As foliage plants, philodendrons (Philodendron spp.) rank among Mother Nature’s classics. Countless climbing or branching varieties of these Central and South American natives have added tropical flair to conservatories and interiors since Queen Victoria’s day. In U.S. Department of Agriculture plant hardiness zones 9 through 11, split-leaf philodendron (P. bipinnatifidum) flourishes outdoors. If these adaptable plants have one shortcoming, it's their susceptibility to bacterial diseases.
Erwinia blight, the most common philodendron disease, can prove fatal in a few days. Erwinia attacks at or below the soil line. Water-soaked lesions appear on the stems; if a plant survives stem involvement, the infection spreads to its leaves. New growth is yellow and stunted. Older foliage develops wet, yellow or tan lesions. In high heat and humidity, the lesions engulf leaves and their stalks. Infected, collapsing tissue emits a disagreeable smell. Cool, dry conditions don't help; the lesions thin and tear, leaving leaves full of holes. Erwinia thrives in a damp environment with temperatures between 71 and 93 degrees Fahrenheit.
Pseudomonas Leaf Spot
Fiddleleaf philodendrons (P. bipennifolium) are no strangers to Pseudomonas chicorii leaf spot. Signs of the disease often appear within 72 hours. They include dark-centered, yellow-haloed watery lesions spreading to as much as 1 inch across. In dry conditions, the lesions fade to tan. Infected leaves may drop in moist environments. Regularly misted philodendrons growing at temperatures between 82 and 85 degrees Fahrenheit are primary targets, but the bacteria also infiltrate wounded leaves.
Xanthomonas Leaf Spot and Tipburn
Red-edge leaf spot bacteria (Xanthomonas campestris pv. dieffenbachia) attack philodendron leaves through wounds, the pores or stomata on their lower surfaces or moisture-releasing glands called hydathodes. Yellowing begins at the leaves’ tips and moves to their margins. Yellow-haloed, reddish spotting develops along the leaf edges. These spots age to brown. As the infection advances, foliage becomes entirely yellow and falls from the plants. Threat of Xanthomonas rises in humid conditions at temperatures between 70 and 90 degrees Fahrenheit.
Stress and Disease
Stressed philodendrons invite disease. Stress factors include under- or overwatering or fertilization, poorly-draining medium, significant temperature swings and inadequate light. The damage they cause worsens during winter's short days, when the philodendrons are dormant.
A few precautionary measures keep infectious organisms in check. Watering philodendrons from underneath and housing them at a temperature of 70 degrees Fahrenheit eliminate bacteria-multiplying warmth and humidity. Semi-annual to annual repotting in appropriately sized containers of sterile potting medium, and two or three evenly spaced fertilizer applications in spring and summer, keep the plants vigorous.
Treating Infected Plants
Isolate a sick philodendron at the first sign of disease. If more than one-third of its leaves show symptoms, remove them a few at a time, cleaning your pruning tool between cuts in a solution of one part household bleach to nine parts water. Maintaining the plant in cool, dry conditions with proper light, water and fertilizer may restore its health. If the infection is systemic, however, you won't be able to save it.
- Floridata: Philodendron Bipinnatifidum
- University of Illinois Extension Report on Plant Disease: Bacterial Diseases of Anthurium, Dieffenbachia, Philodendron and Syngonium
- Penn State University Extension Fact Sheet: Philodendron Diseases
- University of Minnesota Extension: Bacterial Leaf Diseases of Foliage Plants
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