How to Get Rid of White Spots on Plant Leaves

Sometimes it builds slowly, but other times it explodes overnight. Your garden plants look healthy and fruitful, then suddenly white stuff covers your leaves. When your plants get hit by pale powder, diseases or insects are usually to blame. By learning to identify the source of white powder on your plants, you can get rid of white stuff and prevent its return.

Diseases That Cause White Powder on Leaves

Diseases that cover leaves in white fuzz or powder affect many types of plants. If you inspect a white leaf closely and don't see any insects, disease is likely the culprit. Two common diseases cause a white, powdery covering on garden plants and crops:

Powdery mildew causes white powder on rose leaves.

Powdery mildew is a fungal disease that covers leaves and stems in white powder. Unlike many fungal diseases, powdery mildew strikes hardest in warm, dry, shady conditions and high humidity. Different types of powdery mildew affect various plant families, but white powder on rose and tomato leaves frequently trace to this source. Zucchini squash and cucumber leaves also struggle with powdery mildew. The white powder usually starts on the upper sides of plant leaves.

Downy mildew coats the undersides of leaves.

Downy mildew is more closely related to algae than fungi, but it looks and acts a lot like fungal disease. In contrast to powdery mildew, downy mildew thrives in cool, damp weather when leaves stay wet for long periods. Crowded conditions aid its spread. Veggies such as broccoli, cabbage and cauliflower are frequent targets. Squash and cucumbers suffer this mildew, too. The grayish-white fuzz usually appears on leaf undersides, while yellow spots dot the top sides of leaves.

Disease Control: Focus on prevention and quick intervention to stand against diseases that cause white powder on plants. Once infections are active, they're harder to control. Daconil Fungicide Ready to Use and Daconil Fungicide Concentrate offer rain-proof, three-way protection to prevent, stop and control more than 65 plant diseases, including powdery mildew and downy mildew. Treat early to prevent disease; treat active disease regularly to stop its spread.

Insects That Cause White Stuff on Plants

At first glance, all white stuff on your plant leaves looks like disease. But a closer look may reveal movement you didn't expect. Several types of insect pests leave powdery white stuff on plant leaves. Three culprits are common in houseplants and gardens:

Mealybugs look like fungal disease — until you take a closer look.

Mealybugs get their name from the white, meal-like powder that covers their bodies. They usually gather in large groups that look like a thick white mold at first. Mealybugs can reproduce without mating, so they multiply quickly. They excrete ant-attracting honeydew as they feed, adding sticky residue to the waxy powder. Mealybugs attack many plants, but citrus trees, fruit trees and houseplants are frequent targets.

Cottony scale insects often attack lemon trees and other citrus.

Scale insects are closely related to mealybugs and come in different colors, including powdery white. Female cottony cushion scales carry large, cottony egg sacs — two to three times as long as the scale's body. When gathered to feed, they look like puffs of cotton wrapped around stems and leaves. As immature scales molt, they litter foliage with white, cottony skins. These cottony white scales produce profuse amounts of honeydew as well.

Photo credit: Whitney Cranshaw, Colorado State University, (CC BY 3.0 US)

Whiteflies are tiny, winged pests covered with waxy, white powder. Like their mealybug relatives, they reproduce rapidly. White powder on lemon tree leaves often comes from these pests. Whiteflies gather on the undersides of leaves, creating a blanket of insects, waxy silvery-white debris and sticky honeydew. Shake affected plants gently and the "powdery white stuff" takes flight. When the shaking stops, the pests return.

Insect Control: Insects that look like white powdery deposits on plants and leaves can be tough. Effective control starts at the earliest sign of trouble, so don't delay inspecting that white stuff. Sevin Insect Killer Ready to Spray and Sevin Insect Killer Concentrate kill more than 500 insect pests by contact, including mealybugs, scale insects and whiteflies. Then they keep protecting against this pest trio for up to three months. Always take houseplants outdoors for treatment. Let plants dry thoroughly before they go back inside.

Plant Care to Prevent Disease and Insects

Most problems with plant diseases and insects begin long before those pests arrive. Like healthy people, healthy plants are less susceptible to insects and disease. But when plants are stressed or undernourished, pests seek them out. To help keep your plants free from unwelcome white powders, give them plenty of room to grow so air and light can reach their leaves. Try drip irrigation instead of overhead watering to keep leaves dry. Then feed your plants the nutrients they need for vigor and strength.

With Pennington Epsom Salt, you can tap into the secret gardeners have used for years to prevent unattractive leaves due to certain nutrient deficiencies. Pennington UltraGreen All Purpose Plant Food 10-10-10 feeds your plants an ideal blend of essential nutrients that promote beautiful leaves, more flowers and bigger vegetables. One application keeps feeding for up to four months. OMRI-listed Alaska Fish Fertilizer 5-1-1 enhances the strength and vigor of plants indoors and out to help them stay productive all season long.

With proper plant care and nutrition, you can help keep your plants free from diseases, insects and white stuff that threatens to appear. We're here with premium lawn and garden products and timely tips to help you succeed. From homegrown vegetables to native plants and pollinator gardens, let us help you grow the plants of your dreams.

Always read product labels thoroughly and follow instructions, including guidelines for pre-harvest intervals (PHI) and application frequency.