By MATTHEW D. ERNST

Missouri Correspondent

AUBURN, Ala. — The apparent entry of cotton blue disease (CBD) into Alabama cotton fields will keep Gulf Coast cotton growers and crop scouts extra vigilant this season.

The disease is caused by the cotton leafroll dwarf virus, which is transmitted by aphids. Researchers have tentatively identified the virus present in cotton plant samples taken in two southeastern Alabama counties in 2017. The identification has not yet been confirmed by the USDA.

Confirming the disease can be tricky. “This virus may be unstable and may ‘disappear’ in host tissues over time,” said Austin Hagan, Auburn University plant pathologist, in a May 16 update.

The disease symptoms appear on new leaves, which appear stunted, small and thick. Infected leaves have deep green color that can appear bluish. Leaf veins may be yellow on young leaves, according to Plant Health Australia, Australia’s counterpart to USDA’s Animal and Plant Health Inspection Service, which is also on the lookout for CBD.

The virus can apparently also be hosted by some weeds, including pigweed, according to Hagan. He said weed control, including around field edges, could help check the potential spread of the virus, including to other states.

All cotton varieties grown in the United States and Australia are susceptible to the disease, according to USDA and Plant Health Australia. Some resistant varieties were selected in the 20th century for Africa, where CBD was identified in 1949. It was only in 2005 that researchers identified the virus causing the disease.

In 2008, researchers at the USDA Agricultural Research Service and Monsanto Co. identified genetic markers to assist developing high levels of CBD resistance in cotton breeding programs.

If confirmed, CBD spores will have likely been carried into the U.S. by hurricanes from the Southern Hemisphere. Brazilian cotton farmers have long dealt with the disease, which can reduce yields in susceptible varieties by up to 80 percent in Brazil, according to USDA.

For now, the disease will just keep producers and crop scouts vigilant. “At this point, disease incidence in Alabama cotton appears to be very low,” said Hagan.