The efficacy of different neem preparations for the control of insects damaging potatoes and eggplants in the Sudan

In greenhouse (Khartoum, Sudan), the effect of NeemAzal-T/S® (NA, at 20 g a. i. ha −1 ) on mortality of third instar nymphs of Jacobiasca lybica was not significantly different from that of Omethoate at 200 g a. i. ha −1 . Neem oil (at 0.2 g a. i. ha −1 ) was less effective. In two semi-field tests, numbers of J. lybica and potato yield were negatively correlated. The percentage yield losses were equal in both years. Two field experiments conducted in potato, using a VLV-technique with weekly treatments of 20 l ha −1 , showed similar mortality by NA and fenvalerate (20% EC at 140 g a. i. ha −1 ) in J. lybica and Bemisia tabaci . In Aphis gossypii , fenvalerate exerted a stronger effect (84%) than NA (77%). Potato yield was highest in NA and fenvalerate, lower in neem kernel water extract (NKWE; with 2–5 g a. i. ha −1 ), and equal to water treatment in neem oil (NO). In three similar field experiments in eggplant (aubergines), fenvalerate reduced J. lybica , B. tabaci and A. gossypii by 92%, 70% and 82%, respectively, followed by NA (86%, 61% and 78%). NO and NKWE were less effective. Eggplant yield was highest following NA-treatment, fenvalerate having a lower yield in one of the experiments. NO and NKWE increased the yield in only one of the three experiments. In eggplant, the frequency of stenophagous antagonists of the homopterous pests was affected negatively by fenvalerate, resulting in an unfavourable prey/predator ratio. The neem preparations induced only mild reduction of the antagonists, producing a favourable prey/predator ratio. Based on availability, the effects on pests, beneficials, and on yield, the use of NKWE may be recommended for plant protection in vegetables in the Sudan. Optimal concentrations, in excess of 2–5 g a. i. ha −1 , as used here, and new formulations remain to be studied.