Key points

There are several factors that can influence how well a spray application is going to work. Some of these include the:

• characteristics of the target (growth stage, stress, genetic traits);

• environmental conditions before, during and after spraying;

• choice of product (mode of action and formulation);

• rate of product used;

• application volume, sprayer set-up and spray quality;

• water quality and adjuvant selection; and

• choice of tank mix partners.

If just one of these factors is less than ideal you can end up with a poor result. When several of these factors are less than ideal the outcome may be a spray failure.

In paddocks with emerging herbicide resistance, these factors are often magnified. Where a particular antagonistic mixture; wrong choice of adjuvant; poor spray set up; or compromised environmental conditions may have been possible to be managed with susceptible weeds (commonly by a modest increase in application rate), this same situation often 'fails' when in the presence of emerging herbicide resistance.

It is important that all applicators have an understanding of how each of these factors can affect – either alone or in conjunction with each other – the outcome of the spray job.