Resistant ryegrass reliability controlled in winter rape

UK - October 12, 2006

The spread of resistant black-grass is well documented, but now resistant ryegrass is becoming as great a problem for arable growers. 

Cropwise agronomist Mike Thompson believes the threat of herbicide resistant ryegrass is underestimated which could become a very serious burden to arable growers.  As more ryegrass species are used in margin and conservation mixes as well as in set-aside the problem could accelerate. 

“Resistant ryegrass is as damaging to cereal yields as black-grass.  As it spreads, achieving high levels of control of resistant ryegrass in winter cereals and many break crops will be an increasing challenge.  One reliable solution I have found is using Quaver (propyzamide) in winter oilseed rape,” says Mr Thompson. 

Mr Thompson’s experience is backed by trials carried out by ADAS and sponsored by Dow AgroSciences where propyzamide gave close to 100% resistant ryegrass control in winter oilseed rape.  The size of the ryegrass had little impact on the level of control achieved.  Later germinating plants were also controlled due to the herbicide’s residual nature. 

He advises growers to wait until soil temperatures have dropped to at least below 10 ºC, without any mild spell interruptions, and there is moisture down to at least 5 cm soil depth before applying Quaver.   

“The optimum timing for ryegrass control is a little later than that for black-grass because of prolonged germination.  I advise growers to use the full rate of 2.1 l/ha for persistence against late germinating ryegrass.  Where very high levels of resistant ryegrass are present I use Quaver as part of an integrated programme with stale seedbeds and an early graminicide.  Quaver is probably the best choice for growers facing the combined threat of resistant ryegrass and black-grass because of its additional action on ryegrass over its competitors,” says Mr Thompson. 

Dr Stephen Moss from Rothamsted Research explains that resistant Italian ryegrass is the main problem, and no cases of herbicide-resistant perennial ryegrass have yet been confirmed.  Resistance could occur in perennial ryegrass, but it is generally much less of a weed problem in arable crops than Italian, or hybrid varieties. All ryegrass species can cross-pollinate freely, so resistance could transfer to established fields of ryegrass.  

“Growers and advisors must be on their guard to identify the presence of the ryegrass problem in its early stages of development, and eliminate it quickly.  Ryegrass is more competitive than black-grass, and more farmers should be having resistance tests done before it becomes a major problem on their farm,” says Dr Stephen Moss.