Killing Johnson Grass

Ya can't SPRAY over another grass. Use a wipe with wicks. The Johnson grass is well above your Bermuda grass. You will be OK

MSMA is the expensive way.

Round-Up (glyphosphate) is the cheap way. The end result is the same.

The last 2 years I have sprayed Round-Up at 1 pint per 10 gallons per acre (=1.6 ounce per gallon). Bermuda that is good and tall barely shows a hint of yellowing. The Johnson grass gets smoked. Do it before the Johnson grass makes a seed head for longer lasting results.

And before anyone says you can only do that in early spring. I record date, and temp. Every time I've done it, the temps were 90° to 100°F.

This will likely kill St.Augustine in a broadcast spray. If the Johnson is in patches, spot spray it.

Ya can't SPRAY over another grass. Use a wipe with wicks. The Johnson grass is well above your Bermuda grass. You will be OK

Where can you find MSMA? Home depot carried it years ago but doesn't seem to anymore.

So what can I spray on Johnson Grass that won't kill Bermuda or St Augustine grass in my yard?

Control Practices
To eradicate Johnson grass, control measures must be thorough. Various cultural practices and chemical herbicides will effectively control germinating seed, seedlings, and established plants. Objectives of a good control program include:

Prevent production and spread of seed
Destroy seedlings before rhizomes are formed
Weaken and kill existing rhizomes
Control new infestations as they appear

RECOMMENDED PRACTICES IN NATURAL COMMUNITIES OF HIGH QUALITY

Initial effort in areas of heavy infestation
Johnson grass does not infest areas of high natural quality heavily except for the naturally disturbed environment such as along river banks where it is difficult to control selectively. Seed panicles should be cut and removed from the area where practical. Dense patches can be controlled by spraying the foliage with 2 percent Roundup (a formulation of glyphosate). Best results are obtained when glyphosate is applied to plants that are 18 inches tall to early flowering stage.

During this period the herbicide will be most effectively translocated to the roots and rhizomes. Care should be taken to avoid contacting non-target plants, since Roundup is a nonselective herbicide. Do not spray so heavily that herbicide drips off the target species. The herbicide should be applied while backing away from the area to avoid walking through wet herbicide. By law, herbicides may only be applied as per label instructions.

Effort in areas of light infestation
Clumps and individual plants may be hand pulled during June, just after a rain when the ground is soft. All plant parts should be removed from the area. Broken stems and roots left in the ground should be dug up if only a small area is involved. It is more effective to spot-treat the individual plants with herbicide than to pull them, and large clumps can be sprayed with 2 percent Roundup using a hand sprayer or backpack sprayer. Herbicide treatment may need to be repeated for several years to ensure good control.

Maintenance control
Preferred treatment is hand pulling of individual plants immediately upon discovery. All plant parts, including rhizomes, must be removed. It may be necessary to hand pull a population several times to obtain control. Surrounding seed sources should be eliminated where possible to prevent continual re-invasion.

Just keep mowing at two to four inches. It will eventually cause the Johnson grass to die off.