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Pre-emergent herbicides and you

Wayne Hobbs
Posted 10/19/16

The scourge of any homeowner who cares to have a beautiful lawn and garden is weeds. Every season, or sometimes multiple times a season, a new crop springs from the ground costing you time and money …

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Pre-emergent herbicides and you


Posted

The scourge of any homeowner who cares to have a beautiful lawn and garden is weeds. Every season, or sometimes multiple times a season, a new crop springs from the ground costing you time and money to manage them.

Most of the time this is done with extensive hand weeding or spraying chemicals to control the issue after adult plants have appeared. But never fear, it can all be handled with proper timing and pre-emergent herbicides as part of your management plan.

Pre-emergent herbicides work by stopping weed seeds from germinating, stopping all growth from the seed. The key to using these, however, is timing and identification as they will do nothing once the plant is already growing or if the plant happens to be a perennial weed.

In regards to timing annual weeds – those that germinate, grow, produce seed, and then die – need to be broken down into two main categories. The first category is cool season weeds and the second category is warm season weeds.

Warm season annual weeds such as crabgrass, chamberbitter and spotted spurge should be treated in the early spring in February while cool season annual weeds, such as chickweed, annual bluegrass and henbit should be treated now, in October. Proper timing should help the seeds that are in the soil from germinating. For perennial weeds such as nutsedge, torpedo grass and dollar weed, pre-emergents do not work well as the weeds come back each year from the roots and will need to controlled by hand or with other post-emergent chemicals.

Another note with timing is that a normal application will last 6-12 weeks so an additional treatment may be necessary around that time. When using any chemical make sure to follow the label of the product and with pre-emergent herbicides you want to make sure to irrigate after application to allow the chemical to penetrate into the soil.

When it comes to the type of pre-emergent to use identification of the plant is key. Not only will identification help you determine if the weed is annual and what time you should apply your chemical, it will also determine the product. The three main types of weeds are grasses, broadleaves and sedges and each normally requires a different chemical when dealing with lawns.

Grasses can be identified by the parallel veins on the leaves that never touch and by their hollow stems. Broadleaves are those that have netted veins that attach to the middle vein of the leaf and often are your flowering plants. Sedges tend to look like grasses but have angular stems with edges. By choosing the right product you can help to ensure the treatment will have the desired result.

Another item to note with pre-emergent herbicides is to make sure to be wary about their use on recently seeded lawns or beds. Most pre-emergents will also effect grass seeds and no seeding should be done in the area for at least 9 weeks after chemical application. With turf, wait until the grass has become at least two to three inches tall or has begun to knit by runner or stolon well and then only use half of the recommended rate. Once grass is well established you can apply the full rate.

If you have any more questions about weed control, any other lawn or landscape topics, or need plant materials identified, contact the University of Florida/IFAS Extension Office online at http://www.clay.ifas.ufl.edu, follow us on Facebook, or call by phone at (904) 284-6355.