Weed control strategies best designed to focus on realistic outcome

Weed control strategies are, therefore best designed to focus on realistic outcomes and require careful assessment and planning to avoid wasted resources.

Some potentially damaging weeds, if detected early, can be eliminated before they become a major problem.

However, if they have already spread extensively across a farm, total elimination can be unrealistic, but containment to manageable levels may be more feasible.

Weeds like blue heliotrope commonly fall into this category, as well as ones like galvanised burr, St Johns wart, and African lovegrass.

Many weeds, like saffron thistle and fleabane, are very much seasonal related.

They tend to be always present to some extent, bad periodically, and in some seasons, hardly ever noticed.

A common option for such weeds is to address the problem in seasons that they are bad, but don't worry too much in years with relatively low levels.

Bio-control of some weeds can be effective to the extent that control via other methods, such as herbicides, can be scaled back.

For example, about seven years ago, we became increasingly concerned about Paterson's curse.

However, several biological agents released have proven effective in its control.

These include root weevil (Mogulones geographicus), leaf-mining moth (Dialectica scalariella) and crown weevil (Mogulones larvatus).

Biological control combined with competitive pastures has negated the need for other control options, including not needing to use herbicides.

Read more: Boost to pasture legume seed supplies following bumper harvest

A number of almost impossible to eradicate perennial weeds once they get away, like blue heliotrope, warrant a strong effort to eliminate them if detected before they gain a hold.

Blue heliotrope, a perennial creeping weed, easily introduced via water movement, wildlife, humans, implements and purchased animals, periodically has infested our property.

If away from trees and streams, spotting small outbreaks with residual herbicide tebuthiuron (200g/kg ) via pellets has proved effective.

On arable country with dense blue heliotrope, cleaning up via cropping has been successful. Weeds are killed via repeated glyphosate treatments over the summer fallow.

Winter crops are sown for three years and then sown down to tropical grass pasture.

Strong pastures help outcompete weeds returning via residual seeds.

Weeds like African lovegrass can be handled in a similar manner to blue heliotrope via appropriate spot herbicide or cropping where weed levels are too extensive.

In non-arable situations, a good approach can be to ensure the pasture is well managed via the inclusion of appropriate legumes, good grazing management (not extended set stocking) and inclusion of urea-based licks in extended dry periods, at least for cattle.

Weeds like capeweed and St Barnaby's thistle can be worth considering for elimination if levels are yet to become extensive.

Like many weeds, when they get a hold on the property, it is impossible to eliminate them, and the sensible strategy is to learn to live with them.

For about six years, we have endeavoured to eliminate relatively small but scattered infestations of both these weeds.

Paddock surveillance, via up and down paddocks on four-wheel bikes during flowering, when most of these weeds are visible, has worked well.

We still pick up a few weeds each year but feel we are on top of them with close to complete elimination.

For most pasture weeds, the better the pasture, the more weeds are outcompeted and the less their bulk and seed set.

Better pastures generally are a combination of species type, soil fertility and grazing management. African lovegrass is an example of good competition helping to reduce its impact.

Plus, a pasture with a strong legume content helps ensure the weed's nutrition and palatability are as high as possible, increasing its utilisation and reducing its smothering of valuable plants.

On arable country, cropping is also an important option for weed reduction.

Next week: Pastures with the best waterlogging tolerance.