Will longer crop rotations really help manage weeds?

Peter Newman, Communication Leader with the Australian Herbicide Resistance Initiative says the real culprit is always a lack of diversity. He recalls a grain grower friend taking him to a paddock that had been in a lupin / wheat rotation for 30 years. “He said his wheat was always full of brome grass and his lupins were full of wild radish and blue lupins,” he says. “Then one year he decided to break the cycle and planted barley after wheat, instead of lupins, and the barley came up full of wild radish and blue lupins.”

This grower concluded that his weeds were responding to what had become a predictable farming system.

“Managing resistant weeds requires farming systems that are diverse—using different crops, different chemical modes of action and including non-herbicide control tactics,” Mr Newman says.

The days of simply changing from one chemical to another when the first one becomes ineffective are gone. All chemical options need the support of other tactics and this is where longer crop rotations can provide much more diversity to confuse the enemy than short rotations.”

“Diverse rotations can include longer rotations with different crop species, using varieties with different herbicide tolerance traits or sowing dates, and using an array of tactics to reduce weed numbers and prevent seed set.”

“We are seeing growers win in the battle against herbicide resistance and that is great news,” he says. “It’s time to get serious and to start looking for ways to make every farming operation as diverse as possible.”

Peter Newman, Communication Leader with the Australian Herbicide Resistance Initiative says the real culprit causing herbicide resistance is always a lack of diversity.

How does lengthening a crop rotation help manage herbicide resistance?

Short answer: By adding diversity.

Longer answer: A longer crop rotation means having more tools in the toolbox—better herbicide rotation, a range of seed set control options, varied planting times, competitive crop species or varieties and the ability to implement a variety of harvest weed seed control options.

What can I do if I need to keep a fairly tight rotation?

Short answer: Still look to add diversity.

Longer answer: If you can’t see your way clear to lengthen your crop rotation, look for ways to increase diversity within the crops you grow. Changing varieties may allow a different sowing time and in herbicide tolerant crops such as canola, you can rotate between the RR and TT hybrids. In a tight rotation harvest weed seed control and maximum crop competition are even more important.

Peter Newman, Tom Murphy and Rob Hughes discuss the benefits of narrow row spacing for yield and weed suppression.

What other benefits can I expect from longer crop rotations?

Short answer: A more sustainable farming system.

Longer answer: Increasing diversity in the crop rotation is good for pest and disease management as well as weed management. Adding a legume will also have a lasting impact on soil nutrition. In the longer term a diverse rotation reduces overall production risk.

Are there limiting factors?

Short answer: Yes.

Longer answer: Crop sequencing can have impacts beyond weed management. A rotation should be planned and the use of residual herbicides must take the following crop into account.