cause other lasting damage if the grain is not handled properly. The pathogen can "be a problem in storage if grain moisture is 20% or above," Robertson says. Bissonnette adds that once corn in the field dries to 18% moisture, it's no longer susceptible to Diplodia rot damage.

"Ear rot fungi will continue to develop in the field or in storage at moisture above 18%. If dry weather is expected, you can try to save some drying costs and leave the grain to dry a bit longer in the field. If you have moderate infection, though, and wet weather is expected, harvesting and drying to at least 18% is probably your best option," Bissonnette says. "Do you really have to dry to 18% moisture? Well, that depends on what you are planning to do with the grain. If you are planning on long-term storage, you actually should get the moisture down below 15% to 16%."

The latter figures aren't just for Diplodia, though, as other similar fungal diseases -- like aflatoxin -- can thrive in moisture conditions between 14% and 18% moisture, she adds. So, if you're taking action to stem Diplodia damage, it's advisable to take precautions against similar fungi, she says.

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