Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 176

and the amount of soil movement.Depending on the setting of the gangs,soil
flow is strictly toward or away from the row. Rolling cultivators dig out large
weeds less effectively than shovel-type cultivators, but they work the surface
soil more thoroughly.Because soil flow is strictly in one direction,and because
the gangs can be tilted to work very shallowly next to the crop row,rolling cul-
tivators can safely cultivate closer to the crop than can shovel cultivators. Mt.
Pleasant, Burt & Frisch (1994) found higher weed cover in maize following
rolling cultivation than following shovel cultivation. Mohler, Frisch & Mt.
Pleasant (1997) found that the relative effectiveness of a shovel cultivator and
a rolling cultivator equipped with inter-row sweeps varied between years.
Rotary tillers for cultivation consist of gangs of power-take-off driven
rotating curved or L-shaped tines that chop up weeds and mix them into the
soil. They are the best tools currently available for strip tillage in cover crops
and living mulches prior to planting. Their principal advantages in cultiva-
tion are that they completely incorporate all above-ground weed tissues, and
probably chop roots and rhizomes to smaller fragments than other imple-
ments.Nevertheless,they can cause deterioration of soil structure by excessive
pulverization.
Near-row tools: vegetable knives,disk hillers,spyders,basket
weeders,and brush weeders
Several tools have been invented to cultivate 5 to 12 cm from the crop.
To avoid root damage, typical working depth for near-row tools is shallow: 2
to 5 cm. Furthermore, when working close to the crop, soil must flow either
parallel with,or away from,the row to avoid burying small crop plants.Basket
weeders and brush weeders can work closer to the row than disk hillers and
spyders because their rotation is parallel to the row and thus the leading edge
is no closer to the row than is the point of contact with the soil.
Vegetable knives (beet knives) are L-shaped knives with a low pitch so that
soil movement is minimal. For early cultivations, the vertical portion of the
knife is run close to the row and the tip points toward the inter-row. At later
cultivations, the tip is reversed so that the surface soil can be cultivated under
the crop canopy.
Disk hillers and spyders are optional equipment on shovel and rolling cul-
tivators.They mount in the front-most position, next to the row.Early in crop
growth they are set to cut soil and weeds away from the row; later they may be
used to hill up soil around the base of the crop. Disks are sharp, aggressive
tools that can dig out large annual weeds and cut the stems of rank perennials.
They also perform well in heavy crop residue. Spyders are star-shaped wheels
(Figure 4.12) that dig rather than cut the soil. They are smaller diameter (32