Using bipyridyls as part of your resistance strategy
It appears last month’s column on prolonging glyphosate use in vineyards generated a fair bit of discussion. Many properties are now entering the critical timeline modelled by researchers Paul Neve and Art Diggle, who predicted that after 12 to 15 years of continuous glyphosate use, the probability of resistance would begin to increase.
It led to enquiries on herbicide ‘double-knock’ and also the best use of GRAMOXONE® 360 PRO and SPRAY.SEED® under vines. Both are non-selective contact bipyridyl herbicides that belong to the herbicide Group L. Where each one should be used really depends on the weed spectrum. GRAMOXONE 360 PRO is better suited to areas where annual grasses are more prevalent. SPRAY.SEED, which is a mix of the paraquat in GRAMOXONE 360 PRO and diquat, should be used where more annual broadleaf weeds are present - for example capeweed or erodium species.
Being contact herbicides, water volumes and spray coverage are very important with these products. Calibrated sprayers with flat fan jets, adjusted to a height that gives a double overlap of the spray at the top of the weeds, are ideal. Spraying pressures should be in the range of 200 to 300 kPa. Select nozzles that give droplets in the 200 to 250m volume median diameter range at these pressures. Speed of travel should be in the range of 6 to 10 km/hr. Good weed coverage while spraying is essential, so adjust the water volume according to density of weed growth.
Interesting results are being seen in broadacre areas where they are noticing improved results when these contact herbicides are applied in lower light conditions, such as just before nightfall. The bipyridyls quickly destroy green plant tissue on contact and the speed of the cell destruction is largely influenced by the intensity of light; the higher the light intensity the faster the reaction.
Spraying at dusk does two things; it slows the speed of cell damage and often also extends the drying time of the droplet on the leaf. Longer drying time allows the active ingredient more time to absorb into the leaf. A slower speed of cell damage can enable the active to move more within the leaf. Paraquat has the ability to move down and away from the site of application and while this translocated movement may be small, it can be very important. So spray at the end of the day if you can. It may increase your control over the weeds, for example from five days to six or seven, and the final results will often be better.
Bipyridyl’s bind strongly to clay particles in the soil. That’s an agronomic strength because they are deactivated as soon as they contact clay in the soil and provide no residual activity. However, they can also bind to clay particles suspended in the spray solution and this will reduce efficacy. If you can see dirt in your spray water, chances are it will negatively impact on the spray result.
Finally, if the intent is to use a ‘double-knock’ as a resistance strategy, both herbicides should be applied at the registered rate to effectively control weeds. Apply glyphosate or SPRAY.SEED first, then wait around seven days before applying the second application of SPRAY.SEED. To ensure a really robust eradication of some difficult to control weeds, such as marshmallow, stinging nettle or erodium, the addition of a Group G herbicide spike mixed with SPRAY.SEED is very effective.
For more information contact:
Solutions Development Lead
E: [email protected]
M: 0429 133 436