|
The goal of blind cultivation is to remove
the initial flushes of weeds when they are very small and
most sensitive to disturbance. Blind cultivation takes advantage
of the difference in size and sprouting depth between crop
and weed seeds. Most weed seeds are smaller than crop seeds,
and they germinate shallower in the soil. Annual weeds are
most sensitive to disturbance from after germination to emergence.
At these early stages, breaking contact between the tiny roots
and the soil will kill most weed seedlings.
Blind cultivation works best when the soil is loose and in
good physical condition and the crop is actively growing.
By stirring and shaking the top inch of soil, early season
weeding or blind cultivation creates a loose dry layer of
soil that is too dry and airy for weed seeds to germinate
or grow in. This layer also serves as a dry mulch that conserves
soil moisture. The crop seeds are safely below this layer
and are not hurt by a shallow weeding before emergence.
Field preparation stimulates many weed seeds to germinate.
These annual weed seeds quickly sprout and emerge before or
with the crop. At this point, a rapid and brutal race ensues
which will quickly determine which type of plant will have
dominance in the field. We must work decisively to give our
intended crop the advantage and to reduce the competition.
If our blind cultivation eliminates most of the first flush
of tiny weeds, the crop will rapidly begin to suppress subsequent
germinating weed seeds. Therefore, our goal in blind cultivation
is to give the crop the greatest possible initial size advantage
over the weeds before we come in with the row cultivator.
If we can establish a favorable crop/weed size differential,
the crop will then achieve dominance and we will then be almost
assured a clean crop, or at least one where row cultivation
will be much easier, faster, and more effective.
We have a short window of about two to three days, depending
on weed species, when the first flush of germinating weeds
are at their most susceptible. This window starts the day
you can see the white hair roots when you scratch the soil
surface with a stick or knife and continues until about a
day after the weeds have emerged, depending on the weather.
At this point you don’t see any weeds from a truck window
or tractor seat, but if you kneel down on the ground, there
is a light reddish-green haze over the soil. Sometimes you
can just see tiny weeds growing in soil cracks.
The success of the first blind cultivation is extremely important
because it must give the crop an initial head start. The intention,
of course, is to remove the weeds without harming the crop.
The first pass usually takes place just before the crop emerges.
At that stage the crop is able to survive a fairly aggressive
weeding and weeds are usually small enough to be easily destroyed.
Crop susceptibility to weeder damage is very low until the
tip of the plant shoot is near the soil surface. The potential
for crop damage rises rapidly as the crop emerges and until
after the first leaves extend.
The crop can suffer some of the same types of damage by the
weeders as the weeds do, and because of that, we have to be
aware of what the weeders are doing. If the crop has emerged
but is too small, it can be buried too deeply to re-emerge
and may be suffocated. The crop can also be broken or plucked
out. Soybean hypocotyls, for instance, are very fragile in
the crook stage. If the weather is cool during this time,
they are much more brittle. Usually the crop and the weed
points of greatest susceptibility don’t coincide. However,
sometimes when our timing is less than ideal, it is important
to assess how much crop damage is occurring and to get a sense
for how much damage can be tolerated.
If we do the first pass too early, the crop may need a second
weeding before the crop is large enough to withstand the action
of the weeder; too late, and the weeds will be already resistant
to the weeders, and/or the crop may be at a stage where it
is too sensitive to survive an effective aggressive weeding.
It is always best if we can hit this ‘sweet spot’,
with the crop, weeds, weather and equipment at the ideal point
for control!
The timing of the second blind cultivation is critical to
eliminate the ‘second flush’ of weeds that emerged
after the first weeding. The second pass must occur before
weeds are big enough to become tolerant to the weeder action.
We try to wait until the crop is as large as possible so the
machine can be adjusted to a more aggressive setting, reaching
more of the weeds. This is often a rather delicate balance,
tempered by weather and labor. But when we can hit the second
weeding right, the crop is off to a good start and we have
several weeks of a breather before we have to come in to row-cultivate.
We need to have the tools available that can take out the
weeds without doing excessive damage to the crop in all the
different situations that we may have to deal with. This is
why, on our farm, we have several different blind cultivation
tools with varying configurations. This isn’t an exact
science, and there are some days when we switch between two
or three tools before we are satisfied that we have chosen
the best one for the conditions.
An experienced operator with a clear understanding of his
soil, the weeds species, the crop stage, and the influence
of the weather can do a great job with less-than-ideal equipment.
The fanciest or most expensive equipment will not ensure good
weed control. Instead, success is determined by the skill
of observation and the agility to make the right decisions
at the right time. When the relative stages of the crops and
the weeds don’t occur as we want, or when the weather
prevents weeding at the right time, having the right equipment
and the skills and experience to make the right adjustments
can help make the difference between success and a weedy field.
There are a number of tools used for blind cultivation. They
fall into two main categories – the various types of
harrows and the rotary hoe.
Tine weeders
Tine weeders, or flexible harrows, are the most widely used
tools for blind cultivation. Examples of tine weeders are
the Kovar coil tine harrow, the Einboeck tine weeder and the
Lely finger weeder. The action of a tine weeder is determined
by tine shape, tine size, tine spacing, tine length, type
of toolbar, and the suspension of the units. Tine weeders
are effective in a wide range of crops and conditions. They
perform well in stony soil and can pass over moderately large
stones without being damaged. The variety of available tines
and adjustments make doing a good job of weeding possible
under difficult soil conditions and when weather prevents
proper timing of operations.
Most tine harrows are either drawn by a toolbar and suspended
from chains or attached to ‘U’ shaped pieces,
or “wishbones”, that can self-level laterally
and be leveled from front to rear with a hydraulic top link
that tips the toolbar back and forth.
 |
|
It is important to operate tine weeders so that all the tines
penetrate equally and the units are level. In the more rigidly
mounted models, this can be accomplished by adjusting the
length of the top link until all the tines are running evenly.
Using a hydraulically adjustable top link makes fine tuning
the weeders very easy. With the chain suspended models, this
adjustment is more difficult to achieve, especially in hard
or crusted soil. The front tines often have to work harder
than the others to break the soil. This tends to lift the
rear tines or to spring the front tines back farther than
the ones at the back of the implement. To compensate, we need
to raise the toolbar so that the front chains pull up at the
front of the unit, leveling it and forcing the rear teeth
deeper into the soil. This is much easier to do on three-point
hitch mounted machines than in trailing models. Adding a little
weight to the rear of the tine units may also help make them
run level.
If chain-mounted weeder units begin to hop, rock, or lunge
while weeding, the tines can’t move properly in the
soil. The springs may all bend back and then snap out of the
soil together causing the whole weeder unit to jump. This
action repeats in a cycle that makes the whole unit jump up
or twist around in a regular rhythm. When this happens, the
unit moves, instead of the teeth. Reducing speed usually stops
this erratic motion. The most common cause of this problem
is hard or crusted soil with too much speed for the conditions.
Sometimes units running in wheel tracks will jump while the
rest of the units are working fine. This is due to the compaction
in the wheel tracks. To address this problem, the operator
must slow down or use rigidly mounted weeder units.
Straight-tine weeders freely move forward,
backward, and side to side, producing a rotating action. They
move soil sideways and level the land by filling low spots
and knocking down ridges. This action covers weeds more than
it uproots them. Small seedlings are easily killed by this
tool, and even most large weeds are covered with soil. The
sideways movement of the tines can damage young soybean plants
by knocking off leaves and breaking stems and can also bury
small corn seedlings. Corn that is buried between emergence
and the 2 leaf stage can push back out of loose soil if rain
doesn’t come too soon after weeding. If it rains before
the buried corn seedlings push back out, they can be sealed
in the ground and die.
Some farmers operate weeders at an angle to the rows on the
first pass and then with the rows when they make the second
pass. The cross hatch pattern that results covers the field
very thoroughly. This approach works well in large wide fields
but is more difficult to use in long narrow strips.
It is important to check how much additional soil is pulled
over the rows, especially when weeding a field that is soft.
It is possible for the weeder to bury the yet-to-emerged crop
much deeper than it had originally been planted. With small
seeds or seed with low vigor, this could hurt the stand quite
severely. This can be especially true if a hard rain after
weeding causes crusting. If this happens, it is important
to weed the field again to break the crust and help the crop
emerge. A rotary hoe or bent-tine weeder may be better than
a straight-tine weeder for helping a crop emerge through a
crust. These tools are more gentle and tend to lift the soil
at the surface from over the buried seedlings rather than
pushing it across the top of them.
The straight-tine weeder is excellent on any large seeded
crop that has not yet emerged. It’s aggressive action
is very effective on weeds and does very little crop damage
when used pre-emergence. Once the crop has emerged, it becomes
much more vulnerable. Crops are softer and less likely to
break off in hot weather and, if possible, should be weeded
in the afternoon during the hottest part of the day. Corn
becomes more vulnerable to damage when the leaves begin to
unroll. Soybeans are most sensitive after emergence but while
still crooked.
In soft, loose, uncompacted soil, it is possible to operate
a weeder at a much higher ground speed than when the soil
is hard. The straight-tine weeder does not perform as well
in crusted or hard tight soil. In crusted soil, it helps to
add some weights to the back of the units to make them go
in better. John Saeli, an organic farmer in Geneva, New York,
has added a hitch to the back of his units so that they can
be turned around and pulled backward in hard soil. The tines
are worn on an angle from being pulled in the normal direction
so that the sharpened points cut through the crusted soil
quite effectively when pulled in reverse. A second pass immediately
after the first will often improve weed control in hard soil.
Driving at an angle to the rows may also help. Kreher Farms,
in Clarence, New York, has had good success in crusted soil
by row cultivating with a Danish tine cultivator first to
break the hard crust and following a day or so latter with
a weeder.
It is very important to weed early if a crust begins to form
to prevent it from becoming hard. Once a soil crusts, it must
be broken up as soon as possible to stop it from getting worse.
A crust will continue hardening and become thicker if it isn’t
broken up. It is important to get air back into a crusted
soil as quickly as possible.
In a wet season, it is better to bury weeds than to uproot
them. Seedlings re-root easily when they lay on top of damp
soil. Weeders with straight tines that level the field and
can move soil sideways will cover weeds more than uproot them.
Rain after a weeding is very likely to seal the surface enough
to prevent even shallowly buried weeds from coming back up.
When soil is hard or crusted, some extra weight on the back
of the weeder sections may help. Transferring some weight
from the toolbar to the units by changing to the newer self
leveling supports may help.
Forty-five degree bent-tine weeders are
very good for loosening tight or crusted soil. The 45°
tines are more effective at uprooting weeds than they are
for covering them. The longer tines are better able to follow
the surface of the soil so that they loosen the soil evenly.
These tines will give the same action in low spots that they
do in high spots. Because of this, there is much less soil
leveling in the action of these weeders than with the straight
tine units. The 45° teeth loosen soil uniformly but do
not move much soil sideways. For this reason, these tines
are usually less damaging to emerged soybeans than the straight
tines. They are less likely to bury small crops deeply but
more likely to pull plants out.
|
|
The angle of the tines on the 45° units is adjustable
from a very flat swept back orientation to an aggressive angle
where the teeth are pointed forward so that they pull themselves
in. These units will penetrate a hard soil much better than
straight tines, especially when the teeth are set into their
most aggressive position. We have found that the close spacing
and the stiffness of the tines on the Einboek machine can
be overly aggressive with some soils and crops, especially
when the weeders are equipped with the shorter (390mm), stiffer,
and larger-diameter tines. The Kovar machine has widely spaced,
long flexible tines (25-inch) that sometimes deflect sideways
away from ridges, leaving narrow strips on each side of the
rows unweeded. This has not been a problem as long as the
cultivator is adjusted properly, because the cultivator cleans
up these strips of missed weeds if they occur.
Eighty-five degree bent-tine weeders will
penetrate deeper than other weeders. An example of such a
weeder is the Lely finger weeder. The angle of the teeth,
rather than down pressure or the weight of the units, causes
the 85° teeth to pull into the soil. This type of tooth
can lift and break up a heavy crust despite the small light
teeth. These weeders are exceptionally well suited for tap-rooted
crops. The hooked tine goes in deep but does not pull out
soybeans, kidney beans or other crops with a straight tap
root. Instead, weeding seems to stimulate the crops’
growth.
While the 85° tine is very gentle on beans, it can do
serious damage to crops with branching root systems, such
as corn and small grains. Corn produces axillary roots that
branch off from the stem. The 85° bent tines will penetrate
deep enough in soft soil to get under the branched roots and
pull out the small corn seedlings. If an 85° tine weeder
is to be used in this type of crop, it must be watched carefully
and adjusted to stay above the branches of the crop roots.
The crop should be examined carefully for damage after going
a few yards, and the operator needs to be aware of areas in
the field with softer soil where the tines can go deeper to
be sure that the crop roots are not being damaged.
In warm, dry weather with good sun and/or wind, the newer
weeders with longer bent tines work better to uproot weeds,
lay them on top and dry them out. The 45° tooth works
well with corn and beans, while the 85° tooth weeders
are better on beans or other tap-root forming crops. The branching
roots of corn are damaged and pulled out by the aggressively
hooked teeth of the Lely type weeders, while the straight
tap roots of beans are unaffected.
The 85° tines primarily break the connection between
the soil and the weed roots. They are particularly effective
at uprooting weeds because they penetrate so deeply. They
are the most effective weeders for quackgrass because the
tines can pull up quack roots very efficiently. In fields
with a lot of quackgrass, these weeders may plug with roots
and so may need to be cleaned out by hand or sometimes by
shaking the weeder up and down by the lift arms. This should
be done outside of the field over a ditch or in a driveway
to insure that the roots can’t reestablish themselves.
This also prevents the tangled weed piles from plugging cultivators
later in the season.
Rotary hoes
Rotary hoes are best used from before weed emergence to very
early post emergence. Weeds must be very small or not yet
emerged for good control. It’s very important to keep
hoe tips in good repair as they lose their effectiveness quickly
with very little wear. “Hoe-bits” are replacement
tips that can be welded onto the worn tips; these actually
make the hoe more effective than it was originally. Rotary
hoes generally work by uprooting and desiccating (drying out)
tiny weed seedlings. They are very gentle on the crop and
can be used when more aggressive weeders cause too much crop
damage. Best results with a rotary hoe come right after a
light rain when the soil is just lightly crusted and breaks
apart easily into ‘chips’. It’s important
to maintain high speed when using a rotary hoe.
|
|
The height of the tool bar together with the strength of
the ‘down pressure springs’ on a rotary hoe determine
the ground pressure of the hoe wheels. This adjustment is
usually controlled by setting the position of the tractor
lift arms. In tight or crusted soil, it may be necessary to
add some weights to the tool bar to achieve enough down pressure
to do a good job. If the tractor has a quick hitch, this adds
enough weight to hold the tool bar in the right position under
most conditions. Rotary hoes generally need to be set to be
level with the ground. In extremely hard soil, extending the
top link to tip the machine back may increase the ground pressure
slightly, but this should only be done if none of the other
adjustments are sufficient to make the machine penetrate correctly.
Ground speed with a rotary hoe should usually be between
8 and 12 mph, and the hoe tips should penetrate deep enough
to go through any crust that has formed. In soft soil, the
hoe tips may penetrate as deep as 1.5 to 2 inches without
excessive harm to most crops. A very shallowly planted crop,
however, can be damaged by a rotary hoe that is set too deeply.
Some farmers have improved the weed control by adding a second
set of hoe wheels behind the first set so that the crop is
actually hoed twice with each pass, or by going over the field
twice.
Rotary hoes work primarily by uprooting weeds and/or by loosening
the soil from the tiny roots of the weed seedlings. Stony
soils can present a serious problem to rotary hoes. Large
stones can bend and damage the delicate parts of these machines.
Smaller stones, especially those 2- to 3-inches in diameter,
can get stuck between the hoe points, bending them or stopping
the wheels from rotating. If this happens directly over a
row and is not immediately detected, it can tear out a long
section of a row in a very short time.
Other harrows
Spike-tooth harrows have been used as weeders
for many years. They were probably the first tools to be used
by farmers as weeders.
German farmers used spike-tooth harrows extensively to control
weeds in small grains fields before the coming of herbicides.
American corn farmers throughout the United States used spike-tooth
harrows as weeders in the early part of the twentieth century.
George Washington Carver promoted their use widely in the
American South by taking some of the machines from town to
town to demonstrate how effective they were. Spike-tooth harrows
fell out of use around World War II with the advent of chemical
weed killers.
Spike-tooth harrows are very effective weeders. They can
both uproot and bury weeds. The angle of the spikes can usually
be adjusted with a handle from straight up and down to angled
back at a flat angle to the soil. Rocks are a big problem
with spike-tooth harrows. Rocks can easily get caught in the
harrow and take out a row of crop, or they can roll under
the harrow and lift the teeth out of the ground so that the
weeds aren’t controlled.
Spike-tooth harrows can sometimes be overly aggressive and
damage the crop especially in cool weather when plants are
brittle. Spike-tooth harrows work best on very hot afternoons
when the corn is soft and flexible. Tine weeders have largely
replaced spike-tooth harrows because they are effective and
have better crop safety.
Spring-tooth harrows are extremely aggressive,
but they are sometimes used for weeding. Because of their
potential to do crop damage, spring-tooth harrows are generally
only used in emergencies where the crop will otherwise be
lost. If a field is so infested with big, grassy weeds or
crusted so badly that no other tools can loosen it, a spring-tooth
harrow may be able to save it. This is a drastic measure but
it often works as a miracle rescue if done carefully.
A drag (springtooth harrow) with worn teeth set just as shallow
as possible while still having all the teeth in the soil should
be used. Often, the drag is drawn across the rows rather than
with them. The tractor needs to be run slowly, and the driver
should be prepared for a scary sight when they look back.
Corn treated like this often perks up and starts to grow rapidly
after being dragged. The stand loss from the dragging is usually
high. But in cases where nothing else will work, there is
really nothing to lose by trying this tool, because the stand
would be worthless anyway if nothing is done.
Chain-link harrows are more commonly used
on pastures, but they can do a good job of weeding. If plugging
is not a problem and no other tools are available, a chain-link
harrow can do a good job of controlling weeds before crop
emergence. A chain link harrow would not be a good choice
for post-emergence use because of crop damage. 
Part 3: In-row cultivation >>
|
