Daniel Gill | 3/31/2015 8:21:59 PM
PHYSICAL CONTROL IN BEDS
When oxalis is growing in beds, hand weeding can be done. However, this plant produces tubers, roots or bulbs that break off and stay in the ground during hand pulling, and the leaves will soon grow back.
To control the oxalis, you must dig up and remove the roots and bulbs attached to the leaves using a trowel or weeding tool. This should be done repeatedly through the cool season when oxalis is in active growth.
Mulches are not effective in controlling this weed. It will simply grow from the rhizomes through the mulch. Weed barriers and landscape fabrics applied over a thoroughly weeded area are more effective at preventing reemergence of this weed. These can be useful, to some degree, when practical for a particular situation.
CHEMICAL CONTROL IN LAWNS
The best lawn herbicide to use to control oxalis in St. Augustine, zoysia and centipede lawns is Atrazine. Make two applications following label directions in late summer or fall when oxalis is noticed in the lawn and temperatures are in the mid-80s or lower. Any spots or small patches of oxalis that are noticed after that should be spot treated by just spaying the spot of oxalis. Do this during mild weather (high in 60s or above) anytime during the winter or spring.
CHEMICAL CONTROL IN BEDS
There are no selective herbicides that will only kill the oxalis and not damage ornamentals if it gets on them.
The nonselective systemic herbicide, glyphosate (KillzAll, Eraser, Roundup, Grass and Weed Killer and other brands), is effective if you are persistent and make several applications as the oxalis reappears (generally, 3 to 5 treatments are required). Use glyphosate carefully as it will damage or kill any plants if it gets on their foliage.
Shield the foliage of desirable plants with a piece of cardboard during spraying or cover those plants with plastic bags. Or put a funnel-like devise on the end of your sprayer to focus the spray only where you direct it. Do not try to spray on windy days. Although we can use glyphosate quite close to desirable plants, it is critical not get glyphosate on their foliage. Spray just enough to thoroughly wet the foliage of the oxalis.
Oxalis often grows in among ornamental plants. In this situation, it is virtually impossible to spray glyphosate and not get the herbicide on the foliage of the desirable plants.
See above a method for oxalis control in these types of situations with no potential for spray drift injury. It involves applying glyphosate (purchase a product with at least 41% active ingredient) with the rubber glove/cotton glove wipe method and gently wiping the glyphosate carefully and specifically to the foliage of the oxalis.
This method is tedious and is generally only practical for small beds. And, just like when spraying, you will need to make several applications for it to be effective.