Symptoms and reports of sudden death syndrome are showing up in Illinois and Missouri fields, agronomists from both the University of Missouri and the University of Illinois say.
SDS – and white mold, too, in some instances – is likely to cause economic losses in some growers' fields this year, U of I plant pathologist Carl Bradley reports.
In Illinois, Bradley explained that symptoms of SDS that currently are being observed include interveinal chlorosis and necrosis of the leaves (veins remain green while the tissues between the veins turn yellow and then brown).
"These symptoms look exactly like the foliar symptoms caused by a different disease, brown stem rot. Brown stem rot, however, causes internal browning of the pith in soybean stems while SDS does not affect soybean stems," he said.
Related: Know Symptoms Of SDS
On SDS-affected plants, the leaves will fall off eventually, while the petioles will remain attached to the stems and branches. In some cases, Bradley said, a bluish-white mass of spores of the SDS fungus (Fusarium virguliforme) may be observed on the roots.
"Although the foliar symptoms of SDS are now being observed, infection by the SDS fungus occurred during the seedling stage, not long after planting. The symptoms that are now being observed are the effect of toxins that the SDS pathogen produces that are phytotoxic," he said.
Cool and wet weather after planting along with recent rainfall received in parts of Illinois have been favorable for infection and disease development and are the reasons that SDS incidence is high in some areas this year, Bradley explained.
"The primary method of managing SDS is to choose the most resistant soybean varieties available. Some evidence has shown that high soybean cyst nematode egg populations may also increase the likelihood of severe SDS; therefore, managing SCN populations through resistant varieties and crop rotation may also reduce the risk of SDS," he said.
University of Missouri Extension plant pathologist Laura Sweets also confirms that the wet, cool spring followed by the second-coolest July on record in Missour created conditions favorable for SDS.
High numbers of early season soybean root rot due to weather conditions may have been a precursor to SDS, adds MU Plant Diagnostic Clinic director Patricia Wallace.
"SDS is a big problem this year," she said.
The disease sometimes appears as a circular or oval area of yellow or dying plants in fields. It may appear in irregular or wavy streaks that follow drainage patterns in the field, MU says. Little can be done once plants are infected. Weather over the rest of this growing season influences the severity of loss.
Source: University of Missouri/University of Illinois