Dear
Jeff,
Enjoy your posts at New Farm. I am looking into getting certified
organic, but one concern is that of velvet leaf in our corn.
I know the problem is related to some other problem in our
soil. Any suggestions?
Thanks,
Roger
Hi, Rodger,
Velvet leaf is not a big problem for me in corn; I do have
some spots where I see it but not too much. I tend to see
it more often in soybeans. It is a large-seeded weed that
germinates from deeper in the soil profile than most annual
weeds do, making it more of a challenge than other annuals.
The best result I’ve had is by rotating annual crops
with hay or forages and by hand-pulling the bad spots to prevent
seed from re-infesting the location. It’s one of those
weeds where depleting the seed bank is an issue. I’ve
copied others here at The Rodale Institute® with this
answer in the hopes that they may also have some comments
for you. I thank you for reading The New Farm® and my
brief articles and wish you the best with your transition
to organic.
If I can be of any help, email me again and I’ll do
my best.
Jeff
Rodger and All,
Paul Hepperly here, the research manager at The Institute.
Just had an additional thought to complement Jeff's comments:
Jeff is getting some real good results with no-till corn
and soybean on rolled-down rye and/or vetch. These systems
change the weed composition significantly.
For instance, we had a lot of ragweed in our no-till, and
in our tilled soybeans we had a lot of foxtail. Generally,
the ability of the mulch to control certain weeds in particular
and weeds in general is quite amazing.
You may want to experiment with a rye/vetch mixture as a
way of getting a good increase in soil nitrogen and stimulating
a weed control that requires less cultivation. We are pretty
encouraged at the progress in this area.
Sincerely,
Paul
Hi Roger,
Dave, here—one of the researchers at The Rodale Institute®.
I’d like to add some more detail to the discussion.
There are typically two types of weed control in organic systems:
preventive and reactive).
If the velvet leaf weed is already an established problem,
then the reactive measure Jeff mentioned is an appropriate
control (actively hand cutting areas where the weed infestation
in the field is the worse, to keep the plant from producing
new seed). This type of control is often overlooked because
it is labor intensive, but sometimes it is required. Cutting
weeds before they go to seed will greatly reduce future weed
problems.
Since velvet leaf is a summer annual, germinating in the spring,
a rotary hoeing regime and a spring tine weeder are initial
tools for mechanical weed control early on. Pre-plant tillage
will promote the annual weed seeds to germinate by exposing
dormant seeds to oxygen and sunlight. A pre-plant tillage
timed 1 to 2 weeks before planting reduces the weed pressure
by stimulating weed growth 1 to 2 weeks before planting and
then killing the weeds with a second tillage operation immediately
before planting the corn. Sometimes this pre-plant tillage
is referred to as "false seedbed" or "stale
seedbed tillage" Some use a rod weeder or light harrow
for this. A rotary hoe, chain harrow or finger weeder can
also be used effectively. If there is a lot of stubble in
the field, a disk can be used.
After the corn is planted, pre-emergent tillage (blind harrowing)
is done after the corn seed has sprouted but not yet emerged
from the soil. The field is harrowed to kill the weeds which
have already sprouted, then the corn will emerge soon afterwards.
This lets the corn gain a competitive edge on the next germinating
generation of weeds. This is effective on annual broadleaf
weeds like velvet leaf. The timing of this is usually 3 to
4 days after planting. Ideally, blind harrowing should be
done 24 hours before crop emergence. This works best on dry
loose soil. During a rainy spring weather spell it's not so
good.
The above methods get the weed seed close to the soil surface.
The weed seeds that germinate from deeper in the soil have
to be managed with inter-row cultivation. This will uproot
the small weeds and cut off the larger ones.
If a particular field has a widespread problem, it is probably
best to rotate that into a grass or clover hay. When considering
and planning your rotation for organic corn, weed seed bank
populations are dramatically reduced with rotations that have
a higher proportion of grass or clover in the rotation. Depending
on your farm rotation plan either a rotational pasture if
you have animals or a rotational hay crop worked into the
rotation will work. Rotations that have grass in them have
been shown to have a 68 percent reduction in the weed seed
bank. On the other hand, rotations that don't have grass in
them have a 59 percent increase in the weed seed bank.
So the planning of the grass/clover hay or pasture into a
rotation is one of the best preventive measures. Using perennial
phases in crop rotations combined with mowing or intensive
grazing to control perennials and to interrupt the life cycles
of annual weeds in cultivated crops is a strategy that helps
to maintain weed control in organic rotations. Also managing
the frequency that a particular crop is grown within a rotation
affects the population of certain weed species. Spread your
rotation out as much as possible.
If there is a particular field that has problems with any
weed, take it out of production, if you can afford to, and
put it into summer fallow. Then, perform frequent tined cultivations
during the hot summer months. This strategy can result in
desiccation of the weeds and reduction in the population and
seed bank. Summer tillage should be as shallow as possible
to avoid bringing new weed seeds to the surface. It may be
used to control perennials and some deep seeded later germinating
summer annuals. Tillage is most effective when the soil surface
is dry and the air temperature is high. Summer fallow is typically
considered a "last resort" method. Where soil erosion
is a high risk, tillage should be integrated with other methods
to protect the soil.
If you plan a small grain into the rotation, then inter-sowing
and under-sowing with clover in the cereals can also reduce
weed growth.
To expand on what Paul suggested: We’ve found a cover
crop/no-till scenario to be very effective for weed suppression.
In the no-till scenario, the cover crop growing in the field
that is then rolled and killed as a weed suppressing mat gives
early weed control.
Spring tillage can stimulate the germination of annual weed
seeds. With the organic no-till, since there is no disturbance
of the soil, many of the typical weeds that show up because
of spring tillage are not present. With the rye and hairy
vetch cover crops, we obtained early weed control in our no-till
corn for 16 days. After that time, the weed pressure from
in the slits in the cover crops where the corn was planted
became more pronounced. Fortunately, the early weed suppression
achieved by the mat of the rolled cover crop was sufficient
and did successfully suppress weeds during the most critical
period--the early stages of crop growth until canopy formation.
After that, you still can go in and cultivate if need be.
We’re still working to perfect this "organic no-till,"
and will keep you informed about new innovations and new results.
Dave
Have some questions to Ask Jeff? E-mail him directly at jeff.moyer@rodaleinst.org.
|
