Effects of Photoselective Shadehouses on Ornamental Plant Pests

An emerging approach in the production of ornamental crops is the use of photoselective (colored) and color-neutral dispersive shade netting. Unlike traditional black nets, dispersive shade nets scatter radiation, creating more diffused light that can penetrate inside plant canopies. Colored nets contain additives that selectively filter solar radiation to promote specific wavelengths of light to promote desirable plant growth characteristics. Compared with black nets of equivalent shading factor, growing ornamental, vegetable and fruit crops under certain colored shading nets can increase perceived aesthetic quality and yields. However, relatively little information exists regarding how this technology might affect a range of pests and disease issues in horticultural production. We surveyed insect and mite populations inside replicated shade net structures containing ornamental plants [Azalea ‘Red Ruffle’, Hibiscus (3 cultivars), Croton ‘Petra’, and Mandevilla (3 cultivars)] in 11.3 L containers between March and September in 2012 and 2013. The structures were fitted with full covering of ChromatiNet^® shadecloths (50% shading factor) arranged as a randomized Latin square. The shade net colors tested included two photoselective (red and blue) and one color neutral (pearl) and black nets for comparison. The uncovered central area of each block served as a control (full sun) comparison. In both years we observed consistently higher numbers of thrips inside blue compared with other colored shadehouses, and fewest inside pearl, ostensibly due to attraction and repellency, respectively. A similar trend for blue (but not pearl) was also observed with whiteflies on plants. Interestingly, fewer plants in outside locations (sun) were infested with aphids compared with those inside shadehouses. Plant growth indices were greater for plants grown under all shade nets compared with outside, primarily due to the greater height obtained. Our results suggest that pest populations may be affected both directly, and indirectly through changes in plant physiology, in response to environmental modifications inside photoselective shade net structures.