Wild radish control strategy rethink
Western Australian agronomist Grant Thompson has a clear message for southern region grain growers when it comes to wild radish – aim for early control when weeds are small and learn from the mistakes made interstate. WA growers are battling radish that is becoming resistant to multiple herbicide groups.
The problem is a combination of factors – overuse of cheap Group I and Group B chemistry, exposure to Group F and Group C herbicides used in cereal crops, expensive broadleaf herbicides used below label rates, poor application conditions and water volumes that are too low for effective coverage.
Cross-pollination between radish plants is ensuring that multiple resistance genes are accumulating, or ‘stacking’, in paddocks.
Mr Thompson, from Crop Circle Consulting, says some paddocks with highly resistant populations may have four or five radish germinations per year.
“The seed has a long dormancy and in summer it can flower within three weeks of germination,” he says.
“Our trial work has focused on finding alternative sequential spraying options to avoid two sprays of Group H pyrasulfotole chemistry, such as new herbicides Precept® and Velocity®, for radish control in cereals.
“We are trying to avoid speeding up the onset of Group H resistance.” Mr Thompson’s recommendations for radish control include:
- spray early for most effective control – WA trial work has shown that spraying radish at the two-leaf stage is far more effective than trying to tackle it at a later maturity (this is supported by BCG research in the Wimmera–Mallee);
- two sprays are best for resistant populations – for radish with multiple-herbicide-group resistance a two-spray strategy involving an early spray at two-leaf stage followed by a second spray at the five-leaf spray is most effective; WA trials found leaving out the early spray puts extra pressure on success of the second spray for control;
- canopy penetration – high-density radish populations (such as 200 plants per square metre) can cause shading of radish by other plants; delaying spraying to five-leaf stage in big canopies will not achieve good coverage; and
- cultural options – consider methods such as tickling paddocks for good germination, chaff carts, and seed capture at harvest by creating windrows behind the header and burning; however, this selects for radish biotypes that drop pods before harvest.
“The take-home message is when you go in early at the two-leaf stage with the registered options that are available to you, it’s pretty easy to kill small radish,” Mr Thompson says.
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GRDC Project Code CRC00003, BWD00023
Region South, West, North