Herbicide Options for Hardwood Management Mississippi landowners intent on growing hardwoods Please note: The information given here is for educational are fortunate to have one of the most accommodating sets purposes only. References to commercial products, trade of environmental conditions in the nation. Long growing names, or suppliers are made with the understanding that seasons, great climatic conditions, and the wide variety of no endorsement is implied and that no discrimination appropriate species make establishment and maintenance against other products or suppliers is intended. of hardwood stands attainable as long as appropriate silvi- cultural methods are used. Artificial Regeneration Even a casual observer of nature can see how easily Chemical Site Preparation various woody and herbaceous species colonize most sites Pine and hardwood silviculture differ in many aspects, in the South. Consequently, land managers face a multi- but both systems benefit from proper competition con- tude of problems associated with unwanted vegetative trol. While post-planting herbicide options differ greatly competition. These problems typically involve reduced between pines and hardwoods, chemical site preparation growth in established stands and reduced survival in treatments are very similar. Applications using imazapyr planted stands. (e.g., Arsenal AC, Chopper Gen2) and glyphosate (e.g., Any given tract of land may have a wide variety of na- Accord Concentrate, Accord XRT II) are the “gold stan- tive plant species. Many of these species are not problemat- dard” for cutover sites. Phytotoxic symptoms on planted ic and do not warrant special consideration. Typically, they hardwoods due to residual soil activity of imazapyr have are controlled with herbicides during the establishment not been documented when herbicide applications are period or are deemed to have insignificant negative effects performed at least 12 weeks before planting. Glyphosate, on hardwood survival and growth. However, some species a foliar-active-only herbicide (works only when applied to can be problematic in hardwood management. leaves), has no soil activity and no residual effects. Using herbicides has proven beneficial by lowering Because it is very expensive and has limited her- establishment costs, increasing growth, reducing mortal- baceous control, very little chemical site preparation is ity, and lessening vine-induced stem deformation. This performed in hardwood management. Treatment applica- publication discusses options available in the treatment of tions of this nature are intended to help control species that undesirable vegetation in hardwood management efforts. cannot be eliminated with herbicide applications after trees It is extremely important to follow labeled application rates are planted (e.g., controlling woody species that cannot be and timing because many of the most effective herbicides removed using herbicidal means without severe damage can have negative impacts if applied improperly. This is to planted seedlings). If chemical site preparation should not intended to be an all-encompassing list, but it includes prove necessary, currently the standard recommendation is product names, rates, and application timings of herbicides as follows: that have proven to be effective in controlling some of the 28–32 ounces/acre Chopper GEN2 + 4–5 quarts/acre of a forestry- more common problem species. labeled glyphosate product. Application should occur in August to late October before planting. Chemical Site Preparation 5–6 quarts/acre of a forestry-labeled glyphosate product + an appropriate for Retired Agricultural Fields surfactant Retired agricultural areas have a unique set of environ- 14–16 ounces/acre Arsenal AC + 4–5 quarts/acre of a forestry-labeled mental variables that most cutover sites do not have. While glyphosate product + an appropriate surfactant chemical site preparation on cutover sites primarily targets 16 ounces/acre Arsenal AC + an appropriate surfactant woody competition, former agricultural fields often do not have a woody component. Woody species in former fields 28–32 ounces/acre Copper GEN2 + an appropriate surfactant are often beneficial to planted seedlings, with improvement to desirable stem quality outweighing possible associated Applications should be performed from August to negative effects. A forester or other natural resource profes- October. sional can help determine when nonplanted woody plant density reaches a level that is detrimental to planted stems. Herbaceous Weed Control Site preparation will not provide control of herbaceous Herbaceous weed control (HWC) is a treatment de- competition after planting unless a product with residual signed solely to control herbaceous competition during soil activity like Oust XP is added to the mixture. Again, the first growing season after planting. While broadcast chemical site preparation should only be considered if it is applications can be used for HWC, herbicides are typically necessary to control existing on-site vegetation that cannot applied in bands 4 to 6 feet wide. Banding herbicides in be eliminated using growing-season herbaceous weed con- this manner reduces overall treatment cost and maintains trol. The expense of chemical site preparation is not justi- cover and food sources for wildlife. Research over the last fied unless one or more of these problem species is present. 25 years regarding herbicide rates and application timing Current application recommendations that vary by has resulted in the following HWC recommendation in situation follow: hardwood plantings (excepting cottonwood): 2 ounces/acre Oust XP (Applications should be performed before bud break.) (February–March) (Consideration should be given to soil pH. See below.) Figure 1. Vegetation on a retired agricultural site 1 year post-chemical site preparation. Photo by Brady Self 2 Applied as a pre-emergent, Oust XP (sulfometuron Occasionally situations arise that dictate the use of a methyl) provides excellent control of most grass and broad- grass-only herbicide for HWC. Two products labeled for leaf species. Special consideration is warranted if treating grass control in hardwoods are Select 2EC (clethodim) and areas with higher pH soils (applications of 1 ounce/acre Fusilade DX (fluazifop-P-butyl). Both herbicides are foliar- Oust XP should be used if pH is 6.5 or higher) or areas that active and effective only on grass species. These two her- flood from March to July. bicides offer the best option to control “problem” grasses If HWC is necessary in areas that typically flood, Oust such as bermudagrass or johnsongrass, with Select gener- XP should be avoided. Oust XP will move with water and ally being more effective in single-application treatments. may result in wasted application expense as well as off- Use a nonionic surfactant with either product. Spray rates target impact if flood waters reach application areas. Goal and appropriate application timings depend on growth 2XL (oxyfluorfen) is a good alternative in these situations. stage and target species. Long used in cottonwood HWC, Goal-treated hardwood Different herbicides exhibit different lengths of vegeta- seedlings have exhibited no phytotoxicity. Like Oust XP, tive control when applied on targeted vegetation. None of Goal 2XL provides best results when used as a pre-emer- the herbicides used in HWC will provide complete control gent, but it exhibits less residual soil activity and controls of vegetation for an entire growing season. The intent of fewer species. Of particular note, Goal can be applied post- these applications is not to achieve complete growing- emergent, but it does not control most grasses. Standard season herbaceous control, but rather to provide adequate use rate recommendations are: time for planted seedlings to become established in a “free- to-grow” status. Pre-emergent = 64 ounces/acre Goal 2XL+ an appropriate surfactant Post-emergent = 32 ounces/acre Goal 2XL + an appropriate surfactant Natural Regeneration Light is one of the most important factors in natural re- Application timings for Goal 2XL vary by targeted spe- generation of hardwoods. Many regeneration attempts fail cies. Consult the herbicide label to determine appropriate when established shade-tolerant midstory stems outcom- timing for treatment. pete newly germinated shade-intolerant seedlings. Even Figure 2. Banding of Oust XP in HWC application. Photo by Brady Self 3 the best planned and timed overstory treatments combined October) are most effective; applications from November with a proper harvesting schedule will fail to produce to February and July to August give slightly less control. adequate natural regeneration if available light levels are Avoid injection during March to June. insufficient for germinant survival. Midstory injection is an While injection typically works very well, other effective way to control undesirable stems competing for methods/compounds may be justified at times because of light in the midstory. This increases light at ground level so species resistance and numbers. There may not be enough young shade-intolerant stems can grow. target small-diameter stems to warrant the expense of Several compounds have been tested and are labeled injections. Conversely, the number of target stems may be for injection. Historically, injections were performed by so great as to make injection cost-prohibitive. For more girdling trees using frill cuts and “painting” a solution of detailed information regarding stem