Charles Karavina

Maize streak virus: a review of pathogen occurrence, biology and management options for smallholder farmers.

Maize streak disease is a major threat to cereal crops amongst smallholder farmers in sub-Saharan Africa causing up to US

Farmer knowledge, attitude and practice on cotton (Gossypium hirsutum L.) pest resistance management strategies in Zimbabwe

480 million losses annually. It is caused by Maize streak virus (MSV), a geminivirus that is indigenous to Africa. The virus is transmitted by at least 11 Cicadulina species, with Cicadulina mbila being the main vector. In addition to cereals, the virus also infects wild grasses. There are 11 known MSV strains, designated with the letters A to K, according to alphabetical order. MSV-A is the most severe and economically important strain that attacks maize. The other strains attack cereal crops other than maize. The control of MSV is most effective when cultural and chemical methods are integrated with plant breeding for resistance. While host plant resistance is the best method of MSV management, it is not usually easy to conventionally produce resistant cultivars. Genetic engineering has been successfully employed in producing MSV-resistant maize. However, opponents of genetic engineering have prevented the adoption of the technology by most African countries. This means that smallholder farmers have to continue growing susceptible cultivars or buy the slightly more expensive conventionally-bred cultivars.

Weed seed bank response to tillage and residue management in semi-arid Zimbabwe

Cotton is an important cash crop and a means of survival for Zimbabwe’s smallholder farmers who are located in the semi-arid areas. However, it is plagued by a wide variety of pests. The cotton industry in Zimbabwe came up with sustainable pest management strategies which include within the season rotation of bollworm pesticides, a closed season and acaricide rotation scheme. The land reform programme brought new players in the cotton industry and it was critical to determine their knowledge on the pest management strategies. A survey was conducted to determine farmer knowledge, practice and perception on the resistance management strategy. Responses indicated that both communal and new farmers based their spray on egg counts. Communal farmers knew when to use pyrethroids compared to new farmers. Farmers observed the acaricide rotation scheme although they use some non acaricide pesticides. More than half of the new farmers could not say which acaricides were in the acaricide scheme. The majority of the farmers reported that they adhered to the closed season although field observation revealed otherwise. A significantly higher number of new farmers knew when to slash cotton compared to communal farmers. Knowledge of acaricides was not common among farmers. Use of pyrethroids was not limited to 1 February onwards as stipulated in the cotton pest resistance management strategy. The results suggest the need for training among the cotton farmers especially the new farmers or refresher courses among the communal farmers.

Tackling diamondback moth Plutella xylostella (L.) resistance: a review on the current research on vegetable integrated pest management in Zimbabwe

The influence of conservation agriculture (CA) on weed ecology has been a concern to many researchers across the world and is the focus of this study in southern Africa. An experiment to look at the impacts of various tillage systems with different levels of crop residue on maize (Zea mays L.) was established in 2004/2005 season. The experiment was carried out at the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), Matopos Research Station, Zimbabwe. Three main tillage systems were compared, ripping tillage (RT), planting basins (PB) and conventional tillage (CT), with three different crop residue levels: 0, 4 and 8 tons ha−1. In 2007 soil samples were collected in the inter-row and in-row positions prior to tillage at 0–50 mm, 50–100 mm and 100–200 mm depths. The objective was to determine the effect of the treatment factors on weed seed bank species after three cropping cycles using the germination method. Nine major weed species were identified, with all the weeds unaffected by either tillage or mulching level. Eleusine indica, Corchorus tridens and Setaria species were the dominant weed species across all treatments. Setaria spp. was the dominant weed in the inter-row position of ripped plots. Although there was no significant individual treatment effect, there were significant (p < 0.05) interactions, with CT having reduced seed banks of Setaria spp. and E. indica compared to RT and PB. Percentage increases point to E. indica and Setaria spp. increasing under PB and RT compared to CT. C. tridens was significantly higher in PB compared to RT and CT in the 0–50 mm depth in the in-row position. This study probably coincided with the transition period in the weed bank succession process and needs to be repeated at a later date in the rotation. The majority of the weed species were not affected by any of the treatment combinations, a response attributed to plasticity of weeds to the tillage and residue level selection pressure.

Jatropha curcas Production in Zimbabwe: Uses, Challenges and the Way Forward

The diamondback moth (DBM), Plutella xylostella (L.) is a destructive pest of brassicas globally. Control of the pest is dominated by insecticides. Studies have shown that in some African countries, there is a great reliance on broad spectrum insecticides such as pyrethroids, organophosphates and carbamates, that are applied weekly or twice per week. Use of unregistered insecticides has also been reported. The quality of insecticide application has also been reported to be poor or ineffective. It is therefore not surprising that DBM is fast developing resistance to the major insecticides used against it. Adopting an integrated pest management strategy may be a good arsenal to use against the pest.