Asked September 25, 2018, 8:23 PM EDT

WE HAVE A SEVERE INFESTATION OF OXALIS, PARTICULARLY TROUBLESOME where it invades ornamental grasses and other grasslike ornamentals. As I'm sure you know, it's virtually impossible to pull it by hand. We've even tried digging the clump of grass. washing the root mass for better visibility, and pulled the oxalis at the root level. The only thing we've accomplished is killing the grass. I've read on your site about naphthalene acetic acid (NAA) but cannot find a commercial source. Please - do you have any suggestions? Other than to just get rid of the infested plants?

Thank you for any assistance you can give.

Bob Boysen

Frustrated Master Gardener in Eugene

Lane County Oregon

2 Responses

This is not something I'm finding easily in our consumer publications. I'll refer this to OSU experts. You may need to call the local Extension Service office if we can't help you through this Ask an Expert forum.

PNW Weed handbook

dithiopyr (Armortech CGC 2L, Dimension 2EW Specialty Herbicide, Dimension EC Specialty Herbicide, Dimension Ultra 40WP Specialty Herbicide, Dimension 270-G Turf & Landscape Ornamental, Dithiopyr 2L Specialty Herbicide, Quali-Pro Dithiopyr 40 WSB Specialty Herbicide, many fertilizer products with dithiopyr on granules.)

Rate Using maximum rates of Dithiopyr 40SB is equivalent to 4 water-soluble pouches/A or 0.46 oz/1,000 sq ft (1.25 lb/A of product) per application, and 12 water-soluble pouches/A or 1.38 oz/1,000 sq ft (3.75 lb/A of product) per year, respectively. For Dimension EC, use no more than 1.5 fl oz/1,000 sq ft (2 quarts/A) per application, and no more than 4.5 fl oz/1,000 sq ft (6 quarts/A) per year, using split of sequential applications.

Time Apply preemergence when soil is about 50°F (about when forsythia blooms). Apply postemergence before crabgrass and annual bluegrass are in first tiller stage.

Remarks Dithiopyr is available in EC, 40WSB and 40WSP formulations, as granules, and on fertilizers. Gives preemergence control of crabgrasses, foxtails, barnyardgrass, and a number of broadleaf weeds, including purslane, Oxalis species, and spurge. Also gives preemergence control of annual bluegrass (Poa annua). Gives postemergence control of crabgrass up to the first tiller growth stage. Dithiopyr appears to be safe on mature creeping bentgrass, Kentucky bluegrass, perennial ryegrass, tall fescue, and some fine fescues.

Caution Do not use on seedling turf; injury will be severe. Do not apply to turf under environmental stress.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Pyridine

-hard to find but may find at Springfield Coastal, Sure Crop Farm Service J. City.

The entire root system must be removed or the plant will grow back from any pieces left in the soil. Use a weed killer. For a few scattered oxalis weeds in the lawn, use a ready-to-use product like Scotts® Spot Weed Control for Lawns.

Some herbicides will knock down Cape oxalis. Glyphosate-based herbicides, such as Roundup, do so, and will also kill lawns and other plants if they come in contact with Roundup. Those based on triclopyr, such as Turflon Ester, are selective for broadleaf plants and some grassy ones, but will spare fescue.Feb 21, 2007 Roundup kind of works, but will kill anything the spray contacts.

After two hours, found a label but it was very difficult to read. Try Scotts Spot Weed Control For Lawns. The only place it said it was located was WalMart but other garden stores should care it.


I found other herbicides but they were no long available or need gallons to buy the product.

Here is an available spray: Scotts Spot Weed Control for Lawns

The label of chemicals it should have -

Quinclorac – 0.10%

Microprop-p dimethylamine – 0.22 %

2,4D – 0.12 %

dicamba – 0.05%

Other ingredients – 99.51%

- These chemicals are good at controlling broad leaf weeds – oxalis.