Control Of Azalea Lace Bug Using Insecticidal Soap And Neem
Stanton Gill and Michael Raupp
University of Maryland
College Park, Maryland
At the present time there is great interest in the use of insecticides with low toxicity to non-target organisms for controlling pests of landscape plants. We studied one such material in 1987 by comparing insecticidal soap and the systemic acephate (Orthene) for efficacy in controlling the azalea lace bug,
(Scott) (Gill and Raupp 1988). Lace bugs on evergreen azaleas treated with acephate (Orthene) were all killed. Insecticidal so
Neem is a relatively new botanical extract with insecticidal activity that is receiving increasing attention and is being marketed by W.R. Grace Company under the name Margosan-O. The neem tree, Azadirachta indica A. Juss. (Meliaceae), is a native of Africa, India, and Pakistan. It has been introduced to Cuba, Haiti, Barbados, and southern Florida (Jacobson 1981). Neem seeds and leaves contain azadirachtin, an agent toxic to insects but relatively non-toxic to humans and animals. Lewis and Elvin-Lewis (1983) found that sticks from the neem tree are used for cleaning teeth in Southern Asia, and that its oil and other constituents are used to produce toothpaste and tooth powder. Its oil is also widely used in India as an anti-inflammatory for treating skin diseases and its leaves are employed as an antiseptic, insecticide, and antipyretic.
As a foliage spray, neem seed extract acts as a feeding inhibitor, an insect growth regulator, or both (Warthen 1979). Zehnder and Warthen (1988) reported that a 1.2% neem and piperonyl butoxide treatment resulted in 99.4% mortality of second instar Colorado potato beetle larvae. Larew and Webb (1985) conducted a test with neem extract in a commercial greenhouse and found that both a 0.1 and 0.4% drench caused significant reduction in the pupal and adult stage of chrysanthemum leaf miners of 89 and 100%, respectively. The effectiveness of neem extract on leaf miner and Colorado potato beetle indicated that it was worth investigating as a potential low-toxicity material for lace bug control.
Material and Methods
The test site was a townhouse complex with azaleas growing in mulched beds. All plants were growing in full sun for approximately half of the day and building shade the other half of the day. Forty evergreen azaleas in four separate planting beds were used in this field experiment. In each of the four beds, 10 plants were tagged for treatment or to serve as untreated controls. The cultivars were 'Hershey's Red', 'Delaware White', and 'Rosebud'. The plants ranged in size from 2.0 - 2.5 ft in height and 2.0 - 4.0 ft in width. One bed was randomly selected as the control bed; another bed was treated with neem extract at a dilution of 1:150; the third bed was treated with a 2.5% rate of insecticidal soap and the last bed was treated with a 5% rate of insecticidal soap. A five gallon Birschmeyer sprayer with a hollow cone nozzle was used to apply the materials to the undersides of the foliage.
Prior to the treatment, lace bug densities were determined by sampling each plant. The samples consisted of removing ten 6" terminals, placing them in a bag to prevent escape of lace bugs, and counting all nymphs and adults with the aid of a microscope. Twenty four hours after treatment, ten 6" samples of terminal growth were again taken from each shrub and the number of live lace bug nymphs and adults was recorded. Vitality was determined by probing the lace bug with a needle. If no response was observed, then death was assumed. The effectiveness of the treatments was assessed by comparing the mortality observed in treated beds with expected levels of mortality estimated from the control bed with Chi-square contingency tests (Zar, 1974).
Results and Discussion
Following the application, the untreated control plants exhibited a slight reduction (37%) in the number of living lace bugs. This could have been due to migration of adult lace bugs or natural mortality. Lace bugs on azaleas treated with neem extract experienced a 50% reduction in the number of living lace bugs between pre- and post-treatment counts. This proportion was not significantly different from that observed in the control plants. Neem extract is suspected to act primarily as an insect growth regulator. Assuming this is true, if counts were taken one week post-treatment the kill may have been higher. This possibility needs to be explored more thoroughly, Insecticidal soap treatments were effective at both the 2.5% and 5.0% rate. In the bed treated with 2.5% insecticidal soap, a 91% reduction was observed and in the bed treated at the 5.0% rate a 88% reduction occurred. Both of these reductions differed significantly from the decline observed in the control bed (Chi-square test, p<0.001).
These results clearly demonstrate that insecticidal soap is an effective, control material for suppression of azalea lace bug. The neem extract, with a 50% rate of kill did not give rapid suppression as effectively as acephate or insecticidal soap (Gill and Raupp 1988) but warrants further testing with population changes being assessed over longer periods of time.
Lee Hellman and John Davidson of the Department of Entomology provided helpful comments on a draft of this manuscript.
This is Scientific Article Number A-4951 Contribution Number 7994 of the Maryland Agricultural Experiment Station.
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Stanton Gill is Regional Specialist in Commercial Horticulture for the University of Maryland Cooperative Extension Service.
Michael Raupp is an Entomologist with the University of Maryland Cooperative Extension Service.