Karen Cambre, Sharpe, Kenneth W.
News Article for June 19, 2017
Over the past week or two I have noticed a number of crape myrtles that have red, orange and yellow leaves. That is a condition that I typically equate with fall foliage, not this time of the year when summer is just beginning.
Once you get close to the trees you notice that the leaves are changing color and some are already dropping from the tree. The leaves have a small dark leaf spot. This is a problem that we have seen many times before in wet weather conditions and is known as Cercospora leaf spot.
Cercospora leaf spot is caused by a fungus that likes wet conditions and high humidity. While it is not new this is as early as I have ever noticed leaf spot on crape myrtles. I have a number of crape myrtles at my office and some of them are dropping leaves and some show no signs at all. There are differences in varieties. Some varieties have natural resistance but even those resistant varieties can get leaf spot if the disease pressure is great enough.
Unless you get repeated defoliations there should not be any long term detrimental effects from the disease. The most practical way to deal with it is to rake up the leaves that fall from the tree and put them in your garbage. If you just mulch the leaves with your lawnmower you are leaving the inoculation source for more disease problems.
Another control method would be to use fungicides but this has not proven to be very effective due to the number of sprays required throughout the growing season. On smaller trees where you can get good coverage you might try fungicides. You could try fungicides with chlorothalonil (Daconil), myclobuthanol (Immunox), thiophanate methyl (Halt). Fungicides that are systemic such as propiconazole which are found in Ferti-lome Liquid Systemic Fungicide or tebuconazole such as Bayer Advanced Garden Disease Control for Roses, Flowers and Shrubs may give longer protection in rainy periods.
I have had lots of reports of satsumas not setting much fruit this year. Citrus like good drainage and do not perform well in wet soils. Excessive rains tend to leach fertilizers and adds to the poor performance problems.
For mature citrus trees of 4 years or older, we recommend a June application of nitrogen to boost growth and fruit production. Broadcast ½ pound of calcium nitrate per year of age of the tree under the canopy of the tree. Satsumas have a bad habit of producing a good fruit crop every other year and this June fertilization will help them to produce every year. Since fertilization will stimulate new growth you do need to get to this task quickly, by July 4th. Woody plants need time to produce new wood and time to harden off new growth before winter, especially citrus.
The LSU AgCenter and the LSU College of Agriculture