Splitbark and glyphosate is there a relationship?
The following article was written by Candace Pollock from Ohio State University based on research conducted by Dr. Hannah Mathers and has information that would be of interest to Michigan nursery and landscape professionals - Thomas Dudek ,MSU Extension Educator, Grand Haven, Michigan.
Glyphosate products, like Roundup, may be killer on weeds, but researchers are finding that the product may also do damage to landscape and nursery woody plants.
Hannah Mathers, an Ohio State University Extension nursery and landscape specialist, said that glyphosate applied improperly or in too high of a dosage is causing a phenomenon known as split bark, where, through the tree's uptake, the chemical is deteriorating the bark structure and destroying the winter hardiness of the plant. The cosmetic damage makes the plant unsaleable, and is costing the landscape and nursery industries millions of dollars per year in damaged product.
"The
economic cost to the U.S. nursery industry from bark cracking is
conservatively estimated at $6.6 million a year. That's roughly 2.5
percent of finished inventory," said Mathers, who also holds an
appointment with the Ohio Agricultural Research and Development Center.
"Add to that the conservative estimate of $14 million in landscape tree
failures, and we've got a national phenomenon that has been happening
for several years but only now are people taking seriously."
Mathers is teaming up with agricultural company, Monsanto, to help
develop a glyphosate product that is safer to use for weed control
around landscape and nursery woody plants. She has been leading national
public research on the impacts of glyphosate on woody plants, as well
as educational efforts on which glyphosate products to use and how to
properly apply the chemical.
"For a long time, industry felt that split bark was an environmental
problem, driven mainly by cold temperatures. But we were receiving
reports of split bark in warmer parts of the country, such as Georgia,
the Carolinas and California. Why would it be a cold issue if splitbark
is happening in those areas?" said
Mathers. "Winter temperatures are part of the problem, but only because
glyphosate weakens the bark structure enough to cause the trunks to
split under stress. There's a large body of national research that
supports those findings."
Mathers said that the first step in controlling split bark is education:
recognizing that glyphosate could be a contributing factor, which
glyphosate product to use, and using that product properly.
"The first thing I tell nursery and landscape professionals is to use
glyphosate only when necessary," said Mathers. "We want to stress
pre-emergent glyphosate applications to kill weed seedlings, rather than
a post-emergent application that kills the entire weed plant. It
reduces the impact on woody plants, as well as saves money. Adoption of
integrated weed management programs with reduced reliance on glyphosate
can cut herbicide expenses and application labor by up to 50 percent."
In situations where glyphosate is required, users should pay attention
to which product they apply. Research has shown that it's not the
glyphosate itself that is causing split bark, but the surfactant found
in some glyphosate products that is causing the problem. A surfactant is
a wetting agent that allows for easier spreading of the chemical, and
increases uptake of the chemical in woody plants. Surfactants are known
as adjuvant loads on glyphosate product labels.
"When glyphosate use is necessary, use a glyphosate product around woody
plants that has no adjuvant load," said Mathers. "Products that have a
full adjuvant load are the worst around ornamental plants because of the
increased potential for uptake of the glyphosate by the surfactant into
the bark."
Fourteen registered glyphosate products contain no adjuvant load. They
include: Backdraft, Campaign, Expert, Extreme, Fallowmaster, Fallow
Star, FieldMaster, Glypro, Landmaster BW, Land Star, ReadyMaster ATZ,
Rodeo, Roundup Custom and RU SoluGran.
Mathers also encourages nursery and landscape practitioners to apply
glyphosate products properly. An Ohio State University Horticultural
Research Institute-funded project conducted last year, found that many
growers and nursery/landscape professionals were using glyphosate
indiscriminately -- making applications (one quart per acre) as
frequently as eight times a season, or approximately every 2.5 weeks;
removing suckers with glyphosate products; and applying product so close
to woody plants as to increase uptake through drift exposure.
"Glyphosate should not be used to remove suckers, there should be a
30-foot buffer between the weeds you are spraying and the woody plants,
and glyphosate should not be applied so frequently," said Mathers. "The
formulations for glyphosate have changed over the years. I don't think
people realize that the glyphosate they use now is more potent than
older products they are used to. Plus, more generic brands are now
available and they are cheaper to come by, so users are getting more lax
in their applications."
Mathers said that glyphosate with surfactants are dangerous for woody
plants because it takes years for the plant to break down the chemical
once it's taken up. Research has shown that one single low dose of
glyphosate stays in the plant for at least a year.
"Just imagine what kind of damage you are doing to a woody plant when
you apply glyphosate two times a month," said Mathers. "Glyphosate
injury is also difficult to diagnose because symptoms may not be present
for up to two years after glyphosate absorption."
In addition to split bark, other symptoms include witches broom,
stunting, loss of apical dominance, individual dead limbs, chlorosis and
death.
Woody plants most susceptible to glyphosate uptake include: Pyrus species, especially Callery pears; Prunus
species, especially Yoshino cherry and Kwanzan cherry; Crab apples;
Sycamore; Serviceberry; Hawthorn; Mountain Ash; Black Gum; Paper bark
maple; Japanese maples, especially variety dissectum; Norway maple, especially‘Emerald Queen'; Red maples; Dogwood, especially Kousa dogwood; Magnolias, especially Magnolia ‘Elizabeth’;and the yellow magnolias such as Magnolia ‘Butterflies’, ‘Sawada’s Cream’, Magnolia ‘Yellow Bird’ and Magnolia ‘Yellow Lantern’.
Specifically, glyphosate uptake leads to an accumulation of a type of
acid called shikimic acid that results in a reduction of phenolics --
plant compounds that serve a variety of roles in plant development and
survival including defense against pathogens. Research has found that
the more glyphosate is taken up by the plant the higher the shikimic
acid levels. In addition, glyphosate stays within the plant for years,
being stored in the roots with sugars in the summer and fall, and then
translocating to areas of the plant where growth takes place in the
spring and continuing to cause injury.
Mathers said that until safer glyphosate products are developed, a
change in weed management practices in the nursery and landscape
industries is required to control the split bark phenomenon.