Glyphosphate Causes Bark Split/Other Damage to Woody Plants

Below is a copy of an article I came across in this months American Nurseryman magazine and also on the web. It's disturbing.

http://www.extension.org/pages/Use_Glyphosate_Properly_to_Protect_Woody_Plants

COLUMBUS, Ohio -- Glyphosate products, such as Roundup, may be a killer on weeds, but researchers are finding that the product may also damage 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 the 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 split bark 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. A 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.

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This message was edited Aug 15, 2008 8:23 AM

I have to say one thing about this. I've always been very careful with round up and the easy solution is just don't go nuts with it. My neighbor will literally spray entire beds with the stuff, every inch and that just can't be a good thing.

It's like Dursban. Stuff worked great for me but they took it off the market because people went nuts using the stuff.

This message was edited Aug 15, 2008 2:51 PM

It looks to me like the problem first surfaced in nursery grower's fields. The professionals were having a problem. Roundup, or specifically glyphospahte, was not supposed to have any root action. Apparently it does when it is combined with a surfactant. So before we blame overuse by the average homeowner, we have to look at the lack of research done by Monsanto when the product was first developed. And we have to look at the "off label" use of nurseries using it to control sucker growth. Even I know you shouldn't do that with Roundup or any glyphosphate product and I am an average homeowner. This product was never supposed to have any root action. It does. Big difference.

If your using it off lavel and something bad happens it debateable who's to blame.

I would re-read that article you quoted, and then read some more. There is nothing there mentioning root absorption of this chemical or chemical combination. Please don't misinterpret, and lead others to believe something other that what is stated.

I think you will find that the problem is increased absorption of glyphosate through bark cells when combined with surfactant, which creates the problem in the plant. Glyphosate can be absorbed and cause problems in cells that photosynthesize, which includes most young bark cells. Many people believe glyphosate only kills plants by absorption through a plant's leaves. Inappropriate application of this herbicide which results in contact with bark of non-target desirable plants leads to this issue.

This seems to be good research, but it is by no means the first time that this is a recognized problem. I practiced as a horticulturist and landscape manager for many years back in the '80s and '90s, and I knew about it back then (more than 15 years ago). The problem of bark absorption of glyphosate on young trees was recognized then, by nurserymen who would apply Roundup from side-mounted sprayers as they drove down rows of nursery stock. All the trunk damage was on the sides of the trees from which the herbicide was applied, and it did not coincide with winter sun exposure (where sun scald or frost cracks were purported to only occur). It was also recognized by extension agents and landscape managers in damage to landscape plantings when herbicides were not so carefully applied to control weeds in planting beds.

Making the additional connection that increased damage occurred with surfactants or adjuvants, that may be new and additional proof. But I don't read anywhere in that article or otherwise that says glyphosate (with or without surfactants/adjuvants) is aborbed through any mechanism other than green photosynthetic tissue, including leaves, stems, and young bark.

"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."

That's what I get from this statement. Perhhaps you can better explain what translocating to areas of the plant where growth take splace in the spring means. Read it again your self. I also talked to tone of the garden horticuturalists at the Toledo Botanical Gardens with this very same article in hand. It was his take also. He was present when the study results were initially presented.

This message was edited Aug 16, 2008 7:42 AM

That's exactly the sentence I meant, plus this one:

...into the bark."

Translocation means moving molecules through the plant.

"...stored in the roots..." means that the molecule was translocated there from somewhere else initially via the plant's vascular system (xylem and phloem).

This article speaks about repeated herbicide applications contacting the bark of woody plants, via direct spray or through drift, and how that is a much worse situation now than in the past because of the increased killing efficiency of the current formulations of glyphosate/adjuvant load products.

It also points out that less product and labor is necessary when used at early points in the target pest organism's life cycle (seedling stage of weeds versus mature), thus exposing the nearby desirable woody plants to the herbicide less often and at lower rates.

Nowhere in the article posted (nor in what I've read over my past twenty years of practice) is there a statement that this chemical is absorbed by the root system of any plant growing in normal conditions and when the product is applied at label rates, even when there are multiple applications in a season (don't have one handy, but I think the label allows that). I am not a chemist, nor do I claim to be, but I do try to keep up with information about standard products that I am likely to use. I am certainly not going to be a denier of reproducible research that shows these products to be problematic.

The garden horticulturist from Toledo should be able to access this same information.

This isn't meant to be one-upmanship. I really think that it is a disservice to not clearly understand what is being said. Maybe a contact with Ms. Mathers is more in order than a "did not - did too" here.

I'm comfortable with my position. You can have the last word.