Tomato is a fruit rich in Vitamin C, Vitamin B9, and Vitamin K which is known to reduce the risk of heart disease and cancer as it contains antioxidant lycopene. In the Nepalese market, the year-round demand for tomatoes is increasing due to their multiple uses as a vegetable, salad, and pickles. Tomato plantation is recommended to cultivate above 900 masl. In past, farmers used to cultivate plants only in open fields on a seasonal basis i.e. February to June but the production is short-term and low. However, with an increase in demand farmers started to cultivate it in the rainy season too. But due to heavy rainfall, it is unfeasible to produce it in open-fields therefore, farmers started constructing plastic tunnels to protect plants from heavy rain. The rainy season is an opportunity for hilly farmers to produce vegetables as in terai the production rates of vegetables is minimum due to flood and uncontrolled drainage system.
Nowadays, the number of off-season tomato growers is increasing every year. The plastic tunnel is more found to be popular among the farmers of the western development region. Due to the regular production of the same crop on the same land and other environmental conditions, many biotic and abiotic factors are found to decrease the production of tomatoes.
a. Diseases :
Damping-off, Late blight and Early blight, Fusarium wilt, Bacterial wilt, Leaf curl virus, Root-knot nematodes are the main diseases that are found to be an upsurge in off-seasonal tomato production. High temperature, warm moist soil, relatively high relative humidity, and unmanaged drainage system are the main phenomenon of these diseases. Fusarium wilt is a soil-borne fungal disease which survives in unfavorable conditions for many years and is found to be spread by cucumber beetles. In Bhaktapur, out of 20 plastic tunnels, 8 tunnels were infected with Fusarium wilt which leads to complete deterioration of plants.
b. Insects :
Tomato leaf miner affects tomatoes more on early-stage which can result in up to 80-100% yield reduction. Aphid sucks sap and tomato fruit borer bore into the fruit making holes and leave the fruit inedible.
c. Environmental condition :
With a decrease in height of the plastic tunnel and lesser area for ventilation, temperature and relative humidity become higher inside which is the main cause of diseases to outbreak. Due to higher and lower temperatures in summer and winter respectively, leaf curl problems are seen inside a plastic house which can be overcome by proper ventilation in summer and burning of woods inside drums in winter. Heavy irrigation followed by dry spell causes cracking of fruits. Weeds and heavy doses of nitrogen also act as the source for the entry of pathogens and pests.
For proper maintenance of temperature, humidity, and ventilation, farmers must increase the height of the tunnels. Crop rotation, field sanitation, soil solarization, ploughing, high ridging, staking, weed management, top-dressing with nitrogen, use of well-decomposed organic matters is necessary. Resistant varieties are the cheapest means of control example, the Srijana variety is tolerant to blight and bacterial wilt whereas NSITH-162 gives higher yield under a plastic house and resistant to bacterial wilt, mosaic and leaf curl virus. Nursery bed should be well-drained and selected in a sunny area with good aeration. Quality seeds must be provided to farmers for the germination of healthy seedlings. Irrigation should be provided only in the required amount. Mulching helps to maintain soil temperature and soil moisture. Use of sticky traps and lures to control adult insects i.e. TLM lure for tomato leaf miner and Heli lure for tomato fruit borer. Marigold and Chrysanthemum act as a trap crop against fruit borer and leaf miner respectively. Different biocontrol agents like Trichogramma and Bacillus thuringiensis are used to control lepidopteran pests and Trichoderma harzianum, Trichoderma hamatum, Bacillus subtilis and Pseudomonas fluorescens for controlling Fusarium wilt, Verticillium wilt and early blight disease and neem-based pesticides like Azadiractin can be used for pests. Different types of chemicals are used to manage diseases and insects. For example spray of copper+ bavistin and sulfur help to control the spread of bacterial speck, bacterial spots, damping off and powdery mildew, Spinosad 45% SC and Mancozeb are used to control leaf miner and blight respectively.
But nowadays consumers demand to have organic fruits and vegetables. So the governmental and non-governmental organization should pave their attention to provide training on the preparation of ‘jholmal’ by using locally available botanicals and use of cultural methods and biocontrol agents. Government, NGOs, and INGOs should provide subsidy and crop insurance to the farmers which encourage farmers to involve in commercial vegetable production. Pesticide residue test is done only on few markets of Nepal that’s why organic and inorganic produced vegetables are used to be mixed in the same basket. So it should be done on every market of Nepal which causes price variation and encourages farmers to produce organic vegetables.