Reflective Mulch Enables Fall Vegetable Production Without Pesticides

 

Whitefly free cucumber plants growing over reflective mulch (top) and plants heavily infested with silverleaf whitefly growing over bare soil (bottom)

In the San Joaquin Valley, production of fall vegetables, particularly squash, cucumbers and pumpkins, is severely hampered by several aphid-transmitted virus diseases and also by the silverleaf whitefly. Attempts to control the virus disease vectors with insecticides have proven unsatisfactory. Silverleaf whitefly management with chemicals also has not been very effective and the whitefly can rapidly develop resistance to all classes of insecticides.

 

 
UC scientists took advantage of the fact that both aphids and whiteflies are repelled by ultraviolet light. At the Kearney Agricultural Center, Dr. Charles G. Summers and Dr. James J. Stapleton used reflective mulches (polyethylene covered with a thin layer of aluminum) to reflect incoming ultraviolet light back toward the sky, thus repelling aphids and whiteflies attempting to land on plants.

When plant foliage finally covers 60-70% of its surface, the mulch ceases to be effective. At this point, however, many plants have reached maturity and can better tolerate disease. In most situations, yields are nearly as high as in non-diseased plants.

In addition to reducing aphid and whitefly numbers and the incidence of virus diseases, plastic mulches retard weed growth, conserve soil moisture and promote improved soil nutrient absorption.
 

 
Reflective mulches have decreased the incidence of non-persistent, aphid-borne viruses in cantaloupe, squash, cucumber and pumpkin by 75-85%. In addition, the initiation of disease symptoms is delayed up to four weeks. The buildup of whitefly numbers has been significantly delayed in these crops as well. On pumpkins and cucumbers, whitefly density on plants growing over reflective mulch was reduced 10 to 14-fold compared to plants growing over bare soil. Thus, the use of reflective mulch permits the production of disease- and whitefly-susceptible crops during late summer and fall without using insecticides.

Reflective mulches can be used in either commercial production or by the home gardener. The technique also provides organic growers with an insecticide-free method of producing quality vegetables.
 

Supporting Unit: UC Davis, Statewide IPM Program and Kearney Agricultural Center
 
Dr. Charles G. Summers and Dr. James J. Stapleton, Kearney Agricultural Center, 9240 S. Riverbend Avenue, Parlier, CA 93648
(559)646-6564 chasum@uckac.edu
(559)646-6536 jim@uckac.edu