February 1998

Good Weeds for Bad Deeds

David M. Kopec, Extension Turfgrass Specialist

Late February means pre-emergence weed control for summer annual weeds and perhaps desperate attempts for Poa annua (post emergence).

The most common "problematic" summer annual weed on golf course turf is southwest cupgrass (Erichloa gracilis). Southwest cupgrass has the same life cycle as crabgrass (Digitaria spp.) Both of these grassy weeds tolerate most or any and all mowing heights, and form seed heads to boot. The "most popular" broad leaf summer annuals include the spurges (Euphorbia spp.). There are several species, and the ones found on golf courses all take a mowing. They will also produce an abundant amount of seeds you will never see (until next year). Cupgrass and crabgrass are easily controlled with many of the dinitroanaline herbicides, as well as others. You should consider cost, turf tolerance and length of control as part of you overall application decision. For example, Surflan cannot be used on overseeded bermudagrass, but Treflan, Balan, Pendimethalin, Barricade and others can. Surflan will stunt the ryegrass. Balan may require two split applications, while Dimension usually provides season long control (up to five months for pre-emergence control). Barricade and Pendimethalin products also have good control of spurge. Goosegrass (Elusine indica), which is often a pesky weed on greens and tees in more eastern regions, is more of a weed in Arizona on older shaded roughs, especially on compacted soils. Goosegrass germinates about a month later than cupgrass. An excellent control agent for pre-emergence control of goosegrass is Ronstar. Most dinitroanaline herbicides have the capability of preventing new bermudagrass stolons from rooting (pegging) at the knuckles. Ronstar does not prevent pegging at recommended rates. This is less of a problem if the bermuda (under the ryegrass) is well established with a good stolon density.

Existing Poa annua is now, or soon will be in full bloom -- in all its glory! Many members do not understand the life cycle and biology of one of the worlds most popular weeds, and this results in "blame" rather than "budget" considerations. On heavily contaminated fairways and roughs, you can apply 1/8-3/16 lb. AI/A of Embark. This will prevent seed head emergence with some discoloration and stunting. I am guessing that three applications starting in mid February (depending on location) may prevent or severely hamper further seed head emergence. Existing seed heads will not be controlled. Embark is absorbed by the foliage and is not soil active. Although I have never added iron as a tank mix, I think it might help to minimize discoloration. The iron should be applied 7-10 days before the Embark is applied.

Primo and Primo WSB contain information on their labels for Poaannua conversion/renovation. Primo must be applied before seed heads emerge and will not control existing seed heads. For use on fairways or roughs, contact Novartis for the most recent and clear recommendations.

For non-overseeded areas, you have several options. These include Round-up or Finale (if it's warm enough and the weed is not moisture stressed) or Diquat. Kerb will kill all cool season grasses. I have seen Kerb damage bermudagrass in some years and not in others. I don't know why. Collecting seed heads by removing fairway clippings? It's like collecting lemmings before they run over the cliff. If it makes you feel good, do it!

Products listed are for example purposes and do not imply endorsement. Absence of like or similar materials does not imply exclusion. Always read the label and MSDS information. 

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