Sunday, February 17, 2019 By: Ask A Master Gardener

Use Preemergent Herbicides Now to Prevent Crabgrass this Summer

Use Preemergent Herbicides to Prevent Crabgrass
Allan Robinson: Ask Master Gardener
Sunday, February 17, 2019
Q: When is the best time to apply preemergent herbicide to help control crabgrass? Johnathan W., Tulsa
A: Preemergent herbicides are definitely helpful in preventing weed establishment. They are used in early spring (mid-February through mid-March) to prevent crabgrass and other summer weeds. They also are useful in the fall (mid-August through mid-September) to prevent winter weeds such as henbit. Many of the herbicides will need a second application in spring 60 days after the first application for complete coverage of crabgrass. The product label will indicate if this is needed.
Many people are reluctant to use herbicides of any sort for weed control. That is a reasonable choice for those who are willing to tolerate some weeds. The best preventative is to maintain a healthy, well-established lawn, as this will help prevent much of the weed invasion. A healthy, thick lawn depends on good soil, proper turf grass for the area, adequate sunlight and supplemental irrigation. Most lawns need some fertilizer, and there are organic and synthetic sources available for nutrients.
The Tulsa Master Gardener website contains several helpful lawn maintenance calendars indicating what to do, what to use and when to use it for Bermuda and fescue lawns. Specifically, see the “Turf” section of the Master Gardener website for complete details.
Master Gardeners are often asked if there are any “organic” preemergent herbicides, as opposed to commercial or “synthetic” ones. Unfortunately, while there are other organic pesticides, there is no effective organic preemergent herbicide.
Corn gluten is an organic sold as crabgrass prevention. Some reports state that if it is applied during a narrow window in spring, there may be some benefit. OSU turf grass specialists cite studies that show little benefit.
For those wishing to use a synthetic pre-emergent herbicide, OSU has some recommendations. While there are several varieties of preemergents available on the market to prevent weeds, especially crabgrass, OSU feels that one of the many commercial brands containing the chemicals dithiopyr, pendimethalin or prodiamine are good choices. These preemergents cost a bit more than other types but last a lot longer and, in many cases, can kill crabgrass and other weeds after they have sprouted.
The labeled directions of all such products must be followed. These herbicides usually come on a dry particle such as fertilizer or other inert material. They may also be found less often as liquids. They must be washed onto the soil with at least ½ inch of water after application. After washed onto the soil, they form a barrier for weed prevention, which may last for months if undisturbed.
One of the benefits of these three products is that they are not soluble in water and, thus, do not leach into groundwater or spread from where they are applied. They are broken down in nature by sunlight and soil microorganisms.
Garden tips

• Now is a good time to cut back your perennial ornamental grasses, such as Pampas grass. Cut back to remove the dead grass, but avoid damaging new buds and early green growth at the base.
• Begin planting blackberries, raspberries, strawberries, grapes, asparagus and other perennial garden crops this month.
• Most bare-rooted trees and shrubs should be planted in February or March. The roots of these plants are easily damaged and should never be left exposed to air. Plant them at the same depth as in the nursery and make sure good root and soil contact is made by gentle tamping and irrigation after planting.
• Finish pruning shade trees, summer-flowering shrubs and hedges. Spring-blooming shrubs, such as forsythia and azaleas, may be pruned immediately after flowering (not before). Do not top trees or prune just for the sake of pruning.
• Applying preemergent herbicides earlier rather than later may be desirable to prevent crabgrass and other summer weeds.


Post a Comment