According to Teagasc, the area of cereals sown-out over the past three weeks that has received a pre-emergent herbicide is quite low.
Tillage specialist Kieran Collins explains: “When weather is difficult at sowing, following-up with a pre-emergent product is difficult.
“However, many of the crops that were sown out before the break in the weather, hopefully, received a pre-emergent product. This is the only way to tackle brome grasses effectively.
“Patchy crop emergence will leave light for weeds to colonise areas within a crop,” he added.
Herbicide sprays of any kind that are applied in changeable weather conditions can be easily washed through the soil. As a result, annual meadow grass has a greater opportunity to get established within a new cereal crop, when such conditions prevail.
“The other point worth making is that most residual herbicides are root-acting. They move through the soil to the weed rooting zone,” Collins continued.
“So, in very wet soils those actives could move deeper to the crop root zone. And, there can be effects here as well.”
Impact of herbicide
Teagasc will be formally assessing the impact made by residual herbicides during the 2022 autumn planting season. But Kieran Collins is already flagging up the distinct possibility of their impact being reduced because of the recent weather.
In cases where a pre-emergent product was not applied and crops are just coming through the ground now, Collins recommends the specific targeting of annual meadow grass now.
“This is particularly so in the case of barley crops,” he stressed. “Products such as Stomp, Firebird and Defy meet this need.”
Stomp contains the active ingredient, pendimethalin. Defy contains prosulfocarb while Firebird contains the active ingredient, flufenacet.
According to Kieran Collins, these products can be applied pre-emergence. However, they can also be used shortly after the new crop has emerged.
“Getting in before annual meadow grass starts to tiller is important. Up to that point, these products will deliver a satisfactory outcome for growers,” he said.
The tillage specialist also pointed out that farmers should avoid going into fields with machinery when shoots are just breaking through the ground. This is called the peri-emergent stage of growth.
“Getting in at the two-leaf stage should give reasonable control of meadow grass. But it is best to avoid spraying crops at those times when they will be under stress.
“And weather will always be a key factor in this regard,” Collins stated.