Citrus canker disease has been found in Louisiana in the summer of 2013, after ruining about 20% of Florida's crop. LSU AgCenter has a descriptive publication (#3269) available by e-mailing rsingh@agcenter.lsu.edu. I found it in my orchard in Algiers, Louisiana about a year later. It was mostly concentrated in 10 large grapefruit trees on the site.
Figure 1: Typical spotting of leaves a n d fruit with chlorosis displayed on Grapefruit: Algiers, LA, Tree#4
Figure 2: Spotting of leaves and fruit. Algiers, LA, Tree #7
Bacteriologists taught us that Penicillin was an antibiotic of choice for Gram-positive bacteria and that Streptomycin would be indicated for Gram-negatives. The agent of Citrus canker is a Gram-negative, Xanthomonas citri. Over the past 20 years, I have been treating a condition of Sycamore trees, called "Xylem-limiting bacterial disease" with injections of Streptomycin and have seen quick and permanent recovery. The bacterial agent of this disease is another species of Xanthomonas (or, maybe the same one). Since the disease is deemed "incurable", the only recommended treatment mode is quarantine and eradication – a death sentence for your citrus trees. Technically, an infected tree is already dead.
Figure 3: Infected trees marked for treatment
Figure 4: Tree #7
So, on July 21, 2014, we set out to administer a treatment to 10 grossly infected Grapefruit trees (numbered) as well as 25 symptomless trees: Kumquats, Satsuma's, Navels, Lemons, Pomelos and Louisiana sweets. First, all the trees were given a foliar spray of Copper hydroxide (Kocide 2000) to reduce inoculum levels in the stand. Four drill holes were spotted out on the trunks of the 10 trees and one each on the others. A saturated solution of Agri Strep (R) was squeezed into each hole using a plastic veterinary syringe. 4 – 2 oz. containers were used in this treatment and holes were refilled as needed until the materials ran out. Finally, the holes were capped with a bit of clear silicone. Agri Strep is available at most feed stores.
Figure 5: Materials needed to treat for citrus canker: (left to right: Copper liydroxide, spreader/sticker for foliar spray, veterinary syringe, Agristrep container, silicone gun, portable drill with 3/8 inch bit.
Figure 6: Agristrep container: 21.2% Streptomycin sulfate
Figure 7: adding water to Streptomycin in the original container for injection
Figure 8: Packing drill holes with silicone
Two weeks later (August 4) – Chorionic crowns greened up, new spot-free growth was present and the trees appeared healthier already. Though it is too early to tell whether they were "cured" or not, the results look promising. Some of the drill wounds were suppurating a gummosis, and the existing spots were still present on the leaves. But things are improving.
November – December 2015: All the trees that were treated with Streptomycin in 2014 are healthy, though some lesions on some of the fruit remain. We produced a bumper crop of oranges, grapefruit, pommelos and kumquats. There is a moderate amount of symptom expression on the treated trees and some symptoms on untreated trees. This will require a follow-up treatment in May of 2016, once all the fruit has been harvested.
A small part of the citrus harvest from our 1 acre lot in Algiers, La. There is about 1000# of fruit in plastic cartons in the rear. January 2016
Figure 9: Tree #1: greened up with new, unspotted growth
Figure 10: Tree #4 Recovered from chlorosis (compare with Fig. 1)
Figure 11: Tree #7, greener with new, unspotted growth
Figure 12: Gummosis around drill holes Tree#7.