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Drip, or trickle, irrigation was used as early as the late 1800s, although it was not until the development of modern plastics during World War II that drip irrigation became economically possible. Developed initially to reduce or prevent moisture stress in the plant, drip irrigation systems also offer an excellent method to apply agrichemicals to the root zone of plants. The application of insecticides through a drip irrigation system was first attempted in the 1980s by using various carbamates and organophosphates, although success was limited. Currently, several newly-developed insecticides such as the neonicotinoids and anthranilic diamides are drip-injected for the control of many vegetable insect pests. The advantages of drip-injection of insecticides over ground application methods include a uniform distribution of insecticide throughout the plant; a reduction in pesticide application inputs, including manpower and vehicle or tractor fuel; and a reduction in soil compaction, plant disturbance, and applicator exposure to pesticides. Insecticides applied through a drip irrigation system can replace or reduce the number of foliar insecticide sprays, reducing the risks to nontarget species.

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No abstract

Laboratory, greenhouse, and field studies were conducted to characterize the biological activity of a genetically altered form of Autographa californica (Speyer) nucleopolyhedrosis virus (AcNPV). The altered baculovirus (vEGTDEL) had a deletion in the ecdysteroid UDP-glucosyltransferase gene. Results from bioassays conducted with neonate and 3rd-instar tobacco budworm, Heliothis virescens (F.), as well as with 3rd-instar cabbage looper, Trichoplusia ni (Hübner), showed vEGTDEL caused larval death slightly, but significantly, quicker than AcNPV. Based on supposition (LT50 values were not calculated), it appeared that larval mortality occurred 0.5-1.0 d faster following exposure to vEGTDEL versus AcNPV. Greenhouse studies conducted against H. virescens on cotton showed that hastened virulence exhibited by vEGTDEL led to improved plant protection versus AcNPV. For example, following 5 weekly sessions of foliar application and H. virescens artificial infestation, cotton treated with wettable powder formulations of vEGTDEL or AcNPV at 2.5 x 10(12) OB/ha averaged 25.7 and 61.8% damaged flower buds, respectively. Although vEGTDEL tended to provide more consistent control of T. ni than AcNPV in greenhouse and field trials conducted on leafy vegetables, differences in efficacy between the 2 baculoviruses were marginal and usually not statistically significant. Generally, results from these studies suggest that genetic modification of NPVs to hasten their lethal effect may be a promising strategy for improving the insecticidal properties of the insect-specific pathogens.