AgMemo Central Agricultural Region

Control weeds to optimise crop yields

DAFWA senior development officer Jeremy Lemon has warned landholders to control weeds using different strategies for different regions, following recent heavy downpours across the grainbelt.
Control weeds using different strategies for different regions, following recent heavy downpours across the grainbelt.

Landholders who received high rainfall in recent weeks are advised to manage weeds carefully to capture their crop potential this growing season.

Soil water probes and paddock inspections by the Department of Agriculture and Food, Western Australia (DAFWA) have revealed soil water profiles in many areas are as wet as they were during winter last year.

With wet soil and warm temperatures, weeds are expected to be a problem throughout the grainbelt.

The soil water bucket is full in many areas and that sub-soil moisture would help set grain growers up for a good start to the growing season – provided weeds are well managed.

Different weed control strategies will be required for different regions.

In low to medium rainfall areas, summer weeds will reduce soil water and mineralised nitrogen and reduce crop yield potential, if not controlled promptly.

Growers in higher rainfall areas with soils subject to waterlogging should consider leaving weeds to dry the soil, as large weeds can dry soil as effectively as a summer crop.

These paddocks can be left until a minimum of four weeks prior to seeding, before applying herbicide.

If specific weeds like melons will cause too much problem if left unchecked, consider selective weed control to leave less troublesome weeds to dry the soil.

Growers should be mindful that delayed control means weeds will be larger and harder to control and may support soil pests, such as root lesion nematodes.

The risk of winter waterlogging and the uncertainty of both autumn and winter rainfall make decisions about delaying weed control in high rainfall areas difficult.

Soil water simulations and research measurements show that sandy and loam soils will lose about 20-30 millimetres of moisture during a fallow period prior to sowing, if average rainfall prevails and less, if there is further rainfall before the break of the season.

Subsoil constraints would also influence soil water availability to the crop.

Soil water deeper than 30 centimetres is largely protected from evaporation loss.

Subsoil constraints, however, will prevent the effective use of this water, such as salinity, soil acidity and compaction.

Landholders should monitor their paddocks for weeds and the risk of crop pests and diseases, if leaving weeds to dry the soil.

More soil water management advice is available on the Summer Weeds page of the DAFWA website.

For more information contact Jeremy Lemon, Senior Development Officer, Albany on +61 (0)8 9892 8413.