Velvetleaf is a very competitive, well adapted weed in agroecosystems. There are many reasons for this: seed bank longevity, adaptation to physical stress, disease resistance, growth plasticity, competitive ability in many habitats, and resistance to herbicides.
The seedlings in the picture below are emerging in a refuse dump. This field in adjacent to Lake Erie in Michigan, next to a carp pond. Dead carp are dumped and sit rotting in the sun as velvetleaf exploits the opportunity next to a dead carp fish head:
The same plant with a broken stem is seen in the pictures below, taken at the same time. On the left you can see the stem has been broken almost completely off. On the right is the branch laying on the ground, but with its leaves doing fine and showing no signs of wilting. Enough vascular strands (very few) are still connected to keep the leaves growing.
Velvetleaf will frequently show signs of infection by verticillium wilt, a disease it seems to survive and thrive with. The plant below is infected with this disease, yet it will still survive and produce seed:
Velvetleaf will adapt its size and productivity to the resources it gets at a
particular place.
On the left is a plant I cut all the leaves off to reveal
the extensive branching and seed capsule formation. This plant was grown with no
neighbors; as a consequence it is relatively short and had many leaves and capsules
because it had lots of resources.
The picture to the left shows my old friend Matt standing
next to a pure stand of very tightly packed plants, they tower over his head. Because they
lots of resources, but were close together, they grew very tall. They get tall by because
when velvetleaf gets shaded, it responds by increasing internode length (the distance
between branches) to get taller than its neighbors. This is one of its best competitive
traits for success over crops like soybeans.
This little velvetleaf plant has only a few leaves and
capsules. It is growing in the gravel immediately next to a concrete roadway, not a very
favorable or resource-rich habitat. The county road crews would mow along the roadside and
cut it down. Despite this adversity it managed to put a few capsules out late in the
season and continue the species for another year (or maybe 100). Many feel that managing
velvetleaf means never allowing one plant on a farm to set seed. It is difficult to
disagree with this strategy to velvetleaf management.
Velvetleaf competes in many habitats, agricultural as well as others.
Corn grows fast and early in the season, making it much
better in competition with velvetleaf (left), but the weed still does well.
Notice the large flowering velvetleaf plant in front of
the picture window of this house. I guess one adaptation velvetleaf has is the ability to
fool urban homeowners that it is an ornamental plant. Hey, whatever it takes.....
Velvetleaf is susceptible to many herbicides, but it also has some well-expressed
herbicide detoxification systems. Below are a few survivors, all which probably set seed
later:
This plant (left) was just a little to big to kill with
glyphosate, although the leaves on the left are yellow, chlorotic from inhibition of the
EPSP synthase in its leaves.
The plant on the left was also just a little to big to
kill with 2,4-D, although its stems and leaves are twisted and curved (epinasty) due to
differential growth subsequent to blockage of the phloem in its stems.
The leaves of this plant are necrotic and the leaf edges
dried and curled up due to a dose of bentazon. a photosynthesis inhibitor. It too will
probably survive because the treatment came too late in the plants development to kill it.
