Flakey Bark Scale

In 1997 and 1998, grapefruit trees in several locations in southwest and central Florida were found with patches of bark that were severely scaled or curled upwards in rectangular sections. The bark scaling was located on the trunk near the soil line and upwards into scaffold branches. Trees with the symptoms were typically 4 to 7 years of age. Affected grapefruit varieties were White, Marsh, Rio Red, and Flame. Trees in commercial blocks were on Carrizo, Swingle, and Rough Lemon rootstocks. A decline of trees with bark scaling has been reported by several of the growers and trees with bark scaling were removed in at least once location due to decline. Trees were initially examined by researchers for insect pests, fungal or bacterial pathogens, viral or viroid pathogens, environmental stress, and nutritional or pH related damage. An association exists between a budwood source and the disease and at least one of the other sites. An experiment to determine whether a transmissible agent is responsible was established in July 1998 at SWFREC, Immokalee, in which 2 yr. Flame/Swingle trees were inoculated by grafting buds from healthy or bark scaling trees. The disease was monitored for one year at a commercial site on selected trees and both the percentage of infected trees and the visual severity of disease symptoms increased indicating both persistence and slow spread of the problem. Despite these efforts, a causal agent has not been identified nor has the impact of the problem been determined.

Click photo to enlarge

There is currently ongoing research for the following:

1. Identify the cause of the bark scaling disease.

2. Determine the impact of bark scaling on tree health; with particular attention to the decline syndrome.

3. Determine the extent of the problem on citrus in different production regions.

4. Measure the increase and spread of bark scaling to determine its potential infectivity and potential threat to other plantings.

5. Formulate control methods where appropriate.

* We are asking for help form all growers. If you think this problem might be affecting your grove, please contact one of the following people:

• P. D. Roberts, University of Florida, Southwest Florida Research and Education Center, 2686 SR 29 N, Immokalee, FL  34142.  Tel: 941/658-3429  Fax: 941/658-3469.

• T.R. Gottwald, USDA-ARS, 2001 South Rock Rd, Ft. Pierce, FL  34945.  Tel: 561/428-5883  Fax: 561/428-5986.

• P.J. Sieburth, Bureau of Citrus Budwood Registration, Winter Haven, FL  33881.  Tel: 863/298-7769  Fax: 863/298-7738.

• S.M. Garnsey, University of Florida, Citrus Research and Education Center, 700 Experiment Station Rd, Lake Alfred, FL  33850.  Tel: 941/956-1151  Fax: 941/956-4631.

• M. Hilf, USDA-ARS, 2001 South Rock Rd, Ft. Pierce, FL 34945.  Tel: 561/462-5859 Fax 561/462-5986.