Thursday, October 16, 2014

Management strategy against thrips in grapes by NRCG.


High thrips incidence and damage is being reported in Nasik grape growing region currently. A
large number of vineyards have been pruned during last 10-20 days. These vineyards are now in 
sprouting and young shoot growth stages which are highly susceptible for thrips incidence and high
level of damage. Further, the temperature conditions during last week were also favourable for thrips 
development in the region. The weather forecasting for next seven days in Nashik region indicates 
favourable conditions for thrips development. There are mainly two thrips species which cause damage in grapes in Maharashtra, viz., Scirtothrips dorsalis (chilli thrips) and Rhipiphorothrips cruentatus (grapevine thrips). Chilli thrips is most common and regular in occurrence in Maharashtra and is being reported in Nashik region currently. The adult thrips of this species are very small, elongated and fast moving measuring about 2 mm in length with four narrow fringed wings. One female thrips produces about 50-100 eggs. Eggs are very small and inserted in the tender tissue on the underside of the leaves, therefore, the eggs are protected from ovicidal action of chemicals. At high temperatures the hatching may even take place in about 2 days. Life cycle of thrips comprises four immature stages namely first instar and second instar larvae (nymphs), pre-pupa and pupa. Nymphs move down to the soil or fallen leaves and pupate. The life cycle is completed in about 14 days depending upon temperature. Damage is caused both by nymphs and adults by rasping the lower surface of the leaf with their stylets and sucking the oozing cell sap.

The chilli thrips have been reported to have wide host range. Around vineyards in Nashik, the 
major susceptible plant species are maize, banana, brinjal, tomato, chilli, rose, groundnut, onion, etc
which may also be a contributory factor aiding to the high thrips incidence. During the rainy season, 
weeds have grown in or around vineyards which also favours thrips development. Therefore, proper 
management of thrips on alternate host plants and weed management are essential to achieve effective 
thrips management. Thrips has the ability to cause economic damage within a day or two if left 
uncontrolled with high population levels. Heavy incidence may cause the curling and necrosis on 
newly emerging leaves or pre-bloom bunch within very short period of time. Therefore, regular 
monitoring and timely spraying of insecticides become very important. If the thrips population is more than 10 thrips per shoot, single application of insecticide may not be sufficient to provide desirable reduction in thrips popoulation. Therefore, second round of spray may be taken on the next day, if thrips population is still more than one –two thrips per shoot.

Many insecticides were found to have bio-efficacy against thrips in grapes. However, the key to 
achieve thrips management is to maintain right doses of insecticides. The volume of water may vary 
depending upon type of sprayer, however, the dose of insecticide should not be reduced even if the
water volume required to provide coverage is less than 400 liters per acre. The following insecticides 
have been found effective against thrips at ICAR-National Research Centre for Grapes, Pune;
Fipronil and emamectin benzoate may take about 2 days to show the effective results. 

Therefore, in case the thrips population is more than 10 thrips per shoot, then application of spinosad 
will provide immediate relief. However, during present favourable conditions, it is advisable to monitor the vineyards during both morning and evening hours as the thrips population may attain high number within very short period of time. Sometimes application of insecticide may not provide reudction of thrips which may be due to development of resistance in them. In these situations, application of cyantraniliprole may provide good result as it is a newly registered insecticide with completely different mode of action. However, there should not be more than two applications of this chemical as its EU MRL value is very low and PHI is high. Further, there should not be more than one spray of fipronil during fruiting season and care should be taken to not to use it during flowering stage and after.

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