MATERIALS AND METHOD
Investigation into the effectiveness of two insecticides (Force 60 EC and Nemesis 112 EC) in controlling bollworms in Zimbabwean cotton were carried out in field trials in 2018-19 season at Cotton Research Institute (CRI) in Kadoma, Dande (Mahuwe) and Shamva in Mashonaland Central Province, Matikwa in Manicaland Province, Checheche area of Chipinge South district and Umguza in Matebeleland North Province. The trials were laid in a randomized complete block design with eight treatments and four replications.
Cotton was grown using the basic agronomic practices as outlined in the Cotton Handbook of 1998, partial revised edition standards, (CGA, 1998). The experiment was hand planted at all sites using a commercial Cotton Variety SZ 9314. Measurements were bollworm eggs and larval counts as well as predator counts and counts of other pests. The treatments were: the control treatment, chemical control of bollworms with Larvin 375 SC (Thiodicarb), and the new insecticides were: Force 60EC evaluated at three rates of 400 ml, 500 ml and 600 ml/ha, while Nemesis 112 EC was evaluated at 200 ml, 300ml and 400ml per hectare. Scouting for bollworm eggs and other pests was done once a week in all treatments, while scouting for bollworms larva and predators was also done in the same week whenever a chemical spray for bollworm control was applied in any one of the treatments. At CRI, Umguza, Shamva, Dande and Matikwa scouting started on 24/01/19, 28/02/19, 10/02/19, and 17/02/19 and ended on 18/02/19. First treatment applications started on 05/02/19, 21/03/19, 11/02/19, 18/02/19, and 14/03/19 and ended on 17/04/19, 18/04/19, 05/04/19, 14/03/19 and 31/03/19 at CRI, Umguza, Shamva, Dande and Matikwa respectively. Chemical sprays for control of other pests were applied over the whole trial area when the pests reached or exceeded action threshold.
Table 1: Treatments
|1||No control of bollworms (Control treatment)|
|2||Larvin 375 SC at 1100ml/ha (Standard)|
|3||Force 60 EC at 400 ml/ha|
|4||Force 60 EC at 500 ml/ha|
|5||Force 60 EC at 600 ml/ha|
|6||Nemesis 112 EC at 200 ml/ha|
|7||Nemesis 112 EC at 300 ml/ha|
|8||Nemesis 112 EC at 400 ml/ha|
Nemesis 112 EC at 300ml and 400ml/ha and Force 60 EC at 600ml/ha performance was comparable to Larvin 375 SC and at times better than Larvin 375 SC on control of red and heliothis bollworms as well as seed cotton yield across the five sites. Nemesis 112 EC has both a Zimbabwean and South African registration on control of lepidopterans.
Nemesis 112 EC at the rates 300ml, 400ml/ha and Force 60 EC at 600ml/ha is recommended for a 2 year temporary registration for control of red and heliothis bollworms in cotton in Zimbabwe, while further evaluation of the two products continue.
Nyasha Rushwaya (Research)