Ruth East: June Column

I appear to be struggling to get my thoughts together this week – the classic symptoms of organophosphorus poisoning – maybe due to the amount of chlorpyrifos that appears to have been applied with gay abandon in the region to combat the elusive orange blossom midge.

I have heard of people putting half rates in with flag leaf sprays, and then topping up with the other half at T3 getting the timings all wrong.

Why are people apparently ignoring all the excellent work generated by our scientists at Rothamsted Research, and by the eminent entomologist John Oakley and his team?

The idea of pheromone traps is that they give you an indication that the males are arriving in the field, and merely that crops need to be monitored, not necessarily sprayed.

In most crops midge levels have been low, so they haven’t needed treatment. Odd fields have merited it, but at nothing like the levels of 2004.

It seems that some farmers have responded to work by a well known independent trials group that showed you get a yield increase, even in the absence of midge, by applying chlorpyriphos.

It’s well known that by applying any insecticide you boost yield, even in resistant varieties, as you remove sub-clinical levels of pests. However it does not justify the intensive use of OP sprays.

Some of the defences that I have heard for such treatments have no scientific backing. One is that chlorpyriphos removes the wax from the leaves and allows the plants to photosynthesise more efficiently.

What rubbish!

Another apparent reason for treating resistant varieties is that the plants use energy repairing the feeding sites with wound plugs. We need scientific evidence to confirm that before widespread treatment.

If anyone bothers to read Mr Oakley’s work they would know that only in high infestation years do resistant varieties need spraying.

I’m surprised at how many people have adopted a cavalier approach to midge this year, especially when you consider what is happening with pesticides in the EU at the moment.

In winter barley blind grain sites can be found. They are due to frosts we had in April when the crop was at the critical stage for pollen formation. I expect we will also see a lot in some fast-developing wheat varieties.

I also think grain set will be poor, bad weather during flowering leading to low pollen production – the ‘Moulin effect’ for those who can recall that variety. But I am sure it will be put down to midge damage.

Anybody who has had poor results with Atlantis (iodosulfuron-methyl-sodium + mesosulfuron-methyl) should examine their herbicide history.

If other sulfonylureas have been used, such as flupyrsulfuron-methyl and chlorosulfuron + metsulfuron-methyl, I suggest you have the seed tested for resistance.

Our leading herbicide researcher, Rothamsted’s Steve Moss, predicted that Atlantis would only be around for three years. And guess what? There are no new products on the market for blackgrass with different modes of action.