A series of experiments were carried out to identify potential climate-management techniques for the suppression of humidity-promoted and powdery mildew diseases in greenhouse-grown sweet pepper, tomato and sweet basil. Elevated daytime temperatures were obtained by closing the side walls of the greenhouses. When sweet-pepper greenhouses were closed, the temperatures inside these structures reached 35 degrees C and we observed significant suppression of Leveillula taurica (anamorph: Oidiopsis sicula). When commercial-like greenhouses were kept closed during autumn and winter, the temperatures inside these greenhouses reached 27-34 degrees C and we observed season-long suppression of tomato powdery mildew (Oidium neolycopersici). Severe epidemics developed in aerated greenhouses maintained according to the common practice (control). The combination of day-heating with applications of disease control agents, such as plant extracts, biocontrol agents and sulfur, improved the control of powdery mildew diseases in both sweet pepper and tomato. Temperatures in polyethylene-covered sweet basil greenhouses that were kept closed for 6 h each day reached 42 degrees C during the winter period. The incidence of gray mold (Botrytis cinerea) in these greenhouses was significantly reduced and basil yields were increased. A significant negative correlation was observed between the duration of temperatures above 30 degrees C and the incidence of gray mold. The suppressive effects of high daytime temperatures on the examined pathosystems can be attributed to a direct effect of temperature on the pathogen inocula, as well as an indirect effect involving the induction of resistance in the host plants. It should be noted that partial aeration to release humidity is essential in daytime-heated greenhouses, in order to prevent outbreaks of diseases that thrive under humid conditions. In tomato greenhouses, additional measures were taken to ensure pollination and fruit set, processes that are negatively affected by high temperatures.

Since greenhouse heating is abandoned by most Israeli growers of lisianthus (Eustoma grandiflorum), gray mold caused by Botrytis cinerea, severely affects the base of the stems of whole plants as well as cut stems that are left after flower harvest. We studied B. cinerea infections of lisianthus plants under laboratory and commercial greenhouse production in a moderately arid Mediterranean area typical of Israel. We evaluated cultural methods that use least energy for manipulating disease development in commercial greenhouses. The development of infection along lower leaves toward the stem was found important in stem infection. It was significantly less at 26 degrees C compared to 18 or 20 degrees C, and was highest at relative humidity (RH) close to saturation. B. cinerea infection developed in all of the stem wounds exposed to 65 to 99% RH and at temperatures ranging from 12 to 29 degrees C. Severity of infection in stem cuts on whole plants was least at 26 degrees C, and was high at 99% RH. Similarly, severity was greatest at temperatures of 15 to 22 degrees C and RH levels of 85 to 99%. Under commercial conditions, applications of supplemental calcium in spray or fertigation led to some reduction in disease incidence. Treatments of polyethylene soil cover, the use of buried drip irrigation instead of surface drip irrigation, plant spacing and blowing air inside plant canopy, each alone or in combinations suppressed gray mold on stem bases and plant cuts. Flower yield quantity and quality were increased by these treatments.

Oidium neolycopersici causes severe powdery mildew on all aerial parts of tomato, excluding the fruit. Plants may die dew to powdery mildew. Chemical fungicides are commonly used for its management in covered structures and 6-15 sprays may be applied each season. The objective of the present work was to identify potential agro-technical methods such as climate management and integrate it with other means of control for tomato O. neolycopersici powdery mildew suppression. Under controlled conditions, in growth chamber experiments, disease did not develop at 28 degrees C. Within the range of 70 to 99% RH, disease was less severe under the higher RH than the drier conditions. Data collected in three commercial-like greenhouse experiments involving various climate regimes were used to draw correlations regarding the effects of temperature and RH on the development of epidemics. Development of disease was negatively correlated with the temperatures in the low and high ranges and low RH. Elevated temperatures regime during day time were obtained by closing the side greenhouse walls to allow day temperatures of 27-34 degrees C. These conditions were found very effective in reducing the disease under commercial-like greenhouse conditions in the autumn-winter season. Combination of this method with control agents such as plant extracts and sulfur is effective in O. neolycopersici powdery mildew suppression in greenhouse tomatoes.

Photoselective nets were designed to selectively filter different spectral bands of solar radiation, and/or transform direct light into scattered light. The spectral manipulation intends to specifically promote desired physiological responses, while the scattering improves the penetration of the spectrally-modified light into the inner plant canopy. The current paper reviews the photoselective concept and its assessment in various crops. It further describes a recent study on photoselective shade-netting of bell peppers, demonstrating the potential uses of this technology for improving both crop performance and pest control. Thus, the replacing of the traditional black shade net by either a Red, Yellow or Pearl nets (ChromatiNets (TM)) of similar shading factors, resulted in 15-40% higher fruit production in different cultivars. The major response to the photoselective filtration was producing more fruits per plant, with essentially no reduction of fruit size or quality. Additional benefits relate to photoselective improvement of pest control. The Yellow shade net decreased whiteflies penetration and establishment by 2-3 folds compared to black nets, even though the net holes were large enough to allow free passage of the pests. The incidence of an aphid borne cucumber mosaic virus (CMV) disease was significantly lower under white, Pearl and Yellow shade nets compared to black or Red nets. Additionally, a photoselective 50 mesh screen (OptiNet (R)) reduced thrips infestation 3-4 folds relative to the standard screen. The photoselective, light-dispersive shade nets and screens provide a new tool for improving both crop performance and pest control.