The influence of temperature and vapor pressure deficit (VPD) on the rate of predation by the predatory mite, Amblyseius cucumeris (Oudemans) on Frankliniella occidentalis (Pergande) was determined under controlled laboratory conditions. The survival of first instars of F. occidentalis was initially determined by themselves. Then the number of first instars that were killed by a single female adult of A. cucumeris was determined for the same density of thrips. The differences in the mortality between the two experiments were used to calculate the rate of predation by A. cucumeris under a range of temperature and VPD regimes. Rate of predation was expressed as the number of thrips killed per h to account for the different time periods that the trials lasted. A quadratic model was fitted to the data. At a constant temperature, the rate of predation decreased with increasing VPD for VPDs ≤ 1.24 to 1.44 kPa. Above these VPDs, the rate of predation started to increase again. At a constant VPD, the rate of predation decreased slightly at the lower temperatures and increased at the higher temperatures. The rate of change was dependent upon the VPD. By using the quadratic model, the rate of predation can be predicted for the range of hygrothermal conditions that would be encountered in the greenhouse. The optimal condition for maximum rate of predation by A. cucumeris on first instars of F. occidentalis in the greenhouse is a VPD ≤ 0.75 kPa at the recommended production temperatures and VPDs (17 to 25°C and ≤ 1.5 kPa).
Eastern black nightshade is a problem weed in soybeans primarily due to interference with harvesting operations and reductions in crop quality. Field and greenhouse studies were conducted in 1990 and 1991 at Harrow, Ontario, to determine whether sublethal rates of imazethapyr and metolachlor could suppress growth and berry production by eastern black nightshade. In the greenhouse, plants treated with metolachlor PRE at 0.8 kg ai ha−1or imazethapyr POST at 30 g ai ha−1(1/3 to 1/2 the labelled rates) produced significantly fewer berries in the first flower cluster, with fewer seeds per berry, than untreated plants. When a surfactant was added to the imazethapyr, almost all flower buds in the first cluster were aborted. Treated plants recovered from the damage, however, and did not differ significantly from control plants in dry weight or berry production 110 DAP. In the field, application of 50 g ai ha−1imazethapyr POST (2/3 of the lowest labelled rate), with or without a surfactant, resulted in delayed flowering, abortion of most of the flower buds in the first cluster, and greatly reduced growth and total berry production between soybean leaf abscision and harvest. Application of metolachlor + metribuzin PPI in the field at 2/3 of the labelled rate (1.6 + 0.25 kg ai ha−1) was not sufficient to reduce nightshade growth and berry production after soybean leaf abscision. Sublethal rates of imazethapyr and metolachlor did not reduce seed viability in either the greenhouse or the field.
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