Foliar Applied Herbicides
Downwardly Mobile Herbicides [Symplastically Translocated
(leaf to growing points)]
These herbicides are capable of moving from leaves (sources
of sugar production) with sugars to sites of metabolic activity (sinks of sugar
utilization) such as underground meristems (root tips), shoot meristems (shoot
tips), storage organs and other live tissues. Since movement to sites is
essential for continued plant growth, these herbicides have the potential to
kill simple perennial and creeping perennial weeds with only one or two foliar
applications.
Symptoms are evident on new growth first. Pigment loss (yellow or white),
stoppage of growth, and distorted (malformed) new growth are typical symptoms.
Most injury appears only after several days or weeks. Plants die slowly.
Herbicides in this group are usually molecular (non- charged) at low pHs found
in the cell walls and negatively charged at higher pHs encountered in the
cytoplasm of leaf sieve cells of the phloem (the ionization inside the cytoplasm
of the phloem accounts for trapping and movement of these herbicides).
Of these one class are called Amino Acid Inhibitors (Aromatic):
Glyphosate (Rodeo is the aquatic
trade-name of the herbicide the DEP approves of against Phragmites) and sulfosate are the
compounds with this mode of action. Uses are limited to foliar applications
only, since these chemicals are rapidly inactivated in the soil. Symptoms
include yellowing of new growth and death of treated plants in days to weeks.
These relatively nonselective compounds control annual grasses, annual
broadleaves, johnsongrass, quackgrass, yellow nutsedge, cool season pasture and
turf grasses, cattail, Canada thistle, hemp dogbane, Jerusalem artichoke,
poison ivy, and multiflora rose.
The above information was provided by: Merrill A. Ross, Professor of Weed Science
Daniel J. Childs, Extension Weed Specialist
Department of Botany and Plant Pathology, Purdue University Cooperative Extension Service
Purdue University
West Lafayette, IN
| 
