Sooty Mold

Control sooty mold on plants by stopping it before it starts

Understanding how a problem starts can save time and effort in trying to control it. That's the case with sooty mold. The name is pretty descriptive. If you have gardenias or crape myrtles, you've probably seen it.

Sooty mold is a black-colored growth that can completely cover the leaves of a plant. This fungus is basically a cosmetic problem; however , it can reduce the amount of sunlight a plant gets, causing some minor growth difficulties. The bottom line is that it just makes a plant look ugly.

This fungus does not attack the plant itself. It feeds on a material called honeydew. Honeydew is excess, sugary sap that is excreted by aphids and whiteflies. The way to control sooty mold is to control these insects. This may sound simple enough but sometimes it can be a challenge to control these little soft-bodied pests.

Unless you're looking close, it can be difficult to see these insects on a plant. You can't depend on seeing portions of leaves eaten away because aphids and whiteflies don't have the ability to chew. They have mouth parts similar to mosquitoes that are designed to pierce the plant tissue and suck out the plant juices. Their size also make them difficult to see. The largest species are not more than a quarter inch in length.

There are more visible signs that indicate these pests are present. First, look for new leaves that are malformed or distorted. Aphids and whiteflies prefer to feed on new, tender leaves; it is easier for them to insert their mouths into the new growth. Second, look for the sticky honeydew. Third, shake the plant. Whiteflies will quickly fly away from and back onto a plant when disturbed. Fourth, look for ants running up and down the trunk and stems of the plant. Ants love honeydew. They feed on it. Usually when you see ants crawling all over okra plants, or various trees and shrubs, they are looking for aphids producing honeydew. If you see any of these signs, inspect the underside of leaves for aphids or whiteflies.

Plants located under large trees many times will have problems with sooty mold. Pecan trees commonly cause the foliage of plants underneath them to have sooty mold problems. There is not a lot that can be done in this situation to control the sooty mold because the aphids are feeding in the tree and the honeydew is dropping onto the plants under the tree. It is not practical or economical to spray a large tree to control aphids.

Aphids and whiteflies can be controlled on smaller plants like crape myrtle and gardenia in a number of ways. If the infestation is small, you can simply spray them off the plants with a heavy stream of water from a garden hose. With larger populations, you may need to use an insecticide. Insecticidal soap, malathion, diazinon and orthene can be used, but spray to get good coverage underneath the foliage and always follow label directions. These insects can also be held in check in nature by adverse weather conditions including low temperatures and heavy rains. There also are a number of insects that eat aphids and whiteflies. The most important one is the lady beetle.

The way to control sooty mold is to stop it before it gets started and the way to do that is to control the aphid and the whitefly.

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Larry Williams

Horticulture Agent

Phone

850-689-5850
850-729-7476

Fax

850-689-5727