Bringing your A game to herbiciding

By Don Osmond

Don is a long-time expert volunteer steward. He invites suggested edits and feedback generally.

Veteran practitioners will be tempted to skip this article, but I tried to include items of interest for all skill levels using a wide variety of high quality sources plus my own experience.

If I could suggest only one thing to herbicide applicators, what would it be?

Get the herbicide operator/applicator study guide for your state & read it cover to cover.  It’s easy to forget stuff or develop bad habits & hitting that guide every few years for my license renewal was an excellent way to get back on track.

 

How to decide if herbicides are needed

An invasive species management plan is essential.  It sets priorities for each invasive & land parcel based on available resources for the number of years required to suppress the invasive to the desired level.  It forces you to think about the entire ecosystem, the life cycle/seed longevity of each invasive & whether herbicide use makes sense.  At the steward level, you don’t need the rigor of an ecologist generated site restoration plan.  It’s fun to watch the plan evolve as you learn new things & it serves as a blueprint for your successor, so all your hard won knowledge isn’t lost.  There are many other benefits to a plan, such as nailing down the dates when mechanical control should start for each invasive & at what date to switch from one invasive to another.

 

Explaining to visitors (and reminding yourself) why herbicides are necessary

Most of us would probably not use herbicides if each nature preserve had an army of young, physically fit volunteers or contractors who were available over 4-12 consecutive years at the right time period to cut, pull or dig every weed.  Since that will never be the case, most of us will need to herbicide.  The exceptions are sites that are very small, have good native competition with few weeds or where the management goal is not related to preserving or increasing the percentage of conservative plant species.  The following are some reasons to use herbicides:

• In the 1960’s, Rachel Carson correctly shifted public opinion away from the view that large scale use of pesticides have no risks.  But concluding that all pesticide use is bad would be an overcorrection.  A balanced approach is usually the best & that means using the proper techniques to apply low toxicity herbicides targeted at specific plants or patches.
• Mechanical control of weeds without herbiciding can overload the restorationist for several reasons.  It must occur in a limited window of time.  The plants usually must be in bloom to ensure finding most of them, but if you wait too long, seeds are set.  Plus some weeds like wild parsnip & sweet clover have a proportion of plants with delayed emergence, requiring multiple passes separated in time, taking time away from controlling other invasives.  Weeds can have occasional bumper crop years due to the plant’s life cycle, controlled burning, brush clearing, etc.  Also, some years can be too hot or wet to finish mechanical control before seed drop.  Seed drop must be avoided at all costs if native competition is weak or the soil microbial diversity is low, because it can set you back years, depending on seed longevity.
• I used to think about each invasive plant in isolation, but now I see that all the efforts during a given growing season are related to each other.  For example, if I herbicide wild parsnip in the fall & spring, that reduces the time needed to mechanically control it in summer, which in turn allows me to get white sweet clover at peak bloom when it is easily found, which in turn lengthens the knapweed window, giving me time to dig or pull the root out instead of the less effective but quicker method of wacking.  So herbiciding just one invasive increases your effectiveness for multiple invasives, making it more likely you can increase your weed control area over time.
• Herbicides are essential for woody plant control.
• Some other advantages of herbicides are the ability to get multiple generations simultaneously for biennials, less physical toll on the body compared to mechanical control, better control for invasives that reflower compared to cutting or mowing & less disturbance of soil for invasives that must be pulled or dug (soil disturbance=more weeds).

 

Keep-out areas

I don’t recommend herbiciding in high quality remnants, with the exception of careful application to crown vetch and woody plants.  In addition to the possibility of off-target kill, we don’t know enough about herbicide effects on the soil microbiome.  If you think herbiciding in a remnant is necessary, consult with an expert first.

 

In addition, I avoid shores, riverbanks, areas known to flood if heavy rain is forecast a few days after spraying & well traveled footpaths.

 

How do I know if herbicides are working?

Seeing the leaves curl & turn color may not be enough.  You want to be sure the root was killed & not just the top.  When trying a new herbicide/adjuvant or concentration, flag a spray plot & a nearby non-sprayed control plot with the same density of weeds, competition level & habitat type in each.  It’s helpful to have 3 spray plots with concentrations a bit above & below your target to see if you are on the edge of effective control.  Monitor a year later to verify density reduction compared to the control plot.  Again, the climate should have been somewhat average during the previous year.  Make sure no controlled burns occur in the year after application because that may affect results.  Also, don’t experiment if the weather before spray time has been abnormally wet or dry.  Relying on the experience of others can provide a starting point for herbicide use, but there are enough variables involved to warrant doing your own experiment before spending a lot of time & money.

 

Treatment failures

If a treatment fails, you may not know about it for months since root death won’t be evident until the next growing season.  That could mean a lot of work down the drain, so it’s important to get it right the first time.  Good detective work is needed to find the root cause of failures, so it’s best to investigate your entire process for the following:

• Errors in calculating concentrations, sprayer calibration or mixing.
• Rain too soon after application or applying with too much dew on the leaves.
• Not getting enough herbicide on the plant, especially true for painting, rolling or wick/sponge application.
• If multiple people have access to herbicide: somebody created a custom mix or transferred herbicide & forgot to relabel the jug.
• Spraying foliage when the plant isn’t actively growing or is under drought stress.  Also, some plants are most vulnerable during the stage when they are pushing resources into the roots.
• Using hard water with glyphosate without a water conditioning additive like spray-grade ammonium sulfate.  One study found a 60% decrease in toxicity when used with water at 50 ppm hardness.
• A mix that is above or below the label recommendation for concentration or rate.  If you experiment with a lower rate, failures can occur even if your experiment was successful.  The lower rate may work for a given competition level, stage of growth, age of plant, drought severity, etc but if those variables change, that rate may no longer work.  Recommended rates create a margin that reduce the effect of variables.  If you try a rate higher than recommended, it may kill the leaf too quickly, interrupting translocation to the root.
• Not using an adjuvant such as methylated seed oil.
• Spraying rosettes too early, resulting in many new plants emerging after spray application, making you think the application failed.
• Inconsistent spray method for a given applicator or inconsistency due to having multiple applicators.  Also poorly trained applicators.
• For clonal plants: not treating every stem or treating only part of the clone & then waiting too long to finish the rest of it.  Note that clones (especially older ones) can require several years of repeat treatment, 
• For woody plants
• Waiting too long between cutting/frilling & herbicide application
• For basal bark: band of herbicide too narrow or not herbiciding the entire circumference
• Not cutting stems close to the ground
• Not cutting horizontally (herbicide runs off the cut stump)
• For some plants like dogwood, herbiciding when the plant is pushing sap upward in the spring.

 

Off-target kill

Spraying invasives when native plants are green will be a judgement call based on what is best for the entire ecosystem in the long term.  Sacrificing a small number of common native plants is usually acceptable if the invasive plant being sprayed is known to displace natives, the invasion is beyond what mechanical control can handle & your management plan designates the area as high priority.

 

Practice proper technique regarding wind speed limits, nozzle height above ground & nozzle type (avoid those with droplet size rated as “fine”).  Decide if the weed can be effectively controlled in the rosette stage when most natives are dormant.

 

Wind causes spray drift, but with the low pressure sprayers we typically use, it is often not a big deal.  Plus the wind at ground level is much less than at your head.  I’ve sprayed in degraded areas with no problems up to 15 mph average as long as gusts are below 20 mph.  For spraying where many natives are present, spraying near property lines or for foliar brush spraying, winds should be below 7 mph or so.

 

Exceeding the maximum use rate on the label may result in off-target kill or unintended environmental effects.  This rate is listed in a different place than the spray rates for particular weeds.  For example, the Garlon 4 label states a max use rate of 8 quarts per acre per year for cut stump/basal bark.  Lets say you want to basal bark a 30’ x 30’ brush clone.  Convert to acres: (30 * 30) square feet/43560 square feet per acre = 0.021 acres.  8 quarts per acre * 0.021 acres = 0.168 quarts or 0.158 liters is the maximum amount of Garlon 4 you can use.  If you mix Garlon 4 at 20% in bark oil, that means 0.158 liters/20% = 0.79 liters or 27 ounces of spray solution in your tank or bottle is the max you can use on that clone in a year.  I use about 1.2 liters in 6 hours of cut stump treatment of small diameter brush.

 

If the label indicates potential for volatilization, don’t use when temperatures are in the 80’s or higher.

 

Don’t apply oil based solutions when ice is on the ground because the herbicide will readily move off-target.

 

See the woody plant section for more.

 

Dealing with precipitation

Some labels don’t specify rainfastness.  Rain too soon after application can reduce efficacy & potentially cause off-target kill due to runoff.  I shoot for 8 hours rain-free after application but that may be overkill.  Basal bark requires a few days rain-free (see woody plant section).

 

“I have a pair of chemical gloves from a home improvement store & I’m careful not to walk in sprayed areas that are still wet.  Good enough?”

I’m afraid it isn’t.  We have to think about long term exposure to any type of chemical, whether it’s in our everyday life or while herbiciding.  The reason to wear protective equipment is not because herbicides are highly toxic, but instead as an insurance policy to keep exposure to a minimum over many years of use.  The degree of exposure for yourself is a personal decision, but if non-applicators are present while the herbicide is wet, assume they want zero exposure.  I’d like to hear from others on how they ensure volunteers at group events never walk into wet herbicide.  Do you have a systematic way for applicators to follow the brush cutters?  Or do you delay herbiciding until the area is clear?  If the latter, how do you find all the stumps if they are small & hidden in vegetation?

 

How to determine toxicity

The herbicide label contains a signal word from most to least toxic in this order: danger, warning, caution.  Try to use the least toxic herbicide, but as a point of reference, household bleach & toilet bowl cleaner are labeled “Danger”.  If the label recommends chemical resistant footwear or an apron for mixing/loading, consider substituting a less toxic herbicide.

 

If you hear about court cases regarding herbicide toxicity, research may reveal the plaintiff is not directly claiming the herbicide caused a disease or you may find the majority of credible scientific studies don’t support the plaintiff’s claims.  Public & media understanding of science is poor, so juries are easily swayed by pseudoscience or their own antagonism against corporations.  Any claim that an herbicide caused cancer in an individual cannot be proven beyond doubt because so many things can cause cancer, it’s impossible to know the relative contribution of a given substance.  

 

What is the most risky activity?

Mixing & loading because you are working with undiluted herbicide.  Always wear chemical resistant gloves & some form of eyeglasses, pour liquids from below eye level, block the wind from blowing the liquid stream around, have paper towels & water available to cleanup spills & have a bottle designed for eyewashing available, filled with fresh water.

 

Tips to minimize exposure

I’m not a fan of having open herbicide containers at the job site (e.g. using a paintbrush or roller) due to the potential for splashing or spilling on clothes or shoes with no means of immediately showering & changing clothes.  The practice also increases the odds of getting it in your eyes.

 

Always wear some form of eyeglasses when using sprayers in case the trigger is accidentally depressed with the nozzle pointed at you.

 

Check state law, rules from your managing agency & the herbicide label to see if posting of signs is required in non-agricultural, non-landscaped areas.  If herbiciding near active trails, you should post signs directing people & their pets to stay on the trail.

 

If you offload herbicide into a smaller container, always remove the original label of that container & relabel with herbicide name & concentration.  Obtain containers that don’t look like they could hold food or drink.

 

Chemical resistant gloves

They are not a barrier, but instead slow down the process of chemicals migrating through the glove to your skin.  National Institute for Occupational Safety & Health says chemical protective clothing should be the last line of defense, not the first.  I don’t recommend regularly contaminating gloves with diluted or undiluted herbicide because by the time you rinse them, some herbicide has likely entered the glove material & will be making its way to your skin.

 

• Material: I couldn’t find breakthrough time data (time it takes for chemicals to travel through glove material) for herbicides we use.  Schwope¹ found that solvents (like those in Garlon 4 & bark oil) will break through the glove material sooner than most other chemicals & will take the other substances with them in the process.  A generalization of their findings is that butyl rubber, nitrile rubber & PVA, all about 15 mils thick, were the best.  Natural rubber & PVC were not recommended.
• Thickness: Never use thin disposable gloves.  I’ve found 15 mil thick nitrile gloves are a good balance between cost, dexterity, availability & chemical protection.
• Maintenance: Illinois Dept of Agriculture & herbicide labels recommend washing gloves after every use, probably partly due to breakthrough time & partly to prevent contaminating your skin during donning & doffing.  I replace gloves after 10 days of use or monthly (whichever comes first) to guard against eventual herbicide migration to the inside & potential degradation of the glove by physical movement & ultraviolet rays.  If I accidentally get undiluted product on them, they are discarded.

 

Why should I read herbicide labels when most of it is aimed at farmers?

• The label is the law.
• It gives the maximum application rates to avoid off-target kill & pollution of the environment.
• It gives application rates to control particular weeds.  If you don’t see your weed on the label, there may be one listed in the same plant family to give you a starting point for concentration.  Please don’t exceed these rates.  More herbicide concentration is not necessarily better.  For example, higher concentrations can kill leaves too quickly, preventing translocation to the roots.  What if the label doesn’t mention spot spray but instead recommends amounts in quarts/acre?  Assume you are using a 3 gallon backpack sprayer calibrated to 40 gallons/acre (see the backpack sprayer section for how to calibrate) & the label calls for a maximum of 5 quarts/acre or 1.25 gallons/acre for your weed.  So to spray 1 acre you will use 1.25 gallons of product in 40 gallons of spray.  1.25/40 = 3.1%.
• It states how toxic the herbicide is & what protective equipment you must wear.
• It has valuable information such as use around wetlands & how persistent it is in the soil.
• Labels can change so download the latest one at regular intervals.

 

Spray additives

• Adjuvants: These include oil concentrates like methylated seed oil (creates better penetration of leaf surface-I use this in all my applications), surfactants (causes water to spread on the leaf instead of beading), water conditioners (offsets the negative effects of hard water on herbicides like glyphosate) & stickers (increases the ability of chemicals to stay on the leaf, leading to better rainfastness).
• Dye: Always use it because it alerts you to missed plants, prevents walking into sprayed areas, alerts you to leaks in the sprayer & makes it apparent if herbicide accidentally gets on your skin.

 

Backpack sprayers

• A sprayer setup for those without a pickup truck is shown below.  The herbicide tote contains dye & herbicide offloaded into small, easy to handle bottles along with nitrile gloves, measuring cup & paper towels.  For transport, the sprayer is put into a large plastic tote with a pvc pipe bolted to the inside, which holds the sprayer wand.  Bungees are used to hold it down.  To keep things clean, a plastic baggie is wire tied over the nozzle during transport.

 

Portable backpack spraying setup

 

• Shoulder straps are hard on the body so I bought a harness that transfer some of the weight from shoulder to hips.  Unlike hiking backpacks, they are poorly designed & often need to be modified to fit well, but are still well worth it.
• Be situationally aware & walk slowly because the sprayer throws your center of gravity off.  If you trip, step in a hole or lose your balance, the added weight of the sprayer can turn a minor injury into a major one.
• Get in the habit of engaging the trigger lock when not spraying to avoid accidental discharge.
• Hold the spray wand upright as you walk to prevent drips.
• As you walk, the sloshing herbicide can leak from the filler cap.  Yep, it has happened to me-right down my back.  First, look at the cap gasket to make sure it isn’t twisted from the factory.  Buy gasket grease from the manufacturer & use a Q tip to apply it every month.  This will help the gasket remain soft & seal better.  Obtain a white sock made from absorbent material & cut a few inches wide section from it.  Each time you screw the cap onto the sprayer, stretch this sock section over the cap so it rests just below the bottom edge of the cap.  This will absorb leaks & will alert you to the need for gasket maintenance by dye discoloration of the sock.  Walking slowly & steadily when the sprayer is full will minimize herbicide splash into the cap area.  Never lean forward since that can cause herbicide to leak from the cap vent hole on some sprayers.
• You can wear a fanny pack across your chest or gear vest to carry cellphone, gps, maps, first aid, cleanup kit for sprayer leaks, water, food, etc
• For some sprayers, every few weeks use nitrile gloves to unscrew the nozzle over a drip catcher.  There may be a small screen in there that can be rinsed or wiped clean.  During disassembly, note the order & orientation of the nozzle components so you can put it back properly.
• At the end of the day, I put a little water in the sprayer & spray that out, then hold the sprayer up high to get all the herbicide out of the hose & wand.  I don’t know if this is necessary, but I never have clogged sprayers.
• Calibration
• Labels don’t always tell you how much product to use per gallon of water by volume.  Instead they tell you how much product per acre to use.  That’s because herbicide customers are mostly farmers & landscapers who spray large areas with herbicide mixed in a big tank.  In contrast, we spot spray with handheld or backpack sprayers.
• This process must be repeated for every nozzle you intend to use.  You’ll need a tape measure, a way to measure time in seconds & a clear container marked in ounces.  Put a gallon of water into the sprayer.  Find a spot where it is safe to spray herbicide & mark a small area such as 20’ x 20’.  Measure how long it takes to spray that area with the same sprayer pressure & height above ground that you typically use.  Spray enough to wet the vegetation but not to the point of dripping.  Now, refill the sprayer if necessary, spray into the container for the same amount of time & measure how much liquid is in the container.  First, convert your test plot into acres by dividing square feet by 43560.  For this case: (20’ * 20’)/43560 square feet per acre = 0.00918 acres.  Let’s say you collected 56 ounces in the container.  56/128=0.4375 gallons.  So you sprayed at a rate of 0.4375 gallons/0.00918 acres = 48 gallons/acre which is ballpark for a backpack sprayer with a hollow cone nozzle.  If we use Garlon 4 as an example, the recommended application rate for broadleaf weeds is 1-4 quarts product per acre.  If we choose 2 quarts/acre, that means we will need 2 quarts product in every 48 gallons of spray or 0.0417 quarts/gallon.  1 quart is 32 oz so that is 0.0417 * 32 = 1.3 oz product per gallon of water or 3.9 oz of product in a 3 gallon backpack sprayer. 

 

Some herbaceous weeds

• Crown vetch (CV): See the 7/5/23 post on this blog.  Herbicides used most often are Transline & Milestone, but be aware both are persistent in the soil & will harm some natives.  The Milestone label has a good list of the plant families affected by it.  The manufacturer (Corteva) recommends Milestone over Transline & the latter’s label doesn’t include CV as a controlled species.  Multiple sources, including Corteva, report reduced herbicide effectiveness at bloom stage.  It’s important to coat as much of the stem & leaves as possible.  GPS is essential for not missing patches.  Tom Wise (Military Ridge Prairie Heritage Area in southern Wisconsin) reports that the number of years to control a patch is highly variable & can take 5 years or more.  He sprays known patches before blooming & for ones found at bloom stage, he rotary mows them into tiny pieces to prevent re-rooting & seed set, then sprays after it resprouts.  That method may facilitate better herbicide coverage of all stems/leaves & may also reset the plant into active growth stage, when herbicides are more effective.  Then again, it’s conceivable that mowing could create stem fragments that can re-root.  Losure² found no viable seed in mature CV patches & cited other sources that support mostly vegetative reproduction.  They also found that stems without nodes won’t root themselves but stems with nodes will.  So it’s unclear whether CV persistence after spraying is due to poor translocation to the entire root system, persistent seedbank, leaf/stem defenses that prevent herbicide entry or unsprayed nodes rooting themselves.  More long term experiments are needed.
• Garlic Mustard: See the 5/10/23 post on this blog for my method in mostly degraded woodland without the resources to perform consistent mechanical control on a large site.  In summary, after many years of experimenting, I settled on spraying small patches of 2nd year plants at full bloom & fall spraying moderate patches of 1st year rosettes, combined with cutting or pulling scattered or unsprayed plants.  Large patches are left alone to see if a biocontrol develops.  In higher quality areas, I only sprayed rosettes when natives were dormant.  Many broadleaf herbicides & glyphosate are effective.
• Spotted knapweed: I believe herbiciding followed by wacking/cutting of missed plants is better than wacking/cutting alone for large populations in average quality or degraded areas.  This is because seeds can remain viable for 7+ years & the plant can live up to 10 years.  That means many years of wacking/cutting without missing a year, while also dealing with other weeds like sweet clover, something many sites will find hard to pull off consistently.  Also, stems tend to lie down in the vegetation, making them easy to miss while wacking.  Digging the root is an alternative to herbicides, but its labor intensive & often a large clump of soil comes out with the lateral roots, creating disturbance that leads to more weeds.  It’s best to spray after a burn for better visibility of rosettes since they are hard to find in vegetation or thatch.  Herbicides used most often are Transline & Milestone but be aware that both are persistent in the soil.  The Milestone label has a good list of the plant families affected by it.  
• Wild Parnsip.  Combine spring (early to mid May) & fall (late Sept-Oct) herbiciding of rosettes with summer digging of the root.  Spraying too early can result in missing late emerging plants.  Soil temperatures will influence emergence dates in the spring.  Spraying after a burn will ensure finding more rosettes.  Mature invasions in areas with weak native competition or poor soil microbial diversity can take >4 years of effort.  Flowering usually occurs in the 2nd to 4th year of life, so herbiciding rosettes is effective in targeting multiple generations.  Delayed emergence creates a long blooming season requiring 2 passes of digging separated in time, which is another reason herbicides are helpful.  Many herbicides will work.  After 2 years of use, I’m happy with 0.5% Garlon 4 in water with 0.5% methylated seed oil.  0.5% Garlon 4 worked as well as 1% in an experiment I conducted.

 

Woody plants

• See other discussions on this blog.
• Commonly used herbicides are 20% active ingredient glyphosate in water or 20% Garlon 4 in bark oil, applied in winter or when native herbaceous plants are dormant. The following are the pros & cons of each herbicide.  “Triclopyr” refers to triclopyr ester in bark oil & “glyphosate” refers to glyphosate + surfactant in water (cut stump only).
  • Applying at below freezing temperatures: Favor triclopyr.  But I had good results in the upper 20’s F & a local contractor uses it down to 10F.
  • Applying among native bunchgrasses that are still green: If you have experimented & determined your methods don’t cause off-target kill, favor triclopyr.
  • Basal bark: Triclopyr only
  • If concerned about off-target kill (especially in remnants): Experiment before committing to triclopyr, including an untreated control plot.  For cut stump, favor treating the cut surface only (instead of cut surface + stump sides) if your experiment shows it works.  See “cut stump & basal bark off-target kill” below.
  • If the smell of bark oil bothers you while transporting sprayers in a car or if you store them in the garage, favor glyphosate.
  • If you have hard water & cannot find a source for spray grade ammonium sulfate, favor triclopyr.
  • If you can’t treat the stump soon after cutting: Favor triclopyr.
  • Also consider the differences in cost of each herbicide & the availability of bark oil.
• Clonal plants:  These include dogwood & sumac.  Treat a given clone all at once rather than piecemeal.  A few years of treatment will often be necessary to kill the root system, especially on older clones.
• Methods include
• Cut stump or cut surface.  The stem is cut as close to the ground & as horizontally as possible, then the stump is herbicided as soon as possible.  If performed in that way, it is the most reliable method for controlling woodies, but is also the most labor intensive. Cutting low ensures best translocation of herbicide to the root, minimizes trip hazards, facilitates subsequent weed control & is better aesthetically.  There are reports of cut stump herbicide failures with certain plant species, but there are also plenty of reports that glyphosate & Garlon 4/bark oil work just fine for all woodies (which is also my experience).
• It avoids having standing dead brush, which can be an impediment to controlling weeds after removal of dense brush clones, a deterrent to grassland bird nesting or an eyesore in some situations. 
• Stems cut at a strong angle will have too much herbicide runoff.
• If snow forces you to cut higher than normal, be prepared for poor control.  Don’t let snow deposit on the cut stump or herbicide will get diluted or run off.
• If you can’t spray soon after cutting (for example, waiting for volunteers to leave the area), favor Garlon 4 over glyphosate.  Glyphosate based labels say to spray immediately after cutting, but I found Roundup effective in shady habitats on good sized buckthorn even with a 2 hour delay between cutting & herbiciding³. One theory is that the stump dries out over time, reducing it’s ability to absorb water based herbicides.  So delays may be more of a problem in sunny areas or if humidity is low. In an experiment, I found a small percentage of buckthorns resprouted after Garlon 4/basal oil herbicide treatment in a shady habitat (even when applied immediately after cutting), but after 2 years the resprouts died.  So a long followup period is needed before declaring success or failure. The Garlon 4 label recommends spraying the sides of the stump as well as the cut surface to control resprouts.  That may increase off-target kill if enough herbicide falls on the soil nearby.  I have good results treating only the cut surface, but it’s likely there are situations when treating the stump sides are necessary.
• Note that painting the stump with a roller, brush or sponge may not apply enough herbicide to be effective, so experiment before settling on that method.  It’s interesting to note the Garlon 4 label mentions spraying for cut stump or basal bark but not rolling or painting, perhaps an indicator that those methods are not consistently effective.
• Basal bark.  The stem of the uncut plant is coated in herbicide (typically 20% Garlon 4 in bark oil) from the ground to a particular height based on stem diameter & plant species.  The oil helps the herbicide penetrate through the bark.
• If significant rain falls within a few days after application, runoff can cause off-target kill.
• You may have a dead zone around the treated plant if the herbicide is applied in spray form.
• As with cut stump, painting or rolling onto the bark may not transfer enough herbicide compared to spraying.
• It’s best to conduct an experiment to verify that your choices for the application dates, amount of bark treated, application method & herbicide type/concentration is effective on all species of interest before you treat large areas.
• Cut stump & basal bark off-target kill.  There are reports of this (see 8/28/20 entry on this blog) but many others report no such problems.  Potential causes include root exudation of herbicide into soil⁴, movement of herbicide by mycorrhizal fungi, rain runoff, overspray error or exceeding the labeled maximum use rates.  Woody plant herbicide mixtures are much more concentrated than herbaceous mixtures so it doesn’t take much in the soil to cause problems.  That is why I use a solid stream nozzle instead of a cone or flat fan for cut stump, so I can flow herbicide onto the stump.
• Foliar spray.  The leaves are sprayed on shrubs, small seedlings or resprouting mowed/cut brush in degraded areas or if the woody plant is leafed out while the native ground layer is dormant.  This can be a very risky method.  Usually large areas need to be sprayed with the nozzle far above the ground, which increases the possibility of wind drift onto the applicator & the ground layer nearby.  There are plenty of reported failures with foliar that may be related to herbicide concentration/type, species of woody plant or season of application, so conduct a 1 year experiment before treating large areas.
• Frill.  Cuts are made in the bark & cambium around the stem using a hatchet or similar tool, then sprayed with herbicide.  See other posts on this blog.
• Spray equipment
• Handheld sprayers

 

Handheld sprayers L-R: lower quality Hudson 62227, high quality Tolco 942

 

• Drawbacks are the need to stoop very close to ground level & the weight combined with pulling the trigger all day is hard on your hand & wrist.  Stooping risks eye or nose injury in dense brush clones.
• Avoid the cheap ones at brick & mortar stores.  If they don’t leak from the get go (often from the pump shaft if you tilt the bottle too far off vertical), they will leak or fail sooner rather than later.
• See grasslandrestorationnetwork.org/2020/11/05/hand-held-herbicide-sprayer-comparison/
• 2 quart capacity is necessary for a full day of cut stump without refilling.
• To keep the bottle outside surface free of poison ivy & herbicide when working alone, place it in a 5 gallon bucket when not spraying.  Use spacers of some kind to place the sprayer in the bucket such that the nozzle sits over a drip catching tray.
• Standalone sprayer
• Advantages are no stooping required, the trigger is easy on your hands/wrist & a wide selection of nozzles are available.
• I put the sprayer in a bucket as shown below.  Without the bucket, the sprayer will tip over on uneven ground & can become contaminated with poison ivy & herbicide.  It also makes working alone much easier.  I can spray some stumps soon after cutting so all can be found, hang the sprayer wand on the coat hook, cut some more stumps with loppers, then spray again.  The nozzle I use is a single stream type, which is just a cylindrical tube.  With low pressure, a light hand & a hose clamp trigger stop, I can place the nozzle against the stump & flow just enough herbicide to prevent drippage onto the soil.  

 

Woody plant spray fixture for working alone.  Sprayer is Smith 190504.

References

 

1) Schwope, A. D., etal, 1992, Permeation Resistance of Glove Materials to Agricultural Pesticides.  AIHA Journal 53(6):352

2) Losure, D.A., K.A. Moloney and B.J. Wilsey. 2009. Modes of crown vetch invasion and persistence.  American Midland Naturalist 161:232–242.

3) Osmund, D., 1997, Cut-stump treatment of buckthorn effective despite two-hour delay between cutting & spraying (Illinois).  Restoration & Management Notes, 15(2): 197.

4) Graziano, G, etal, 2022, Herbicides in unexpected places: non-target impacts from tree root exudation of aminopyralid and triclopyr following basal bark treatments of invasive chokecherry (Prunus padus) in Alaska.  Weed Science, 70(6): 701-714.