From the Gamekeeper Podcast Studio – Episode 461 Old Field Management – Joined by the great minds of Bronson Strickland and Bonner Powell of Wildlife Investments. We talk about an often overlooked area on hunting properties, old fields. Subscribe on YouTube or Apple
Every Gamekeeper managing an old field eventually runs into the same enemy. Sweet gum and green ash seedlings creep in from the edges, grow faster than anything planted around them, and within a few short years can shade out an entire field of valuable native forage. Wildlife biologists Bronson and Bonner Powell of Wildlife Investments walked through exactly how these two trees take over, and the specific chemical and fire combination that actually pushes them back.
Why These Two Trees Are Such Persistent Problems
Sweet gum and green ash are the two woody species that come up most often when Gamekeepers describe frustration with old field encroachment. Bonner noted that green ash tends to be the bigger problem specifically in soils where it grows well, since it can be even more aggressive than sweet gum under the right conditions.
Both species share a trait that makes them especially difficult to manage once they get established. When a Gamekeeper cuts, mows, or bush hogs these trees down, they do not simply die off. Instead, they respond with stump sprouts, new growth erupting directly from the existing root system. Because that root system already has years of stored underground biomass built up, stump sprouts grow far more aggressively than a brand new seedling ever could, making round two of any given tree noticeably tougher to kill than round one.
The First Line Of Attack Has To Be Chemical
For any old field where sweet gum or green ash has grown taller than head height, Bonner is clear that chemical treatment needs to come first, either through direct spraying or by bush hogging the trees down to a manageable height before following up with herbicide on the resulting stump sprouts. Attempting to jump straight to fire on a densely wooded old field almost never works.
The reason comes down to fuel. A field choked with sweet gum and green ash saplings has essentially no grass growing underneath that dense canopy, since the trees are shading out the very fuel a fire would need to carry across the ground. Without grass to burn, fire simply will not move through the area with enough intensity to damage established trees, no matter how badly a Gamekeeper wants it to work. The herbicide step has to happen first to open the canopy and give grass a chance to reestablish before fire becomes a useful tool again.
When Mechanical Treatment Makes Sense Alongside Chemical
Herbicide is not the only tool available for the initial knockdown phase. Depending on the density and size of the trees involved, bush hogging can serve as an effective first step to physically remove standing biomass before or alongside a chemical application. Bonner noted that for smaller diameter sweet gum and green ash, mechanical mulching equipment can also make quick work of dense thickets that would otherwise take a long time to treat with herbicide alone. The tradeoff is that mechanical treatment by itself, without a herbicide follow up on the resulting stump sprouts, tends to produce exactly the kind of aggressive regrowth described earlier. Cutting or mulching without a chemical follow up essentially resets the clock rather than solving the underlying problem, since the root system remains fully intact and ready to push out vigorous new growth almost immediately. The most effective approach usually combines mechanical removal for the heaviest biomass with a targeted herbicide application on the fresh stump sprouts that follow, giving a Gamekeeper the benefit of faster initial clearing without sacrificing the long term kill rate that chemical treatment provides.
Choosing The Right Herbicide Depends On What You Have Left
Not every herbicide behaves the same way once trees enter the picture, and choosing the wrong one can undo months of careful old field work. Imazapyr, sold under the brand name Arsenal, is highly effective at killing trees, which makes it an obvious first choice for many Gamekeepers. But Bonner pointed out an important complication. Imazapyr was originally developed in part to help young pine trees survive by eliminating grass competition, which means it kills grass just as effectively as it kills trees.
In an old field that already has little to no grass base because of heavy tree encroachment, spraying imazapyr solves the tree problem but simultaneously wipes out whatever thin grass component might still be clinging on, leaving a Gamekeeper with bare ground and no fine fuel to work with going forward.
This is where garlon, also known by its active ingredient triclopyr, becomes the better choice in these specific situations. Garlon kills trees effectively but does not harm grasses, which means a Gamekeeper dealing with a grass deficient field can use it to clear out sweet gum and green ash while preserving whatever grass base already exists. Bonner recommends sticking with garlon or a similar triclopyr based product for a couple of years in these tough starting conditions, allowing a workable grass base to build back up before eventually transitioning to a more standard herbicide and fire rotation.
Building Toward A Burnable Field
Once enough grass has reestablished through this garlon based approach, the long term goal becomes reaching a grass composition of somewhere around 30 percent at minimum, with 40 to 50 percent considered ideal for a field that needs to carry fire reliably. Bonner explained that grass functions as the fine fuel in an old field the same way pine needles function as fuel in a managed pine stand. The further a field’s composition drifts away from that 50 percent grass benchmark, the harder it becomes to carry a controlled burn through it with any real effectiveness.
Transitioning Into A Fire Rotation
Once chemical treatment has knocked back the worst of the sweet gum and green ash and a reasonable grass base has developed, fire becomes the primary long term maintenance tool. Bonner described using annual burn rotations for several consecutive years in situations where tree encroachment was severe, essentially wearing down the remaining trees year after year until they are finally killed off rather than simply topped and allowed to resprout again.
Once that initial aggressive phase has accomplished its goal, the burn frequency can typically back off to something closer to a two year rotation for ongoing maintenance. The exact interval still depends heavily on site conditions. Bottomland areas with rapid tree growth may need annual burns indefinitely just to stay ahead of resprouting, while a dry ridge top with thin topsoil might only need fire once every three years to stay in good shape.
Why Stump Sprouts Deserve Extra Attention
Because stump sprouts draw on an established root system rather than starting from scratch, they demand a different level of persistence than a first year seedling. A Gamekeeper who cuts or burns a sweet gum or green ash once and assumes the job is finished is likely to be disappointed the following season when that same tree comes back thicker and more vigorous than before. Following up with a targeted herbicide application on the resprouting stump, rather than relying on mechanical cutting or fire alone, gives a much better chance of actually killing the root system rather than simply setting it back temporarily.
Putting The Whole System Together
The full sequence Bonner and Bronson recommend for reclaiming a sweet gum or green ash choked old field starts with an honest assessment of how much grass fuel currently exists in the field. If grass is essentially absent, garlon or a similar triclopyr product becomes the starting herbicide, since it clears trees without eliminating the grass base a Gamekeeper is trying to rebuild. That approach continues for roughly one to two years until enough grass has returned to reach that critical 30 percent threshold.
From there, fire takes over as the primary tool, starting with an aggressive annual rotation to continue wearing down any surviving trees and stump sprouts, before eventually settling into a more relaxed two year rotation, or longer on poorer, drier sites, once the woody competition has been brought under control. Imazapyr can reenter the toolkit at this later stage as well, once the grass base is well established and its grass killing tendency becomes less of a concern relative to its strength against remaining trees.
Conclusion
Gamekeepers who skip straight to fire on a heavily wooded old field, or who use the wrong herbicide for their specific starting conditions, often end up frustrated and convinced that old field management simply does not work on their property. In reality, the sequence matters just as much as the tools themselves.
Matching the right herbicide to the actual grass content of a field, being patient enough to rebuild a fuel base before relying on fire, and following up persistently on stump sprouts rather than assuming one treatment is enough are the details that separate a field that gets reclaimed from one that stays locked in a losing battle against sweet gum and green ash indefinitely. With the right sequence and enough patience to see it through multiple growing seasons, even the most heavily wooded old field can eventually be turned back into the kind of productive, open habitat a Gamekeeper originally set out to create.
