Beatrice Tenge is currently work at Kenya Agricultural and Livestock research Organization (KALRO), Njoro, Kenya. She have been undertaking Master of Science degree at Egerton University-Njoro and completed writing my thesis on stem rust of wheat which was submitted to graduate school. In the course of her studies two papers were generated from the work with titles ‘ Assessment of advanced Kenyan selected wheat lines for resistance to the prevailing stem rust races (Puccinia graminis f.sp.tritici) in Kenya’ and ‘Wheat stem rust disease incidence and severity associated with farming practices in the Central Rift Valley of Kenya’.
The existence of a disease caused by a biotic agent (stem rust) absolutely requires the interaction of a susceptible host, a virulent pathogen, and an environment favorable for disease development (Agrios, 2005) as quoted by Francl (2001). A host which is resistant or susceptible, pathogen virulent or avirulent stem rust races, environment being conducive humid, low temperatures. Conversely, plant disease is prevented upon elimination of any one of these three causal components (Francl , 2001).
The stem rust disease incidence showed that there were many factors that were related to the % disease observed. Crop management and production process affected the level of disease incidence. Variety grown fungicide use such as the rate of spray, number of sprays, seed source. Disease severity was connected to fungicide use, spraying rates, number of sprays and varieties grown which determined the severity levels. The fields sprayed twice or thrice with recommended or above the recommended rate reported medium to low severity of stem rust disease. A report by Prabhu et al. (2003) indicated that two applications of tricyclazole or benomyl controlled panicle blast in rice, as indicated by lower values of disease progress curve and relative panicle blast severity, and increased grain yield.
Ganesh et al. (2012) observed that three fungicide applications in rice Tricyclazole or Ediphenphos or Kitazine sprayed thrice at weekly interval managed leaf blast disease in rice.High disease incidence and severity were found in the fields with Robin and NjoroBWII which appeared to have become susceptible to stem rust. Generally the fields with Korongo, Duma and Kwale did not report any disease incidence largely due to the number of fungicide sprays used which was twice or thrice as recommended. The low disease incidence could be attributed to genetic resistance which according to Park, (2008) remains the most economical means of rust control. Resistant cultivars also contribute significantly to reducing off-season rust survival.
Crop rotation as reported by Khoury and Makkouk, (2010) is one of the most important means of managing disease in small grains. Cultural control methods such as crop rotations, fertilizer use and certified seed not only serve in promoting the healthy growth of the crop, but are also effective in directly reducing disease inocula potential.
Two or more sprays at the recommended or above recommended rates showed either no or low disease incidence or severity from the study. In addition the variety grown and seed quality determined disease incidence and severity. Use of uncertified seeds of susceptible varieties increased disease levels. A multi-tactic approach involving optimal use of fungicides, resistant varieties, quality certified seed and crop rotations with legumes would be the best option for stem rust disease control.