Spray topping bent grass to create opportunities

Published: 1998
Updated: September 2011

How do you start a renovation program on a bent grass dominated pasture? You may not have high stock numbers to utilise summer feed or enough quality autumn/winter feed to start rotational grazing. Or you may not have enough clover to justify applications of fertiliser as bent grass is relatively insensitive to applications of phosphate fertiliser. Spray topping of bent grass enables farmers to start managing bent grass better.

Objectives of Spray Topping

Spray topping stops the formation of seed heads, prevents maturity and forces the bent grass to remain in a nutritious vegetative growth stage. It also stops the development of rank, unpalatable growth and reduces the amount of carry-over dry feed which follows a wet summer. Stock will lose condition if forced to graze dead carry-over trash in mid-winter, so control of bent grass in late spring and summer is very important.

The technique of spray topping involves applying low rates of glyphosate, (as instructed for pasture topping or seed-head suppression on the agricultural chemical product label), in early November. This needs to be completed before any seed heads have emerged. Do not use a wetter in combination with the glyphosate if there is a significant component of improved species, as it reduces the amount of feed on offer. Be sure to observe any relevant withholding periods when using agricultural chemicals.

Spray topping stops bent grass seed head emergence. On the left the bent grass has been allowed to go to head. On the right the bent grass was spray topped in early November.

How often should you spray top?

Spray topping enables you to initiate fertiliser and management programs which should keep bent grass under control for a number of years. It may be 5 to 7 years before the next excessively wet summer leads to a problem requiring further manipulation of bent grass.

Sheep preferentially grazing spray topped sections of a paddock 12 months after spraying.

Effects of Spray Topping

Short term

If there is very little rain in November 4 to 6 weeks after application, the pasture will yellow off and palatability and feed quality will be reduced. If good November/December rains fall, there will be very little yellowing and palatability will be increased.

Medium term

If there is insufficient rain during December/January to stimulate new green growth, spray topped paddocks will have less dry feed than unsprayed paddocks and there will be no nutritional benefit to be gained from the technique. The need for hand-feeding may be increased but it is likely that the bent grass will be thinned out, allowing clover and other desirable species to germinate.

However, if normal summer rains fall, the spray topped bent grass will not form seed heads and will produce new palatable and nutritious green leaf. Animal condition will increase on spray topped bent grass. They will utilise the feed better, recycle nutrients and leave the ground relatively bare by the autumn break. Unsprayed bent grass, if under-grazed, will develop seed heads by mid-January and become rank, stalky and unpalatable and animals may lose condition.

Long term

Spray topping allows farmers to break the dominance of bent grass. Over average to wet summers, spray topped bent grass will provide valuable feed. Over dry summers, the bent grass is likely to be thinned out which will leave significant areas of bare ground. Irrespective of the amount of summer rainfall, spray topping creates an opportunity for farmers to fertilise the clover which should germinate. This in turn builds up soil fertility and eventually allows for a knockdown spray and direct drilling of new pasture if there is an early break. Although re-sowing may not always be economically justified, at least there is an opportunity to start managing the pasture. This will ensure that the bent grass does not regain total dominance of the pasture.

Very dry summers, or spray topping, can create opportunities for good fertiliser responses. Heavy rotational grazing and altering seasonal stocking pressure (Refer to: "Grazing management tools to control bent grass"), may enable you to stay on top of the next summer's excess growth and provide a starting point for a whole farm pasture management program (Refer to: "Developing a bent grass control program"). It is important to remember that spray topping creates an opportunity but it is no more than a starting point.

Acknowledgements

This Information Note was developed by Neil James and Reg Hill in 1998. It was reviewed by Neil James and Samantha Clayfield in September 2011.