Weed War: When & How to Use Chemical Herbicides Responsibly

Sometimes, despite best efforts, chemical herbicides become necessary. Think carefully — they should be part of an integrated pest management approach:

• Identify the specific problem plant.
• Understand its life cycle (annual/perennial; spread by seed, roots, or both; germination timing).
• Use cultural (weed-discouraging conditions) or mechanical controls first.
• Recognize when weed invasion threatens natural habitat, crops, or structures.

Once herbicide use is justified, evaluate options and select the right product.

Herbicide Terminology

• Pre-emergents: inhibit seed germination.
• Postemergents: work on actively growing plants.
• Nonselective: affect any contacted plant.
• Selective: control only specific plants.
• Contact: affect only applied tissue.
• Systemic: absorbed into entire plant/root system.
• Natural vs. synthetic: both regulated for safety. Ideally applied by licensed pesticide applicator.

Natural Herbicides

Active ingredients from plants/minerals. Read labels thoroughly.

• Corn gluten meal: selective pre-emergent for annual weeds (oxalis, purslane, spurge) in lawns. ~10% nitrogen — promotes healthy turf. Apply twice yearly before germination; dry period after helps. Learn timing specifics.
• Vinegar (horticultural, <20% acetic acid): nonselective postemergent contact herbicide for annual weeds. Spray foliage — acid desiccates (“burns”) leaves, not roots. Most effective on annual weeds in summer heat.
• Horticultural soaps (fatty acids): nonselective postemergent contact. Smothers foliage, inhibits growth. Best on young, actively growing annual weeds.
• Iron (FeHDTA chelate, 1.5%): selective systemic postemergent. Toxic to common broadleaf weeds, safe for turf grasses.

Synthetic Herbicides

Man-made components, regulated. Read/follow labels carefully.

• Glyphosate & glufosinate ammonium: nonselective systemic. Effective on noxious perennials (field bindweed, myrtle spurge, quackgrass). Specific application regime (timing, life cycle stage, method) crucial for efficiency.
• 2,4-D & Triclopyr: selective systemic postemergent. Control many annual/perennial broadleaf weeds (puncturevine, kochia, Canada thistle, orange hawkweed). Effective in lawns and around conifers.

Local Cooperative Extension Office has region-specific weed ID and control research.