The emergence of a new virulent race of stem rust (Puccinia graminis f. sp. tritici) of wheat (Triticum aestivum), TTKS (Ug99), calls for urgent measures to contain the disease, which is a serious threat to wheat production in Kenya. Nine commercial fungicides were evaluated for control of stem rust in the field in three locations in 2005 and 2006. Ten treatments, including untreated control, were applied on field plots in a randomized complete block design with four replications. Assessment of stem rust severity was done at growth stage (GS) 55 (heading), GS 65 (flowering), and GS 75 (late milk) and expressed in terms of mean rust severity and area under the disease progress curve (AUDPC). In general, fungicide treatment significantly (P ≤ 0.05) reduced rust severity, AUDPC, and losses in grain yield and 1,000-kernel weight for cv. Duma compared with the untreated control. Stem rust was severe in both years across all sites, resulting in significantly less grain yield in the control treatment. The 1,000-kernel weight was significantly less at two locations in 2006. Fungicides azoxystrobin at 200 g/liter + cyproconazole at 80 g/liter (AmistarXtra 280 SC), tebuconazole (Folicur 250 EC), tebuconazole + tridimenol (Silvacur 375 EC), and tebuconazole (Orius 25 EW) were more effective in reducing stem rust across the sites. Fungicides trifloxystrobin + propiconazole (Stratego 250 EC), hexaconazole (Cotaf 5 EC), epoxiconazole + carbendazim (Swing 250 EC), cyproconazole at 80 g/liter + propiconazole at 250 g/liter (Artea 330EC), and epoxiconazole at 125 g/liter + carbendazim at 125 g/liter (Soprano C 250 EC) were inconsistent in the reduction of the disease. The results suggest that fungicides can be used effectively in reducing stem rust severity and increasing yield of susceptible wheat cultivars in stem-rust-prone areas.

The genotype and environment interaction influences the selection criteria of sorghum (Sorghum bicolor) genotypes. Eight sweet sorghum genotypes were evaluated at five different locations in two growing seasons of 2014. The aim was to determine the interaction between genotype and environment on cane, juice, and ethanol yield and to identify best genotypes for bioethanol production in Kenya. The experiments were conducted in a randomized complete block design replicated three times. Sorghum canes were harvested at hard dough stage of grain development and passed through rollers to obtain juice that was then fermented to obtain ethanol. Cane, juice, and ethanol yield was analyzed using the additive main effect and multiplication interaction model (AMMI) and genotype plus genotype by environment (GGE) biplot. The combined analysis of variance of cane and juice yield of sorghum genotypes showed that sweet sorghum genotypes were significantly (P < 0.05) affected by environments (E), genotypes (G) and genotype by environment interaction (GEI). GGE biplot showed high yielding genotypes EUSS10, ACFC003/12, SS14, and EUSS11 for cane yield; EUSS10, EUSS11, and SS14 for juice yield; and EUSS10, SS04, SS14, and ACFC003/12 for ethanol yield. Genotype SS14 showed high general adaptability for cane, juice, and ethanol yield.

The traditional natural fallows are no longer practicable in sub-Saharan Africa and technologies to replace them are being popularised through management of short fallow systems. Dolichos [Lablab purpureus (L.) Sweet] is among the legumes used to improve such fallows and its residues are incorporated to improve yield of succeeding cereal. Two field studies were conducted to determine dolichos residue mineralisation schedule and response of maize to timing of the residue incorporation, to establish if the current residue incorporation practice maximises nutrient benefit to succeeding cereal. Dolichos residue was applied at 2 t/ha in litterbags, buried in the field at 15-cm depth and retrieved after 1, 2, 4, 8 and 16 weeks, and the remaining debris analysed for loss of weight, N, P and K. A parallel split-plot experiment was set up to determine response of maize to time of residue incorporation, with or without fertiliser nitrogen supplementation. The main plot treatments were nitrogen fertiliser applied at 0, 30 and 60 kg/ha at sixth fully opened leaf in maize. The subplot treatments were residue management regimes, which included four residue incorporation times of 2, 4, 6, and 8 weeks before sowing maize, residue removal off the field, residue mulched on surface and traditional weedy fallow. Results show rapid loss of N, with 50% being released within the first 2–4 weeks after burying. Residue incorporated at 2 and 4 weeks before sowing improved maize yield, while residue removal off-field reduced yield comparably with the traditional weedy fallow. However, there were no statistical differences among the timing of the dolichos residue incorporation. These results reflect poor synchrony of mineralised N and uptake by succeeding maize as currently practiced and suggest residue incorporation closer to sowing maize to benefit the cereal.

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