FACTORS INFLUENCING INFESTATION AND INJURY OF RUTABAGAS BY ROOT MAGGOTS (DIPTERA:ANTHOMYIIDAE) IN PRINCE EDWARD ISLAND. I. FIELD STUDIES

Abstract

Examinations of more than 100 rutabaga fields per year, from 1951 to 1955, showed that Hylemya brassicae (Bouché) was the only species of root maggot that injured rutabagas in Prince Edward Island. H. liturata (Mg.) (= H. trichodactyla (Rond.)), H. cilicrura (Rond.), and Muscina stabulans (Fall.) were associated with H. brassicae but did not injure the roots. H. brassicae flies [note Whitcomb (12) for illustrations] began to emerge from overwintered puparia early in June in sandy soil areas and late in July in clay loam areas. Heavy texture and high moisture content of soils were closely correlated with the delay in emergence. The flies laid their eggs near rutabaga plants, usually in crevices in the soil, and upon hatching the larvae entered and fed on the roots. Larvae generally entered the roots at a depth of one inch or more below the surface of the soil. In general, early-planted rutabagas in sandy soil areas and late plantings in clay loam areas were severely damaged by larvae of H. brassicae, whereas late plantings in sandy areas and early plantings in clay loam areas were lightly infested. However, in the sandy soil areas where all of the rutabaga crops were harvested early in August damage was relatively light. Also, fields isolated by other rutabaga fields from sources of infestation such as storage bins and infested rutabaga crops, of either the current or the previous season, were usually slightly damaged. Use of barnyard manure increased H. brassicae infestations early in the season but did not significantly influence the damage caused during the whole growing season.