We investigated the relationship between the density of twospotted spider mite (Tetranychus urticae), plant size and the prevalence of browning on older leaves on ivy geranium, Pelargonium peltatum. A technique for rating browning was developed. Results showed that a linear model, y=0.66x + 4.74 (r2=0.88, p < 0.0001) adequately described the relationship.
We then explored the use of biological control to reduce mite numbers. Two studies were conducted using six-week-old ivy geranium plants to assess the effectiveness of the predator Phytoseiulus persimilis at three release ratios. We first compared release ratios 0.017 and 0.05 at two levels of twospotted spider mite (TSM) infestation, 50-150 and 200-300 TSM/plant. In the second study, release ratios of 0.05 and 0.25 were assessed using infestation levels of 50-150 and 150-250 TSM/plant. In both cases,
P. persimiliswas allowed to interact with TSM for four weeks. P.persimilis was able to significantly reduce TSM populations at all the three ratios in plants with 50-150 TSM. However, at ratios of 0.017 and 0.05, significant differences existed in TSM population reduction with the amount of reduction being proportional to the release ratio. There was no significant difference in TSM population reduction for the ratios 0.05 and 0.25 on plants with 150-250 TSM . Release ratios of 0.017 and 0.05 failed to control TSM in plants with 200-300 TSM. These studies indicate that effective control of TSM on greenhouse ivy geranium can be attained by P. persimilis at release ratios of 0.017 and 0.05 if introduction takes place when TSM population is low.
Species 1: Acari Tetranychidae Tetranychus urticae (twospotted spider mite)
Species 2: Acari Phytoseidae Phytoseiulus persimilis
Keywords: Biological, Control
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA