Abstract:
Experiments were conducted in 2001,2002 seasons at Gedarif and 2002 at Damazin, to compare the efficacy of diazinon treatments on the midge-susceptible and resistant sorghum cultivars for control of sorghum midge, Stenodiplosis sorghicola (Coquillet) (Cecidomyiidae:Diptera).
At Damazin, where the average midge density was high, 7.9 adult midge per head, diazinon treatments resulted in significantly lower damage on the panicles of MCR/117 (16.5%) than on the Korokoro cultivar(26%), when the same diazinon treatments applied five and three times every three and five days respectively. Even untreated, theMCR/117 cultivar exhibited significantly less damage (4.5%) than Korokoro (13%) regarding diazinon treatments of five or three applications at 3- and 5- days intervals. The untreated (control) of MCR/117 significantly exhibited less damage than (29%) than untreated (control) of Korokoro cultivar.
The MCR/117 cultivar treated three times every five days exhibited significantly less damage (17.6% ) than Korokoro treated five times every 3 days. No significant differences of midge damage were found between diazinon treatments, 5 and 3 applications at 3 –5- days intervals for midge-resistant and susceptible cultivars .The results indicate that, at moderate to high level of midge density, midge-resistant cultivars receive more protection from insecticide applied three times at 5-days interval, when compared with midge-susceptible cultivar treated five times at 3-day intervals.. No significantly differences of percentage of yield loss were found between treated with diazinon and untreated for both cultivars Korokoro and MCR/117.
At Gedarif, where midge density was low, average 1.9 adult midges per head, the damage on the panicles of the MCR/117 was about equal whether treated or not. The Korokoro cultivar treated five or three times at 3- and 5- day intervals exhibited significantly less damage than (control) (14 and 14.5%), respectively. The control of Korokoro significantly exhibited more damage (20%) than the control of MCR/117 treated three times every 5- days showed significantly less damage (6.3%) than Korokoro treated five times every 3- day. The percentage yield loss on Korokoro treated five times or three times were significantly lower than the control (30 and 25%), respectively. But between diazinon treatments of MCR/117 no significant differences were found. The percentage yield loss on the of control of Korokoro was significantly greater than the control) of MCR/117 (27.6%). However, when comparison was made between Korokoro and MCR/117 treated five or three times, no significant differences occurred. The evaluation of results revealed that, when variable diazinon applications were made at 50% panicle flowering stage, and where midge density was high, the midge resistant cultivars responded more efficiently to diazinon treatments in terms of percentage yield loss, compared with midge-susceptible cultivars.
