Thursday, June 10, 2010

DIE Dieback!

I have recently gotten into Camellia growing the past couple of years. I am a very competitive person and wanted to get into the flower showing contests. I figured it would be about as hard as Citrus growing or anything else that I do. I read up on all the different diseases and cultural requirements, so I figured I was ready to go. Then came this season. I am living in Dieback City! Nasty little fungus. This is one of the most serious of all camellia diseases. It attacks Camellia sasanqua, Camellia reticulata, and Camellia hybrids more severely than Camellia japonica, although it causes damage and plant death among all of the camellia species. It seems to be mostly on my japonicas.
It is botanically known as Glomerella cingulata. I know it as a pain in the gluteus maximus.
This is what my plants look like that have it:

Basically, the progression goes like this.
The new Spring growth wilts, then in rather quick order, the leaves turn a dull green color, later brown, while often remaining attached to the stem. The wood at the base of these stems is dead and discolored in appearance if the bark is scraped off. This prohibits the movement of water to the leaves causing the wilting and eventual death. The fungus needs a wound or opening to enter into the plant. Natural leaf scars are probably the most common entry point. However, injury by mowers, rodents, yard tools, grafting, etc., create wounds where infection may occur. Warm, wet and humid weather in addition to high nitrogen fertilization favors disease development. Is it any wonder, why we have a problem with it here in the Southeast?
The fungus continues to destroy the adjacent wood tissue while the surrounding healthy wood continues to grow, thereby enlarging the stem diameter. This area of dead cells appears to be sunken since there is no new growth of the stem, resulting in a canker. The canker, composed of this area of dead wood, provides the food base for the fungus so that it may survive from season to season and reproduce by producing millions of spores. The fungal spores are easily disseminated by insects walking across wounds or by splashing rain and/or irrigation water. If cankers form on the main trunk of the plant, this disease may eventually cause the death of the entire plant.
Fungicides can be used during the Spring at leaf drop to prevent spread of this disease. The fungus is sensitive to some fungicides. However, once the organism invades the plant tissue, these fungicides are ineffective on the canker, but still can provide protection against future infections. Just a reminder, ALWAYS follow label directions for any chemical....this is the LAW!
I asked some friends of mine, that are major Camellia growers, if they are having a higher than usual occurrence of this problem this year. I got a resounding, YES! The discussion then turned to the reason, why. The best we have been able to come up with is because of the unusual Winter we had. Brutal cold, snow in unusual places, and the relatively short Spring we all had. I haven't been able to find any research to back this up, but it sounds good to me.
Their really is no good cure for this, Control is the goal. Keeping a plant as healthy as possible, maintaining good sanitation, avoiding excessive fertilization and providing good ventilation by not planting too close is the best advice I can find.
What am I doing and what should be done, once a plant is infected? A friend of mine in Florida spelled it out in three words: Prune-Prune-Prune! You should prune two to four inches below the infected area into healthy tissue. Make cuts just above vigorous side branches. Always disinfect pruning tools after each cut by wiping blades with rubbing alcohol or dipping them into a 10 percent bleach solution (1 part bleach in 9 parts water). Burn or discard disease branches and twigs, preferably NOT in your compost bin.
As for me, I have MORE pruning to do. This is my second attempt at eliminating this thing.
Happy Growing!

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