Western Flower Thrips Management in Marigolds, 2014 * Open Access

The WFT is an ornamental pest that causes scarring of leaf tissue and flower surfaces through its feeding action, and vectors plant pathogens. The objective of the experiment was to assess efficacy of candidate insecticides in reducing WFT density on Marigolds relative to that of water-only applications. The trial was conducted at the Biological Control Facility greenhouse at Texas A&M University in College Station. Marigolds ( Tagetes erecta L., cv ‘Discovery Yellow’, donated by Benary, Dekalb, IL) were germinated en masse and transplanted individually into 4 inch pots with Sunshine Complete Mix #1 soil (Sun Gro Horticulture, Agawam, MA) on 16 May approximately 1 wk after germination. Plants were placed into two 6 by 4 by 4 ft rearing cages and watered as needed. Insects used in artificial infestations were reared in a laboratory colony using established methods adapted from Doane et al. ( Thrips Biology and Management , 1995, Vol. 276, 587–893). Plants were infested by releasing 100, 75, 75, 80, 112 and 70 insects per cage on 3, 5, 6, 11, 13 and 16 Jun, respectively. Six infested plants per treatment, equal to the number of sampling periods, were placed into clear, cylindrical cages (experimental units). Greenhouse benches, each holding one replicate of each treatment (ten cages) were blocks in an RCB design with six replicates of 10 treatments defined by trade name and rate in Table 1 . Prior to insecticide applications, a pretreatment sample was taken and treatments were assigned to experimental units using a stratified random process resulting in no significant difference in WFT immature populations between treatments. Application dates are in Table 1 . All treatments were foliar sprays using 750-ml hand sprayers; each plant was sprayed downward directly from above, then spraying at an upward angle while rotating the plants to ensure coverage of the underside of the leaves. On each sampling date ( Table 1 ) one plant per cage was cut at the base with gardening pruners, placed into a small plastic container with tight-fitting lid and taken to the laboratory. Once in the lab, samples were individually placed into a larger 10 by 4 by 4 inch plastic container with a lid and shaken for 4–5 s to dislodge insects from foliage. WFT were collected from the walls of the container using an aspirator for 90 s and placed into small vials containing 70% ethyl alcohol. WFT were counted under magnification using a dissecting microscope. Counts were recorded separately for adult or immature WFT. Count data were analyzed by sample date using SAS Web Editor 2.5 and PROC GLIMMIX with DIST = Poisson and LINK = Log as options in the model statement. Response variables were block and number of immature or adult WFT with block and treatment as fixed independent variables. When the treatment effect was significant ( P  < 0.05), means comparison was carried out using the LSMEANS statement with Dunnett’s test and water only as the check.

Results were inconsistent when comparing mean number of adult WFT in the water-only treatment to the insecticide treatments ( Table 2 ). However, treatments of Mainspring at high and low rates, GF-2860 at a high rate, and Conserve consistently resulted in fewer mean number of immature WFT (Dunnett’s test, P  < 0.05) when compared to the water-only treatment ( Table 3 ).

Author notes