Integrated Weed Management - What Needs to be Done?

Now is the time in the season for the assessment of the effectiveness of weed control programs to be undertaken. Observing paddocks prior to and during harvest for residual weed populations, weed “escapes” and unknown weed populations, can provide valuable insight into the success of weed management strategies. All too often though, this highlights the need to implement diversified control strategies to effectively manage weeds. Integrated Weed Management (IWM) is not an easy management philosophy, but when successfully implemented can reduce weed numbers long term, reduce the risk of creating unmanageable weed populations, plus maintain crop productivity into the future.

For an understanding of some of the aspects associated with IWM, three of the key objectives are outlined below:

1.  Reduce weed density

The greater the number of weeds, the larger the impact on productivity which can be measured directly in yield loss or through increased input costs. Understanding the various chemical and non-chemical weed management techniques that are available, plus the effectiveness of each, is important when selecting the most appropriate strategy to implement.

Pre-sowing weed control is critical and delaying sowing to allow weeds to germinate before sowing should be considered. Encouraging crops to be competitive with weeds by utilizing higher seeding rates and narrow row spacings, are simple techniques which reduce weed numbers, improve herbicide efficacy and reduce reliance on chemical control alone.

Complete control may not always be an option, so management of weed numbers needs to be considered. Simple operations to control low density or isolated weed populations, such as spraying or cutting out patches in paddocks, can prevent long term problems developing.

2.  Manage herbicide resistance

It is highly unlikely that a new “silver bullet” herbicide will be available in the near future, to solve the increasing herbicide resistance problem. IWM allows for the effective life span of current herbicides to be extended – meaning herbicides are still available to use. Rotation of chemical groups is an important part of an IWM strategy, but must not be the entire strategy.

Management techniques such as fallowing, brown or green manuring, crop topping, a pasture phase (winter cleaning, hay etc) or stubble burning, all need to be included in the strategy to break the weed reproduction cycle. Allowing herbicide resistant weeds to germinate and grow, but not set seed and reproduce the resistant genetics, is an important strategy for reducing herbicide resistant weeds.

3.  Deplete the weed seed bank

Weed seeds in the soil can be depleted over time to very low levels, but levels can increase quickly when replenished by new seeds from surviving plants. Preventing seed set of isolated weed populations in crop, minimising incursions of weeds from paddock edges, general farm hygiene and avoiding the introduction of weed seeds from off-farm in grain, hay or machinery, are all important components of a successful IWM program. Windrow burning or destruction of weed contaminated header chaff should also be considered.

Weed seed management is a numbers game – the aim is always to reduce the number of seeds entering the seed bank that will require future control.

Weed control can no longer rely on a small number of control techniques. Effective Integrated Weed Management focuses on planning, optimum application timing, plus use of multiple control techniques and monitoring. This will allow sustainable crop production into the future.