Black root rot rising in Mississippi beans
While black root rot is no stranger to cotton growers, the fungal disease has been detected across Mississippi in soybean fields for the last two growing seasons. Plant pathologists with the Mississippi Agricultural and Forestry Experiment Station at Stoneville, Miss., have begun conducting studies to learn more about the fungus and the conditions under which it affects soybeans.
According to Gabe Sciumbato, plant pathologist and Experiment Station researcher, black root rot has been known to infect soybeans in other states for some time, but has just recently started being a problem for soybean growers in Mississippi.
“Black root rot has been in cotton in the Delta for years, but because of the area’s recent shift to soybeans, signs of the disease are increasing statewide and are likely to impact yields,” says Sciumbato. “We are monitoring for signs of outbreaks and trying to isolate them, then get a diagnosis confirmed.
• Black root rot is a fungus commonly found in cotton.
• As cotton acres have declined, the fungus has moved to soybeans.
• Plant pathologists are starting trials for resistant soybean varieties.
Sciumbato notes that Extension Station pathologists are beginning trials to screen soybean varieties for resistance to the fungus. Other significant factors that seem to affect the development of root rot are unusually cool, wet planting seasons and the presence of high numbers of reniform nematodes, a destructive species of underground worms.
Tom Allen, also an Extension Station plant pathologist, says evidence of the fungus can be seen aboveground within the first few weeks of growth. Symptoms include stunting, stacking of leaf nodes and alternating yellow and green spots along veins. These symptoms are similar to other plant disorders such as soil compaction, nutrient deficiencies or more generalized plant stress, and diseases like sudden death syndrome, stem canker and red crown rot.
“If a grower suspects black root rot in his soybeans this spring, we recommend they contact us, or their local Extension office so we can test the affected plants,” notes Allen. “Collecting this data from the fields will be important to our studies of conditions that lead to the presence of the disease.”
Resistance proves elusive
Although the fungus that causes black root rot often shows up in soybeans that are following cotton, according to Scott Monfort, assistant professor of plant pathology at the University of Arkansas Division of Agriculture, the disease is probably indigenous in the region’s soil. The University of Arkansas has been conducting research into the fungus’ impact on soybeans for the past two years. They have screened some 50 to 75 varieties of soybeans, and at this point none have proven to be significantly resistant to the disease.
Black root rot has been controlled in cotton with the development of resistant varieties and seed treatments. Both methods potentially could be the answer for controlling the impact on soybeans, but to date, nothing conclusive has surfaced from studies.
According to the Mississippi Agri-cultural and Foresty Experiment Station agricultural economists, in 2009 Mississippi growers planted an estimated 2.2 million acres of soybeans, with a farm-gate value of $432 million. Despite concerns about the rise in the incidence of black root rot in Mississippi soybeans, the good news is that the fungus doesn’t typically affect entire fields, but shows up in isolated pockets. Also, since the past two planting seasons have been unusually cool and wet, MSU plant pathologists are hoping more normal temperatures and moisture during the 2010 planting season will prove to discourage widespread incidence of black root rot.
Sciumbato and Allen may be reached by calling 662-686-3221 and 662-402-9995 respectively.
Turnbull writes from Alabama.
This article published in the August, 2010 edition of MID-SOUTH FARMER.