Citrus Canker

Of all the agricultural pest and diseases that threaten citrus crops, citrus canker may be one of the most devastating. Citrus canker, is a highly contagious disease of citrus crops caused by bacterium Xanthomonas axonopodis pathovar citri, is a leaf, fruit, and stem spotting disease that affects numerous species, cultivars, and hybrids of citrus relatives. Grapefruit and Mexican lime are highly susceptible to canker; Navel, Pineapple, and Hamlin sweet oranges, lemons and limes are moderately susceptible; Valencia orange, tangors, tangelos, and other mandarin hybrids are susceptible; and tangerines are moderately tolerant.

Young lesions are raided on both surfaces of the leaf, but particularly on the lower leaf surface. The pustules later become corky and crater-like with a raised margin, sunken center and are surrounded by a yellow halo. Fruit lesions vary in size because the rind is susceptible for a longer time, and more than one infection cycle can occur on the fruit. Stem lesion can support long-term survival of the bacterium.

Major outbreak of citrus canker occur when new shoots are emerging or when fruit are in the early stages of development. Frequent rainfall in warm weather, especially during storms, contributes to disease development. Citrus canker is mostly a leaf-spotting and fruit rind-blemishing disease, but when conditions are highly favorable for infection, it causes defoliation, shoot die-back, and fruit drop.

The bacterium reproduces in lesion on leaves, stems, and fruit. When there is free moisture on the lesions, the bacteria ooze out can spread to new growth and other plants. Wind-driven rain is the main dispersal agent, and wind speed >18 mph aid in the penetration of bacteria through the stomatal pores or wounds made by thorns, insects and blowing sand. Leaves, stems and fruit become resistant to infection as they mature. Almost all infections occur on leaves and stems within the first 6 weeks after initiation of growth. The most critical period for fruit infection is during the first 90 days after petal fall. Infection after this time results in the formation of only small and inconspicuous pustules.

In regions where canker is endemic, windbreaks are planted to reduce wind speeds and canker spread. Frequent applications of copper-containing bactericide sprays have shown to be effective for protection against fruit lesions. Because young fruit is particularly susceptible to canker, a protective coating of coppers should be maintained on the fruit surface in the first 90 days after petal fall. Leafminer control is particularly important on young trees and in those cultivars that have frequent flushes of growth.

This epidemic of citrus canker (1995 - present) has impacted areas of Florida including 15 counties.

If you see or have seen plants with citrus canker - like symptoms, DO NOT TOUCH THEM. Contact the Bureau of Pest Eradication and control.

Satellite Offices of the Bureau:
Avon Park Office
Serves: Highlands, Okeechobee, Hardee and Glades Counties
3397 US HWY 27 South
Avon park, Florida 33825
Phone: (863) 314-5900
1 (800) 282-5153

Visit or Call the Master Gardener’s Office at (863) 402-6540 - You may also speak with the Citrus agent. Please do not bring the affected plant into the office.

I will continue this discussion next week.