Herbicide application for aquatic weeds in fall and winter is generally not recommended due to low effectiveness and potential risks. However, applying herbicides for land management during the fall and winter months can be an effective strategy for managing weeds, particularly perennials, biennials and winter annual species. Perennial weeds are plants that live for multiple years, often regrowing from roots, rhizomes, or tubers after being cut or removed. Biennial weeds are flowering plants that complete their life cycle in two growing seasons. Winter annuals plants germinate in the fall and winter and grow actively in the spring. The approach of treating these types of weeds in the fall and winter leverages the natural life cycle of weeds and environmental conditions to improve control and minimize competition with desirable plants.
In the fall, perennial weeds are actively transporting nutrients to their roots to prepare for winter dormancy. Systemic herbicides, applied at this time, move along with these nutrients, ensuring deeper penetration and improved root kill. Winter annuals germinate in the fall, making this the ideal time to control young, vulnerable plants before they establish. Cooler temperatures and higher soil moisture levels in the fall can enhance herbicide absorption and effectiveness. There is often less risk of herbicide drift, as wind speeds tend to be lower in fall compared to spring or summer.
Common Weeds Treated with Herbicides in Fall and Winter
Perennial Weeds
These weeds store nutrients in their roots during fall, making systemic herbicides particularly effective as they translocate deep into the root system.
Dandelion (Taraxacum officinale): Found in lawns, pastures, and agricultural fields. Best treated with systemic herbicides like 2,4-D or glyphosate.
Johnsongrass (Sorghum halepense): Grass with creeping rhizomes; invades row crops and pastures. Common in disturbed soils and grows year-round in Florida’s climate.
Torpedograss (Panicum repens): Thrives in wet agricultural areas and waterways. Spreads aggressively via rhizomes.
Cogongrass (Imperata cylindrica): Highly invasive and forms dense mats that outcompete native vegetation. Remains green during Florida winters, making it identifiable for treatment.
Kudzu (Pueraria montana var. lobata): Invasive vine that smothers trees and shrubs. Semi-dormant in winter but still treatable with systemic herbicides.
Brazilian Pepper Tree (Schinus terebinthifolia): Woody shrub/tree that invades forest edges and disturbed areas. Actively grows in warm winter months.
Tropical Signalgrass (Urochloa subquadripara): Found in lawns and disturbed areas. Spreads aggressively through stolons and remains green in winter.
Winter Annual Weeds
These weeds germinate in fall, grow through winter, and produce seeds in early spring, making fall applications critical for control.
Henbit (Lamium amplexicaule): Common in turfgrass and no-till fields. Treated with pre-emergent herbicides like pendimethalin or post-emergents like glyphosate.
Chickweed (Stellaria media): Found in lawns, gardens, and fields. Controlled with pre-emergents or post-emergents like 2,4-D or dicamba.
Annual Bluegrass (Poa annua): A problematic grassy weed in turfgrass. Managed with pre-emergent herbicides like prodiamine.
Shepherd’s Purse (Capsella bursa-pastoris): Grows in agricultural fields and disturbed areas. Treated with glyphosate or other broad-spectrum herbicides.
Hairy Bittercress (Cardamine hirsuta): Found in turf and gardens. Controlled with pre-emergents or systemic post-emergents.
Biennial Weeds
These weeds germinate in one season, overwinter as a rosette, and flowers and seed the next year. Fall treatment targets their vulnerable rosette stage.
Wild Carrot (Daucus carota): Found in fields and roadsides. Treated with systemic herbicides like clopyralid.
Bull Thistle (Cirsium vulgare): A spiny weed common in pastures and fields. Controlled with 2,4-D or dicamba.
Garlic Mustard (Alliaria petiolata): Invasive in wooded areas and gardens. Best treated with glyphosate during the rosette stage.
Common Mullein (Verbascum thapsus): Grows in pastures and roadsides. Treated with broadleaf herbicides like 2,4-D.
Herbicide Selection
Systemic Herbicides: Absorbed by the plant and translocated to roots, ideal for perennials and biennials. Examples: Glyphosate, 2,4-D, triclopyr, imazapyr.
Contact Herbicides: Act quickly on aboveground tissues; effective for small annuals. Examples: Diquat, endothall.
Application Tips
Timing: Apply herbicides after weeds have resumed active growth in late summer or early fall. Apply herbicides when temperatures are consistently above freezing for active plant absorption. Ensure applications occur before a hard frost, which can halt nutrient transport in plants.
Weather Considerations: Avoid application during drought stress or freezing conditions. Watch for rain forecasts, as precipitation shortly after application can wash away the product.
Label Instructions: Always follow the herbicide label for recommended rates, mixing instructions, and safety precautions.
Environmental and Safety Considerations
- Use buffer zones to protect waterways, as fall rains can increase runoff risks.
- Choose herbicides with lower environmental persistence to minimize residual effects.
Fall herbicide applications offer a strategic advantage in managing weeds by targeting them during key physiological stages. By using the right products and techniques, you can reduce weed populations and ensure better weed control.
