Tom Powers
The habitat I am going to discuss this week is the fencerow.In Iowa, the
fencerow is the six to ten feet wide area between two row crop fields, or
between a row crop field and the adjoining road ditch. The qualities of this
habitat are similar those of the field next to it, but there are some important
differences. The most important is that there may or may not be a fence in
place. Thirty to forty years ago almost all Iowa row crop fields were surrounded
by a fence, but as livestock production has dwindled, so have the fences. Many
have been removed, but the fencerow tends to stay in place, where it acts as a
landmark to separate land owned by different people. Another difference between
the fencerow habitat and the surrounding field is that the fencerow tends to be
a collection point for rocks found in the field. Also, woody brush is sometimes
allowed to grow in the fencerow. Another important difference is that a fencerow
is often slightly elevated compared to the adjacent land (more on this later).
This increased elevation causes this habitat to catch more snow, so in a very
dry spring, the fencerow would have somewhat better moisture conditions than the
surrounding area. Human affect the fencerow habitat in many ways. Obviously the
first change is the building of the fence. Most of the time posts were dug into
the existing vegetation and woven and barbed wire strung in between. The fence
has a major impact on this habitat, because it totally eliminates any tillage or
mowing for at least a foot or two on each side of the fence. This limits the
effectiveness of two of the human's favorite habitat influencers: tillage and
mowing. When moldboard plows were heavily used in Iowa, good farmers would plow
in one direction one year, throwing the soil away from the fence. The next year
they would plow the other direction, throwing the soil towards the fence. Some
farmers still use this practice, but most just disc or field cultivate as close
to the fence as possible. Humans also alter this habitat in other ways. They may
allow livestock to graze there. They may use fire to burn it off on an annual
basis. They may apply herbicides to this habitat, either directly with a
fencerow sprayer, or indirectly through spray drift from the adjoining cropland.
The weed I'm going to talk about today is "giant ragweed. It's a summer annual that reproduces by seed only. It can grow to a height of 18 feet! It has developed several traits that allow it to flourish in the Iowa fencerow habitat. Because of the lack of mowing and tillage right in the fencerow, the plants that grow there end up being taller than the surrounding vegetation, at least for part of the year. This allows the fencerow to act as a windbreak, which leads to more soil being deposited there, which makes it even higher. Some fencerows are 2 to 3 feet higher than the fields they surround! Giant ragweed seeds can be dispersed by the wind, so the elevated fencerow ends up catching more of them than the surrounding soil, so the fencerow habitat ends up with relatively more giant ragweed seeds in its seed bank than the surrounding habitats. The farmer's attempts at tillage to this area leaves the soil in the fencerow rough and cloddy, which favors the ragweed seed in comparison to grass seed, which germinates better in smooth soil. This tillage can disturb the soil enough to kill perenial plants,which reduces competition for the giant ragweed. This attempted tillage can also "plant" any giant ragweed seed that was lying on the soil surface, or bring seed that was buried too deep to germinate closer to the soil surface. When humans mow a fencerow it also helps the giant ragweed, which can vigorishly regrow from the stem and outcompete the other fencerow vegetation. Burning of the fencerow with fire will remove old giant ragweed plants, but it also leaves the soil bare, which gives giant ragweed a huge advantage. Giant ragweed is one of the first annual weeds to emerge in the spring, and it grows extremely fast, allowing it to outcompete most other plants. Animal grazing can also help this weed dominate the fencerow habitat, because most grazing animals prefer grasses to giant ragweed, so when they are eaten down, it can continue to grow. Finally, herbicides used to control weeds in fields and in the fencerow can exhibit varying degrees of effectiveness in controlling giant ragweed. The drift from herbicides used in rowcrop fields may kill competitors of giant ragweed in the fencerow, but usually won't kill the ragweed because the dose recieved is often sub-lethal. This may shift the giant ragweed population towards those resistant to the chemicals applied to the crop ground. The same is true for herbicides applied directly to the fencerow. Some farmers in Iowa spray their fencerows once a year, and some never spray them at all.Those that do treat their fencerows typically use a hand heldsprayer to "hose down" the fencerow with an inexpensive contact herbicide like 2,4-D. These herbicides are effective in controlling giant ragweed, but only if most of the plant gets covered, which is extremely difficult because of this weed's size and bushiness during the normal time of treatment. This can again lead to the application of a sub-lethal dose, and possibly select for those ragweeds that exhibit at least some level of resistance to these fencerow herbicides. So, if a farmer continues these same management practices year after year, the giant ragweed population will continue to shift towards one that can thrive in this fencerow habitat.
Brian Hartman
One weed habitat that a lot of people have problems with is fence rows. This is
one area farmers often overlook and can be so tough to keep weed free. The soil
remains undisturbed in a fence row and is usually pretty fertile soil making it
an excellent seed bed for weeds. The fence row is a place that alot of our wind
blown weed seed ends up and can tend to have rather high populations in this
area. Some seed ends up there by birds who drop seed when taking a break on a
fence post. Most people don't like to take the time or spend the money to spray
this area since it doesn't provide them with any income. Some spray this area
when spraying their row crops, the problem with this is the herbicide you are
spraying might not control the weeds in the fence rows, or the crop on the other
side of the fence might be highly sensitive to this herbicide. This can be a
larger problem than the weeds themselves if you injure your neighbors crop.
Another problem with this is if foxtail or any other grass gets to be a problem
in the fence row you really don't have a lot of options to get rid of it because
the herbicide you spray to kill the foxtail will also kill the grass that is
supposed to be in there.
To help keep weeds out of the fence rows you should seed them down with a grass
with a deep root system that allows it to compete with the different weed
species. You should plant a perinnial grass for example Big Blue Stem which puts
roots down several feet below the surface or the more popular Brome Grass which
has the ability to reproduce by rhizomes and seeds. Both of these types of
grasses are highly competive and allows them to have an advantage when competing
for nutrients and moisture.
One pesty weed that often gets out of control is the Siberian Elm Tree.
This pesty weed reproduces by its seeds and can reproduce by basal sprouts. I
often wonder how a tree can become such a problem when it takes so long to grow.
This is an excellent example of our neglegence when it comes to taking care of
our fence rows. This weed can destroy fences by growing through them(some get
creative and just make the tree part of the fence by stapling barb wire right to
the tree)and knocking the fence down when the branches fall on it. The Siberian
Elm tree can grow up to 50 ft. tall and are kind of a crappy looking tree. They
often have shallow root systems which doesn't allow them to with stand heavy
winds, but is extensive, competitive enough to grow even in not so perfect
conditions. This weed can provide shelter for livestock in the summer heat in a
pasture and in storms, but it is too weak to withstand strong winds and often
limbs break off and can injure the livestock, ruin the fence or fall into your
field of corn or soybeans which can make harvest even more of a battle. The best
way to treat this weed is to cut it when it is small and spray the top of the
stump with a product we frequently use call Tordon RTU (its a pretty blue
color). I have seen time and time again when people cut the tree and don't treat
the stump, the tree will still be able to provide a shoot and will continue to
grow. The Siberian Elm Tree is such a problem because it is labor intensive to
remove from the area. It often takes a chain saw to cut the tree (unless it is
small enough to pull or clip off) and then you have to cut it up and haul it
away and it isn't a real good wood to burn in the fireplace. It isn't like a
thistle in which you can spray or pull and let it lay to decay. It isn't hard to
manage a fence row habitat and it doesn't have to be labor intensive if we stay
one step ahead of the weeds and nip them in the butt before they get the best of
us
