Teagasc is advising farmers growing oilseed rape this year to count plant numbers before applying a post-emergent herbicide.

This, tillage specialist Ciaran Collins said, is to ensure the correct amount of herbicides is applied.

“Given current conditions, grows will be expecting very high establishment percentages this year,” the advisor said.

“However, herbicides containing the likes of metazachlor as an active ingredient will hit emerging rape plants as well as weeds.

“This is why actual plant numbers within an emerging crop must be high enough to allow for any losses when a post-emergent herbicide is applied.”

It has been shown in the past that non-uniform germination within an emerging rape crop can create challenges, where the use of post-emergent herbicides is concerned.

For example, these products can kill emerging plants at the cotyledon stage.

“It’s critical that the established rape plant population in the files is at the desired number,” Collins said.

The right mix

There are a number of post-emergent herbicide chemistries that can be used under Irish conditions. According to Collins, Belkar is one that fits well within this category.

“This is a synthetic auxin, which is co-formulated with picloram. The advantage here is that it has a stronger foliar action and can be applied later than some other post-emergent products,” he said.

“So, if the weather goes against a grower, it is a definite option in this context.”

While the product would not have the same effective range, from a weed control perspective, Collins said, “it is really good on weeds like cleavers, fumitory and poppies”.

According to the Teagasc representative, Belkar will need a follow-up.

“Grass weeds are the obvious issue,” he said.

“But for anyone planning to grow oilseed rape over the coming weeks, the use of a pre-emergent herbicide, such as Katamaran Turbo, will give the widest level of control over broadleaf weeds.”

Collins went on to confirm that fast-emerging volunteer barley and wheat plants can provide very high levels of competition for a germinating rape crop. Both cereals have the ability to germinate very quickly.

“Bare patches are often visible in fields of oilseed rape if there were high numbers of volunteer cereals at the outset,” the advisor continued.

“In such cases getting in with a graminicide is very important. The earlier the better, however, tackling volunteer cereals at the one or two-leaf growth stage is key.

“Issues with staggered emergence can be an issue in this context as well.”