Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 5/16/2011
Publication Date: 8/22/2011
Citation: Zhu, H., Wang, X., Reding, M.E., Locke, J.C. 2011. Distribution of chemical and microbial pesticides delivered through drip irrigation systems. In: Stoytcheva, M. editor. Pesticides - Formulations, Effects, Fate. Rijeka, Croatia:InTech. p 155-180.
Interpretive Summary: The current lack of scientific data for effective delivery of pest-control agents for soil pests leaves the nursery or greenhouse industries vulnerable to possible crop loss or damage, rendering the crop unmarketable either due to appearance or quarantine. The capability of drip irrigation systems to discharge water soluble and insoluble materials of chemical and microbial pesticides with different physical properties was evaluated. Tests included the measurement of uniformity and recovery rate of these chemical and microbial pesticide materials through drip lines and in the sandy clay soil. Drip irrigation could uniformly dispense the water-soluble material, water-dispersible insecticide and suspended nematodes throughout drip lines, but not the suspended powder formulation of the microbial insecticide or the suspended granular formulation of the microbial fungicide. Active agent distribution patterns in soil varied with the formulation and the emitter flow capacity. Our evaluation demonstrated that drip irrigation could be a viable alternative method for water-soluble pesticide applications. However, the use of drip irrigation systems for the delivery of suspended powders and granular agents may be limited because of their poor uniformity and low recovery rates throughout drip lines. Any materials with sizes larger than the width or depth of emitter flow paths would clog emitters and should not be applied through drip irrigation systems.
Technical Abstract: Scientific information is needed on distribution uniformity and mobility of environmental-friendly pest control agents through drip irrigation system and in the soil to help improve soil insect control efficiency. The uniformity and recovery rate of water soluble and insoluble materials of chemical and microbial pesticides with different physical properties discharged from emitters throughout drip lines was evaluated. In the other test, distribution profiles of these chemical and microbial pesticide materials in the sandy clay soil discharged from drip emitters were also evaluated. The materials were a water soluble fluorescent tracer (BSF), a flowable water-dispersible insecticide (Imidacloprid), a suspendible microbial entomopathogenic fungus (EPF), a suspendible microbial soil fungicide (SF), and microbial entomopathogenic nematodes. They presented different physical properties, water soluabilities and suspendibilities. Treatments also included three different flow capacities of emitters with nominally rated flow capacities of 1.9, 3.8, and 7.6 L/h, respectively. Although all materials were readily deliverable through the drip irrigation system, the uniformity of the materials discharged throughout drip lines varied with the material formulations and emitter flow capacity. For all emitter flow capacities, BSF had the lowest coefficient of variation, followed by nematodes, Imidacloprid, SF, and EPF. Conversely, the recovery rate of the five materials throughout drip lines was in the reverse order. Emitter flow capacity affected the recovery rates of Imidacloprid and SF discharged from the emitters, but not of BSF, EPF and nematodes. The distribution patterns of active agents in the soil also varied with the formulation of individual materials and the flow capacity of emitters. Higher emitter capacity produced less variation of distribution uniformity of EPF and nematodes in the soil. EPF had the highest mobility in the soil, followed by nematodes and then Imidacloprid. EPF travelled with water and spread widely in the soil while Imidacloprid exhibited limited spread beyond the emitter. When the active agents were discharged from the 2.0 L/h flow capacity emitters, BSF and EPF were recovered throughout the entire 30 cm deep and 91.2 cm, the nematodes were recovered from about 57% of the 30 by 91.2 square centimeter area; and Imidacloprid was recovered from 29% of the area. The microbial insecticides EPF and nematodes provided better distribution profiles in the soil, adding additional advantages of using drip irrigation systems to apply microbial pest control agents over the traditional chemical pesticides. Drip irrigation was demonstrated as a viable alternative for application of water soluble and insoluble materials; however, the discharge rates of EPF and SF must first be determined to compensate for their non-uniformity of delivery and low recovery rates from emitters.