The high price of supposedly free feed

How many times have your farmers told you grass is not a worry in brassica crops because it’s free feed and the cows will eat it?

Treated swede (left) vs untreated, at time of harvest.

This season, thanks to results of a new trial, you can hopefully persuade them to see things a little differently. They’ll be better off as a result, and so too will their animals.

Nufarm technical specialist Sonja Vreugdenhil has some compelling data that clarifies in no uncertain terms the true cost of that perceived free feed.

She ran a dryland brassica trial in Canterbury last season that included comparing the dry matter yield at maturity between swedes that were sprayed post emergence for early grass weed control, and those that weren’t. Even she was surprised at the disparity between the two.

“It really showed grass is the largest robber of yield in a forage brassica crop. Prevailing weeds in the trial area were couch/twitch and perennial ryegrass, and they would not have covered more than 15% of ground area at the time of herbicide application.

Yet the difference in crop yield between treated and untreated swedes was 50 per cent, and grass weeds themselves made up only a small percentage of the untreated yield. Treated bulbs were the size of a person’s head, and untreated the size of your fist.”

The trial was sown in a high rainfall area near the foothills in early November 2024, and yield was measured in April.

Weed control was applied to the treated swedes when the crop was at the six true leaf stage, and comprised 3 litres per ha SeQuence, with Bonza Gold at 500 ml per 100 litres of water. Prestige was included for broadleaf control at the same time, tank mixed at 350 ml per ha.

As a way of demonstrating exactly what happens when grass is not controlled in forage brassicas, the trial was very successful.

“Sometimes it’s hard for farmers to visualise how much yield they can lose from what doesn’t seem like a lot of grass infestation in a young crop, especially when they often look at that grass and think of it as free feed.

So this is a great visual representation of the value of grass weed control. I worked out you would need 500 kg dry matter per ha of extra yield to cover the cost of that herbicide application, which is not a lot in the context of a crop that yields 12-15 tonnes dry matter per ha.”

This work was done on winter brassicas, but the same principle holds true for summer brassicas too, she says. Every day farmers hold off applying a grass weed herbicide in affected crops can impact their yield.

“If they’re going to put a crop in, they need to look after it, or they will be disappointed when it comes to grazing.”

There’s another equally important reason to control grass weeds: They compete with the new pasture which usually follows forage crops.

“Once new pastures are sown, your farmers do not have an opportunity to control undesirable grass species.”

SeQuence is a selective herbicide registered for many spring-sown forage crops, including fodder and sugar beet, forage brassicas, chicory, plantain, lucerne, clovers and other legumes. It contains the active ingredient clethodim (Group 1) and is registered on 22 grass weeds, including ryegrasses, annual summer grasses, wild oats, cultivated couch and annual poa.

Best results come from applying SeQuence when target grasses are actively growing. This only happens when soil moisture and temperature are at the right level to support growth, so it pays to be aware of how conditions are shaping up at the start of the season.

SeQuence must always be applied with Bonza Gold and may be tank mixed with Archer 750 (Group 4) or Prestige (Group 4) if broadleaf weed control is also required in forage brassicas. Attack may be added to SeQuence when pest control is needed.