SPRING WEED CONTROL
David M. Kopec, Extension Turfgrass Specialist
February to mid-March is the time to apply pre-emergence herbicides for your upcoming summer annual weed brigade. It is also time for post-emergence control of Poa annua and other broadleaf weeds in roughs.
Among the first summer annuals to emerge are the grassy weeds like southwest cupgrass, and to a lesser extent, crabgrass. These are followed by goosegrass and the broadleaf spurges. These are the most troublesome on turf.
For pre-emergence control of these weeds, you must ensure that the pre-emergence herbicide will not injure the turf.
For example, surflan applied at the high label rate will control cupgrass, crabgrass, and spurge, but it will stop ryegrass in its tracks. Surflan can be used effectively, however, on dormant bermudagrass.
Perennial ryegrass (active overseed) is tolerant of benefin (BALAN), benefin + treflan (TEAM), benefin + oxidiazon (REGAL STAR), dcpa (Dacthal), dithiopyr (DIMENSION), pendimetholin (PROWL or PR-EM), prodiamine (BARRICADE) and siduron (TUPERSAN).
DIMENSION provides long-term control (up to five months) for cupgrass and crabgrass.
RONSTAR provides excellent pre-emergence control of goosegrass (elusine indica). This grass germinates about three weeks later than cupgrass or crabgrass. My target application for Phoenix will be the last week in March, and April 10 in Tucson.
Note that siduron (TUPERSAN) will ding bermudagrass. If you use this, verify that the bermudagrass underneath the ryegrass is dormant.
For bentgrass greens, only bensulide (BETASAN) and benefin + oxidiazon (REGAL STAR) are somewhat safe as pre-emergence herbicides. Dithiopyr (DIMENSION) is also labeled safe for bentgrass greens. However, I have not had safe experiences with DIMENSION on bentgrass. If you wish to use DIMENSION, apply it to some small areas on a green and see if you obtain a desirable response. Note that it sometimes takes 10-12 weeks for bentgrass roots to show symptom responses to pre-emergence herbicides.
For Poa annua on highout overseed turf (not greens), you can apply EMBARK on a repeat basis program right now. Apply 1/16 to 1/8 lb active ingredient per acre every month. Do NOT exceed label rates.
Some of you are trying PROXY for seed head suppression. We hope to do this ASAP!
In non-overseeded fairway and rough areas, low applications of ROUND-UP can do a very good job of eliminating POA. Apply it now and while it is still mostly vegetative.
REWARD (diquet) is another non-selective herbicide use to knock-out Poa annua and other broadleaf weeds.
If you have burr-clover on your roughs, fairways or other areas, you can apply CONFRONT. This is a mixture of trichlopyr and clopyralid. The clopryalid component is very active on legumne weeds, such as clovers and wood sorrel, and so forth. It is also active on palo verdes, acacias and mesquites. Therefore, be careful around these trees. Hand-spray if necessary. Standard auxin type post-emergence herbicides (24, D, MCPP, dicamba) also work well. Make sure the formulation you select is appropriate for environmental conditions. Amine salts are less likely to vaporize and drift as are ester formulations.
NOTE: Products mentioned are for reference only, and do not imply endorsement. Likewise, exclusion of similar or other products does not exclude valid use selection. Always read the label for use restrictions and safety information.
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.