Pre-emergent herbicides are a useful tool for combating weeds and depending on the application rate, can control weeds for up to six months.
They are generally applied before the spring break—before weeds start germinating.
Pre-emergent herbicides are useful for newly worked ground or areas where weed pressure is high.
Selecting the appropriate pre-emergent herbicide to control the weed spectrum present in an orchard can reduce the need to apply multiple herbicides during the year.
Soil preparation
Pre-emergent herbicides need to be applied to bare ground with little or no organic matter.
Pre-emergent herbicides are only effective on germinating seeds within the soil profile and can be applied with a knockdown herbicide if weeds are already present.
Resistance management
For hard to control weeds, tank mixing more than one pre-emergent herbicide can help increase the weed spectrum controlled.
Remember to rotate herbicides and use products from different chemical groups to reduce the risk of resistance and selection of problem weeds in the orchard (see Table 1).
Soil activation
Rain or irrigation is needed to incorporate the herbicide into the soil.
This helps avoid the adverse impact of UV light breaking down the herbicide and thereby reducing the herbicide’s efficacy. Incorporating the herbicide into the soil also ensures it comes into contact with any germinating seeds.
Choosing a product
Things to consider when choosing a pre-emergent product are: tree age, weed spectrum, soil type and crop registration.
There are a number of pre-emergent herbicides available (see Table 1) and they all have strengths and weaknesses with respect to the weed spectrum they control.
For more information on addressing your weed control requirements consult your technical expert.
To see Table 1 and for more information, download the August 2012 issue of Tree Fruit.
