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GRASS WEED CONTROL POLICIES CAUSING FUNGICIDE & PGR ‘LOG JAM’
Date added: 07/04/06 |
Over reliance on Spring herbicide applications is causing congestion in the critical Spring fungicide & PGR spray window aswell as storing up weed problems for the future, says ProCam technical director David Ellerton.
“This year is a classic example of fungicide programmes backing up because of cold wet weather in February and March stopping herbicide applications and due to a lack of tank mix options they are now holding up critical fungicide & PGR applications until they are done,” Dr. Ellerton explains.
“Relying on herbicides in the Spring alone for grassweed control causes three immediate problems. They might not work if weather conditions are unsuitable, it can compromise timing of other sprays and it means there has been significant weed competition for the crop for six months over the winter.”
The other more serious problem is one of weed resistance.
“We are now mainly reliant on just two main groups of chemicals - ACCase and ALS inhibitors, including Fops, Dims and Sulfonylureas. Resistance to Fops and Dims is now so great that they are extremely unreliable particularly on large blackgrass plants.
That leaves the Sulfonylureas as the main means of late post emergence grass weed control.
“Our 4cast data shows that last year 70% of crops had their main grass weed control applied in the period February to April, with many applications towards the end of that period. In one trial the yield difference between autumn treated and spring treated crops was 11.2t/ha to 9.2t/ha – a drop of nearly 2t/ha, despite high levels of blackgrass control.
“By spraying late, you’ll knock out everything except the resistant strains and the seeds of these are what you are left to deal with next year. If you really want to drive resistance across the country – spray late on big weeds!”
The only way back is to think more about basic weed control approaches for next season, Dr. Ellerton says. Growers should challenge agronomists who advocate a purely chemical approach.
“We need to think more about cultural methods of weed control within the context of an integrated crop management approach. For example, be prepared to drill later on difficult grass weed fields, so you can get appropriate pre-drilling treatments on stale seed beds and avoid the main flush of germination occurring in the crop.
Use pre-drilling and early autumn herbicide treatments appropriately and use Spring applications as a last resort.
“If we can do this, not only will we be able to keep on top of weeds, we’ll also get better disease control by relieving the Spring log jam and allowing more timely applications of critical fungicides and PGR’s.” |
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