NEEM RESEARCH YIELDS RESULTS

The neem tree (Azadirachta indica), whose seed and leaf extracts are known to kill more than 60 types of insects, has recently been the subject of several interesting studies. Researchers at Virginia Polytechnic Institute and State University effectively control the Colorado Potato Beetle (CPB) in eastern Virginia using extracts from seed kernels of the tree. Meanwhile, in Louisiana, USDA researchers have found that leaves from the India native may block fungi from producing aflatoxins in stored grains. Another study in Israel conducted on pest and predacious mites indicates that neem extracts are considerably more toxic to the pest than to the predator.

Neem and the Colorado Potato Beetle

VPI scientists conducted laboratory and field experiments to test neem against eastern Virginia CPB populations which are showing increasing resistance to broad-spectrum insecticides. In laboratory experiments, concentrations of 0.4 percent, 0.8 percent and 1.2 percent seed extract (active ingredient, azadirachtin) were tested with and without the synergist piperonyl butoxide. Potato leaves were dipped in the neem solution and allowed to air-dry, and cuttings were then placed on moist filter paper at 25 degrees C, 65 percent relative humidity, with a photo- period of 16 hours light and 8 hours dark. Experiments were conducted using 2nd instar larvae and adult beetles. Mortality for the CPB was determined at 24-hour intervals up to 72 hours. Field experiments were conducted in plots of 'Superior' variety potatoes in 3 rows spaced at 0.9 meters. The same three concentrations of neem extract solution were applied weekly to each plot. CPB counts were made three days after each spraying by visual examination of 10 randomly selected stems per plot. In the lab, leaf treatments of 1.2 percent neem extract solution plus PBO resulted in almost 100 percent mortality of 2nd instar larvae at 72 hours, but less than 25 percent mortality of adults.

In the field, all treatments with neem extracts resulted in significantly lowered CPB populations. PBO appeared to increase the activity of the neem treatments. Defoliation was much more apparent in control plots while tuber yields were significantly higher in neem plots. The plot sprayed with the 1.2 percent extract (with PBO) did, however, give lower yields than the other two sprayings, indicating that high neem concentrations may have adverse effects on potato growth. Results also indicate that sprayings are most effective with young CPB larvae, and should thus be conducted as soon as possible after the eggs hatch. A commercial formulation of neem is presently being produced in the United States on a small scale.

The Vegetable Growers News, 42:6, May-June 1988

Contact:

G.W. Zehnder, Assistant Professor
Eastern Shore Agricultural Research Station
Painter, VA 23420

or

J.D. Warthen Jr., Research Chemist
Insect Chemical Ecology Laboratory
USDA, ARS
Beltsville, MD 20705