Grain pest treatment MRL reduced: but don’t panic

The commonly used insecticide deltamethrin has been undergoing a new review process that sees its Maximum Residue Level (MRL) reduced in some crops. 
The legislation change was announced on 13th October and will come into force on 7th May 2017. The new MRL for deltamethrin applies to wheat, rice and beans only - where the legal concentration of the active has been reduced from two parts per million (PPM) to one PPM. 

But, with the benefit of regulatory foresight and extensive consultation, the impact of the change to the Maximum Residue Level (MRL) on wheat for a commonly used grain insecticide has been such that the treatment remains a valuable option. 

“Deltamethrin based K-Obiol® from Envu is one of a relative few products that can be applied directly to grain. With regard to this change, the product is already well within the newly prescribed MRL limits, meaning application rates will stay the same,” says Dave Ross, global market segment manager from Envu. 
“This legislation only applies to treated grain - the residual levels of product applied to the fabric of the grain store, up to two months before grain goes in, won’t be affected,” he confirms.
“Grain store pests can be split into two categories - primary and secondary. Primary pests have the ability to attack whole unbroken grains, while secondary pests attack only damaged grain, dust and milled products. It’s important to be aware of both to ensure the correct control measures are used. 

“Traditionally the most damaging pest to stored grain is the grain weevil, with the females burrowing into the grain, laying their eggs and the larvae then eating their way out - hollowing the kernels out so they are in effect more like ‘Rice Crispies’ in appearance than quality, saleable grain. 

The saw-toothed grain beetle is now the most common primary insect pest of grain stores in the UK. The beetles can cause the grain to heat if infestations are heavy, which in turn leads to moulding and even sprouting and both the quality and the weight of the grain may be reduced,” says Ken Black, Envu Pest Solutions Team. 

“Secondary pests like grain mites can be just as destructive because they can build up very quickly and damage the grain by feeding on the germ (the embryo part of the seed), tainting the produce with allergens and spreading fungal spores,” he says. 

Ken reminds growers that deltamethrin is a long-term grain protectant. “It will treat pests when applied, but it can’t kill the larvae if it’s inside the grain. When the larvae eat their way out of the grain, that’s when they ingest the active and are treated.

“Some farmers might see bugs present in the grain even after it’s been treated, and this will be larvae that’s eaten through grain after it’s hatched. It could take up to a month before they all hatch, eat the grain and are ‘knocked down’, so patience is required. Because, while some grain will be damaged, the risk is far less than if it isn’t treated at all.

“As always, prevention is better than cure, and cleaning grain stores thoroughly, then treating the fabric of the building with K-Obiol up to two months before harvest, will give you the best chance of a pest-free crop. If the risk of pest infestation is high, then it’s advisable to treat the grain as a precautionary measure. Then it’s important to monitor for weekly using ‘pit fall’ traps, ensure optimal grain temperature and grain moisture - optimum moisture levels for long term storage of cereals is below 14.5% and 7.8% for oilseed rape. 

“Although direct grain treatment should only be employed when the risk of infestation is high, it’s a crucial product in our armoury. Responsible use of chemicals is central to maintaining vital pesticides, and Envu works hard to safeguard products, by future-proofing formulations such as this, and encouraging best practice,” adds Ken. 

It’s important to remind farmers that the MRL legislation change also includes the review of a number of other active ingredients on wheat: aclonifen, fluazinam, methomyl, sulcotrione and thiodicarb.

If you have any questions on products or legislation changes, get in touch with the Envu Pest Solutions Team on 00800 1214 9451 or pestsolutions@bayer.com.