PTM control
No single control measure can provide adequate protection to potato from PTM, especially when the population remains quite high and the infestation starts from fields and later on reaches the country stores. Therefore, integration of different management practices is the only solution for effective suppression of the PTM population and minimization of its losses by avoiding heavy infestation.
Cultural and mechanical: Planting seed tubers at a depth of 10 cm reduces its damage to a great extent. The fields should be ridged after 6 to 7 weeks of planting so that the tubers are buried at least 25cm below the soil surface. In areas where PTM population remains quite high and severe tuber damage is expected in such cases ridging should be done twice so that the tubers are not exposed at any time for egg laying and infestation.
Timely and adequate irrigations minimize soil cracking and thereby reduces the risk of tuber exposure to PTM attack or their egg laying. This problem is quite common in areas where potato crop is raised in heavy soils.
Harvested tubers must be removed from the field as early as possible and should not be kept overnight in the field. Leftover tubers, after harvest, should also be collected. All the plant debris including the weeds belonging to solanaceae family should be collected and destroyed. The crops like tomato, tobacco, chillies and brinjal should not be grown in the vicinity of potato fields, particularly in PTM prone areas.
Varietal resistance remains the first line of defence in the control of insect pests. However no PTM resistant variety has been released so far.
PTM sex pheromones are commercially available. These sex pheromones are commonly used for monitoring of field population, detecting the occurrence, facilitating proper use of insecticides and mass trapping of PTM for direct control. These sex pheromones can be used effectively in funnel, water or sticky traps. For monitoring purposes, two traps per field should be installed in the crop 50 meter apart. The traps should be checked at 7-day intervals.
Chemical: Spraying the crop with monocrotophos (0.6 kg a.i./ha) has been found effective for the management of PTM in fields. In country stores, potatoes meant for seed purpose can be protected from tuber moth’s attack by dusting them either with fenvalerate 2%, malathion 5% or quinalphos 1.5% dusts @ 125 g dust/100kg potato. Care should be taken to see that potato meant for table purposes is not treated, in any case, with any insecticide to avoid serious health hazard to the consumers.
Biological: Some of the parasitoids are Chelonus curvimaculatus Cameron, Bracon gelechiae Asheamd, Apanteles sp., Pristomerus vulnerator Panzer and several other braconids have been reported to cause 4-17% parasitisation under field conditions. Copidosoma koehleri Blanchard,an exotic egg/larval parasitoid, gave 28.4-60.8% parasitization in Maharashtra . Bacillus thuringiensis (Berliner), a gram positive, flagellated, rod shaped bacterium, which produces a para poral crystal during sporulation, has also been reported to be effective in controlling PTM.
For last several decades, farmers have been protecting their potato crops and produce (potatoes) kept in country stores with the help of natural insect repellents like leaves, stems, flowers and fruits of various plants possessing repellency properties. Three plant species viz. Lantana camara Linn., Eucalyptus globulus L.Herit. and Minthostachys sp. either dried/shredded leaves or powder form, are effective in preventing PTM damage to potatoes stored for four months in country stores. In India, out of the several plant species tested against PTM, Lantana aculeata L. provided the best protection by reducing PTM damage from 70% to below the 5%. Likewise, sprout damage was also reduced from 45% to below 3%. For this purpose, fresh leaves of lantana are chopped, dried and spread in 2cm thick layers both below and above the stored potato.
Integrated management: In areas where the PTM population is high, various control components have to be integrated for evolving an effective, eco-friendly and sustainable IPM strategy.
In stores, i) store healthy (PTM free) potatoes in cold stores, ii) the sex pheromone can be used for mass trapping the males, iii) covering of healthy tubers stored in country stores with 2-3 cm thick layers of chopped dried leaves of either Lantana , soapnut, neem, eucalyptus oreupatorium, iv) treat potatoes with the dust of granulosis virus before storing the potatoes. For this purpose a mixture in the ratio of 1.0 kg of talc powder + 20 GV infected larvae + 1.0 litre of water + 2 ml of triton should be prepared and used @ 5kg of mixture/ tonne of potatoes.
In fields, i) use healthy (PTM –free) seed potatoes for planting at 10cm depth in PTM-prone areas instead at traditional planting depth of 6 cm, ii) fill the soil cracks in potato fields by timely earthing up and covering the exposed tubers properly, iii) irrigating the crop in a manner to avoid cracking in the fields, iv) the pheromone traps should be placed in the field @ 20 caps/ha for mass trapping, v) spraying the crop either with quinalphos EC or monocrotophos EC at 0.05% alternately once or twice with bio-agents like Bacillus thuringiensis (Bt) or Granulosis Virus (GV), vi) do not leave the harvested potatoes in the field overnight and never cover them with infested potato foliage. Collect the leftover tubers after harvesting for table purpose or destroy them. Also remove the volunteer plants.