Archive for Sunday, April 12, 1998


April 12, 1998


A critical window period for controlling crabgrass is about to pass.

Did you know that mowing your lawn higher can help with crabgrass control?

While it is true that a short lawn greens up faster in the spring, continuing to mow it short through the spring may allow weeds to get established, especially annual grasses like crabgrass.

A dense lawn mowed high helps with crabgrass control.

To prevent crabgrass seeds from germinating, use a pre-emergent herbicide for crabgrass prevention. Timing is important for good results. The preventers are effective for about 60 days. Crabgrass typically germinates about May 1 in our area, making April 1 to 15 a good time for applications. Weather varies from year to year so as a guide, when Eastern redbud trees are approaching full bloom and lilacs are beginning to bloom, apply crabgrass preventer. The product label will tell you if a follow-up application is needed.

Barricade and Dimension are the only two products that will give season-long control of crabgrass from a single application. Barricade can be applied in the fall for crabgrass control the next season. Dimension can be applied as early as March 1. One inch of water, either rainfall or irrigation, is required to activate the chemical.

Preventers will have no effect on existing crabgrass. Use postemergent herbicides for crabgrass when weeds are actively growing but still small. Soil should be moist before and after the application. Do not mow two days before and after the application. Air temperature should be above 70 degrees Fahrenheit, but below 90 degrees. Do not apply to turf that is under heat or drought stress. Repeat application at one to two week intervals. Rain or watering within 24 hours after the application will reduce the effectiveness.

For perennial broadleaf weeds such as dandelions, use postemergent herbicides such as 2,4-D when the weeds are actively growing and temperatures are 55 degrees to 75 degrees Fahrenheit. Do not treat if rain is expected within 24 hours. Spring and summer treatments do not give results as good as those obtained in the fall. At that time, weeds grow vigorously and consequently fall-applied herbicides are translocated to the roots and the entire plant is killed. Do the best you can with control now and mark your calendar for a fall application.

Postemergent broadleaf herbicides can injure turfgrass and surrounding landscape plants if applied to turf that is drought stressed or when temperatures are above 80 degrees. To avoid injury to landscape plants, do not spray if the wind speed exceeds 5 mph. Be especially careful in the spring when landscape plants are most vulnerable.

Remember, always carefully read and follow all label instructions.

The Garden Calendar is sponsored by K-State Research and Extension-Douglas County and written this week by Master Gardener Pat Lechtenberg. For more information call the Master Gardener Hot Line, 843-7058, from 1 p.m. to 4 p.m. Monday-Friday.

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