Row covers: effects of wool and other materials on pest numbers, microclimate, and crop quality.
An investigation evaluating the potential of biodegradable woollen crop covers to protect vegetable crops from low temperatures, weed competition, and insect pests was conducted in the South Island of New Zealand. Needle-punched wool felt covers were compared in a randomized block design experiment (3 replicates) containing 3 synthetic covers (spun-bound polyester, polyolefin fabric, and clear polythene) with uncovered pesticide-treated plots and control plots. The 21 plots each contained 30 cabbage cv. Derby Day and 30 lettuce cv. Great Lakes plants. Numbers of Brevicoryne brassicae adults; Artogeia rapae [Pieris rapae] larvae; thrips (Thysanoptera) larvae; and slugs, Sarasinula plebeia, were recorded on the plants 7 weeks after planting. There were significantly more B. brassicae recorded on cabbage plants beneath the 80-g/m2 wool than on plants in the other 6 treatments. This was possibly caused by the plants penetrating the 80-g/m2 wool cover, making them available to insect pests and thereby reducing the effectiveness of the product as a protective barrier from insect pests. No plants penetrated the other covers tested. There were significantly fewer slugs under the wool cover (80 g/m2) than under the polyolefin fiber cover. Higher and less variable temperatures were recorded under the wool covers. The possible improvement of the wool cover by strengthening, and its commercial viability as a biodegradable row cover, are discussed.