See everything you need to know about scouting for and treating algal spot in citrus to stop the disease, including a new treatment.
Algal spot is “a disease that is not always at the top of mind for growers,” according to a UF/IFAS Tip of the Week article, but it is one that you should pay attention to. According to the article, algal spot can cause bark to “crack and crumble under lesions,” stunt limbs, and cause branches up to 2 inches in diameter to die. The article shared what to look for and two options for treating algal spot in citrus. See those recommendations below.
Scouting for Algal Spot
According to the article, algal spot “is a disease caused by the algae Cephaleuros virescens” and occurs “mostly on citrus tree limbs.” When scouting for algal spot, look for:
- “A gray-green color that resembles the color of citrus bark,” that “is difficult to see for most of the year.”
- “In mid-summer, often starting in June, the color changes as the algae begins to bloom, becoming bright rusty red in a ring or donut pattern.”
- “The lesions are usually about ½ inch but can often join to encircle a branch.”
- “Spots can also be observed on leaves and over-ripe fruit, but these are much less damaging and can be easily removed.”
Treating Algal Spot in Citrus
The article shares two different options for treating algal spot, a treatment that was recommended in the past and a newer treatment.
Usual treatment: “three applications of 0.5 gallon per acre of a phosphite salt with a fungicide label. The timings for the three applications are:
1. Dormant spray (late January and mid-February).
2. Post-bloom (late April to mid-May).
3. While the algae are fruiting and red (June and July).”
New treatment: “April-May and June or July treatments program with 0.5 gallons per acre of a phosphite product with a pesticide label.”
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