Clover-Looking Weed with Yellow Flowers is Very Difficult to Control

Q. I have oxalis clover look-alike as a weed. How can I control it? I am ready to use chemicals at this point having tried to rid it by digging and pulling with no success. Having it in my grass is bad enough but now that it is in my iris beds I want to kill the dang stuff!

Oxalis looks like clover but has yellow flowers that resemble a daisy with only five petals.

A. Oxalis is very difficult to kill. It may require repeat applications but one of the keys is to try to kill it when it is “happy” and is ready to grow and multiply. This is usually spring and fall. Go to your favorite nursery or garden center (you may have to look at several such as Lowes, Home Depot, Star and Plant World). Go to their weed killer section. Look at the active ingredients. Look for the following in the active ingredients list.

The important chemicals to find on the label are either Dimethylamine salt of dicamba: 3,6-dichloro-o-anisic acid (it may be just called dicamba or Banvel) somewhere on the label.

The alternative would be an ingredient called triclopyr, (chemically called 3,5,6-Trichloro-2-pyridinyloxyacetic acid)

These chemicals are usually combined with other weed killers for better synergism (efficacy or improved performance). In cases of herbicide synergism 1+1 = 3 times more effective. So you may see 2.4-D listed as the first chemical (Dimethylamine salt of 2,4-dichlorophenoxyacetic acid) or you may see 2,4-DP (mecoprop or Dimethylamine salt of (+)-(R)-2-(2 methyl-4-chlorophenoxy) propionic acid) listed as well on the label but the names in RED are the most important for oxalis control.

I am sorry for the detailed technical response but this is really technical stuff to get you the right chemical. There are so many different manufacturers and labels with the same stuff in it, it is impossible to list them all so giving you the ingredients to look for is much easier.

Next is the method of application. These chemicals will not damage a lawn if you apply at the right concentration but they WILL damage other plants. So you must spray them directly to the weeds and not overspray onto other plants! 

Make sure you wear waterproof gloves when mixing and applying and wash thoroughly after an application. They are not THAT toxic but it is always a good precaution. Never spray on a windy day. Spray when weather is warm but not hot because the plants are better able to "absorb" the spray. 

Mix about 1 tsp of ivory liquid detergent per gallon of spray to the finished mix and thoroughly stir it. Do not add it before you add water or it will just give you a lot of weed killer bubbles. This detergent helps the week killer enter the leaves.