Management of potato aphid transmitted viral diseases by integrating border crops, insecticides and mineral oil
Potato (Solanum tuberosum L.) is one of the most important root crops grown in Kenya. However, its productivity is greatly affected by aphid transmitted viral diseases. Lack of enough certified seeds for farmers and knowledge on field diagnosis of viral diseases has led to accumulation of viral diseases in farmers' fields. Two field experiments were carried out in Kabete and Tigoni during the 2006/2007 short rains and 2007 short and long rains. The objectives of the study were to determine the effect of border crops on potato crop growth and management of potato aphids and viruses and to evaluate the effectiveness of combining border crops, mineral oil and insecticides in managing potato aphids and viruses. In one experiment, maize, wheat and sorghum were used as border while Tigoni and Asante potato varieties were the test crops. The experiment was laid down in radomized complete block design with split plot arrangement. Potato crop growth was established by measuring potato and border crops height, photosynthetically active radiation interception and Potato leaf area index. Aphid population was monitored weekly using leaf samples and yellow sticky traps placed inside the potato and the edge of border crops. In the other experiment, maize border together with either mineral oil or bifenthrin or both were tested. The treatments consisted of spraying mineral oil on border crops alone, spraying mineral oil on potato alone, spraying bifenthrin on border crops alone, spraying bifenthrin on potato crop alone, spraying bifenthrin followed by mineral oil on potatoes crop alone, spraying bifenthrin followed by mineral oil on border crops alone, spraying bifenthrin on both border crops and potatoes, spraying mineral oil on both border crops and potato and ,a control which did not have any spray. The experiment was laid down in randomized complete block design. Aphid population was monitored weekly using leaf samples, yellow water pan traps and yellow sticky traps placed inside the potato and the edge of border crops. Tuber yield was determined at harvest and Double-Antibody Sandwich Enzyme- Linked Immunosorbent Serological assay (DAS-ELISA) was used to determined virus titre on potato tubers. Data was subjected to analysis of variance (ANOY A) using the PROC ANOY A procedure of Genstat software and means were separated by the Least Significant difference test at 5%probability level. Border crops had significant effect on the potato height and light interception but did not affect potato leaf area index. Aphid species identified were Aphis gossypii, Macrosiphum euphorbiae, Myzus persicae and Rophalosiphum maidis. More aphids were recorded on traps placed in potatoes than at the edges of border crops. All the border crops significantly (p<O.05) reduced potato aphids and PYY infection. The lowest aphid population was recorded in wheat-bordered plots while lowest PYY titre was recorded in wheat and maize bordered plots. However, there was reduction in potato tuber yield on sorghum-bordered plots compared to the plots without border crops. Although spray treatments did not reduce aphid population and viruses during the long rains, Mineral oil and bifenthrin treated plots significantly reduced aphid population and virus titre on potato tubers during the short rains. Lowest aphid population was recorded in plots where mineral oil was applied on potatoes while control plots had the highest aphid population. Yields were not significantly (p<O.05) different among treatments. The results obtained in this study show that integrating border crops, insecticides and mineral oil is beneficial in the management of potato aphids and associated viruses in seed potato production. The effective distance between border crops and potatoes and the maximum potato plot size need to be determined.