Question of the Week Number 1: July 22, 2021

“How can I tell the difference between dallisgrass, Johnsongrass and crabgrass? The controls, I understand, are all different.”

Let me boil it all down by putting the facts into bullets for each of the three weeds.

Perennial (comes back from its roots).

Dallisgrass is known for its dense, dark green clumps.

Forms very dense clumps that are 10-16 inches across. No runners (stems that trail across the lawn).
Extremely dark green leaves that grow to 5 or 6 inches tall if never mowed.

Fast-forming seedheads of dallisgrass are very recognizable to lawnkeepers.

Seed stalks form within 2-3 days of mowing.
Stalks look like old-fashioned telephone pole crossarms, each bearing dozens of flattened, disk-like green seeds. Each seed is marked with a black peppery piece of chaff.
All dallisgrass seeds are fertile, even without pollination, so it is critical that the lawn be mowed often to keep seeds from maturing.
To control dallisgrass you’ll either have to dig it out by hand or use a one-gallon milk jug with the bottom cut out. Insert a spray wand through the lid into the jug. Place the jug firmly over the clump and spray a glyphosate-only herbicide onto the dallisgrass. The jug will prevent drift onto desirable grass adjacent, and the glyphosate will not contaminate the soil.

Continued Below

Here’s the answer to our question. This vigorous invader is Johnsongrass, proudly growing in the middle of a bed of otherwise handsome ornamental grasses (maidengrass) at a McKinney dairy store a few days ago. So, if you have trouble telling the various grasses apart, apparently you’re not alone.

Perennial weed that is much more common in ditches and alleys than in cultivated lawns and gardens. It cannot stand frequent close mowing.
Leaves are light green, often with a reddish cast along midribs.
Flower stalks are robust, to 18 to 48 inches tall and borne in plumes.
Clumps develop strong, finger-sized roots that are difficult to hoe or dig out. It’s best to rototill as you prepare garden soil, then use a rake to “comb” them out.

This is the way Johnsongrass will often appear in a new lawn. After a couple of months of close mowing it will probably be gone.

Johnsongrass is rarely a problem in home lawns. It cannot withstand close mowing. It should give up and die out within a couple of months. No herbicide action is usually required.

Note: Both dallisgrass and Johnsongrass are easily eliminated with glyphosate-only sprays in open spaces.

Annual weed that germinates in spring and summer and completes its life cycle by frost. It is, therefore, a “warm-season” weed.

These young crabgrass plants have just gotten started growing. You need to apply pre-emergent granules so they never even get this far along.

Medium-green leaves. Short runners (4-5 inches long).
Seedheads look like helicopter rotors.

This is the very characteristic look of crabgrass seedheads.

Only consumer remedy is pre-emergent granules applied before the seeds start to sprout in early spring. Exact timing will depend on where you are in Texas, but first treatment generally should be 2-3 weeks prior to the average date of your last killing freeze in early spring. Repeat 90 days later. Apply Dimension, Halts or Balan granules at those times.
Once crabgrass is up and growing there is no post-emergent herbicide that will kill it without harming your desirable permanent turf.

Posted by Neil Sperry
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