The frequency with which Ortho herbicides can be applied is normally limited to two applications per year: a primary application followed by a second application shortly thereafter to eradicate any lagging or persistent weeds. Wouldn't it be great if the answer were as simple as “mid-May” or “end of July”? Sorry. Applying an herbicide is not a one-time thing. It has to happen several times a year.
Different weeds grow at different times throughout the seasons. That's why our comprehensive lawn care programs make five visits throughout the year. The first round of fertilizer and weed control should be done before Memorial Day. Three more visits take place during the summer.
Fall is the best time of year to control weeds, so take another chance to eliminate them. Post-emergent herbicides are most effective when weeds are actively growing. Selective post-emergent herbicides attack certain types of plants, such as perennial broadleaf weeds, such as dandelions (Taraxacum officinale) and plantain (Plantago major), or annual weeds, but do not harm lawns. The best seasons to apply a post-emergent herbicide to control perennial broadleaf weeds are early fall and spring.
Apply the herbicide on a calm day when the air temperature is between 60 and 80 degrees Fahrenheit and no rain is forecast for 48 hours. The first step to effective weed management is to evaluate the turf and determine what conditions may have contributed to existing weed problems. Start by testing the soil to determine current nutrient levels and soil pH. Once soil fertility problems have been corrected, use appropriate measures to eliminate any soil compaction problems and excess straw.
Mowing the grass too low (also known as mowing the scalp) puts pressure on the grass, and the cutting height must be adjusted by raising the mower to the correct cutting height for your type of grass. Adjust irrigation as needed to apply 1 inch of water per week in combination with rain when the grass is actively growing. Depending on the type of soil, the watering schedule may be once or twice a week. Finally, correct areas with poor soil drainage.
Weak grass stands may also need to be renovated. The chronological lawn weed control chart was developed to help eliminate confusion and guesswork when determining the recommended time of year to control the various weeds in lawns. Pre-emergent herbicides control annual grass weeds as they sprout, meaning that the herbicide must be in the grass before the seeds begin to germinate. Choose a comprehensive, proactive lawn care program that includes preventive and curative treatments to eliminate weeds from the lawn.
Herbicides should not be applied to grass when the temperature exceeds 85°F or when the grass is under water stress (wilted). I wouldn't rush to apply a lawn herbicide to the entire lawn in early spring, as there will be a lot of weeds that won't come to the surface until later.
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