Monday, May 3, 2010

Leaf gall

Here is a question that the guys in the store and I have been hearing repeatedly this spring.

I have a camellia whose leaves are 2-3 times the normal size and are real thick. Can you help me with this?

This is a very common disease that affects camellias. This disease affects Camellia sasanqua (the small leaf camellia that blooms in the fall) more than Camellia japonica (the large leaf camellia that blooms in the winter). The cool nights, overhead irrigation and rains we had in the early spring made this disease flourish. This disease is caused by the fungus Exobasidium camelliae. There is another Exobasidium fungus that affects azaleas in a very similar way.

Leaf gall is the common name for this fungus. The leaves become very large and fleshy. The new growth is much thicker than normal and then the leaves break apart and release spores. When the leaf breaks apart, you can see the lower part of the leaf turns white. The disease spreads by wind and splashing water. A good layer of mulch will help with the splashing water.

The best control for leaf gall is to pick the infected leaves off as soon as you see them in the spring. If you can pull them off before the spores develop, you can prevent the disease from spreading. Once you pull them off, place them in a plastic bag (the one your newspaper comes in is handy or a dog poop bag) and throw them away in the garbage or burn them.

Usually this disease does not require chemical treatment. The manual pulling off of leaves and limiting overhead irrigation in the spring, when the nights are cool, will keep it in check. If you have a severe problem year after year, you could apply Mancozeb at bud break. This should be your last resort.

For this year, pull off as many infected leaves as you can. Soon your plants should go back to producing its normal size leaves. The leaves that were affected by leaf gall will soon wither, turn brown and fall off the shrub.

While eating lunch the other day, I also had a question about a Christmas cactus and the fertilizer for it. A 10-30-20 water soluble fertilizer would be a good start. The nitrogen (the first number) should be 20% or less of the phosphorus (the second number) and potassium (the third number) added together. As I told you then, less is better or the cacti will get diseased.