Cercospora Leaf Spot on Roselle Hibiscus

Ahmad Robertson  |  10/9/2015 12:47:45 AM

Cercospora Leaf Spot on Roselle Hibiscus Leaves

Cercospora leaf spot has been identified as a problem in home gardens this summer. Farmers and school gardens in St. Helena and Tangipahoa have added Roselle Hibiscus to its garden and landscape. Roselle is a robust shrub-like annual that gets 4-7 ft. tall. The dark green leaves are about 6 inches across and deeply dissected into 5 narrow lobes. The stems, branches, leaf veins, and petioles leaf stems are reddish purple. The hibiscus-like flowers, appearing in October, are yellow. At the bottom of each flower, enclosing the bases of the five petals is a fleshy bright red cup-like structure called a calyx. The calyces of Roselle are used to make juices, sauces, jellies, wines and pies. Roselle usually blooms in October when the days begin to shorten. Plant location should be placed in full sunlight. Start seeds indoors and transplant in the garden after all danger of frost which is usually late April in Southeast Louisiana. It’s an annual propagated from seed. Roselle juice is similar to cranberry juice, but not as bitter.

The calyces are harvested while they are still tender and juicy, about 10 days after the flowers appear. The plants will continue to flower and produce if kept picked. Remove and discard the seed pods from the calyces. Use 2 quarts of calyces and 1 quart of water to a boil and simmer for 10 minutes. Then strain and use the juice with sugar to make a refreshing cranberry-like drink, or make jelly or wine as you would with any fruit juice. The strained pulp can be used for jam or pie. I use the plant for medicinal purposes and the results are amazing. I recommend you contact me in March for seed distribution and visit the Tangipahoa annual spring garden day.

Initial infection of leaf spot usually occurs during May, but symptoms don’t become apparent until later in the season. Midsummer environmental conditions contribute to disease severity. Rainfall and overhead irrigation are major factors that play a pivotal role in symptom expression and intensity. Late summer rainfall can be a major contributor to defoliation and decline. In general, leaf spots are first visible on older leaves at the bottom of the plant then spread upward toward the top of the plant. Initial spots are purple and small with a circular shape.

Management:

Spectracide lmmunox Fungicide can be utilized to control Cercospora leaf spot on susceptible hibiscus varieties. This should be started in early summer when the spots are first noticed and continued at one to two week intervals when the weather is warm and wet. Follow directions on the fungicide label. Powdery mildew is a concern that typically affects Roselle Hibiscus production in Late October during the harvest period.

For more information, contact the St. Helena or Tangipahoa Extension Service, 305 E Oak St., Amite, call (985) 748-5462, (225) 222-4136, or email ahmad_robertson@suagcenter.com or arobertson@agcenter.lsu.edu.
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