Mechanical control options: Hardwoods are especially intolerant to competing weeds and grass and may stop growing or die during the first few years of growth. Mowing is most applicable to middle zones between tree rows and can be done using a range of equipment, from walk-behind mowers to tow-behind “bush-hog” type mowers, depending on tree spacing, height of vegetation, and availability of equipment. Handheld trimmers often damage trunks and should be used with great caution. Avoid tree trunk contact that can expose the tree to insects or disease. String trimmers are labor-intensive and time-consuming and most likely to damage the tree trunk. Trimmers work well to reduce competing vegetation along rows between trees (Figure 24).

Use hand pruners or larger tree pruner/loppers to remove individual stems, such as tall, woody stems or entwined vines or post-growth weeds such as privet. Herbaceous vines can grow very quickly and may pull trees to the ground or break stems in just several weeks. When pruning side branches on larger trees, cut them several inches from the trunk to allow callus development. This helps to avoid trunk infection as healing occurs.

Chemical control options: New herbicides are continually being developed and approved. For an up-to-date list, consult the online North Carolina Agricultural Chemicals Manual. Growers can also contact their local county staff of NC Cooperative Extension for recommendations. The following are examples of herbicide classes (chemical name and brand name in parentheses). Please note: Chemical names and sample brand names do NOT represent an exhaustive nor necessarily current list, nor is their mention here intended as a brand-specific recommendation.

Pre-emergent herbicides are used to prevent germinated weed seedlings from becoming established.

• Oryzalin (Surflan ®)

• Prodiamine (Barricade ®)

• Pendimethalin (Corral TM)

Broad-spectrum herbicides control a wide variety of plants and are not discriminatory. They can be very effective at burndown of areas to be site prepared, but can injure or kill young trees.

• Glyphosate (Accord ®, Glypro ®, Roundup Pro ®, many others)

• Sulfometuron methyl (Oust XP ®)

Grass-control herbicides can be used with minimal risk to trees, although direct contact should be minimized.

• Sethoxydim (Poast ®, Segment TM)

Broadleaf weed herbicides labeled for tree plantations control a wide variety of broadleaf weeds with minimal risk to trees, although direct contact should be minimized.

• Clopyralid (Lontrel ® labeled for a variety of hardwood and conifer plantations but not specifically Populus)

• Clopyralid 3 ®

• Transline ®

• Stinger ®

Herbicide application methods: Although large-scale herbicide application equipment, such as tractors with boom sprayers, can be used to do initial pre-planting weed control, later treatments are often done with smaller equipment. Most growers will focus chemical cost to narrower zones along the tree rows (referred to as “banding”) and use less costly mechanical means in the middle zones between tree rows. Grass-specific or broadleaf-specific herbicides are preferable, and broad-spectrum herbicides should be avoided until trees are at least 4 to 5 feet tall. Use shielded sprayers to help avoid herbicide contact with trees.

Herbicide application methods include: backpack sprayers; ATV or utility task vehicles (UTV)- mounted tank sprayers; and ATVs (all terrain vehicles), UVs (utility vehicles), or mower towed sprayers (Figure 25). When it is necessary to apply near but not over tree stems, a shielded backpack sprayer is best

We offer the following recommendations for effective chemical weed and grass control and to avoid major mishaps that may kill or slow growth of trees.

• Within reason, provide a weed and grass-free planting zone at the time of planting.

• During the first two years, control weeds before they reach 30% of tree height.

• Use pre-emergent herbicides to minimize the need for additional herbicides.

• Use labeled herbicides that control the specific weeds or grasses.

• Mechanical methods usually are more efficient weed control for broad areas between tree rows or any time weeds or grass are extremely high.

• Scout every two weeks during the first two years and monthly thereafter.

• Look for areas with difficult-to-control vegetation, such as Johnson grass or woody plants, and spot-treat using appropriately labeled herbicides.

• Avoid contact with planted trees by using shielded sprayers and by avoiding windy days.

• Always use personal protective equipment (PPE) such as rubber gloves and boots, long-sleeved shirts, and eye protection. Always follow label directions.

• Avoid spraying on hot or windy days to avoid drift to tree leaves.