|Disease Profile: Entomosporium leaf spot of photinia and Indian hawthorn
This article was originally published in The Dirt Doctor's Dirt Magazine, April, 2003
Description: Spots on mature leaves have ash brown to light gray centers with a distinctive deep red to maroon border. At the center of the leaf there are small black spots that are producing spores. Many small spots may grow together to form large maroon blotches on heavily diseased leaves. Low levels of this fungus usually cause little more than cosmetic damage, but the spores are a source for future infections. Severe infections cause heavy defoliation, which increases the plant’s sensitivity to cold injury and other diseases and insects.
Disease Cycle: Spots on the leaves and young shoots are important in the survival of the Entomosporium leaf spot fungus. During cool, wet weather (60 to 80 degrees F., 12- to 24-hour leaf wetness), small, circular, often bright red spots appear on leaves of red tip photinia and Indian hawthorn. Fallen, diseases leaves are less important sources of the fungus. Masses of spores are released during periods of wet weather from the fungal spore producing structures in the center of the spots from late winter through much of the year except during the hot periods of summer. These spores are spread to healthy foliage by a combination of splashing water and wind.
Control: Cultural practices can reduce the chance for this disease. The best control is prevention. Do not plant photinia or Indian hawthorn areas that accumulate water, or have poor drainage. Red tip photinia are susceptible to cotton root rot (Phymatotrichum omnivorum) and this fungal disease is exacerbated by poor drainage. Damage from this root disease can lead to weakened plants that are subsequently more susceptible to problems such as leaf spot. Space plants to improve air circulation around them and to promote rapid drying of leaves. Do not water or fertilize more than necessary to avoid promotion of excess new growth, which is more susceptible to disease. If plants require supplemental irrigation, water early in the morning so the leaves dry quickly. Fallen diseased leaves can be removed as they are a potential source of future infections, but are not the most significant source. Moving them could cause an unintended dispersal of more spores. You may try covering fallen diseased leaves with cedar mulch to accelerate their decomposition and suppress the fungus. Use a potassium bicarbonate spray on the foliage of heavily infected plants (4 teaspoons/1gallon water), or corn meal juice. It may be necessary to remove severely diseased plants that have also been damaged by cold injury and replace them with another plant species not susceptible to the disease. Improve your soil health by following the basic organic program.
***A Word from Howard - Although I wouldn’t buy or plant any more ret tip photinia, my photinia program, which evolved into the Sick Tree Treatment, can save the plants and bring them back into a healthy condition. If the root system of the plant is too damaged, however, then the plant may need to be removed. The reason for the acceleration of photinia problems is the unfortunate continued use of harsh synthetic fertilizers and toxic pesticides. Not only do those products not sole the problem, they make it worse. The real problem is not the spots on the leaves, the subsequent chlorosis, or the foliage die back. These are merely symptoms of the real problem.
Red tip photinia breeding led to a fatal flaw: A week root system that is highly susceptible to root fungal diseases. When the roots get in trouble, the symptoms start to appear on the foliage. The problem is the fungal disease in the oil and on the roots. Only the organic products that stimulate beneficial biological activity will help the photinia – again, if its’ not too late. Many people have saved their plants with the Sick Tree Treatment and the basic organic program keeps them happy long term.
Refer to the Sick Tree Treatment on http://www.dirtdoctor.com/ or the March issue of The Dirt.