February 2016

Hello Master Gardeners,

Recently I’ve been receiving calls and pictures regarding camellia flowers being discolored after opening or some being discolored and only partially opening. On white camellia flowers the flower petals take on a tan to brown color and many fall to the ground. After discussions with Dr. Raj Singh, LSU AgCenter Plant Pathologist , and Director of the Plant Pathology Lab at LSU, we concluded that the majority of the problems were caused by cold injury. However another problem that mimics cold injury is Camellia Flower Blight which is caused by Sclerotinia camelliae which becomes active during cool moist conditions.These conditions are what Dr. Singh refers to as favorable conditions for camellia flower blight. To those of you who had the fortune of sitting through Dr. Singh’s plant pathology class as you received classroom instructions to become a certified Master Gardener, you should have recalled that he said in order for infection to take place there are three things that need to be present: favorable conditions , a host, and a pathogen. When camellias are blooming in cool temperatures with abundant moisture, camellia flower blight is highly probable. Camellias growing in shade where moisture is more abundant are more susceptible. The fact that camellia flower blight mimics cold injury may be confusing to home gardeners because of the similar appearance, but remember, if the petals have a slippery, slimy texture then it’s camellia flower blight. If the discolored petals have a dry leathering feel then in all likelihood it is cold injury. If it is camellia flower blight all infected flowers that fall to the ground should be picked up and discarded. Some gardeners even picked the infected flowers off the plant and discarded them. If this is not done, the pathogen will over winter in the old infected flowers and be there to infect the next crop of camellia flowers.

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I’m also receiving numerous calls from home gardeners regarding a high number of broccoli plants that are bolting or as old gardeners say, going to flower and seed. We see this occurring when these plants are repeatedly exposed to warm temperatures, which is common with late season broccoli. If you recall we’ve had several periods of above normal temperatures and since I’m getting calls from all across Lafayette and surrounding parishes it’s safe to conclude that the warm weather patterns are to blame. Bolting is actually a survival mechanism in certain plants , where by if the temperature ranges are higher than what the plant has been genetically programmed to handle, the plant feels threatened and tries to produce the next generation by flowering, followed by seed production. Some research indicates that to some degree as a gardener these plants can be mulched or watered to keep the roots cool which may minimize bolting. However, I’m not sure if that has been proven! All cruciferous vegetables such as broccoli, cauliflower, Brussels sprouts, turnips , kale, cabbage and several others, are susceptible to bolting!!

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One of the most serious diseases of cruciferous crops worldwide is Black Rot caused by the bacterium Xanthomonas campestris. If the pathogen is present in seeds or transplants, and favorable conditions develop such as wind and rain producing splashing water, it is highly likely that infection will take place. Many gardeners have called and sent pictures of browning of the leaves of broccoli, cabbage, and cauliflower within the last month. They should remember the rainy weather pattern we’ve been having and continuing to have. The infection usually begins on the leaf margins where the pathogen enters the plant through natural openings in the leaf or through insect wounds. The leaves begin to take on a tan to brown V shaped lesion in its early stages and progressively moves downward from the leave margin to consume an increasingly larger area of the leaves of these vegetables. This causes plants to sometimes die prematurely, remain small, or lowers the quality of the vegetables produced. Symptoms are sometimes confused with nutritional problems. In the very early stages of development, infected leaves can be removed and applications of copper fungicide can be made to slow the spread of Black Rot.

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Gerald P. Roberts
Horticulturist/Master Gardener Program Coordinator
LSU AgCenterhere to edit.