GREENHOUSE COOLING FOR PRODUCTION OF PEPPERS UNDER HOT-HUMID SUMMER CONDITIONS IN A HIGH-ROOF PASSIVELY-VENTILATED GREENHOUSE

To insure optimum fruit yields of greenhouse pepper crops in Florida in late fall (November) and winter, when prices are high, planting is dictated to be in late July to early August when greenhouse day temperatures can be in excess of 40°C. To reduce daytime temperatures during summer, two cooling methods were examined and compared to no cooling: a) aluminized shade system, and b) mist cooling. ‘Shamrock’ peppers (Capsicum annuum L.) were transplanted on 18 August, 2004 and 13 July, 2005, into 11 L plastic pots containing pine bark in a high-roof plastic greenhouse in Citra, Florida. Plant densities were 1.9, 3.0, and 3.8 plants.m^-2. At transplanting the cooling systems were ‘activated’ when greenhouse temperatures reached 28°C. Mist was applied for 15 sec. every 15 min. PAR (μmol.s^-1.m^-2) was reduced in excess of 50% as compared to outside during mid-day and up to 66% in morning and late afternoon by the shade system. The mist system provided one-third higher PAR than the shade system in mid-day. Temperatures at the plant canopy were reduced, compared to no cooling, by both cooling methods. Plant height was increased and stem diameter reduced in shade, compared to the mist system. Fruits could not be harvested in 2004 due to damage from two hurricanes. In 2005, early fruit yields (6 October) were greater from the mist system, compared to the shade or no shade treatments. More fruits were harvested from the highest plant density compared to the lowest density. No significant difference occurred between cooling method and plant density for total marketable yield per hectare. Yield from plants produced with cooling was 2.5 times greater than without cooling. Therefore, summer plantings of pepper under the hot-humid conditions in Florida, could be established by misting or using aluminized screen. Costs to install the mist system were one-tenth that of the screen system. There were no apparent disease or plant abnormalities by using either system.