White Patches Growing on Indoor Plants
If you love plants, it will make you happy when your home and office are filled with blooming beauties and unusual foliage plants. Live plants lend an air that can’t be duplicated by silk replicas. Unfortunately, live plants can also develop diseases and pests, like powdery mildew and mealybugs, both causing white patches to grow on foliage and branches.
Houseplants are frequently crowded together or planted in pots that remain damp, increasing their chances of developing powdery mildew. This white fungus usually affects the leaves of plants, starting out as circular white spots that may appear furry or powdery, but soon expand to cover large leaf sections and spread to flowers, stems and buds. As the fungus matures, the leaves may discolor or drop and new growth often emerges twisted or dwarfed and covered in powdery mildew colonies.
If you can eliminate the conditions favoring powdery mildew growth, you may not need to use chemicals. Increasing air circulation is paramount to breaking the life cycle of powdery mildew — you can do this by leaving several inches between potted plants, so their foliage doesn’t touch and bringing them out of corners where air may stagnate. The top 1/2 to 1 inch of soil of most indoor plants should be allowed to dry out between waterings — saucers are only good for catching drips and should not be left full of water. Horticultural oils or neem oil can be effective at eliminating stubborn powdery mildews, but make sure to move your plant away from the window before spraying either on its leaves.
Mealybugs are common sources of thick, cottony wax that accumulates on branch crotches and foliage. Wherever these pink to gray, segmented insects are feeding, the filaments that give them a mealy or velvety appearance are shed. Indoor plants may respond to heavy mealybug feeding with yellowing leaves, general weakening or death, depending on the plant. Mealybugs also produce copious amounts of a sticky substance called honeydew that can attract ants and sooty mold colonies, compounding the problem.
Mealybug control is usually simple in small plants. A quick squirt from a kitchen sprayer every few days will knock the pests loose, but if your plant is large or the mealybugs are numerous, try weekly sprays of insecticidal soap or horticultural oil, directly targeted at the pests. In non-food producing plants that spend their blooming period inside, imidacloprid can be applied to the soil. This poison is spread throughout the plant after several days, destroying pests that feed on plant juices. Be careful about using imidacloprid on flowering patio plants before bloom — this chemical is dangerous to bees.
- North Dakota State University Extension Service: Houseplants: Proper Care and Management of Pest Problems
- Purdue Plant and Pest Diagnostic Laboratory: Powdery Mildew on Houseplants
- University of California Statewide Integrated Pest Management Program: Powdery Mildew on Ornamentals
- Iowa State University Extension and Outreach: Mealybugs: A Common Houseplant Pest
- University of California Statewide Integrated Pest Management Program: Foliar-Feeding Mealybugs
- University of California Statewide Integrated Pest Management Program: Mealybugs
Kristi Waterworth started her writing career in 1995 as a journalist for a local newspaper. From there, her meandering career path led to a 9 1/2 year stint in the real estate industry. Since 2010, she’s written on a wide range of personal finance topics. Waterworth received a Bachelor of Arts in American history from Columbia College.
White Patches Growing on Indoor Plants. If you love plants, it will make you happy when your home and office are filled with blooming beauties and unusual foliage plants. Live plants lend an air that can’t be duplicated by silk replicas. Unfortunately, live plants can also develop diseases and pests, like …