Use of high-pressure water spray to dislodge spider mites, aphids, small caterpillars and other pests from host plants has long been suggested as a “non-chemical” or “organic” method of pest control (Meyer and Stone 1989):
Giving infested plants a good, hard hosing down will dislodge many insect pests, particularly aphids, thrips and various caterpillars. Plants should first be inspected to confirm the target pest (p. 69).
Accomplishing this method of pest suppression, however, is not as easy as it sounds. The water pressure in College Station (pressure of water coming out of the end of a hose) is 90 to 100 pounds per square inch (Water Department, College Station, TX, pers. comm.). Merely using ones' thumb on the end of the hose to produce a high pressure spray can produce a high pressure spray, but using that method to dislodge arthropods (insects and mites) may or may not work in certain situations. Control of the spray is difficult and too much force can shred or otherwise damage plants.
Several hose-end attachments are commercially available that are promoted to be capable of dislodging arthropods like spider mites from plant foliage such as roses (Fig. 1). However, most hose-end attachments available at retail outlets product sprays are either too low in pressure (i.e., Dramm 30 Inch Rain Wand™ (Dramm, P.O. Box 1960, Manitowoc, WI 54221), too fine (i.e., Dramm Fogg-it Nozzle Model C-610 Fine Volume 1 GPM manufactured by Fogg-it Nozzle Co., P.O. Box 16053, San Francisco, CA 94116), or produce too much pressure and volume (i.e., Twist Nozzle manufactured by Gilmour Manufacturing Co. Somerset, PA 15501) to be useful for dislodging arthropods on herbaceous plants. Most of these attachments do not have the length or 90 degree angle for the nozzle(s) to spray the underside of leaves within a plant’s canopy to reach insect and mite harborage sites.
Fig. 1. Water Wand for Spider Mites
(top) and Jet-All Water Wand (bottom).
Two wands that work well to dislodge small insects and mites are as follows:
Fig. 2. Demonstrating use of Water Wand for Spider Mites on tomato (top and bottom left), and home-made Jet-All Water Wand used to spray roses (bottom right).
In trials conducted to evaluate these “Water Wand” devices (Drees and Leroy 1991, Drees 1991), they were found to effectively reduce small arthropods from plants sprayed. These devices, and perhaps others (see Organic Gardening: 1) May/June issue 1995, p. 15; 2) May/June issue, p. 68; and, 3) June/July 2004 issue, page 13), use nozzle that produce a fine, even spray with enough force to dislodge small soft-bodied arthropods like spider mites and aphids. Home-made version have been constructed using nozzles sold for pesticide application soldered onto copper tubing attached to a hose.
Use of these devices would be compatible with biological control programs
to dislodge pests before natural enemies are released. In addition, water
spray treatments may be capable of removing the sugary honey dew emitted
by sucking insects deposited on leaves and objects before it is colonized
by black sooty mold.
Many factors affect the success of using high pressure sprays for arthropod control including water pressure. Control of host-specific arthropod pests in sites where there are no neighboring host plants is optimum. If pests being dislodged are merely “blown” from one host plant to another, the population may not be reduced and can actually be spread. This was observed in one trial where two-spotted spider mites were removed from snap peas in a home garden and later found infesting nearby tomatoes (Drees 1991). When dislodging non-host specific arthropods like spider mites, dislodged mites may land on neighboring plants which are suitable alternate food sources. This did not occur, however, when treating host-specific arthropods like crape myrtle aphids or where care was taken to direct the spray away from other suitable host plants as was the case in a miniature rose trial.
Plant canopy density also affects ability to spray undersides of leaves. They provided maximum suppression on open canopy type plants. For instance, plants such as spinach where leaves grow in a fashion similar to roof shingles can present a serious challenge to spray “coverage”. Similarly, plants with low-hanging leaves and ground vines may be difficult to spray. Finally, multiple sprays, started when pest populations are first detected can provide optimum prevention of high populations using high pressure water sprays.
The author is grateful for review of this manuscript by James Reinert and Thomas Leroy.
Drees, B. M. and T. R. LeRoy. 1991. Evaluation of alternative methods for suppression of crape myrtle aphids, p. 21-22. In Upper Coast 1990-1991 Entomological Result Demonstration Handbook, Texas Agricultural Extension Service, Texas A&M University System, 46 p.
Drees, B. M. 1991. Suppression of two-spotted spider mites with high pressure water sprays, p. 23. In Upper Coast 1990-1991 Entomological Result Demonstration Handbook, Texas Agricultural Extension Service, Texas A&M University System, 46 p.
Meyer, A. and P. Stone (Eds.) 1989. The Healthy Garden Handbook. A Fireside Book, Simon & Schuster Inc., New York, 192 p.
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Educational programs of Texas Cooperative Extension are open to all people without regard to race, color, sex, disability, religion, age or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Chester P. Fehlis, Deputy Director, Texas Cooperative Extension, The Texas A&M University System.