“Why do I have crabgrass now in August when I put crabgrass preventer on in March?” There are three possible reasons why:

1. Pre-emergent products must be watered in thoroughly (at least ½ inch) within 24 hours to be effective.

2. If a pre-emergent was put on in March, it was applied about a month too early and by the 4th of July was worn out and the crabgrass started growing.

3. The pre-emergent crabgrass preventer you used may have been put on at the right time but was worn out by the middle of July. Some products keep working longer than others. Products with Balan or Benefin (Team) as the active ingredient, has a residual or lasts only about 60 days. Pendimethalin (Scotts Halts, many box and hardware store brands, and Miracle Gro Pre-emergent) also lasts about 60 days. Barricade (Earl May Crabgrass Preventer with Barricade) and Dimension (Crab & Spurge Preventer with Dimension by Monterey) lasts about 90 days.

Next year, do not apply a pre-emergent weed herbicide until mid to late April because crabgrass will not germinate until about the 1st of May in Lincoln and a few days later in Central Nebraska. Then use a product with a long residual. To make sure you have season long control, put on a second application the first couple of weeks in June. This will give you control for the whole summer. This second application in June will also help to control spurge and foxtail as they do not germinate until mid-June. There is a liquid pre-emergent without fertilizer (Crab & Spurge Preventer with Dimension by Monterey) and a granular pre-emergent without fertilizer (Crabgrass Control with Team by Fortify). You can use one of these for the second application if you don’t want to add more fertilizer in mid-June and thus risk burning your bluegrass or fescue grass.

Many garden centers also carry a pre-emergent weed herbicide that is labeled for use in the vegetable and flower garden. Most of these, such as Preen, contain trifluralin (Treflan). It has a short residual so must be applied more than once during the growing season.       

Crabgrass is an annual grass that will die with the first hard frost. You can try and kill it now but it is very mature, so hard to kill at this time. The most effective product to use to kill crabgrass is Quinclorac. This product only became available to homeowners in the last couple years. It is sold under the trade name of Drive and Earl May Total Weed Control (Ready-To-Spray). The RTS or Ready-To-Spray bottle from Earl May also contains 2, 4-D and Dicamba and covers 6,600 square feet. The Earl May Total Weed Control in the Ready-To-Use (RTU) bottle and in the concentrate does not contain Quinclorac this year so get the right product.

Monosodium acid methanearsonate (MSMA) will also kill crabgrass but is not as effective as Quinclorac. MSMA will take two to three applications 7 to 10 days apart. Even if you do kill it, the crabgrass has already gone to seed. So plan on seeing it next year.

For other broadleaf weeds in your lawn like dandelions and hard to kill weeds such as bindweed, clover, ground ivy (creeping charlie), chickweed, black medic, henbit, dandelion, and poison ivy, wild violets, and white clover, a good time to go after them is after the first light frost in the fall and before a hard freeze.

For the lawn, I like liquid weed killers that you spray on with a spritz bottle or a small pump-up sprayer rather than the granular kind of herbicide such as a “weed and feed” you apply with a spreader.  The granules need to stick to the blades of grass to be effective and usually they don’t stick very well. Another advantage of liquid weed control is you can spot treat the weeds without putting the herbicide on the whole yard and areas where it is not needed.  This is better for the environment. Be careful with a hose end sprayer that you do not put chemicals in areas that have no weeds, or more on the lawn than you really need.

Quinclorac in the ready-to-spray bottle will control bindweed, clover, ground ivy (creeping charlie), chickweed, black medic, henbit, dandelion, poison ivy, wild violets, and white clover, with one application. If you use a liquid weed control that contains 2-4-D, MCPP, and Dicamba it will take two to three applications, 7 to 10 days apart to get a good kill This is sold under the brand names of Trimec, Earl May Lawn Weed Killer, Ortho Weed-B-Gone II, and Earl May Super Brush and Weed Killer.  Triclopyr (Ortho Weed-B-Gone Chickweed, Clover and Oxalis Killer for Lawns) is a good weed killer but will also take 2 to 3 applications. None of the products mentioned above will hurt your grass if applied at the proper rate and according to label directions. Don’t water for 24 hours after application so the chemicals stay on the leaf and do their work. These weed killers are systemic which means when sprayed on the leaf, the chemical will be taken down to the roots. Be sure and read the label and follow the manufacturers recommendations.

Most weeds and many plants have a waxy leaf and the use of a sticker-spreader helps the chemical stick to the leaf and thus makes it more effective. Use a “sticker-spreader” such as “Turbo” at the rate of two tablespoons per gallon of water, or Acme Sticker-Spreader following the label instructions. A “sticker-spreader” will help any liquid spray stick to the leaf of the weed or plant. Use it with a fungicide for black spot on roses and for tomato blight, or with insect killers such as Eight, Malathion, Isotox, or Sevin, as well as with a weed killer.

In the late fall, after the first light frost, the plants start taking nutrients down into their roots for the winter and they take the chemical down with them. In the spring and summer the plants are growing vigorously and pumping lots of nutrients up into the foliage so is harder to get the chemical down to the roots. So late fall is a good time to go after those weeds in the lawn, as well as in the vegetable garden, and in the flower bed. Digging weeds or killing weeds with chemicals in the fall will reduce your work load for next spring and summer.

If the weeds do over winter, apply a weed killer early in the spring before planting. You can replant 7 to 10 days after using Glysophate (Kleen-up or Round-up) but must wait 4 to 6 weeks before planting after use of Quinclorac, Trimec, or Triclopyr weed killers.

          One final tip: Never apply a liquid or a granular weed killer or fertilizer to a drought stressed lawn, or when the temperature is over 90 degrees F. or when the wind is blowing over 5 to 10 miles per hour. An application to dry soil and/or when the temp is over 90 degrees F. may burn the grass and cause more stress.  Water thoroughly at least one day before application. 

Copyright 2008