Integrated pest management studies of the insects affecting oilseed brassicas in Colorado

Abstract

Early evaluation of canola and other oilseed brassicas as potential crops for Colorado indicated several insects as potentially limiting to production - false chinch bug (FCB), Nysius raphanus Howard, western black flea beetle (WBFB), Phyllotreta pusilla Horn, and various Lygus spp., notably pale legume bug (PLB), L. elisus Van Duzee. Studies were conducted to assist in development of pest management systems for these potential insect pests of Colorado oilseed brassica production. Sampling of vegetation outside of canola indicated that winter annual weeds, particularly flixweeds (Descurainia spp.), were important in early season population development of FCB and WBFB. Spring populations of Lygus spp. were greatest in alfalfa, with or without flixweed. Trapping studies with FCB and its tachinid parasitoid, Phasia occidentis (Walker), indicated that yellow was most attractive to FCB and blue to the parasitoid. Both species showed attraction to traps baited with oilseed extracts. Surveys of Lygus nymphs resulted in recoveries of braconid parasitoid Leiophron uniformis (Gahan) from all sites in eastern Colorado but from none in western Colorado. Average percent parasitism was 5.5 and 7.6 percent in 2001 and 2002 collections, respectively. The three Lygus species were present in 2002 collections were L. elisus (58.4%), L. hesperus Knight (29.3%), and L. lineolaris (Palisot de Beauvois) (12.3%). Action threshold studies involved artificial infestation of bagged flowering and pod branches of canola (heads). FCB was more damaging when infestations occurred at early flower stage compared to later, early pod stage of plant growth. On average 10% yield loss occurred with infestations of 12.8 FCB/'head' at early flower stage; 39.7 FCB/'head' at early pod stage. Similar PLB studies with indicated this species was more damaging to crop, causing 10% yield loss with 3.3 PLB/'head' at early flowering stage; 8.7 PLB/'head' at early pod stage. Evaluations of host plant resistance among oilseed brassicas indicated FCB showed strong feeding preference for older plants compared to seedlings. Spring mustard Wl-23 was cultivar consistently least preferred by FCB. Spring mustard ZEM 1 supported the greatest number of WBFB while Wl-23 had lowest numbers of WBFB. Other least preferred cultivars were spring canolas Helios, Sterling, and Alto.