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Control of Downy Mildew in Greenhouse-Grown Cucumbers Using Blue Photoselective Polyethylene Sheets

September 1997 , Volume 81 , Number  9
Pages  999 - 1,004

Reuven Reuveni , Division of Plant Pathology , and Michael Raviv , Division of Organic Agriculture and Horticulture, ARO, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel



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Accepted for publication 14 April 1997.
ABSTRACT

Six types of polyethylene sheets with or without a blue pigment, having an absorption peak at the yellow part of the spectrum (580 nm), in combination with three levels of UV-B (280 to 320 nm) absorbance, were investigated for their effects on sporangial production and colonization of Pseudoperonospora cubensis on cucumbers in growth chambers. The effect of these photoselective sheets on the epidemiology of downy mildew in greenhouse-grown cucumbers has been investigated in several locations. The addition of the blue pigment to the films resulted in a significant inhibition of colonization and sporangial production of P. cubensis, whereas filtration of the UV spectrum enhanced the colonization but had no effect on the sporangial production. The appearance of the first symptom-bearing plants was delayed under the blue covers, and consequently, a significant reduction in the disease incidence of downy mildew was recorded under all blue sheets at each corresponding level of UV-B transmittance in five different field experiments through four seasons. Regardless of the differences in disease incidence, there were no significant differences among the yields that were obtained under the various sheets, probably due to the lower photosynthetically active radiation transmissivity of the blue films. The optimal features required for a desirable commercial sheet are discussed.



© 1997 The American Phytopathological Society