Weed Control Before Seeding

Seed first or spray weeds? Early weed control is an important step in profitable canola production. Saskatchewan research on preseed weed control in wheat showed that early weed control was more Preparing For Overseeding : Yardener.com

Seed first or spray weeds?

Early weed control is an important step in profitable canola production. Saskatchewan research on preseed weed control in wheat showed that early weed control was more important to yield than early seeding.

Pre-seed weed control will manage weeds that emerge ahead of seeding, reducing crop competition for light, moisture and nutrients.

Growers waiting to seed may find that fields too wet for the seeding unit may support the sprayer — although deep ruts are not great for the seedbed. High flotation tires on the sprayer will reduce rutting.

Cool, wet conditions that are holding up seeding can also reduce herbicide efficacy, but early weed control with lower efficacy is generally preferable to no control at all or late control with higher efficacy — as long as weeds are present and not frost damaged.

Clark Brenzil, provincial specialist, weed control, with the Saskatchewan Ministry of Agriculture, explains how cool, cloudy conditions affect herbicide efficacy:

In the case of herbicide applications following a nighttime frost or near-frost event, the herbicide activity on a cloudy cool day would be next to zero. Biological activity would have stopped during the night, and would not start up again until the plant warmed to at least 5°C — and even then it would be very slow. A few hours between 5°C and a daytime peak of 10°C would not be enough warmth to get plant metabolism going to a point where herbicide was all that effective, especially with the cloud. No biological activity = no herbicide activity. Ideally, you want a day or two of warm sunny days and night time lows of 4°C or higher before spraying. If applied more than 48 hour before the frost event, efficacy on living plants will be retained and the plant will continue to decline when it warms up again.

See also  Albino Weed Seeds

If faced with a decision to spray some fields and not others, be sure to spray Clearfield fields before seeding. Otherwise you have to wait until the two-leaf stage of the crop to spray.

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Preparing For Overseeding

Thatch is an accumulation of surface roots, dead plant parts and other debris on the soil at the base of the grass plants. While a thin layer of thatch does not normally present a problem, it must be removed before overseeding to expose bare soil for the new seed.
If the thatch layer is thick, consider renting a dethatching machine or a “power rake” to loosen the thatch and simultaneously scarify the soil without pulling out existing grass plants. With a thin layer of thatch, a very close mowing of the lawn and a brisk raking with a garden rake will do the job. Either way, rake up the loosened thatch and use it as mulch around the yard or store it for later use in a compost bin. See Dethatching Rakes in the Tool Shed.

See also  Weed Seeds

Deal with Existing Weeds

Many annual weeds die out as fall approaches so they are not a problem when overseeding at this time of year. However, if your turf shows a significant number of broadleaf weeds, which are often perennial and will return next year, remove or kill them before overseeding. Judicious use of the herbicide 2,4-D will efficiently rid the turf of dandelion, plantain, ground ivy and their ilk.

Because the vigorous, dense turf that results from overseeding will discourage future weeds of this kind, this is likely to be the only time you will need to use this herbicide. Spray it as directed on the product label at least ten days to two weeks before you plan to sow grass seed. Broadleaf weeds will start to turn brown in three or four days and be completely dead by the end of the 10 day wait. The herbicide will have begun to break down after ten days, so new grass seedlings will not be harmed. What remains is bare soil to be overseeded. See Lawn Weed Control Products in the Tool Shed.

Using Broadleaf Herbicide

Read the label carefully and follow the instructions.
Spray when weeds are actively growing (by late summer weeds have abundant, mature foliage).
Skip one mowing before spraying so weed foliage offers maximum surface for the herbicide application.
Plan to spray 10 to 14 days before the date scheduled for overseeding.
Do not spray when rainfall is expected within six hours.
Do not spray if winds exceed 5 mph to avoid drift onto other plants.
Do not walk on, or allow pets and children to walk on sprayed area for at least 12 hours; a 24 hour wait is better.

See also  How To Prevent Weed Seeds From Germinating

Aerating the lawn is always beneficial and–if time and energy permit–while preparing for overseeding is a good time to do it. It is not essential to the success of overseeding, though.
Punching holes in the turf soil by means of a mechanical or hand aerator introduces oxygen into the top layer where plant roots grow. Existing grass benefits enormously. It also loosens the soil to make it easier for seeds to contact soil and sprout and new grass seedlings to become established.

Mow Lawn Close and Remove Debris

The most important step in overseeding is preparing the seed bed with an existing turf already in place. Since the grass seed needs to contact the soil and the new grass seedlings need lots of light to grow, it is necessary to mow the existing grass very short.
Set the mower as low as it will go–so its cuts at about ½ inch–to remove as much foliage as possible without scraping or harming the crowns of the existing plants. If you have a bag attachment collect the clippings in the mower bag. Then rake up the area or go over it with a blower-vac to be sure that no debris covers the bare soil between the existing grass plants. See Grass Rakes in the Tool Shed.

Spread Fertilizer (Optional)

It is a good idea, but not critical, to spread some slow-acting granular fertilizer when you are overseeding. This will be your fall (or spring) application of slow release nitrogen fertilizer for the lawn. There is no need to spread lime on the lawn when overseeding. Since it takes six months for lime to begin breaking down and affecting the pH of the soil, it will not influence the environment of the newly germinated seed. See organic lawn fertilizers. in the Tool Shed.