STARKVILLE, Miss. -- Blueberry leaf rust has been identified on blueberries in Perry County, and everyone in the state with blueberries is cautioned to be on the lookout for this disease.

Alan Henn, plant pathologist with the Mississippi State University Extension Service, said leaf rust is not a common disease of blueberries in Mississippi, but it has been identified occasionally in several Mississippi counties during the last 10 years.

“Outbreaks tend to be localized but can be severe, causing defoliation and reduced yield,” Henn said.

Mississippi commercial blueberry growers typically have either rabbiteye or Southern highbush blueberry varieties, and these differ greatly in their susceptibility to leaf rust.

“The varieties Bluecrisp, Climax, Delite, Emerald and Jewel are reported to be highly susceptible, and the varieties Powderblue and Star are reported to be moderately susceptible,” he said.

The fungus that causes blueberry leaf rust only survives on living plant tissue, so it often does not survive winters in Mississippi. Rust fungi have complicated life cycles, producing as many as five types of spores on two different hosts.

Rebecca Melanson, Extension plant pathologist, said blueberry growers should scout their fields for symptoms of blueberry leaf rust.

“Early symptoms on the upper leaf surface begin as yellow, chlorotic flecks that enlarge to circles,” Melanson said. “As the chlorotic spots age, the centers turn reddish brown and the chlorotic area reduces to a narrow line surrounding the dark center.

“On the lower leaf surface, the area under the yellow spots will swell into a pustule that will eventually burst. The burst pustule releases visible orangish-brown spores. In late fall and winter, black structures may be visible,” she said.

Overall, infected blueberry leaves may have a light green, chlorotic or reddish appearance. Edges of leaves in advanced infections may have dead, brown edges which may curl before dropping to the ground.

“Defoliation may result in reduced yields the next season,” Henn said.

In southeastern states where the disease has been a problem, fungicides are typically also applied around August to keep plants from defoliating.

“After warm winters when infected leaves have been retained by the plants, fungicide applications prior to harvest may be warranted,” Henn said.

Melanson said if blueberry leaf rust is detected or has been found in nearby areas, growers should include fungicides with efficacy against blueberry leaf rust into their late season and post-harvest spray program for disease management. Completely read and follow the product label instructions, as the label is the law.

“For fungicide label purposes, rabbiteye blueberries are a type of highbush blueberry,” Henn said. “Any label that allows use on highbush blueberry can be used on rabbiteye blueberries unless specifically prohibited.”

Fungicides for blueberry leaf rust are listed in the 2024 Southeast Regional Blueberry Integrated Management Guide at https://smallfruits.org/ipm-production-guides as well as the MyIPM Fruit & Nut tool at https://myipm.app/fruit-nut.

“As far as I am aware, only some biological and copper-based fungicides are labeled for residential use,” Henn said. “If the infection is localized, then picking and destroying infected leaves -- both fallen and still on the bush -- would limit overwintering chances.”

Find MSU fruit and nut disease updates at https://extension.msstate.edu/plant-diseases/fruit-and-nut-diseases/fruit-and-nut-disease-updates.