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Broadleaf Weed ControlIn Virginia we have two major crops of broadleaf weeds in the lawn. They are referred to as summer and winter annuals. Both are can be controlled with "selective" weedkillers that have combination mixtures and are sold at most garden centers. Selective means it will kill the broadleaf weeds but not the grass. Look for products that contain combinations of chemicals such as 2,4-D + dicamba + MCPP. For best results, use a liquid formulation that allows you to cover the leaf surface of small weeds more effectively. The weedkillers work by translocating through the leaves, killing the entire plant, including roots. The temperature must be at least 60 degrees but not over 85 degrees for the herbicide to be effective and safe for use. Dicamba moves in the soil and should not be used within the root area of shallow rooted trees or shrubs. However, the low rate of dicamba in the three-way mixtures reduces the possibility of dicamba injury. Spot treat where weeds are a problem rather than treating the entire lawn.
Summer annual weeds, like the ones above, are best-controlled in May when they are young and tender. Also, certain weed killers can be damaging to other plants if the weather is too hot. Herbicides that are "volatile" can turn into a gas at temperatures above 85. That gas will drift to other plants like tomatoes, dogwoods and others causing the leaves to curl. The bottom line is DON'T use lawn weed killers if the temperatures are expected to exceed 85 degrees within a week. Remember that the herbicides will affect any broad-leaved plant which can include your shrubs, trees, perennials, etc. Use the chemicals only on very calm days to prevent drift onto your desirable plants and always remember to read and follow the label instructions. Weedy GrassesAll lawn weeds aren't broadleaf. Many grassy weeds invade our lawns in the summer. Plants such as wiregrass and crabgrass are common. Hopefully you prevented crabgrass invasion with a pre-emergent back in late March or April. However, many lawns need a second application of pre-emergent around June 1st. This is particularly true if there is a lot of crabgrass in a property adjacent to your lawn. Postemergence control is available for summer treatment of crabgrass. However, by the time it's obvious we are usually into hot dry weather. Under these conditions the herbicide can actually affect your good grass as well. Wiregrass (common bermuda) is another story. It is a perennial and therefore is NOT controlled by pre-emergent herbicides. And because it's a true grass, broadleaf weed killer will not effect it either. That means using a grass herbicide such as glyphosate (commonly sold as Roundup). Since wiregrass is green in the summer, control is best left until mid August. Two weeks after treatment you can aerate and re-seed.
MowingAs the weather gets warmer, it becomes very important to keep your grass at least 3 inches high. Fescue is at its strongest when it's tall. The more leaf surface it has, the more light it can absorb and the more food it can manufacture for its roots. Taller grass also shades the soil helping to slow the development of weeds. Many commercial turf areas are mowed 3 ½ to 4 inches to give added strength (particularly during the hot dry weather in July and August). Scalping the grass to 1 inch tall drastically reduces the leaf surfaces putting the grass under extreme stress. Mow often enough that you never cut off over 1/4 of the plants' height. If the grass is 4 inches tall and you mow it to 3 inches, you've reduced its height by 1 inch or ¼ of its previous height. Cutting 1/2 or more of the plants height can throw it into shock. Research has shown that by mowing regularly and allowing the clippings to return to the lawn, you can provide 25% of the nutrients your lawn needs for a year. That means one full fertilization can be provided naturally by letting the clipping decompose on the lawn. However, if you go away for a few weeks and the grass gets too long, the clipping may be excessive and should be bagged. WateringProper watering can make the difference between a healthy lawn and one that has a lot of problems. Turf needs one inch of water per week. In most Chesterfield soils, that is best supplied by watering long enough to provide ½ inch every three or four days. This type of watering develops deep roots. As the surface dries out, the roots are forces to go deeper to get more water. The end result is healthier grass. Daily watering or even watering every other day tends to cause shallow roots. Water early in the day for maximum moisture retention and minimum the chance of disease. Grass watered in the afternoon or evening will stay wet through the night, which invites fungal infection. The bottom line on watering: deep infrequent watering promotes strong, deep grass roots and deters weed growth. Shallow, frequent watering promotes weak, shallow grass roots, encourages weed invasion and fungal infections, and decreases the lawn's ability to tolerate droughts. Key Points for Summer
Questions? Contact us by e-mailIf you have specific questions about your lawn, email our Extension staff at edwardssu@chesterfield.gov.
DISCLAIMER Commercial products and organizations are named in this publication for information purposes only. The Virginia Cooperative Extension Service, Virginia Polytechnic Institute and State University and Virginia State University do not endorse or warrant these products and organizations and do not intend or imply discrimination against other products or organizations that also may be suitable. Can't find what you need? |
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