by Marilyn Odneal, Horticulture Adviser
(Mountain Grove) – Home gardeners use many tactics to manage weeds in their landscapes, vegetable gardens and fruit plantings. Here at the Missouri State Fruit Experiment Station, we manage many of our fruit planting in no-till systems. At this time, we are apply pre-emergent herbicides to stop weed seeds from germinating and competing with the woody perennial fruit plants for nutrients, water and in some cases, sunlight. Herbicides are one tool in the home gardener’s weed management tool box along with hand weeding, hoeing, tilling, flaming, and mulching.
Post-emergent herbicides kill weeds that have emerged and are already actively growing. When preparing a new garden area, make sure you eliminate perennial weeds before you plant. You can do this manually or by digging up the perennials, tilling several times, or you can use post emergent herbicides applied according to the label when the weeds are at the recommended stage of growth. Post-emergent herbicides are also used to spot treat problem weeds in the landscape. Post-emergent herbicides can be selective (will kill ONLY broadleaved plants and not grasses for example) or non-selective (will kill both grasses and broadleaf weeds). Some will just burn weeds back without killing the roots, and others – like glyphosate – will be taken into the plant and will kill the roots.
Pre-emergent herbicides are applied to the ground before weed seedlings emerge. Pre-emergent herbicides are effective on germinating weed seeds and will not control annual weeds that are already growing or perennial weeds have already been established. Because they only kill germinating seeds, they can be used on existing plantings and lawns. There are several products on the market for various uses, and as we mentioned last week, the herbicide label will have all of the information you need to make a safe and legal application.
Home gardeners frequently use pre-emergent herbicides on lawns to prevent crabgrass. Timing of the application of pre emergent herbicides to lawns is usually cued by forsythia blossom – crabgrass seed germinates and is susceptible to the pre emergent herbicide around the same time as these yellow shrubs are blooming in spring. Home gardeners less often used herbicide in flower beds and borders, raised beds and vegetable gardens after establishment since mulches and tilling are usually preferred.
In any case, if you use a pre-emergent herbicide, make sure you apply the proper amount of product to a given area. Calibration of equipment means that you know the volume of water or weight of granular products that are applied to a given area. Herbicides that are mixed in water are usually applied at the rate of 20 to 40 gallons per acre using a low pressure, large droplet spray. This translates to approximately ½ to 1 gallon of water over 1,000 square feet (example a 50 by 20 foot area). Do a test run with a sprayer and see how much water it takes to cover the area you need to treat. Calculate how much of the herbicide you need for the area and dissolve it in enough water to cover the area. The amount of herbicide per unit area is critical, although you can use more or less water to apply it to the area. Pre-emergent herbicides also come in granular formulations that can be applied with a broadcast spreader calibrated to apply a specific amount over a certain area as directed on the label.
If you choose to use herbicides, make sure you follow the pesticide label to the letter. Remember that THE LABEL IS THE LAW!
Direct comments or questions concerning this column to Marilyn Odneal via email at MarilynOdneal@missouristate.edu; write to Missouri State Fruit Experiment Station, 9740 Red Spring Road, Mountain Grove, Mo. 65711; or call (417) 547-7500. Visit our website at http://mtngrv.missouristate.edu.