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?
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
If I can be of any help, email me again and
I’ll do my best.
Rodger and All,
Paul Hepperly here, the research manager
at The Institute. Just had an additional thought to complement Jeff's
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.
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
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
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.
Have some questions to Ask Jeff? E-mail him directly at email@example.com.