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soil temperature for annual weed seed

Kansas State University

Many recently introduced turfgrasses are vastly superior to older types, especially in their tolerance to wide ranges of cultural and environmental conditions. Unfortunately, even superior turfgrass cultivars have limits to what they can tolerate. In most cases, when cultural or environmental conditions surpass minimum turfgrass tolerance levels, problems arise. For example, the presence of annual weeds such as crabgrass, goosegrass, barnyardgrass, knotweed, spurge, or henbit indicates problem growing conditions that allow these weeds to be more competitive than the desirable turf.

Management practices that discourage annual grassy weed growth of turf include:

  1. Fertilizing according to soil test recommendations, making sure adequate nutrients are available during periods of active turf growth.
  2. Watering deeply and infrequently, allowing the soil surface to dry between watering.
  3. Mowing at the proper height (2 to 2 1/2 inches for most cool season turfgrasses).
  4. Core cultivating, dethatching, or power raking during the fall when the turf is actively growing and weed seeds are less likely to germinate. Proper turf management is primary to a weed control program.

In some situations, turf is grown in environments that favor weed growth and development. Many annual grassy weeds are more tolerant of wet or compacted soils or shade than are turfgrasses. Altering the growing environment to favor the turfgrass can shift the competitive edge away from weeds.

The bottom line is that turfgrass breeding, selection, and evaluation has greatly improved turfgrasses. However, even new and improved turf selections are incapable of competing with weeds when mismanaged or planted into unfavorable environments. If producing high-quality turf is important, cultural practices and environmental alterations that enhance turf growth relative to weed growth are the basis of a sound weed management program.

Chemical Control of Annual Weeds

Maintaining a dense, vigorous turf is the best weed control. Occasionally, herbicide applications are mandated to reduce weed populations to tolerable levels. When annual grassy weeds such as crabgrass, goosegrass, barnyardgrass, fall panicum, or yellow foxtail become a problem, preventive preemergence herbicides are often used for control. When using any pesticide, read, understand, and follow the label directions for the safest, most efficient pest control.

Pre Emergent Weed Control

When it comes to pre-emergent weed control timing is everything, especially when using herbicides like LESCO’s Dimension to control summer annual weeds.

Rule of thumb is to get the application down before the soil temperatures are 50-55 degrees for five or more consecutive days.

This is very important because 20% of the weed seed will start germinating at that time. The other 80% of weed seed germination, especially crabgrass, goose grass and foxtail happens when the soil temperatures reach a consistent 60-70 degrees. By applying the product just before the soil is a consistent 50-55 degrees, you’re giving it enough time to become activated by water, soak into the soil, and create the chemical shield between the seed and the soil before germination.

When To Apply Pre-Emergent For Weed Control

1. Timing

Not sure when the soil reaches 50-55 degrees? Start with the Greencast’s Soil Temperature Map to see what your current soil temperatures are. This map is fed by a collection of climate monitoring stations across the country. Rain and sun exposure can influence the soil temperature and impact your timeline. It is always best to apply your pre-emergent right before the soil reaches 50-55 degrees.

2: Look for the Early Indicators

Forsythia plants are one of the first to show blooms when temperatures start reaching 50 degrees. It’s a great reminder to apply your pre-emergent before it’s too late.

In addition to proper timing, there are a few other guidelines to maximize pre-emergent results:

  • Clear any debris off of the lawn either by raking or blowing to fully expose the turf and allow the application to reach the soil.
  • Follow the label exactly. Do not over apply your pre-emergent.
  • Thoroughly water your turf or beds to activate and start the process.

Visit our store online today for more information and application rates. Have questions? Give us a call and speak with an associate to determine what timing and pre-emergent weed control product will work best for your project.

For overseeding, be sure to check out our Lesco Transition Blend and Tall Fescue Grass Seed options.