Best Time to Kill Thistles such as Non-Native Canada Thistle? Spring and Fall!

Spring and fall are excellent times to attack non-native thistles such as Canada thistle (Cirsium arvense).  Here’s a photo of a very young Canada thistle rosette taken in early spring in a small prairie area that we are restoring.

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I used our Large Foam Herbicide Dispenser with the mesh brush attachment to wipe foam herbicide on the rosettes.  One nice thing about early spring is that the plants are well spaced and you can easily isolate the target weed.  Thus, you can avoid harming desirable native plants.

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As shown below, you can get a perfectly targeted application of the foam weed killer by wiping the foam directly onto the leaves of the thistle.

In terms of herbicide rates, most labels for glyphosate suggest rates that are pretty high for wiping.  In some cases, the recommended wiping solution may have 20% active ingredient.  In my opinion, this is too high.  (That high rate may be suggested because conventional wiping applications with sponges or fabric wipers result in a lot of drippage.)  Foam herbicide reduces the drippage to a minimum.  Using foam herbicide, I have had success with rates that are about 4% to 8% active ingredient.

In terms of timing, in the spring make sure you treat the Canada thistle in the rosette stage before it starts to bolt.  Once it is bolting, it will be hard to control with herbicide.  In the fall, wait until you have had a frost or the weather has become pretty cold in your area.  As long as the thistle leaves remain green, you can treat them.

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Foam weed killer applied to Canada thistle in December. Nearby there was snow on the ground.

 

Best Season to Apply Brush Killer to an Invasive Tree or Vine? Late Winter Works Too!

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Common buckthorn branch with live inner bark exposed in February

In the last post, I talked about wintertime being an ideal season to kill an invasive tree, shrub or or other woody weed.  Why?  During winter woody perennials such as trees, vines, and bushes are dormant, i.e., at rest, but their above ground vascular systems in their stems are still fully alive.  If you cut through the outer bark, you will reach the live inner parts of the weed tree, vine, or shrub.  Part of that live inner bark, the phloem, will readily absorb herbicide and will translocate the herbicide to the roots or rhizomes of the plant.

In spring and early summer, the situation is very different.  Sap will be rising from the roots to feed the above-ground sinks such as leaves, flowers, etc.  If you treat an invasive honeysuckle with weed killer in spring, for example, the top of the shrub may die, but the roots will likely survive and you will eventually get nasty re-sprouts near the base.  Instead of 5 or 6 stems to treat, you might now have more than 20.  The upshot, therefore, is avoid using brush killer in early spring.

What about late winter?  How long is winter and dormancy for purposes of applying a weed killer to an invasive tree, vine or shrub?

The answer depends on where you live.  “The timing of . . . [the] release from dormancy is synchronized with local climates and is highly heritable.”  Yordanov 2014.

Temperature appears to be the key thing to watch.  Bud-break in temperate woody species is “almost exclusively dependent on high temperatures.”  Busov 2016.  If buds don’t seem to be swelling and nights are still cool, the woody perennial should still be largely dormant.

(Note: If you want to get a sense of what bud break looks like, look at the time lapse photos in this article by Sivadasan et al. 2017.  Sivadasan and colleagues divide budbreak into five stages.  The earliest stage with the bud still closed and with no protruding leaf tips, is probably the only feasible time to do the herbicide treatment.

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Buds of common buckthorn in early February – still completely closed

In south-central Minnesota in locations around the Twin Cities  (i.e., pretty far north in the United States!), I have done cut stump treatments on invasive common buckthorn (Rhamnus cathartica)  as late as early April with excellent results.  Those treatments were done when daytime temperatures were warm, but nighttime temperatures were still often near or below freezing.  My guess is that those treatments were successful because the trees were still dormant (or maybe just emerging from dormancy).  However, in years when springtime comes early, a weed killer treatment in my area in early April might fail.

In most other parts of the country, the emergence from dormancy of invasive woody perennials will typically be much earlier.  Someday we’ll certainly have data that is specific to each invasive species in a region.  We already have it for crops such as almonds, pistachio, and walnuts, thanks to a citizen science project the University of California at Davis.  Right now, however, determining the end of the winter herbicide application season will have to be an educated guess.  Consider daytime and nighttime temperatures, bud stage, and possibly even the start of the pollen season.

I really enjoy doing invasive plant control work in late winter.  The sun is stronger and ticks and bugs still shouldn’t bother you.  You can also see really well because the bushes and trees still won’t have leaves.   It is also particularly satisfying to know that you will be opening the canopy to native species that are just waiting for those first warm days of spring!

Best Time to Kill Tree that Is Invasive – Winter!

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When it comes to killing woody invasive plants, winter is generally the best time. This may surprise you.  Herbicide labels may confuse you because labels often say the herbicide should be used when the target weed is “actively growing.”

However, cut stump and basal bark treatments work great in winter as long as the plant has an above-ground stem with live inner tissue.  Weed trees and bushes all have live inner bark – the cambium layer.  Therefore consider winter treatment for invasive woody species such as Asian bittersweet, buckthorn, honeysuckle, kudzu, privet, tree-of-heaven, etc.

There are a number of advantages to working in winter (or late fall):

  • Effectiveness: The greatest success I have had controlling woody species is in late fall, winter, or very early spring (before sap starts flowing up the stem to the branches).  This is true for others too.  Reinartz 2002.
  • Ease of Movement: The absence of leaves and growing plants makes it surprisingly easy to move through dense growth.
  • Comfort: Removing invasives can be a lot of work, especially if you use hand tools.  You can stay warm without being sweaty and uncomfortable.
  • No Mosquitoes or Ticks:  This is a godsend.  If it’s above freezing and there’s no snow, ticks can be out but at very reduced numbers.
  • Identification of Targets: As long as you can identify the invasive by the bark and structure of the plant, Identification is much easier.  Without leaves blocking your view, you can see so much better.

Caveats:

  • Cold Temps: I usually do not work when it’s below about 20 degrees F.  If it gets below that temperature, water-based herbicides may freeze, especially around the nozzle.  Plastic containers also become more fragile.
  • Deep Snow: It is difficult to do either cut stump or basal bark treatments if the snow is more than a few inches deep.  You can remove snow around the base, but this can be time-consuming.

For cut stump treatments, cut the stump as close to the ground as possible (1 to 2 inches) above ground level.  (I find that failed cut stump treatments often result from cutting the stump too high.)  Brush off any debris on the stump face.  (Dirt will neutralize herbicides such as glyphosate.)  Then apply the herbicide immediately after cutting (within 5 minutes or so).

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Freshly cut stump of weed tree

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Foam herbicide applied to cut stump in winter

Good luck!  I hope you are able to get out on a nice warm winter day to remove some invasive plants.  It can really be enjoyable!

Electronic Sprayer – Our Newest Dispenses Herbicides with High Precision as Foam or as Spray

In this piece we identify the key advantages of our new ultra-low pressure electric dispenser (patents pending).  (See also this YouTube video: Electronic Dispenser Dispenses Herbicide with High Precision.)

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First, when used as a sprayer (i.e., for spraying liquid drops), ultra-low pressure (i.e., less than about 15 psi) offers key benefits.  The biggest is less off-target spray.   We did indoor testing in 2016, where we sprayed colored water on white paper using a Hypro(R) 30HCX8 hollow cone nozzle.  We sprayed at a variety of psi’s.  What was particularly striking in these tests was how far the spray extended beyond the primary spray band at higher pressures.  At 30 psi, the spray band extended at least 30 inches beyond the center-line!  This was an indoor test with no wind.  At 9 psi the “shadow spray band” only extend 15 inches.  This means, if you are spraying at a high psi,  you are doing off-target damage to desirable plants and wasting a lot of expensive herbicide.

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Second, ultra-low pressure places far lower demands on the pump and battery.  This means our electric sprayer can be far lighter than the competition.  Other electric systems typically weigh well over 15 lbs.  Ours, even with the fully padded backpack frame, weighs about 10 lbs.!

Third, ultra-low pressure makes great foam!  For example, you can hook up our foam-making attachments with the mesh brush.  Use it to wipe foam herbicide onto foliage or onto stumps.  As shown below, you will get high precision, no drippage (like you do with conventional wiping systems), and extended absorption of the herbicide into the weed’s vascular system because the foam keeps the herbicide in liquid form longer.  (Here’s a YouTube video: Cut Stump Treatments)MeshWiperBrush

We will be producing a limited quantity of our Ultra-Low Pressure Electric Dispenser in the first year (2017).  We are primarily selling it to professionals with a strong need for the benefits offered by the system.  Please contact Green Shoots for availability and pricing!

Basal bark applications of herbicide with new ultra-low pressure dispenser

Our new dispenser works great for doing basal bark applications of herbicide.

015-340x800Basal bark treatments involve the application of an ester herbicide in an oil carrier to the bark of a tree.  We actually dial the pressure in at 2 psi – i.e., very low!  This produces a narrow stream of herbicide that can be precisely applied even to very small stems such as the one shown below.  This reduces off-target harm and reduces herbicide waste.  We posted a YouTube video that goes into greater depth.

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New Product – Electric Backpack Sprayer with Precision Spray Technology

Green Shoots will be offering a new electric sprayer in 2017.  The sprayer will operate on ultra low pressure.  This has lots of advantages including more precision and less off-target spray.  This is especially important when spraying herbicides because off-target spray can harm desirable plants and waste expensive herbicides.  The battery will last for a full day.  The sprayer can also easily be converted into a foam dispenser.  The sprayer will have all sorts of other great features, many of which are shown in the following photos.

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The pressure can be adjusted in increments of 0.2 psi and from 1.5 psi to 12 psi.  Pressure from about 1.5 psi to 10 psi works great for dispensing foam.  Pressure from about 5 psi to 13 psi works great for spray.  Green Shoots will also offer a very comfortable backpack frame with a hip belt.

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Remember with this electric sprayer there is no pump lever, so one hand can hold the spray wand and the other can be free.  Elimination of the pump lever also makes it much easier to maneuver in thick brush.

Ultra Low Pressure Sprayer – New Prototype Being Tested

We are testing our latest innovation – an ultra-low pressure sprayer.  It can operate at under 10 psi.

Ultra Low Pressure Electric Dispenser

Ultra Low Pressure Electric Dispenser

Spray pattern shows evenly spaced droplets

Spray pattern shows evenly spaced droplets

What are the advantages of ultra-low pressure?  First, there is less drift.  That’s because the ultra-low sprayer consistently produces medium size drops, not the very fine, drift-prone drops.  Second, the drops from the ultra-low sprayer travel slower through the air.  This means that the drops are less likely to bounce off the foliage of the target weed.  Finally, the ultra-low pressure sprayer uses very little power.  This means the sprayer can be lighter and still operate for a long time on a single charge.  Here’s a video of ultra low pressure sprayer demonstrating the new dispenser.