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Ten Napier grass [Pennisetum purpureum Schumach (Poaceae)] varieties, used in various parts of Kenya as animal fodder, were tested for their potential role as a trap crop in the management of the gramineous spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), through habitat manipulation. Oviposition preference and larval survival and development were determined for each of these varieties under laboratory and screen‐house conditions. Two‐choice tests revealed that seven of the varieties tested were preferentially chosen by gravid female moths for oviposition over a susceptible maize cv. Inbred A. Larval survival was significantly lower on the majority of the Napier grass varieties (about 10%) than on maize cv. Inbred A (about 60%). Similarly, larval development was about 2 weeks longer on the majority of the Napier grass varieties. It was concluded that four of the varieties tested (Bana, Ex‐Machakos, Gold Coast, and Ex‐Nyanza‐2) had potential for use as trap crops in C. partellus management because they were more preferred by the borer moths for oviposition and allowed minimal survival of the larvae. This minimal larval survival is desirable in the conservation of C. partellus natural enemies when the cultivated host plant is out of season.

Formulations of the insecticide imidacloprid were made using a commercially available pine kraft lignin. The release kinetics of imidacloprid from granules with variation in the loadings of the insecticide and granule sizes were evaluated in water under dynamic flow conditions. The release data were fitted to the generalized model M t /M z = kt n + c, where M t /M z is the percentage of insecticide released at time t, k and c are constants, and n is another constant that indicates the mechanism of release. The results indicated that the release of imidacloprid was diffusion-controlled. The time taken for 50% of the active ingredient to be released into water, T 50, was also calculated for the comparison of formulations. The results showed that the formulation with the higher loading of imidacloprid had the higher value of T 50, which means a slower release of the active ingredient. In a related experiment, it was found that as the size of this formulation decreased, the release of the active ingredient was faster. In addition, mobilities of technical and formulated imidacloprid were compared by using soil columns simulating a layered bed system commonly used under a plastic greenhouse. The use of formulated imidacloprid produced a less vertical distribution of the active ingredient compared to the technical product. Sorption capacities of the various soil constituents for imidacloprid molecules were also calculated by using batch experiments. The results obtained were in agreement with those for sorption in dynamic conditions. Keywords: Controlled release; imidacloprid; lignin; leaching

The leaching processes of the insecticide imidacloprid [1‐(6‐chloro‐3‐pyridinylmethyl)‐N‐nitro‐2‐imidazolidinylideamine] and the fungicide procymidone [N‐(3,5‐dichlorophenyl)‐1,2‐dimethyl‐1,2‐cyclopropanedicarboximide] in a greenhouse soil from the southeastern of Spain were investigated. Four separate pesticide applications were made at dose rates considerably higher than the recommended in normal agronomic practice, representing a worst case scenario. Soils samples were taken to a depth of 40 cm at time intervals after each application and analyzed by high performance liquid chromatography (HPLC). The partition coefficients (Kd) of the samples for imidacloprid and procymidone were calculated by carrying out batch experiments and fitting the experimental data point to the linear isotherm equation. Soil tension, water content, and temperature measurements were also determined during all the experiments. Although the results show a high degree of variability, rapid transport of pesticides through the soil occurred which increases the possibility of groundwater pollution. The leaching of these pesticides, particularly procymidone, generally thought of as immobile, might be possible through formation of stable soluble organic fraction–pesticide interactions in solution, allowing an increased groundwater contamination potential.