WINTER wheat growers concerned about how to tackle dormant black-grass once it starts emerging may need to develop alternative strategies if they are to prevent it inflicting worrying yield damage, a leading expert is urging. Otherwise, it could get out of hand or be too cold to control while at an optimum time to spray.
"Many growers are facing a real dilemma of how to tackle black-grass this season," says grass weed expert Rod Burke of Syngenta. "Following the cool and wet summer, a state of dormancy was induced in seeds of the weed, which means their germination has been delayed.
"With such a delay, many growers have understandably held off from their spraying. However, if it starts emerging while the weather is cold, temperatures could be too low to apply some herbicides. On the other hand, if they wait until temperatures become warmer and black-grass grows, it could inflict unrecoverable yield damage. Black-grass can reduce yield by half a tonne per hectare for each month it is left uncontrolled. So there's a real need for a solution," he adds.
In answer, Mr Burke says if black-grass has started to emerge, but growers feel it is too cold to apply their standard herbicide, then they could consider one which works in cool temperatures – such as the contact and soil-acting treatment Hawk, tank mixed with isoproturon, once black-grass reaches 1-2 leaves.
By using this as a temporary "holding spray" where conditions are suitable, he says it will remove crop competition from the controlled black-grass. "If more black-grass does emerge after this, then there is still the option to consider a sulfonylurea herbicide as a follow-up later.
"The important point is that some of the weed competition should have already been removed by this time, which can make a difference to crop profitability – especially with better grain prices," he adds.
In addition, Mr Burke says with black-grass resistance a concern, then the later that treatment is left and the bigger the weed gets, the more difficult it can be to control – so removing some earlier germinators with a holding spray can help.
"Alternatively, in cases where black-grass germination is already complete and temperatures are sufficiently warm, then there is always the option of tank mixing Hawk directly with a sulfonylurea treatment, such as mesosulfuron with iodosulfuron.
"By doing this, growers add two extra modes of action to the sulfonylurea herbicide, which is also useful for resistance management."
Owing to the planned future withdrawal of the trifluralin active ingredient that it contains, Syngenta will only be selling Hawk up until 20 March 2008, says Mr Burke, but it can still be used by growers up to 20 March 2009, he points out.
