Spray topping – the importance of chemical selection and timing

Spray topping in pastures is an economical tool which can not only utilize and improve the feed value of pasture but decrease seed set in cropping paddock the following year.

The benefits  of correct chemical selection and application timing include:

  • Less disease carry over into next years crop – particularly cereals
  • Better control on resistant rye grass
  • Less pressure on residual type chemicals such as trifluralin, atrazine, sakura
  • Better utilization of nutrition
  • Better utilization of moisture
  • Higher cropping yields

Timing of application is influenced by target grasses

The 4 main grasses of concern include barley, brome, silver and rye grass. Timing of head emergence from flag leaf will differ according to variety, weather conditions and stocking rate.  As a rule of thumb the order of maturity is barley grass followed by silver, brome and rye last.  This applies where there is low stocking rate and/or there is still plenty of moisture in the ground while the plant is setting seed.  Whereas, when there is little moisture available as the grasses come up to head emergence, or a high stocking level is maintained and plants are kept under constant pressure before setting seed, timing of head emergence is much more even.

This method of management with livestock goes a long way to maximising the effect of spraying glyphosate or paraquat with one application.

Guidelines for chemical selection and application

  • Abundant grass of mixed varieties- barley and silver fully emerged, brome and rye half emergence from flag leaf:  1.5 L/Ha glyphosate 450g/L plus 0.2% wetter plus 1% ammonium sulphate.
  • All grasses full head emergence from flag leaf, rye and broome grass seed soft milky dough:  same rate of glyphosate or 1 L/Ha paraquat plus 0.2% wetter with high water rate (70-100/litres / hectare). Silver and barley grass will more than likely be too advanced for seed sterilisation especially with glyphosate.  Providing the brome and rye grass seed is no further advanced than soft milky dough you will find the application about 80% effective. Using paraquat it is all about chemical contact, making it beneficial to use the high water rate and with early morning application. Having a little dew on the plants will also go a long way to improving the contact and effectiveness of paraquat. If you have to spray in warm time of day (temperature >19°C) use 1% oil instead of wetter.
  • Where you have been able to maintain high stocking rate and most seed heads  have emerged, destock so plants can freshen up for a couple of days and then spray with glyphosate at same rate.  You can use paraquat but will have to wait until most of plants have full head emergence for effective job.  Again with high water rate and early morning application.

The above is a broad spectrum recommendation.  Rye grass is the most important weed to target as it is a prolific seed setter and historically enemy number one for crop.  If in the case you are going back into pasture the following year and only want to target the awned seeds such as barley or brome grass then paraquat is the only product to use. It is softer on clover and more effective on geranium.  Timing is again critical, plus the rate should come back to 500ml/Ha of paraquat plus wetter.

For expert advice specific to your needs contact Kojonup Agricultural supplies on 9831 1022.

Call Kojonup Agricultural Supplies.

We provide rural supplies, farm and agricultural services and products to clients in Kojonup, Arthur River, Wagin, Katanning, Tambellup, Cranbrook, Frankland, Boyup Brook, Darkan, Gnowangerup, Williams, Mount Barker, Broomehill, Woodanilling and their surrounding communities.