Thistles are a common and annoying weed that can take over lawns and gardens. They have deep taproots that allow them to spread aggressively and can be difficult to fully remove. When thistles invade grassy areas like lawns, finding the best weed killer to eliminate them without damaging surrounding grass can be a challenge. There are several effective options for chemical thistle control in lawns, but proper usage and timing are key for the best results.
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What types of thistles commonly grow in lawns?
There are several different types of thistles that are found in North American lawns and turf grass. Some of the most common include:
– Canada thistle – Aggressive, spreading thistle with small lavender flowers. Has spiny, deeply lobed leaves.
– Bull thistle – Biennial thistle with spear-shaped, dark green leaves with spiny edges and hairs on top. Produces large purple flower heads.
– Musk thistle – Biennial or annual with large rosette leaves up to 1 ft long with coarse hairs on top and a large taproot. Flowers are large and deep pink-purple.
– Russian thistle – An annual thistle species with small green or purple flowers surrounded by spiny bracts. Leaves are hairy and gray-green.
– Italian thistle – An annual species that starts as a basal rosette with leaves up to 8 inches long. Matures into a spiny, multibranched plant up to 5 ft tall.
– Yellow starthistle – An annual thistle with bright yellow, star-shaped flowers. Forms basal rosettes of lobed leaves with sharp, stiff spines along margins.
All of these thistles can be aggressive invaders in lawns, gardens, and flower beds. Their taproots allow them to access deep soil moisture and nutrients, fueling their spread. The spiny leaves, bracts, and stems deter grazing by animals and make mechanical removal difficult and painful. Using an effective herbicide is often the best control method in areas like lawns where desirable vegetation needs to be preserved.
When is the best time to spray thistles in grass?
Timing herbicide applications properly is important for maximizing effectiveness on thistles while minimizing injury to desirable lawn grasses:
– Spring applications – Spraying thistles in spring as they are just emerging and in the rosette stage is very effective. This prevents them from flowering, going to seed, and spreading further.
– Fall applications – Spraying thistles in fall can also be very effective as the plants are moving nutrients and energy back into the root systems in preparation for winter. Herbicides are readily transported to the roots.
– Avoid summer spraying – Thistles are often under heat and drought stress during summer months, reducing herbicide effectiveness. Summer spraying also increases risks of damage to cool season grasses like bluegrass or fescue.
– Spot spray young plants – Small, young thistles can be selectively controlled with spot sprays versus broadcast applications across the entire lawn. This minimizes herbicide usage.
– After mowing – Applying herbicides right after mowing makes the thistles more accessible to the spray and can improve control. But don’t mow again for several days after spraying.
Following herbicide label directions for proper timing and recommended lawn grass growth stages will ensure you achieve optimal thistle control with minimal lawn damage. Timing applications for spring or fall is ideal.
Most effective chemical thistle killers
Several different herbicide active ingredients are useful for controlling thistles in lawns and turf grass areas. Some of the most effective options include:
2,4-D – A systemic, selective herbicide that controls many broadleaf weeds including thistles. Works best on young, actively growing plants. Often combined with other active ingredients like dicamba, MCPP, or triclopyr. Examples include Trimec, Weed-B-Gon, and Ferti-Lome Weed Out.
Dicamba – Another systemic, broadleaf herbicide. Combined with 2,4-D in many lawn weed killers. Works on emerged thistles along with thistles that germinate later from seed. Found in Scotts Turf Builder Weed & Feed and Spectracide Weed Stop.
MCPP – Selective broadleaf control herbicide used widely for lawn weeds. Effective on thistles, especially when mixed with 2,4-D and dicamba. Included in Ortho Weed B Gon Max and Bayer Advanced All-in-One Lawn Weed and Crabgrass Killer.
Triclopyr – A systemic, broadleaf herbicide often used for tougher weeds in lawn areas. Useful on thistles when mixed with 2,4-D or MCPP. Found in Ortho Chickweed, Clover & Oxalis Killer and Ferti-lome Weed-Out with Crabgrass Killer.
Glyphosate – The active ingredient in non-selective herbicides like Roundup. Can provide full thistle control when carefully spot sprayed on individual plants. Avoid contact with desired grass and plants.
Always read and follow all herbicide label instructions for proper dilution rates, timing, precautions, and re-seeding or re-entry intervals if needed. Combination products like those listed above provide multiple modes of action for the most effective thistle control in lawns while minimizing risks of turf grass injury.
Tips for best results spraying thistles
Following some simple guidelines will help maximize the effectiveness of herbicide applications for controlling thistles in your lawn:
– Mow lawn short before spraying for better thistle exposure.
– Use selective broadleaf herbicides like those containing 2,4-D, dicamba, and/or MCPP for lawn-safe results.
– Spot spray young thistles or do broadcast applications before flowering.
– Adhere to all label directions for concentrations, timing, and required safety gear.
– Spray when air is calm to prevent drift onto desirable plants.
– Mix in a surfactant for better herbicide penetration through thistle foliage.
– Reapply in 3-4 weeks if needed for full control.
– Do not mow lawn again for several days after spraying.
– Acceptable to overseed treated areas 7-10 days after herbicide application.
– When spot spraying, use a cardboard shield to avoid non-target spraying.
– Rinse sprayer thoroughly when finished to prevent corrosion.
Controlling thistles in lawns and turf areas often requires patience and persistence. Integrating proper mowing, fertilization, watering, and herbicide usage will provide the best results long-term. Consult your local garden center or extension office for specific thistle control recommendations in your area.
Organic thistle control options
For those wishing to avoid chemical herbicides, some organic options can help suppress thistle growth but may require repeated applications:
– Vinegar – High concentrations of horticultural vinegar (20% acetic acid) provide nonselective contact weed control. Spot spray thistles.
– Corn gluten meal – Prevents germination of seeds and new seedlings but won’t control existing plants. Use as preemergence weed control.
– Soap-based herbicides – Products like Scythe work as contact weed killers but may require frequent reapplication. Burn back foliage.
– Boiling water – Pouring boiling water directly on thistle crowns can provide spot control of some plants. Takes persistence.
– Physical removal – Digging, hand pulling, hoeing, or mowing can prevent seed production but typically won’t kill plants completely.
– Solarization – Covering areas with clear plastic during hot, sunny weather raises soil temperatures to help kill weeds and seeds.
– Reseeding/Fertilization – Improving lawn density and vigor through proper mowing, fertilizing, aerating, and reseeding helps reduce opportunities for thistles to establish.
For best organic thistle management, focusing on promoting healthy, thick turf through proper cultural practices is key. Hand removal and spot treatment of individual weeds can then help keep populations in check once established.
Conclusion
Thistles can be one of the most problematic weeds that invade turf grass areas like lawns. Their aggressive taproots and prolific seed production allow them to spread rapidly under the right conditions. For selective thistle control in grass, timed applications of liquid broadleaf herbicides containing ingredients like 2,4-D, MCPP, dicamba, and triclopyr provide the most effective and efficient control. Glyphosate spot treatments or organic methods like vinegar can also be utilized. Combining proper herbicide usage with lawn management practices that encourage dense, vigorous turf will give the best long-term control and suppression of thistles.