Understory Foliar Spray Applications in More Developed Stands

Problematic plants and cost-share

An expanse of mature or well-developed forestland in the southeast contains plant species deemed undesirable by landowners. Plants may be suppressing 1. forest regeneration, 2. preferred wildlife habitat, 3. aesthetics, or 4. simply hindering overall enjoyment of the area. These plants may be non-native, invasive species such as tree of heaven (Ailanthus altissima), Chinese wisteria (Wisteria sinensis), Chinese privet (Ligustrum sinense), or a number of others. Some native species poison ivy (Toxicodendron radicans), poison sumac (Toxicodendron vernix), or coralberry (Symphoricarpos orbiculatus) may also hinder landowner usage or the implementation of management activities.

The Natural Resources Conservation Service (NRCS) has a cost assistance program named the Environmental Quality Incentives Program (EQIP). One of the practices covered in this program is brush management (code 314). Landowners whom have gone through the enrollment process and are approved may opt to utilize this program to assist with lessening the financial burden to control such plants in the understory of developed or mature stands. The author has worked with numerous clientele in the past whom were contracted within the EQIP program. The following are results and observations from work on these jobs as well as supporting scientific literature.

Recommended tank mixture

Understory foliar spraying can be an enjoyable experience for those that like to put “sweat equity” into their property. Aside from the cost of herbicides and a backpack sprayer, the financial burden is minimal, especially when the landowner is engaged in a cost-share program. My general, lower cost recommendation for treating a spectrum of plant species would be to combine a triclopyr (either ester or acid formulation) product with glyphosate. Triclopyr would be approximately 1% – 2% (1% if using acid formulation, 2% if ester) of the solution and glyphosate as 2% – 3% of the same solution. These herbicides are arguably the cheapest options and both have little to no residual soil activity. This attribute reduces the potential threat (mortality/crown dieback) to overstory tree species via underground root uptake. Care should be taken to avoid applications when air temperature reaches above 90°F as volatilization by ester triclopyr can occur and damage overstory canopy. According to Miller (2003), triclopyr ester (acid formulation should also work) can be used to control the following:

1. Tree of heaven
2. Mimosa/silktree (Albizzia julisbrissin)
3. Paulownia (Paulownia tomentosa)
4. Chinaberry (Melia azedarach)
5. Tallowtree (Triadica sebifera)
6. Autumn/Russian olive (Elaeagnus sp.)
7. Winged burning bush (Euonymus alata)
8. Chinese privet
9. Bush honyesuckles (Lonicera sp.)
10. Nandina (Nandina domestica)
11. Multiflora rose (Rosa multiflora)
12. Oriental bittersweet (Calestrus orbiculatus)
13. Climbing yam vines (Dioscorea sp.)
14. Winter creeper vine (Euonymus fortune)
15. English ivy (Hedera helix)
16. Japanese honeysuckle (Lonicera japonica)
17. Kudzu (Pueraria montana)
18. Vinca/Periwinkles (Vinca sp.)

***the publication advises basal bark applications (20% herbicide with 80% basal oil) for larger stems for most of the plants listed above. Given the herbicide mode of action, foliar sprays that cover most of the plant foliage at lesser rates should theoretically also provide adequate control. The author has observed this outcome on a number of the species in the field post-treatment.

Triclopyr is excellent at controlling a range of woody plants, but ineffective on controlling most grass species and has a limited spectrum of forb control (based on the Garlon 4^® and Trycera^® label). The addition of glyphosate gives the applicator the ability to control a greater range of herbaceous vegetation. Thus, a combination of these two products will control most of the treated vegetation within target zones.

Glufosinate-ammonium as a substitute for glyphosate

For individuals that would prefer to use an alternative to glyphosate, glufosinate- ammonium (Finale VU^®, etc) can control numerous grasses, broadleaf forbs, and multiple hardwood/pine species (according to Finale VU^® label). Research on invasive plants Glufosinate has been effective (82%-85%) at controlling microstegium (Judge and others 2017). According to Takano and Dayan (2020), glufosinate ammonium has been used on glyphosate resistant crops but there is inconsistency in its effectiveness compared to glyphosate. The study also suggests that grasses are less susceptible to glufosinate compared to broad leaves. Ultimately, the user must identify the target species to be controlled, then ensure the glufosinate-ammonium substitute herbicide will have high efficacy by checking the label to ensure the plant is listed as a species controlled.

Increased rate for waxy-leaved plants

Some of the waxy leaved species such as English ivy, Vinca major/minor, leatherleaf mahonia, holly (Ilex sp.), winter creeper, oriental bittersweet, etc. may not be controlled at lower triclopyr/glyphosate application rates. This may be caused as a result of the epicuticular wax inhibiting herbicide absorption into the plant’s cells. The applicator may opt to slightly raise the application rate up a couple percent or use an oil adjuvant (such as a basal oil or crop oil concentrate) to increase absorption into the plant. In some cases, secondary applications may be warranted to achieve full control in problematic areas.

Aminopyralid use on invasives

The presence of kudzu is arguably the most problematic of all the invasive species in that the vine completely “suffocates” almost the entire plants in an infested area. The author has sprayed multiple herbicides atop of kudzu in a demonstration area at the John De La Howe Governor’s School of Agriculture. Foliar applications included treatments of clopyralid (Clopyralid 3^®), triclopyr (Remedy^®), aminopyralid (Milestone^®), metsulfuron methyl (MSM60^®), and picloram (Grazon^®). All of these herbicides appeared to control kudzu when foliage was dampened with solution. Of all these herbicides however, aminopyralid (Milestone^®) was the only one that completely deadened individual treated vines when only a portion (approximately lower 12’ reached by sprayer) of the vine received spray solution. The author has applied kudzu treatments in multiple states over his career and in the case of vines climbing trees, has always had only partial deadening where solution actually contacted foliage (for every herbicide besides aminopyralid). In those instances, a cut stem treatment was needed to sever the vines then immediately apply a cut stem herbicide treatment. A one-time application of aminopyralid has the potential to reduce labor costs/time spent on control measures.

The Milestone® herbicide label also lists the following additional invasive or problematic plants as being controlled:

1. Tree of heaven
2. Mimosa/silktree
3. knapweeds (Centaurea sp.)
4. black locust (Robinia pseudoacacia)
5. honey locust (Gleditsia triacanthos)
6. sicklepod (Cassia obtusifolia)
7. Japanese stiltgrass/Nepalese browntop (Microstegium vimenium)
8. Wisteria species (Wisteria sp.)

*most legumes are susceptible

Aminopyralid could be substituted in a tank mix for either triclopyr or glyphosate to improve plant control for understory spray applications pending the targeted species. The herbicide should have negligible damage to overstory trees or grass species which may be beneficial for establishing early successional habitat beneath disturbed (commercially thinned) stands. This herbicide is commonly used in pasture or grassland management. Research has found the addition of aminopyralid to tank mixes for forestry applications as being beneficial as well.

Treatment of larger saplings

There will likely be some stems that may be too large/tall to adequately cover enough foliage with herbicide solution to induce mortality. Basal bark applications, cut stump herbicide treatments, or stem injection (hack and squirt) should be used for these stems. Commonly used herbicides for these practices include formulations of triclopyr (Garlon^® products, Trycera^®, etc), imazapyr (Arsenal AC^®, Polaris AC^®, Alligare 4 SL^®, etc), and aminopyralid (Milestone^®). Lowe and others (2008) found up to 100% mortality could be obtained by applying either triclopyr (ester product) or imazpyr with basal oil as basal bark sprays on Amur honeysuckle (Lonicera maackii), autumn olive (Eleagnus umbellata), multiflora rose (Rosa multiflora), and black cherry (Prunus serotina). Similarly, DiTomaso and Kyser (2007) found both imazapyr and triclopyr were effective, applied as either cut stump, basal bark, or stem injection treatments, having <90% reduction in vigor and resprouting of tree of heaven. In the aforementioned study, the poorest rate of mortality of the herbicide treatments was 83% for basal bark application on multiflora rose. One study (found contrary results and suggests that using triclopyr ester with basal oil alone will only control the treated stem but will not completely control resprouting from roots. Timing application during the growing season did not have an impact on results. The addition of a soil active herbicide (such as imazapyr, picloram, or metsulfuron methyl) could achieve control but may be detrimental to overstory stems. Thus, a secondary application would be warranted to control resprouting.

In summary, the triclopyr plus glyphosate solution should provide control of most plant species found in the understory of developed stands. Collateral damage (such as advanced oak regeneration) of desirable plants should be expected even when applicator care is used to avoid direct spraying. These herbicides should not damage overstory trees however due to the lack of residual soil activity. Glufosinate-ammonium is a possible substitute for glyphosate but may be of lower efficacy. Aminopyralid may be the most optimal herbicide to apply on kudzu and also provides great control of leguminous species such as mimosa, locust, etc. And lastly, basal bark applications using ester or acid formulations of triclopyr will provide favorable levels of vegetation control on larger sapling sized plants.

References:

DiTomaso, J.M. and G.B. Kyser. 2007. Control of Ailanthus altissima using stem herbicide application techniques. Arboriculture & Urban Forestry 33(1): 55-63.

Johnson, J.M. 2011. An evaluation of application timing and herbicides to control Ailanthus altissima. M.S. Thesis – Pennsylvania State University.

Judge, C.A.; J.C. neal, and J.F. Derr. 2005. Preemergence and postemergence control of Japanese stiltgrass (Microstegium vimineum). Weed Technology 19(1): 183-189.

Miller, J.H. 2003. Revised 2006. Nonvative invasive plants of Southern forests a field guide for identification and control. US Forest Service – Southern Research Station Gen. Tech. Report SRS-62. 95 Pp.

Lowe, Z.E.; H.P. Weeks, H.A. Holt, and G.R. Parker. 2008. Control of woody invasive plants using mechanical and chemical treatments. Goodrich-Mahoney, J.W., Abrahamson, J.P., Ballard, J.L. and Tikalsky, S.M. eds. Environmental Concerns in Rights-of-Way Management: Eighth International Symposium.

Takano, H.K. and F.E. Dayan. 2020. Glufosinate-ammonium: a review of the current state of knowledge. Pest Management Science 76(12): 3911-3925.

Author(s)

Stephen Peairs, Cooperative Extension, Forestry and Wildlife Specialist

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