Evaluation of biopesticides and harvesting periods for management of potato tuber moth (PTM) (Plthorimaea operculella) zeller on potato (solanum tuberosum)
is the second most important food crop in Kenya after maize. It plays an important role in national food security, poverty alleviation and income generation. The farmers face many problems, such as pest and diseases, expensive farm inputs,poor marketing system and lack of certified seed, storage facilities. Potato Tuber moth (PTM) (Phthorimeae operculeUa) (Lepidoptera: Gelechiidae), is one of the most important pest in potatoes and is capable of causing damage of upto 25% in the field and upto 100% loss in the store if not managed. Management practices for this pest include inert materials such as wood ash, saw dust, sand and rice husks. Insecticides are also used but these have been associated with health and environmental side effects. The objective of this study was to assess PTM activity in the field and in the store, to establish the effect of different harvest periods on PTM infestation, and to evaluate the efficacy of inert materials, insecticides and bio-pesticides in the PTM management. The study was carried out at the National Potato Research Centre (NPRC) Tigoni for two seasons in 2009/2010. Asante and Tigoni potato varieties were used to compare the effect of different harvest periods in the management of PTM. The trial was set up in split plot arrangement in a RCBD consisting of four replicates, the varieties occupied the main plots and the treatments were three different harvest times in the subplots plus a check of recommended harvest time of potatoes in Kenya. The harvested tubers were counted, graded, weighed and assessed for PTM infestation at harvest. Potato tuber moth population build up was assessed in the field, at harvest and in the store. The study demonstrated that PTM infestation in the store depended much on the initial PTM infestation in the field. There was a significant lower PTM infestation observed in the store 0'1 tubers harvested two weeks before physiological maturity for both varieties compared with the check both in the field and in the storage(P<0.05). In the store, inert materials and bio-pesticides were evaluated for the management of PTM. Two potato varieties, Tigoni and Asante and untreated control were used to compare the effect of Cabaryl, Bacillus thuringiensis, Beauvaria bassiana, rice husks, wood ash, sawdust and sand in controlling PTM for three months. The experiment was arranged in a complete randomized design (CRD) with four replications. At the centre of the store, a stock culture of PTM was maintained to provide supply of moths to attack the tubers. Potato tuber moth infestation was assessed and the number of tunnels, larvae and pupae were recorded. In the study, Carbaryl emerged the best treatment in controlling PTM recording the least damage in terms of tunnels, and the PTM larvae infestation of PTM. Bacillus thuringiensis(Bt) and rice husks treatments came second followed by wood ash and saw dust all with significant reduction of the PTM larvae over the untreated control (p :S 0.001). Sand was unable to control PTM. Similar results were obtained in the second season. The rest of the treatments had potential of reducing PTM activity at varied levels of effectiveness. The study also revealed that the population of PTM builds up depending on the initial PTM level of infestation and causes serious potato tuber damages with time. It is, therefore, important to ensure that there is low PIM at harvest by use cultural and agronomic practices known to reduce PTM infestation in the field. The methods evaluated have the ability to reduce the activity of PTM for two and a half months. These results provide alternatives that are cheap and available for use in IPM strategies and to enable farmers preserve both seed and ware potatoes.