Wet or dry, assess individual situations when deciding on pre-emergence herbicide application
It is vital for growers to look individually at their fields and make decisions on the application of their pre-emergence herbicide spray based on the condition of the seed beds and depth of drilling - not levels of rainfall - and be prepared to react quickly and accordingly, advises Bob Mills of Frontier Agriculture.
"Many growers will be concerned about the changeable conditions when making decisions about the relevance of a pre-emergence herbicide application at the moment, but it's not the amount of rainfall that is the deciding factor as to whether a pre- or post-emergence application is applicable, it is more about having the correct seedbed conditions and depth of drilling. Once seedbed conditions are right, a pre-emergence can go on and be very effective, resulting in well-established crops," says Mr Mills.
"It's a delicate balance between delaying application until the conditions are right, and potentially missing an integral part of the grass weed control programme which means the Black-grass pressure will be upped in the spring, or going on too early and not only wasting herbicide, but also interfering with follow-on treatments."
"My advice is simple; familiarise yourself with the field conditions- is the seedbed well rolled and not too cloddy ? Is the depth of drilling correct? Once you are comfortable with the conditions then there is no need to hold back from the use of an effective pre-em, says Mr Mills." If not, and this may be the case for those who drilled early on cloddy first wheats and forced the seedbeds, it may be prudent to wait for a peri- or post-emergence application."
"Black-grass is showing increased dormancy this season, so we are going to get a protracted period of germination, so I would recommend a good residual component, such as pendimethalin, to the pre-emergence grass weed control strategy. If all of these factors are properly considered, then there is no reason that the crops cannot come through well and establish quickly. "
Clare Tucker agronomist with BASF based in the south of the country agrees wholeheartedly with Mr Mills, "don't use the amount of moisture as a measure of when to apply the "pre-em"; the key decision affecting whether you go on pre- or post-emergence of the crop is the quality of the seedbed. Also cooler mornings are bringing more dews, and these often provide sufficient moisture for the movement of the herbicide to the germinating Black-grass."
"Choose a stable product that is going to stay in the soil and provide control throughout the Autumn/Winter, such as Crystal (pendimethalin + flufenacet) at a rate of 4l/ha. The flufenacet adds short term activity but the pendimethalin adds persistence, valuable in an autumn where germination will be longer due not only to the predicted long dormancy but also to cooler soil conditions than we've had in the last two years.," adds Ms Tucker.
