Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 190

maize and soybean growers in the midwestern USA consists of two to three
rotary hoeings followed by two cultivations with sweeps or shovels. It is well
adapted to both ridge tilled and flat tilled fields (Thompson & Thompson,
1984; Gunsolus, 1990; Mulder & Doll, 1993). In this system the rotary hoe
reduces weed density and delays establishment of the weeds relative to the
crop. At the first inter-row cultivation, the crop is usually protected from
burial by shields. As the crop develops, large amounts of soil are thrown
around the plant bases to bury weeds. The machines used are simple, robust,
and pulled at high speeds, allowing rapid cultivation of large fields.Although
the weed control is not as complete as that achieved by more sophisticated
devices, this poses few problems in highly competitive crops.
Mechanical weed control programs without herbicides in high-value vege-
table crops vary greatly in detail, but many share common elements
(Grubinger & Else, 1996; Bowman, 1997, pp. 67-86). A false or stale seedbed
procedure is often used to reduce initial weed density. Harrowing of large-
seeded crops or flaming of small-seeded crops then further reduces weed
density prior to crop emergence.After the crop is up, the emphasis is often on
frequent cultivation close to the crop row using a basket weeder, brush
weeder, or vegetable knives. Inter-rows may be cultivated with shovels after
the crop is large. The value of the crop usually makes hand roguing of weeds
in the crop row economically viable. Consequently, few weeds set seed, and
this facilitates weed management and minimizes the cost of hand-weeding in
subsequent years.
Each grower needs to find the right mix of implements to meet the particu-
lar situations presented by the soils, climate, and crops grown on the farm.
Multiple implements usually are required to meet the diversity of regularly
encountered weeding tasks; additional machines may be useful in unusual
circumstances.
Comparison of chemical and mechanical weed
management
Only a few studies have compared current herbicide programs with
modern cultivation programs that include full-field and in-row implements.
VanGessel et al . (1995 b ) examined various combinations of rotary hoeing,
alachlor, in-row cultivation, and a post-emergence herbicide chosen by a deci-
sion aid. One rotary hoeing plus in-row cultivation resulted in weed control
and yields similar to alachlor plus post-emergence herbicide. Schweizer,
Westra & Lybecker (1994) similarly concluded that in-row cultivation could
successfully control weeds in maize. Mohler, Frisch & Mt. Pleasant (1997)