Ryegrass resistance to some pre-emergent herbicide chemistry is becoming an issue for growers, and alternative in-season chemical options are being sought.
In-season applications can generally be carried out with good results. However, in the high-rainfall zone they can often be missed due to poor traffickability of paddocks in wet seasons. Growers have been limited with alternative management techniques, and hay cutting of ryegrass-affected paddocks is a popular option.
Last year, pre-harvest glyphosate registrations were changed, giving growers a new alternative. There have always been tight restrictions around pre-harvest spray applications of cereal crops in Australia, however the APVMA changed registrations regarding desiccation and spray topping of feed barley crops using glyphosate late last year. This permit will last until July 2019 and is for feed barley crops only, not crops intended for the malt market.
The use of pre-harvest glyphosate in feed barley can prove a valuable tool for grain growers. A late-season application can significantly assist in reducing the amount of ryegrass in a paddock due to seed set being stopped and reducing weed numbers the next season.
Pre-harvest glyphosate applications in feed barley are best applied when the grain is at 30 per cent or less moisture content, or when a thumbnail impression can be left on the barley kernel.
There have been some concerns regarding food safety regulations with overseas markets. Applications made close to harvest increases the possibility of detectable residues being present on the grain. To help reduce these risks, there is a seven-day withholding period on crops that have had a late-season application. The GRDC also urges growers to be in contact with their buyers regarding these practices, as certain markets may have restrictions, even for feed barley.
Overall, if there is a significant ryegrass problem in your cropping system that would benefit from a pre-harvest glyphosate application, it’s best to prepare at the start of the season.
