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“We’ve got a lot of nematodes in our soybean fields,” says Tom Allen, assistant Extension and research professor at the Delta Research and Extension Center, Stoneville, Miss., who spoke at the annual meeting of the Mississippi Agricultural Consultants Association. “And unlike the Midwest, which has predominantly soybean cyst nematodes, we have several species in Mississippi that can cause yield reductions.”
ED WHATLEY, from left, Whatley Ag Service, Clarksdale, Miss.; Greg Williams, Memphis, Tenn., consultant; and Tim Richards, Merrill Normand Consulting Service, Yazoo City, Miss., were among those attending the annual meeting of the Mississippi Agricultural Consultants Association.
Wheat, cotton diseases
Stripe rust was a problem in some isolated Mississippi wheat fields last year, Allen says, “so be aware of the potential for it to occur in 2012. Stripe rust doesn’t look like leaf rust — the pustules produce spores that look more yellow than leaf rust. The main delineating characteristic is that the pustules have a defined pattern to them, as a line or stripe.”
Generally speaking, as plants get older, they become more tolerant of the fungus, he notes. “If you find it on young plants (tillering stages), hold tight and watch the progression of the disease, because in a few weeks it may be less of a concern. Typically, you don’t need to be making fungicide applications to young, vegetative wheat. But with that in mind, the environment could dictate the need for a fungicide if ‘hot spots’ of stripe rust are present in a wheat field.”
A cotton disease, previously known as alternaria leaf spot, is now being called corynespora leaf spot, Allen says. “They’re trying to get the name of the disease changed in cotton to target leaf spot to make it a little easier.
“We’re seeing a lot more of this disease. A few years ago, we thought maybe the disease was more prevalent in fields with a continuous history of cotton, but now it seems to be in most cotton fields, typically in the lower canopy. It’s the main foliar disease of cotton that Georgia’s fighting now, and we seem to have identified more of the disease over the past few seasons. It’s the same fungus that causes target spot of soybeans. Data suggest the presence of the disease isn’t related to nutrient deficiency.”
In Louisiana, Allen says, instances are being documented where sheath blight and aerial web blight, both caused by Rhizoctonia solani, have developed resistance to azoxystrobin, the main active ingredient in Quilt and Quadris.
“Numerous fields in several parishes were sampled, mainly in fields having a history of a rice/sobean rotation,” he says. “In some situations, it wouldn’t be difficult to suggest that there might be some resistance to additional strobilurin products as well. If you have fields this year with aerial blight, we’d like samples so we can monitor for the development of resistance to these materials in Mississippi.”
Two additional states, Louisiana and Missouri, have detected strobilurin resistance to Cercospora sojini, which causes frogeye, Allen says.
“If you have a field with this disease and you have either made in the past, or will make a fungicide application for management purposes, we’d like to have a sample, please.”