Ideal weather conditions for pest attacks unusually early in the year
An unusually hot February has put the essential Rabi crop wheat at risk. Scientists have now warned the ongoing weather conditions are likely to threaten the vegetable crops and pulse yield with attacks by pests like aphids and thrips.
Warm and dry weather conditions prevailing in north and northeast India are ideal for the growth of insects, according to experts. Down To Earth, during a visit to Naugaon of Alwar in Rajasthan earlier this month, black aphids were found on safflower crops.
Roshan Lal, a farmer from the village, pointed out that black aphids have even infested his mustard plantations. “Green aphids are known in the region, but now black aphids have also infested the crops in our area,” he said.
Aphids are small insects that pierce live plants and suck on their sap. The insect is round in shape, measuring about 2-4 millimetres in length and has thousands of species worldwide varying in colours. Thrips are also rasping-sucking insects with wings. Their bodies are long and can be yellow, black or brown.
“These insects thrive in existing weather conditions. Thrips development is at their peak when the temperatures hover between 25 to 30 degrees Celsius,” Debashish Jena, scientist/agrometeorology at Krishi Vigyan Kendra (KVK), Indian Council of Agricultural Research Rice Institute (ICAR-NRRI), Odisha told DTE.
Aphid population grows where weather extremities exist between day and night temperatures, according to scientists.
Maximum temperatures from 26.4-29°C and a minimum of 8.4-12.6°C with relative humidity ranging from 75 to 85 per cent favours aphid multiplication, according to a research Population Dynamics of Mustard Aphid in relation to Humid Thermal Ratio and Growing Degree Days, published in 2013.
Similar temperatures are being observed in north India, where morning conditions are foggy due to the dipping of night temperatures and moisture incursion, followed by a sunny day with temperatures going up to 30°C, said Jena.
A study, Diagnosis and potential invasion risk of Thrips parvispinus under current and future climate change scenarios, published in August 2022, found the pest damaging three states in south India.
It observed that a temperature range of 15-30°C positively influenced the growth of thrips by increasing its generations and population. The invasive pest, native to Thailand, damaged more than 60 per cent of the chilli crops in Andhra Pradesh, Telangana and Karnataka in 2021.
The maximum temperature was 23-28°C from February 15-20, 2023, over Himachal Pradesh and Uttarakhand, according to a special report of the India Meteorological Department (IMD).
Meanwhile, maximum temperatures in Delhi, Chandigarh, Haryana and Punjab were in the range of 28-33°C, added the report published on February 20.
Higher day temperatures are likely to negatively affect wheat crop growth as they approach the reproductive phase, the report also pointed out.
Such weather conditions favour sucking pests, which attack various crops and vegetable plantations. “Besides, wilting may be reported in leaves due to lack of moisture in the air during day time. The crops are at grain filling stage and may directly hamper the yield,” he added.
India has 34.32 million hectares of area under wheat, 4.62 million hectares under rice and 16.78 million hectares under pulses, according to government data gathered on February 3, 2023.
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