Twospotted Spider Mite Control on Marigolds, 1989
Authors: Baxendale F. P. , Kalisch J. A. 
Published: March 2022

Four trials carried out at the University of Nebraska, Lincoln, NE to evaluate the efficacy of selected insecticides/miticides, an insecticidal soap (Safer Insecticide Concentrate), a horticultural spray oil (SunSpray Ultra-Fine Spray Oil) and various combinations of these products for control of twospotted spider mites on marigolds. Treatments included Safer Concentrate and SunSpray Oil combined with 0.5 and 0.125 the labeled rates of Dursban 4 E or Orthene 75 SP. Plot design for all trials was a RCB with 4 replicates. Each trial consisted of four, 10-ft rows (replications) of a single marigold cultivar planted on 36-inch centers. Individual plots, which consisted of 2-3 marigold plants, were delineated by placing 2 × 2 ft sheets of waxed cardboard within rows at approximately 2-ft intervals. Marigold cultivars were Queens Mix, Scarlet Sophia, Crackerjack and Jamie Gold for trials 1-4, respectively. Treatments were applied on 8 Aug. Conditions at the time of application were as follows: air temperature, 76°F; relative humidity, 46%; soil moisture was well below field capacity. Treatments were applied with a COz sprayer using a LF-4 nozzle at 24 psi to the point of runoff (ca. 0.5 pts finished spray per plot). No rain fell during the post-treatment period. Product efficacy was evaluated 3 and 7 DAT by randomly selecting and excising 4 leaves each from the lower, middle and upper portion of plants in each plot (12 leaves total). Leaves were returned to the laboratory where numbers of adult female mites were recorded. Trial 1 (Queens Mix): All insecticides/miticides provided statistically significant reductions in mite numbers at both 3 and 7 DAT. Overall, mite reductions were relatively low with only Tempo 2 at 3 DAT (81.3%) and Morestan 4 F at 7 DAT (90.8%), providing percent mite reductions of greater than 80%. Trial 2 (Scarlet Sophia): Safer Insecticide Concentrate, Dursban 4 E and all combinations of Safer Insecticide Concentrate plus Dursban 4 E provided significant reductions in spider mite numbers at 3 DAT. By 7 DAT, however, only Safer Insecticide Concentrate and Safer Insecticide Concentrate plus Dursban 4 E at 1.0 fl oz continued to provide significant mite reductions. Overall, percent reductions were less than 50% except for Safer Insecticide Concentrate plus Dursban 4 E at 4.0 fl oz, which provided 52.2% at 3 DAT. Trial 3 (Crackerjack): At 3 DAT, only 2% SunSpray Ultra-Fine Spray Oil plus Dursban 4 E at 4.0 fl oz had provided a significant reduction in spider mite numbers. By 7 DAT, however, there were no significant differences among treatments. Spider mite control was poor for all treatments with only the 2% SunSpray oil plus Dursban 4 E at 4.0 fl oz providing greater than 70% reduction. Trial 4 (Jamie Gold): Two percent SunSpray Ultra-Fine Spray Oil plus Orthene 75 SP at 5.25 fl oz and 2% SunSpray were the only treatments to provide significant reductions in spider mite numbers at 3 and 7 DAT, respectively. Percent mite reductions were relatively low for all treatments, with only the 2% SunSpray oil plus Orthene 75 SP at 5.25 fl oz at 7 DAT exceeding 70%. No phytotoxicity was observed in any of the trials.