Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 142

Table 4.1. Effectiveness of tillage implements for uprooting, dismemberment, and
burial of weeds

Implement Uprooting Dismemberment Burial

Moldboard plow Good Poor Good

Chisel plow Moderate Poor Moderate

Field cultivator Moderate to good a Moderate Moderate

Sweep plow Poor Moderate b Poor

Disks Moderate Good Moderate

Rotary tiller Moderate Good Moderate

Notes:
a Depending on depth ofoperation relative to weed roots.
b Especially good at severing shoots from roots,but poor at fragmenting plants.

the soil surface: the shallowly angled sweeps of a sweep plow tend to sever
roots and loosen the soil above with little mixing relative to the more steeply
angled and closer spaced blades of most field cultivators. Finally, disks and
rotary tillers chop up weeds and crop residue, and mix them into the soil
profile to the depth of penetration.Disks tend to cut the weeds whereas rotary
tillers tear, but the effect on the plants is often similar. Because both mold-
board and chisel plows leave large clods and intact weeds, operations with
these implements are generally followed by use of disks, harrows, or some
other implement to further chop and mix the surface soil prior to planting.
Consequently,tillage usually subjects weeds to a variety of destructive actions.
Depending on the implement, tillage thus chops, uproots, or buries estab-
lished weeds. Usually tillage occurs early enough in the life cycle of annual
plants to be fatal to essentially all individuals, regardless of the method
employed, though young grasses sometimes survive noninversion tillage
(Moss, 1985 a ; Cavers & Kane, 1990). Although many studies have noted an
increase in perennial weed species with reduced tillage (Jones,1966; Pollard &
Cussans, 1976; Froud-Williams, Drennan & Chancellor, 1983; Koskinen &
McWhorter, 1986; Conn, 1987; Buhler et al ., 1994), surprisingly little research
has related the mechanical action of implements to damage inflicted on the
weeds. For example, it would be useful to know how different implements
affect the size distribution of Elytrigia repens rhizome fragments, the vertical
depth distribution of Cyperus spp. tubers, or the percentage of damaged buds
on Taraxacum officinale taproots.
Consideration of differences in growth habit among perennial weed
species allows some prediction as to the type of tillage most likely to be effec-
tive (Table 4.2). Here the basic types of weeds discussed in Chapter 2 are