Six key takeaways about Italian ryegrass threat

The largest ever survey of Italian ryegrass in the UK by NIAB and Bayer is providing new information about the extent and resistance status of an increasing threat on arable farms.

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FIVE DISTINCT CLUSTERS WHERE ITALIAN RYEGRASS IS A MAJOR THREAT

FROM the 197 samples sent to NIAB, five regional clusters emerged. The problems in Essex and Kent (south east cluster), and South Yorkshire (north) were well-known, but issues in Dorset (south west), West Midlands (midlands) and North Yorkshire / County Durham (really north) emerged.

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2. RYEGRASS ISSUES NOT RELATED TO SOWING FOR LIVESTOCK OR FORAGE

A QUESTIONNAIRE filled in for each sample about the history of the field showed there was no correlation with previous history of growing ryegrass for livestock or forage.

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3. RYEGRASS COULD FEASIBLY BECOME A PROBLEM ANYWHERE

THE questionnaire did not pinpoint any major factors for the rise of ryegrass.

Common wider trends of reduced cultivation intensity and more spring cropping were mirrored on these farms. This suggests there is nothing specific these farms are doing to encourage the weed, which is also not happening on farms outside these areas.

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4. WORRYING INCREASE IN INCIDENCE

IT is a self-selecting sample, but 39% of farmers sending in samples were finding a big increase in Italian ryegrass on-farm, while 51% recorded a slight increase.

Just 3% were seeing less. Farms in the north (56%), ‘really north’ (46%) and ‘other’ (50%) areas are the ones reporting the highest proportion of big increases.

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5. IT IS ADDING TO COST

MORE than half of the farmers said it was costing them more to control ryegrass on their farm, which can probably be attributed to increased use of residual herbicides. Cost has been controlled on some farms by reducing or stopping the use of post-emergence contact herbicides.

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6. RESISTANCE TESTING WILL BE HELPFUL

RESISTANCE testing of the 197 samples against post-emergence contact herbicides shows considerable variability in resistance status.

For example, about 46% of samples are sensitive to both Atlantis (mesosulfuron + iodosulfuron) and Axial Pro (pinoxaden) meaning their use will be useful. But 47% of samples are confirmed as resistant and either probably or likely to reduce performance.

There are regional differences. In the North Yorkshire and Co Durham cluster, there is a much higher proportion of Atlantis ‘RRR’ resistance (40%) compared with Axial Pro (10%), yet in the South Yorkshire cluster it is the other way round, with just 6% RRR with Atlantis, compared with nearly 30% with Axial Pro.

Knowing your population’s resistance status will help make better management decisions.

WHAT DO THE CATEGORIES MEAN?

S – Susceptible (over 81% control)
R? – Early indications of resistance, possibly reducing herbicide performance (72-80% control)
RR – Resistance confirmed, probably reducing herbicide performance (36-72% control)
RRR – Resistance confirmed, highly likely to reduce herbicide performance (0-35% control)