David M. Kopec, Extension Turfgrass Specialist
Spring time is the best time to prepare for weed control of summer annual weeds. Summer annuals germinate in the spring (late winter at low elevations), grow through the summer and then flower and wither away in the fall.
At lower (desert) elevations, the most common summer annuals include, southwest cupgrass, some crabgrass, stinkgrass, foxtails, crowsfootgrass and the broadleaf weeds like spurge, verde-largo (purse-lane) and prostrate spurge.
At mid to higher elevations (4500 ft. and above) the same weeds generally occur, but there is more crabgrass than cupgrass and goosegrass.
Grassy weeds can be controlled by use of widely used pre-emergence herbicides. These include treflan, surflan, prodiamine, pendimethalin, Ronstar, dacthal and baylan. These are sold as granules or wettable powders. Some are sold as "weed-n-feed" products (lawn fertilizer granules impregnated with herbicide). Most can be applied to all grass lawns, except surflan, which will "ding" ryegrass overseed lawns. Always check the label for turfgrass tolerance.
Broadleaf weeds can be controlled with a pre-emergence product called Gallery. The active ingredient is isoxaben. Gallery can be applied alone, or in a pre-packaged mixture called Snapshot. This is a mixture of Gallery plus surflan and is designed to control both broadleaves and grassy weeds, before they become established.
The irrigation or "rain-in" time after product application of the herbicide is critical. It can be as necessary as 2-3 days, or up to 3-4 weeks. Fertilizer "weed-n-feed" products should be watered in the same day, regardless of the product.
Application dates for spring pre-emergence should take place when the soil temperatures at 2.0 inches are at 50F. General guidelines follow.
Yuma February 10 - March 1 Phoenix February 25 - March 5
Tucson March 1-10 Cochise Cty March 20 - April 1
Globe March 20 - April 1 Kingman April 10 - 20
Payson/Show Low April 20 - May 5 Flagstaff May 1 - May 15
A rule of thumb is to apply these herbicides when bud breaks just occur on pecan trees. If you know of a local tree or shrub which meets this criteria, so much the better. Remember, AZMET weather stations record soil temperatures and are easily assessable.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.