Intercrops, Cicadulina spp., and maize streak virus disease. Ann Appl Biol
Intercrops of bean and finger millet were tested as a possible means of controlling maize streak virus disease (MSVD) in maize by disrupting the mating behaviour of the insect vectors of the maize streak virus, Cicadulina mbila and C. storeyi. A series of three trials were done. In the first, MSVD incidence 2 months after sowing was reduced to 14.9% and 17.4% in millet and bean intercrops compared to 29.5% in the pure maize stand. The number of male Cicadulina spp. caught on sticky pole traps was also significantly reduced relative to the control, but there was little effect on the catch of females. There was no significant yield penalty for the millet intercrop but maize yield was 49% lower in the bean intercrop treatment than in the pure stand. In the second trial, there were two millet and two bean intercrop treatments and a maize only control. Fewer male Cicadulina spp. were caught in the intercrop treatments relative to the control but MSVD incidence was reduced in one millet intercrop treatment only for which the associated maize yield penalty was 89%. In the final trial the bean intercrop was again tested but it had no effect on MSVD incidence. These experiments demonstrated that intercropping maize with bean or millet decreased vector activity and/or vector numbers. Vector catches were predominantly male, and catches of males but not females were reduced in the intercrop treatments compared with pure stands. However the lower vector catch was not consistently associated with a significant reduction in MSVD incidence, and when it was there was often an associated yield penalty in the maize due to the intercrop.
- ", the green stover remains ; and lastly , after the harvest of the dry cobs , the remaining dry stover provides low quality roughage ( Methu et al . , 1997 ; Shirima , 1994 ) . These practices may not only increase forage yields , but may also have serious negative implications for maize diseases espe - cially maize streak virus disease ( MSVD ) ( Page et al . , 1999 ) . Njuguna ( 1986 ) reported that MSVD is the most important disease of maize in Kiambu district of Kenya . Of pests and diseases occurring in the area , farmers perceived MSVD to have the greatest effect on forage yields and was considered the most difficult disease to con - trol in 9 out of 10 farmer groups ( McLeod et al . , 2001 ) "
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ABSTRACT: Maize provides an important source of forage for the maize–dairy farmers in Kenya. However, due to small farm size, maize cannot supply all the feed needed for dairy cattle and forage is in short supply in the dry seasons. This paper examines practices to increase the health and use of maize and increase forage quality and quantity. The paper uses data from participatory on-farm research on cultural management practices of maize and on-station field trials in which plants were artificially infected with maize streak virus disease (MSVD) in the intensive maize–dairy production systems in central Kenya. Findings showed that smallholder farmers have deliberately changed the maize management practices by planting densely and systematically thinning the crop to obtain both fodder and grain. They perceived MSVD to have the greatest effect on forage yields and to be a difficult disease to control. Maize management trials showed that increasing plant density increased forage yields by up to 41% but decreased grain yields by up to 17%when specific thinning regimes were applied fairly late in the growth of the crop. However, grain yields were maintained when maize was planted at high density and then progressively thinned for forage during the growing season according to the crop situation or need for forage. The on-station research s the first study on the impacts of MSVD on maize forage and was carried out to increase production of forage during the wet seasons through use of resistant cultivars and agronomic interventions with a view to mitigating forage shortages during the dry seasons. MSVD infection was achieved with artificially infected leafhoppers (Cicadulina mbila (Naudé) (Hem.: Cicadellidae). In the 2001 short rainy season (SRS),early infection (14 days after crop emergence) reduced thinning yields by 43% in the susceptible cultivar,H511, compared to only 22% in a tolerant one, KH 521. Stover yields were reduced by 24% in H511 while there were no significant losses in KH 521. Interestingly, the local landrace, Gikuyu, was tolerant of MSVD in terms of grain yield but not thinnings. Forage from crops infected 35 and 56 days after crop emergence did not differ significantly from the uninfected controls. In the 2002 long and short rainy seasons, early infection with MSV again reduced thinning and stover yields whereas fertilizer and plant density did not significantly affect the influence of MSVD on either maize forage or grain yields. Use of tolerant cultivars provided insurance against forage and grain yield losses caused by early infection by MSV, but yield benefits varied with season. With respect to forage quality, MSVD had a beneficial effect on susceptible cultivars (H511 and H614) due to the higher crude protein (CP) and lower neutral detergent fibre (NDF)concentrations of infected material in the early stages of growth. However, the reduced yields due to MSVD negate any advantage of increase in CP in infected material of susceptible maize cultivars. Further, the benefit of breeding for high NDF concentrations as a defense mechanism against disease effects is disadvantageous to improving quality of maize forage.
Available from: Darren P Martin
- "Crop rotations and intercropping are considered a possible means of control by disrupting leafhopper mating behaviour. However, studies in Uganda (Page et al. 1999; Owor 2008) have shown that these methods have no discernable impact on MSD incidence, and do not detectably improve yields: in fact Page et al. (1999) reported a maize yield reduction due to intercropping . Despite this, in a recent survey of MSD in Uganda, Owor (2008) found that 81% of farms employed intercropping—rather than being a misguided attempt to control MSD this may instead reflect the fact that land is limited and farmers therefore prefer to mix crops to maximise their over-all food production. "
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ABSTRACT: Maize streak virus (MSV), the causal agent of maize streak disease (MSD), is one of the most significant biological threats
to food security in sub-Saharan Africa. By reducing yields of Africa’s most important food crop, it seriously undermines the
already precarious social and economic wellbeing of subsistence farmers throughout the continent. Despite the availability
of MSD control strategies—ranging from good farm management to the use of chemical insecticides, and the planting of MSD tolerant
maize –MSD remains a problem. The main reason for this is the inherent unpredictability of MSD epidemics which makes it difficult
for farmers to decide where and when to apply appropriate control strategies. Also, without better estimates of the economic
impacts of the disease, there is unlikely to be any motivation for large scale efforts by scientists and national governments
to refine and apply effective control measures. Besides reviewing the epidemiological factors that would need to be modeled
to achieve predictive forecasting of epidemics, we approximate how much MSD costs national economies in sub-Saharan Africa
and evaluate various possible approaches to minimizing the over-all economic impact of the disease.
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ABSTRACT: This chapter considers the main approaches to control of tropical plant virus diseases, with the emphasis on virus diseases of tropical crops. There are many different approaches to controlling plant virus diseases and many of those causing serious losses in the tropics could be controlled through the application of existing knowledge. Cacao swollen shoot, maize streak, rice tungro, groundnut rosette, and cassava mosaic are prime examples of some of the few tropical virus diseases that have been studied intensively and yet it is apparent from the four case histories that many uncertainties remain concerning their control and they continue to cause serious losses. In developing and deploying control measures in the tropics, it is essential to consider the requirements and capacity of the farmers involved and their ability to access and utilize research findings. It is difficult to generalize because of the many different agroecologies that are exploited and the wide range of crops and cropping systems adopted.
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