Cohen, S., Institute of Soil, Water and Environmental Science, ARO Volcani Center, POB 6, Bet Dagan 50250, Israel
Ziv, G., Institute of Soil, Water and Environmental Science, ARO Volcani Center, POB 6, Bet Dagan 50250, Israel
Grava, A., Institute of Soil, Water and Environmental Science, ARO Volcani Center, POB 6, Bet Dagan 50250, Israel
Elad, Y., Institute of Plant Protection, ARO Volcani Center, POB 6, Bet Dagan 50250, Israel
Shtienberg, D., Institute of Plant Protection, ARO Volcani Center, POB 6, Bet Dagan 50250, Israel

The late blight pathogen, Phytophthora infestans, develops on wet leaves in cool conditions. Trials were carried out in 16 small greenhouses at the Besor Experimental Station in the Northern Negev in Israel. Covering all of the soil surface with polyethylene soil mulches during the winters of 2004-5 and 2005-6 drastically reduced the rate of infection in the early winter as compared with greenhouses with bare soil. The objective of the project is to study the microclimate of the greenhouse and model the influence of the polyethylene mulch on night-time air and leaf temperatures, air humidity, and dew. Mulch types investigated include transparent, bi-color aluminized, and black polyethylene. Climate parameters measured include air temperature and humidity, leaf and soil temperature, heat flux, short and long wave radiation balances. Night-time soil and air temperatures were higher in mulch greenhouses, so that on the days when infection occurred in the control, air temperature reached dew-point temperature in the control but not in the mulched greenhouses. Night time soil temperatures and those near the ground were higher under the mulch and the difference between air temperature and dew point temperature in the greenhouse was higher above the mulch, indicating less incidence of condensation on the leaves. Simulations using climate data from other parts of Israel are planned to indicate if the influence of the mulch will be significant elsewhere.