Ecological studies on cucumber (cucumis sativus L.) Pest spectrum, yield loss assessment and potential for use of neem products in Kenya

Abstract

Cucurbit vegetable crops, especially cucumber (Cucumis sativus L.) offer a good potential for urban and export marketing in Kenya. The crop also shows a promise for commercial production in Eastern African while pests are reckoned as one of the major production constraints. There is very little published information on the range and relative importance of different pests on the crop and appropriate control measures in the region. Exploratory studies conducted from November 1998 to August 2000 at KISE, Nairobi and November 1998 to March 1999 at Kibwezi, Eastern province in Kenya brought to focus arthropods (pests and natural enemies) associated with cucumber. The major pests observed included the African melon ladybird beetle (Epilachna chrysomelina L.), three thrips species (Thrips tabaci (Lindeman), Franliniella schultzei (Trybom) and Mycteriothrips sp) infesting cucumber leaves and flowers besides the melon fruit fly, Dacus ciliatus (Loew) that damages fruits through oviposition and larval feeding. Associated with the pests was a range of natural enemies whose majority were predators mostly of aphids and whiteflies. Four hymenopteran parasitoids of aphids and Charaps sp. On Helicoverpa armigera (Hübner) were also recorded. Predatory coccinellids were the most abundant besides a few surphids, anthocorids on thrips and reduviids on both whiteflies and aphids. Substantial marketable yield loss was found to occur due to pests attacking at the reproductive stage (thrips causing flower fall and fruit flies infesting fruits.) Other pests such as white flies and aphids were common but their adverse effects on the crop yields were not so apparent.

Since farmers are expected to comply with the Maximum Residue levels (MRLs), set for chemical pesticides used; they need safer alternatives to pest control. To fill in this gap, botanicals such as neem (Azadirachta indica A.Juss) provide a safer alternative option in an Integrated Pest Management (IPM) system, which formed the basis for testing the neem products on key pests of cucumber since they are also compatible with other pest control methods. Marketable yield levels in plots which received chemical protection at the vegetative stage during the first and the second season (11.4 and 11.6 kg/plot) were highly significantly different from the unsprayed (control) plot yield (10.4 and 10.7 kg/plot) at (P=0.001 and P=0.0001) respectively. Protection at the reproductive stage gave an average yield of 14.6kg, which was also significantly different from plots with protection throughout the entire crop life (15.0kg) (P=0.001). Yields attained under neem product protection compared favorably with the chemical insecticide (lambdacyhalothrin/dimethoate) protected plot yields. Neem products (powder and oil) protected plots gave 8.8 and 7.6 kg/plot in season on one and 9.8 and 6.2kg/plot of damage-free (marketable) fruits in season two which were statistically different at (P=0.0001), and were significantly different from Karate and non-protected (control) plot yields 10.8, 12.8kg and 3.8, 4.0kg respectively for seasons one and two at (P=0.001).