How to Manage Pests

UC Pest Management Guidelines

Some pesticides are less toxic than others to natural enemies such as green lacewings, lady beetles, parasitic wasps, beneficial mites, and predatory bugs. When an insecticide is less toxic to the natural enemy than the pest it feeds on, it is a selective insecticide. Insecticides that are not selective, but may be even more toxic to the natural enemy than to the pest or have an impact on a wide range of pests and natural enemies, are called broad-spectrum. Examples of broad-spectrum pesticides include most organophosphate (e.g., malathion, dimethoate), carbamate (e.g., carbaryl–Sevin, methomyl–Lannate), pyrethroid (e.g., cyfluthrin–Baythroid, fenpropathrin–Danitol), and foliar-applied neonicotinoid (imidacloprid–Provado, acetamiprid–Assail) insecticides. If broad-spectrum insecticides are used in a selective manner, such as in baits, spot treatments, or applied systemically through irrigation water, some of the detrimental effects on natural enemies can be avoided.

Within each of the major groups of pests in citrus, there are selective and broad-spectrum pesticides that can be used to control them. For instance, citrus thrips can be controlled with the broad-spectrum organophosphate dimethoate and the carbamate insecticide formetanate hydrochloride (Carzol) or with selective insecticides such as sabadilla (Veratran), abamectin (Agri-Mek, etc.), or spinetoram (Delegate). Lepidopterous pests, such as fruittree leafroller and citrus cutworm, can be controlled with broad-spectrum organophosphate and carbamate insecticides (chlorpyrifos–Lorsban and methomyl–Lannate) or with selective Bacillus thuringiensis microbial insecticides (Javelin, Dipel, etc.) or the stomach poison cryolite (Prokil Cryolite and Kryocide). Finally, armored scale can be controlled with broad-spectrum organophosphate and carbamate insecticides (chlorpyrifos–Lorsban, methidathion–Supracide, and carbaryl–Sevin), by selective narrow range oil treatments, or by releases of Aphytis parasites. Botanical, microbial, and oil insecticides are not disruptive to most natural enemies. Oil can reduce natural enemies present at the time of treatment but is fairly selective because of its limited persistence. In addition, some broad-spectrum pesticides can be relatively selective when used infrequently and at very low rates: for example, 0.5 pint per acre of chlorpyrifos (Lorsban) for katydids, compared to high rates (6 to 12 pints per acre) used for California red scale.

Some insecticides are selective or safe for one group of natural enemies but not another. For example, lacewings are naturally tolerant of pyrethroids, but parasitic wasps, and predatory mites, and beetles are very susceptible to this group of pesticides. Insect growth regulators such as pyriproxyfen (Esteem) and buprofezin (Applaud) are safe for parasitic wasps but are very toxic to beetles such as the vedalia beetle needed for cottony cushion scale control. The miticide dicofol (Kelthane) is safe for predatory and parasitic insects but is quite toxic to predatory mites.

Both selective and broad-spectrum pesticides can be quite persistent or residues may degrade quickly. For example, both sabadilla (Veratran D) and pyriproxyfen (Esteem) are relatively selective, but sabadilla persists only for a short period of time (several days), whereas residues of pyriproxyfen are quite persistent (2 to 3 months or more with detrimental impacts on beetles). If a persistent, broad-spectrum pesticide has been applied, residues on the plant may be harmful to natural enemies for weeks or months. For example, if adult Aphytis wasps are placed in a jar with leaves that were sprayed in the field with the dilute rate needed to control California red scale, chlorpyrifos (Lorsban) residues are toxic to adult Aphytis for 3 to 6 weeks, methidathion (Supracide) affects adults for 9 weeks, and carbaryl (Sevin) affects adults for 5 months after the treatment. In the case of the predatory mite Euseius tularensis, some San Joaquin Valley populations have developed resistance to chlorpyrifos (Lorsban) and their populations are unaffected by this pesticide, but they are easily killed for several months by the carbamate formetanate hydrochloride (Carzol). Occasional, single treatments of broad-spectrum pesticides are much less harmful to natural enemies than multiple selective treatments.

It is important to carefully consider the selectivity of a pesticide when making a treatment decision. This includes the effect the pesticide has on nontarget species, its persistence in the environment, and whether or not resistance to the pesticide has developed. These factors are listed in the table below and under each recommendation in the guideline. Range of Activity is listed first and denotes the degree of selectivity each pesticide recommendation has, along with the group of organisms primarily affected by the treatment. For example, the range of activity for dimethoate is listed as "Broad (insects)." This means dimethoate affects most groups of insects. It also has an impact on beneficial mites as noted in the next column. On the other hand, Bacillus thuringiensis is listed as "Narrow (caterpillars)" because it only affects caterpillars. Persistence, or the length of time a pesticide remains effective or toxic, is listed next and is categorized as short (days), intermediate (up to 6 weeks), or long (months). And finally, in instances where resistance has been observed in either the pest or natural enemy, this information is included.

Factors Affecting the Selectivity of Treatment Materials for Citrus Pest Management

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
General Pesticide Information
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O‘Connell, UC Cooperative Extension, Tulare County
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
C. E. Kallsen, UC Cooperative Extension, Kern County
D. R. Haviland, UC Cooperative Extension, Kern County

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