Growing crops also supporting populations of desirable weeds for biodiversity could ultimately form part of the options for either Entry Level or Higher Level stewardship, ADAS weed scientist James Clarke believes.
“We need to have a debate about how it could be incorporated into basic practices within cross-compliance, or more likely in ELS or HLS options.”
While many farmers and advisers do not see how weeds and high yielding crops are compatible, Mr Clarke believes there is considerable potential.
“For example, there is a lot of scope on lighter land with wheat, sugar beet-type rotations, and on more medium soils with wheat, oilseed rape or beans.”
But where severe grassweeds are a problem it is unlikely practices will be able to be manipulated to help keep weeds that produce chick food while still controlling grassweeds, he admits.
Trials investigating the potential for leaving desirable weeds suggested the autumn herbicides required for grassweed control reduced the more desirable weeds more than the undesirable.
There also probably isn’t much potential in rotations where there are very high value crops, such as horticultural crops, or in continuous wheat, he adds.
The key to successfully promoting populations of desirable weeds will be understanding how growers’ actions affect the weeds and seed return.
“It is thinking about how cultivations will affect populations, what will come up when, what you kill off by using a certain herbicide.”
Weeds need to be managed over time, as part of a strategy, he says.
“The Weed Management Support System can really help by modelling what the effect of different crops, cultivations and treatments will have on seed return.”
Differential herbicide selectivity will be critical for any strategy to work.
“In our trials a spring herbicide, Eagle, was the only treatment that changed the balance of undesirable and desirable weeds.
Inter-row hoeing and using wide-spaced rows didn’t improve biodiversity.”
More information on herbicide selectivity, and in other areas, is needed, Mr Clarke believes.