Influence of Interval Between Postharvest Lettuce Residue Management and Subsequent Seeding of Broccoli on Cabbage Maggot (Diptera: Anthomyiidae) Infestation on Broccoli.

Larval stages of cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae), attack the roots of Brassica crops and cause severe economic damage. In the Salinas Valley of California, Brassica crops are often planted after successive lettuce (Lactuca sativa L.) crops. The interval between postharvest soil incorporation of lettuce residue and the subsequent Brassica crop can be as short as 7 d, which could influence D. radicum infestation on broccoli (Brassica oleracea var. italica Plenck). In 2014 and 2015, the effect of intervals between crops (IBC) on D. radicum infestation was evaluated. The treatments were 7, 20, 33, and 48 d IBC, and NL (no lettuce), 7, 21, 36, and 49 d IBC in 2014 and 2015, respectively. Insect counts and feeding damage on broccoli was assessed during 3-6 wk after planting. Adult Delia fly captures were significantly greater at 7 d than 36-49 d IBC in both years. In both years, D. radicum eggs collected were significantly greater at 7 d than at 33 d or 36 d IBC plots. Larvae collected were significantly greater at 7 d IBC than all other treatments in 2014, but not in 2015. Similarly, severity of feeding injury was significantly greater in 7 d than 33 d or 48 d IBC in 2014, but not in 2015. In 2015, broccoli with no prior lettuce had significantly lower Delia flies and D. radicum egg densities than 7 d or 21 d IBC. The implication of these results as a cultural control tactic for D. radicum infestation is discussed.

Evidence of Protaphorura fimata (Collembola: Poduromorpha: Onychiuridae) feeding on germinating lettuce in the Salinas Valley of California.

A series of experiments were conducted to determine the impact of Protaphorura fimata Gisin (Family: Onychiuridae) feeding on seeds and germinating seedlings of lettuce, Lactuca sativa L. (Asteraceae). First, various densities of P. fimata were incubated with 25 lettuce seeds for 7 d and feeding injury was evaluated in three soilless arena experiments. As a second step, 100 P. fimata were incubated with 25 lettuce seeds in three arena experiments with soil media. Finally, in a commercial field the incidence and impact of P. fimata on recently planted lettuce was assessed following applications of pyrethroid-insecticides: 2 d before planting, at planting, and 20 d later. In experiments without soil, the number of ungerminated seeds, feeding injury sites, and plants with injury were significantly greater in arenas with P. fimata than without. Similarly, the number of germinated seedlings, shoot fresh, and dry weights, and the length and width of fully opened-leaves were greater in arenas without than with P. fimata in assays with soil. In the field, P. fimata densities were significantly lower in beds that received insecticides at 2 d before and at planting than in untreated beds. Also, the fresh and dry weights of lettuce plants were significantly greater in the beds that received insecticide than in untreated. The results clearly show that P. fimata is a pest of lettuce and can cause severe feeding injury to germinating seeds or seedlings, thereby reducing their growth rate. The potential implications of P. fimata feeding and feeding injury characteristics are discussed.