Midland and eastern growers warned of black-grass surge
Widespread showers forecast this week will mean a return to strong black-grass growth and further emergence in areas beset with drought over the last few weeks. Stalled herbicide programmes now need to be jump-started, according to Jim Orson, special adviser at NIAB TAG.
As yet no one knows the full effect of the dry conditions on black-grass. Seeds will have dried out which could reduce the amount able to germinate but showers predicted this week will prompt further emergence and robust growth.
"Understandably given the condition of some crops, growers have held off residual herbicide applications, but where there is sufficient rain to moisten seed beds they need to be cracking on.
"A moist seedbed at the time of application will improve the performance of residual herbicides, even if it dries soon after," says Mr Orson. "But what you see at the surface may not be representative of the environment surrounding the roots. Digging down a couple of inches will show whether the roots have sufficient moisture to sustain growth. Given current temperatures, if they have moisture around the roots they will be growing, making them more susceptible to the contact sprays too.
"Timing and conditions are key factors in the efficacy of herbicides, as ever it is a fine line between the two but, with a little rain, conditions will be close enough and there is the danger that some black-grass will get away from the residuals, especially where it is patchy.
"Some black-grass is beyond the growth stage when optimum control from the residuals can be expected, here a contact herbicide should be applied. But as we’ll see further emergence, there is a stronger case than normal for mixing a residual with the contact at the post-em timing," explains Mr Orson.
"Atlantis is likely to continue to be the default contact post-em product for black-grass. It needs to be applied at the one-two leaf stage of growing black-grass to optimise activity and particularly where further black-grass emergence is expected mixing it with a flufenacet-based product is a sensible strategy. Clearly, growers will need to bear in mind what has been used at pre-emergence as well as the total dose. Alternatives include prosulfocarb or pendimethalin.
"Reassuringly, should it turn very dry again, field evidence shows that the loss of activity from residuals is not very significant provided that there is further rainfall within the following seven to ten days. Obviously spraying immediately before heavy rain risks crop damage, so allowing at least one to two days is advisable."
