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Author:
D.C. Cloutier Introduction
Weeds are plants that are considered undesirable in a crop at a given time.
Weeds are harmful for a number of reasons. They reduce crop yields,
interfere with the harvest, support pathogens and insect pests and
contaminate seeds.
Weed control is as old as farming itself. However, progress in mechanized
weed management did not begin until the early eighteenth century, when
Jethro Tull invented a seed planter for row crops, which allowed weeds
between the rows to be killed by cultivation.
Physical control was the main method used against weeds until herbicides
appeared in the mid-twentieth century (Wicks et al. 1995). Mechanical weed
control is a proven technique and kept fields free of weeds long before the
advent of herbicides. This technique has experienced somewhat of a rebirth
in the last few years. The objective of this chapter is to present the
principles behind mechanical weeding and to give some examples to illustrate
them.
Before the advent of herbicides, mechanical methods of weed control were
used successfully for several centuries. Cultivator technology continued to
evolve even after the development of herbicides, and these implements are
efficient and versatile. In some cases, they are the only weed control tools
available and they are often a cost-effective alternative to herbicides.
Cultivators are agricultural implements that require careful adjustment to
ensure optimal performance. To kill a maximum number of weeds, cultivators
should be operated as close to crop rows as possible without injuring the
crop. The effective use of cultivators requires a fair amount of experience
and careful observation, which may explain why research teams arrive at
widely varying conclusions in similar situations.
The effectiveness of cultivation is directly influenced by cultivation depth
and degree of soil moisture. Cultivation that is too shallow may spare weeds
and cultivation that is too deep increases the risk of crop damage. Working
depth can be adjusted by means of wheels attached to the frame or the
three-point hitch. The use of weights and reduction of tractor speed can
also increase the operating depth. Cultivating when the soil is too wet
leads to clod formation and may not destroy weeds. The optimal level of soil
moisture depends on the cultivator type, with rotary hoes and harrows being
best suited to moist soils.
In general, two types of cultivators are required for effective weed
control: one at pre-emergence or early post-emergence and a second later in
the season. The vulnerability of crops to damage depends on their growth
stage. For example, legumes are most vulnerable at the hook stage, when
cultivation can reduce yield. In Quebec, two to seven cultivations are
usually carried out, depending on the crop and the degree of weed
infestation. Tractor speeds range from 3 km/h to 20 km/h depending on the
cultivator type and the growth stage of the crop.
Cultivation is not only effective in controlling weeds; it also benefits the
crop by breaking up the surface crust, aerating the soil, stimulating the
activity of soil microflora, reducing the evaporation of soil moisture and
facilitating the infiltration of rainwater.
Cultivator selection is only one component of an effective weed control
program. Technical mastery of the cultivator is critical, as is weeding at
the appropriate growth stage of the weeds and the crop. Delaying treatment
for a few days may significantly reduce the effectiveness of a cultivation
operation. The timing of treatment is probably more critical in successful
weed control than the choice of cultivator.
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