See recommendations for Florida citrus growers for treating algal spot in citrus groves in the UF/IFAS Tip of the Week.

Algal spot has been reported in many Florida citrus groves this season, making it a bigger concern than it has been in the past, according to Megan Dewdney, an associate professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred, author of UF/IFAS’s Tip of the Week. Dewdney shared recommendations on treating algal spot in citrus in a Citrus Industry article on the Tip of the Week, which are based on her field trial in 2019. See the recommendations below.

Treating Algal Spot in Citrus

Algal spot generally presents as a gray-green color on citrus tree limbs, making it difficult to see. However, during mid-summer, the lesions will “bloom” into a “bright rusty red in a ring pattern” that is much easier to spot. Left untreated, algal spot can “crack and crumble bark, stunt limbs and kill branches up to 2 inches in diameter,” according to the article.

Algal spot used to be treated with copper, but this treatment seems to no longer be effective for unknown reasons. Dewdney conducted a field trial in 2019 into treating algal spot in citrus. Thr trial consisted of three sprays—a dormant spray (Feb. 5), post-bloom (May 9), and when the algae were fruiting (red color, June 20)—using copper hydroxide (Kocide 3000), a phosphite (ProPhyt) and an anti-omycete product (Orondis).

According to the article, “a half or quarter gallon rate of ProPhyt showed the greatest effect.” Dewdney maintained in the article “I am recommending growers use 0.5 gallons per acre of a phosphite (54.5% active ingredient) labeled for disease management.”

Dewdney is gearing up for another algal spot trial and is in need of grower input. She is asking Florida citrus growers to fill out a short questionnaire to “better tailor trials” to growers’ needs.

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