The efficacy of Bacillus thuringiensis (var. kurstaki) (Btk) against the diamondback moth (DBM) on cabbage was studied at Botswana College of Agriculture, Gaborone, Botswana. Using five concentrations of Btk: 2, 4, 6, 8, and 10 g/L, bioassays were conducted against DBM eggs and second instar larvae at 30°C ± 5°C. Each treatment was replicated three times. Probit analysis was used to determine the LD50 and LD90 values for the treatments against eggs and larvae. When the treatments were assessed at 72, 96, 120, and 144 hours, LD90 values against larvae were 11.02, 10.22, 5.92, and 4.01 g/L, whereas they were 7.71, 6.94, and 6.24 g/L against eggs when assessed 48, 72, and 96 hours after the expected time of hatching. This indicated that Btk was effective against both eggs and larvae when exposed for long periods. The slopes of the probit lines for larvae assessed at 24, 48, 72, 96, 120, and 144 hours after application were 0.250, 1.064, 0.910, 0.383, 0.453, and 0.414, while those against eggs were 1.153, 1.246, and 0.933 when assessed 48, 72, and 96 hours after the expected time of hatching. This indicates a smaller change in mortality with increase in pesticide dosage for both eggs and larvae. Btk treatments achieved 85.7%–94.6% reduction in DBM damage on cabbage. Therefore, Btk can be used to achieve effective control of DBM eggs and larvae and reduce damage on cabbage under greenhouse conditions.
The efficacy of spinosad against the diamondback moth (DBM) on cabbage was studied at Botswana College of Agriculture, Gaborone, Botswana in 2011. Using five concentrations of spinosad: 0.12, 0.36, 0.60, 0.84 and 1.08 g/L, bioassays were conducted against DBM eggs and second instar larvae at 30°C ± 5°C. Each treatment was replicated three times. Probit analysis was used to determine LD 50 and LD 90 values for the treatments against eggs and larvae. When the treatments were assessed at 72 and 96 hours, LD 90 values against larvae were 0.74 and 0.59 g/L, whereas they were 0.35 and 0.32 g/L against eggs. This indicated that spinosad was more effective against eggs than against larvae. The slopes of the probit lines for larvae assessed at 48, 72 and 96 hours after application were 3.519, 3.810 and 3.427, while those against eggs were 1.725, 1.316 and 1.086. This indicates that there was a more rapid change in larval mortality with increase in pesticide dosage than in egg mortality. The study shows that spinosad can achieve effective control of DBM eggs and larvae under Botswana conditions.
A study was carried out in forest reserves located in Chobe district in Botswana to assess the effect of dieback and associated causes on Mukwa tree, Pterocarpus angolensis Fire, elephant damage and dieback were assessed in Chobe and Kazuma forest reserves and Pandamatenga farming area. Fire damage frequency on mukwa trees ranged between 60 to 100 % and was highest in Pandamatenga and Chobe forest reserves. The frequency of elephant damage in Kazuma and Chobe forest reserves was 75 and 100 % respectively. There was no elephant damage in Pandamatenga farms because the area is fenced out and minor dieback occurred in the area. All areas under study experienced 100 % incidence of dieback, but the severity ranged from 22 to 100 %, the highest being at Chobe forest reserve and the lowest at Pandamatenga. Severity of dieback was associated with elephant damage and age of P. angolensis trees. The incidence of dieback was correlated with DBH and tree age. The results indicate that the cause of dieback is mostly due to elephant and fire damage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.