Unwanted Garden Pests

Probably the most frequently asked questions from our customers are about insect activities in their gardens. There are many good online websites about pests and how to control them. This is a summary of several informative articles distributed by the University of FL, IFAS Extension. We will list various websites at the end of this article to allow those who wish more information.

Pests of ornamental plants may be divided into five groups according to the way they damage plants:

Insects with Piercing-Sucking Mouthparts. These insects have beak-like mouthparts which are used to pierce the plant and to suck plant juices. Examples include Scales, Aphids, whiteflies, mealybugs, thrips, and lace bugs

Foliage-Feeding Insects. They may feed on the leaves, flowers or attack the roots. Examples include caterpillars, beetles, grasshoppers, katydids.

Spider Mites. These pests are not insects but are closely related to spiders. They suck plant juices with their piercing, sucking mouthparts.

Leafminers. These are very small larvae of flies, beetles, or moths that tunnel between the upper and lower leaf surfaces.

Borers. There are many species of insects which bore into the twigs or trunks of plants and trees. These are either the larvae of moths or beetles.

Scales.  These are the most serious pests of ornament plants. There are 135 families of scale in Florida, the most common being armored scales, soft scales, and mealybugs.

Soft Scales. Over 60 species of soft scales occur in Florida. Soft scales secrete a waxy covering attached to their bodies. Soft scales vary in color, size and shape. Because soft scales consume so much plant sap, they excrete honeydew.

Mealybugs. Mealybugs are soft-bodied insects that are covered with cottony white filaments. They infest all plant parts; feeder roots; root crowns; stems; twigs, leaves; flowers and fruits. Injured plants have discolored, wilted and deformed leaves.

Armored scales. Over 175 species or armored scales occur in Florida. They are distinct from other scales because they secrete a wax covering over their bodies that not attached to the body. These scales live and feed under this covering and can be almost any color and shape, depending on the species. Armored scales do not excrete honeydew.

Sooty Mold.  Mealybugs and soft scales excrete large amounts of honeydew, which provides an excellent medium for the growth of a black fungus called sooty mold. Sooty Mold is not only unattractive, it can interfere with photosynthesis and slow plant growth. Ants feed on the honeydew and when ants are observed, plants should be examined closely for these sucking insects.

Detecting infestations:  Scale infestations are often not noticed until leaf yellowing, dieback, or sooty mold are apparent. Monitoring weekly throughout the year, helps prevent severe problems from occurring. Carefully look at the undersides of leaves and stems for scales. Use a 10 power magnifying glass, if needed.

There are several ways to control or eradicate problem insects. We are listing just a few of these approaches.

Cultural Control:  To minimize scale problems, inspect plants before purchase or at installation. If some scales are found, prune off the infested branches and leaves. Destroy any culled or discarded plant material. Scales insects often thrive in warm, humid environments, so you may wish to increase air flow by decreasing plant density in the area. Avoid over-fertilizing, scale insects often lay more eggs and survive better on plants receiving lots of nitrogen.

Non-insecticidal Control:  Insecticidal soaps and oils are available to control insects and related pests. These products are sold as a ready-to-use spray or mixed with water to become a spray. The sprays coat the insects and suffocate them, usually causing them to fall to the ground.

Our two favorite recommendations are Neem Oil and Paraffin Wax which are environmentally friendly. Thorough coverage of the leaves (especially the undersides), twigs, and branches are essential, but spray only to the point of run-off. The insecticide must reach the area of the plant where the insects are feeding. Most failures to control pests are the fault of incorrect application, not one of the insecticide.  Make sure that directions are followed carefully. Additional sprayings may be required and applications are usually best in the cooler early mornings or evenings.

Bacillus thuringiensi (BT):  This a bacterium that can be sprayed on foliage to control caterpillars (think Oleander.) This bacteria has no effect on other groups of insects, including predators and parasites.

The addition of a spreader/sticker to the spray mixture is recommended because it will aid in the pesticide adhering to the leaves and improve the coverage.

Systemic Insecticides:  A systemic insecticide is a chemical compound that is absorbed by the host plant, translocated throughout its tissues and makes the host toxic to certain insect and mite pests. Many systemic insecticides can be absorbed through foliage sprays. Systemic insecticides have been effective primarily in controlling small sucking pests; including aphids, whiteflies, scales, mealybugs, lace bugs, and spider mites. In general, they are not effective for chewing insects.

We recommend the use of Dominion which contains Imidacloprid. This insecticide is not absorbed into fruits and flowers and is used extensively by citrus and other edible plant growers. Systemic drenches last approximately 6 to 10 weeks in our climate and soil conditions, and may need to be applied again as needed.

Palmetto Weavil:  This is a serious and fairly recent insect problem that is attacking some of our favorite palm trees. Bismarkia and Canary Island Date Palms have been affected with subsequent death of the plant. Many believe that these pests are drawn to weakened and more vulnerable palms. Homeowners have been using coffee grounds around these palms as a preventative with some positive results. Imidacloprid, a systemic root drench has been one of the most effective means to prevent and control this unwanted pest.


Leafminers on Ornamental Plants by Eileen A. Buss; U of FL EDIS, publication #ENY-326

Landscape Integrated Pest Management by Scherer, Koehler, Short, Buss; UofFL EDIS, Publication ENY-298

Scale Insects and Mealybugs on Ornamental Plants by Eileen Buss & Jay Turner; U of FL EDIS, Publication ENY-323

For Additional Information:

Johnson, W.T. and H.H. Lyon. 1991. Insects that feed on trees and shrubs

Leaf-mining insects: http://chemical-ecology.net/insects/leafmine.htm

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