Plastic mulches and row covers for early and midseason crisphead lettuce produced on organic soils

Abstract

Plastic mulches and row covers for early and midseason crisphead lettuce (Lactuca sativa L. 'Ithaca') grown on organic soils were investigated over 2 yr. For early production, four mulch treatments (infrared transmitting, silver-on-black co-extruded polyethylene, white-on-black co-extruded polyethylene and a bare soil control) with and without an agrotextile low tunnel were tested. For midseason production, the same mulch treatments were evaluated in combination with normal and high planting densities (54 400 plants ha-1 and 65 200 plants ha-1). Low tunnels combined with mulches accelerated early growth and maturity by 10 d for infrared-transmitting mulch, 7-8 d for silver mulch and 3-5 d for white mulch, relative to production on bare soil control without a low tunnel. Infrared-transmitting mulch alone increased plant biomass early in the season and produced a lettuce head of heavier or similar weight relative to that from bare soil, even if harvested 3-4 d earlier. Lettuce heads grown on silver and white mulches were harvested 1-3 d earlier, and were 22% heavier in the first year and 29% heavier in the second year than when grown on bare soil. Head weights of lettuce under the low tunnels were higher than those from control plots in the first year only, and head size was similar in both years. For midseason production, infrared-transmitting and silver mulches accelerated the early growth of lettuce, but resulted in heads with long cores at maturity, particularly with infrared-transmitting mulch. Silver mulch increased the percentage of marketable heads in the first year and head weight and size at maturity in the second year, and reduced the incidence of aphids in both years, relative to plots without mulch. White mulch resulted in larger and heavier heads than those produced without mulch in the second year, and produced heads with shorter cores than those produced with other mulches in both years, even during particularly hot growing conditions. The percentage of marketable heads was similar for both the high- and low-density plantings and, as a result, the former produced more marketable heads per hectare. However, lettuce plants grown at the higher density were smaller in the second year. During conditions conducive to disease development in the first year, higher density plantings were more susceptible to downy mildew.