Abstract:
The study was conducted in Plant Protection Laboratory and greenhouse (GH) at Haramaya
University under 25±2 oC, 70±5% RH and 30±2 oC, 60±5% RH, respectively, during 2016. The
objectives were to: 1) evaluate the efficacy of some pesticides on Tetranychus urticae in the
laboratory and greenhouse; and 2) evaluate the performance of TSSM to six plants under GH
conditions. The efficacy of five pesticides, viz. Amitraz, Profenofos, Chlorantrniliprole +
λ-cyhalothrin, and Profenofos"Q"720 g/l, @ manufacturers’ rates and Paraffin oil @ 2.5%,
were evaluated, in the laboratory, while the GH study, in addition to the five pesticides applied
alone, rotation of Amitraz with the other four pesticides evaluated. All the studies were
arranged in CRD, and replicated five and four times in laboratory and GH, respectively. The
laboratory study on adult TSSM was conducted by leaf disc spraying and dipping. Adult
mortality was recorded 24 and 48 hrs after treatment. For ovicidal study leaf disc spraying and
dipping were used. In both methods, data were recorded up to nine DAT. Based on 48 hrs
observations on adult TSSM, all treatments applied by leaf dipping showed highly significant (p
≤ 0.0001) difference over the control. All pesticides caused 100% mortality except Paraffin oil
that resulted in 96.41% mortality; likewise 48 hrs later, adults treated by leaf disc spraying,
with all the pesticides showed highly significant (p ≤ 0.0001) difference over the control
provided 100%, mortality except Paraffin oil that inflicted 85.90% mortality. The pesticides
caused higher egg mortality using leaf dipping method and showed highly significant (p ≤
0.0001) difference over the control, provided mortality of Amitraz (99.00%), Profenofos
(92.96%), Chlorantrniliprole + λ-cyhalothrin (91.28%), Profenofos "Q"720 g L-1 (90.14%)
and Paraffin oil (86.82%). Egg mortality using lesf disc spraying method showed highly
significant (p≤ 0.0001) difference over the control, caused mortality of Amitraz, Profenofos
Chlorantrniliprole + λ-Cyhalothrin, Profenofos"Q"720 g/l and Paraffin oil resulted in 99.14,
92.12, 89.78, 87.94, 84.92%, respectively. For the GH study, the results after third spray
indicated a highly significant (p ≤ 0.0001) difference between the treatments over the control. A
week after third spray, all the treatments provided 100% reduction of all stages of the mite. In
the T . urticae performance test, six plants were studied and replicated thrice. Two-spotted
spider mite counts were recorded until four weeks beginning two weeks after infestation. There
were a highly significant (p ≤ 0.0001) difference in the number of mite population among the
xv
hosts. Solanum incanum, Datura stramonium, and S. tuberosum had statistically non significant
population size though the mite population on the hosts vary and were in order of performance.
But these plants differed significantly from S. lycopersicon, Capsicum spp. and P. vulgaris.
Therefore, the study showed that all the tested pesticides were effective to suppress TSSM and
gave opportunity to use them in rotation to slow or prevent resistance development. But, it
needs careful research under farmers’ field conditions. Leaf disc spraying and dipping
identified pesticides and both were effective methods for screening. The study revealed that
Capsicum spp. was least preferred while S . lycopersicon and P. vulgaris were intermediate in
status; however, S. incanum, Datura stramonium, and S. tuberosum were the most preferred
hosts. To this effect, host plants like Solanum incanum and D. stramonium should be removed
from farm boundaries as these weeds are potential shelters of the pest. Further study is required
on other hosts, especially on weeds as documented materials are not available on Ethiopian
conditions to manage the pest.