It has come to our attention that split applications of Imtrade Edge 900 are being used to treat canola crops (half up-front as IBS and half post/PSPE) with a number of undesirable consequences. This is a major concern for a number of reasons.
Firstly, Imtrade Edge 900 is registered for use as an IBS treatment only. There are two reasons for this:
- The MRL (residues) data has only been conducted for this application type; any other form of application is not covered by legislation.
- Removal of the active from the seeded furrow assists in safety to the germinating canola seedling. Any application where Imtrade Edge 900 is made to the seeded furrow is raising the potential risk to the germinating crop, especially where moderate-heavy rainfall is expected.
Secondly, Imtrade Edge 900 is registered for use on ryegrass at 550 g/ha, this amount is required to kill the ryegrass, anything less than this amount will provide a sub-lethal dose. Even though the split application of half rates theoretically completes a full dose, this is not actually the case as outlined below.
- The half rate as an IBS treatment will be applied 3-14 days prior to the second application, any ryegrass germinating in this period will only receive a sub-lethal dose and may outgrow the herbicide band before a second dose is applied and subsequently survive.
- IBS throws the herbicide into the inter-row, leaving seeded furrows free of herbicide; so a half dose IBS leaves you with a half dose in the inter-row and zero dose in the furrow.
- Follow-up half dose post/PSPE applications will provide a second half-dose to the inter-row, but only a single half dose to the seeded furrow, potentially allowing survival of ryegrass following a sub-lethal dose.
What happens as a result of half doses?
This is the quickest way to develop resistance to a herbicide. This technique is often used in controlled experiments to generate resistant populations so the mechanisms of resistance can be investigated. It often only takes three generations of surviving plants to develop resistance when molecules are applied at half doses in these controlled experiments, in field terms this translates to population resistance in three seasons!
By using split applications of half doses, we run the risk of rapidly loosing one of the most important molecules in our arsenal for ryegrass control. To date there is no recorded resistance to propyzamide in Australia and it would be prudent to keep it this way.
How should I treat canola for ryegrass infestations?
The most appropriate method for controlling ryegrass in canola is incorporation by sowing, using a full dose of Edge 900. If you want to use a post-emergent/PSPE treatment for ryegrass, consider using (TT canola only) 1.1 kg/ha of atrazine (or similar) following a full dose of Imtrade Edge 900 up front.
To read our technical bulletin on Imtrade Edge 900 click here.