Comparison of Herbicide Costs
vs. Effectiveness
The following information is a summary of a presentation
given by Wayne Mitchem, North Carolina State University,
at the Winter Apple School
Differences in the degree of control exist
among various preemergence (PRE) herbicides or
combinations of preemergence herbicides. Generally,
tank mixing preemergence herbicides will provide a
broader range of weed and grass control than can be
expected from the use of a single material. Proper timing
of applications can extend the period of control
into late summer.
Application Timing
In established orchards, we recommend a delayed
PRE application program. This program consists
of a late winter application of a non-selective herbicide
(usually glyphosate). An application of glyphosate
alone in late winter controls winter annual weeds,
maintaining a clean herbicide strip until summer annual
weeds emerge in early to mid May. When summer
annual weeds are 2 to 4 inches tall, a tank mix of
glyphosate or paraquat with a PRE herbicide (or combination
of two PRE herbicides) should be applied.
Delaying PRE herbicide application until May will extend
residual weed control into the summer.
Cost vs. Effectiveness
In thinking about costs associated with weed control in an orchard, you should consider more than just the cost of the herbicide(s). The level of weed control must be assessed as well. Use of a single PRE herbicide may be more expensive than one might expect. Research has shown that tank mixing PRE herbicides improves residual weed control, therefore differences in PRE herbicide performance is a consideration that
cannot be overlooked.
Economic figures from Washington State (1999) placed the costs associated with applying an herbicide at $16 per acre of orchard floor. Even when using a delayed PRE program where a single herbicide is used, at least one postemergent herbicide application will be needed by mid-summer in most years. Adding the cost of the postemergent herbicide and the cost
of application may give a total cost equal to or greater than where two or more preemergent herbicides were tank mixed for the delayed PRE application.
Some growers rely entirely on postemergent herbicides and may use several applications over the growing season to achieve weed and grass control. When the application costs are factored in with the herbicide costs, the results are apt to be much higher than using a tank mix at a delayed PRE timing.
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Institute
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