Advertise in Print | Subscriptions
Published July 06, 2008, 12:00 AM

The voracious invader known as quackgrass

Ever wonder why quackgrass is such a difficult weed to control?

By: Will Yliniemi, DL-Online

Ever wonder why quackgrass is such a difficult weed to control?

Quackgrass not only infests all of the northern United States but also southern Canada, almost all of Europe (its native home) and parts of Asia. It even grows in Alaska, past the Arctic Circle in Norway and down through New Guinea. It infests over 32 crops in more than 40 countries.

Quackgrass seed is wind-pollinated and virtually self-sterile, making cross-pollination necessary to produce seed. However, it can produce 15 to 400 seeds per plant stem with 25 to 40 most common. It is efficient in that 95 percent of the spikes contain viable seed, with an average of 13 viable seeds per spike. In the lab, the seed remains viable for one to six years, but in a long-term buried-seed experiment, the seed survived for 10 years.

The plant can spread quickly not only by seed, but also by rhizomes. Undisturbed, it can grow up to four feet tall and produce over 400 feet of rhizomes and as many branches per year.

Decaying quackgrass residues may also release toxins (a natural herbicide) that inhibit the development of some crops.

Tips on mid-season glyphosate management

When a second post-emergence glyphosate application is needed to control plants that survived the first application, Ohio research indicates that about three-week intervals between applications may result in the best control. This provides time for plants to resume growth after the first application so that glyphosate can have activity in the plant, but does not allow time for plants to re-grow to a large size. Waiting until enough re-growth occurs so that plants can be seen above the crop from a road survey is not the best approach. Applying the second glyphosate treatment too soon after the first is also not optimum, since plants that have not recovered from the first application cannot respond to the second.

Glyphosate activity can increase when applied in low spray volumes, but this has to be balanced against the need for penetration of spray into dense weed/crop canopies or to obtain better coverage of large weeds. For the latter situations, it’s possible that spray volumes of 15 to 20 gallons per acre (gpa) may be more effective than 10 gpa or less.

Be cautious also of using too many drift-reduction measures, such as combinations of low drift nozzles and drift-reducing agents. This can result in too few droplets of too large a size, which can reduce control.

Increasing the rate of a glyphosate product applied will usually be more effective than adding nonionic surfactant. Most glyphosate products already contain a relatively high concentration of surfactant. Increasing the rate of product applied results in the application of higher rates of both glyphosate and the surfactants that are part of the formulation.

The time of day of application affects herbicide effectiveness. Previous research has shown that activity can be reduced when herbicides are applied in early morning or in the evening (or at night). We have observed this with glyphosate, Flexstar, and FirstRate, and we assume most other POST herbicides are similarly affected.

A general rule of thumb that might avoid most problems due to time of day effects: avoid POST herbicide application before about 7:30 a.m. or after about 7:30 p.m.

For more information on crop production information please contact: Will Yliniemi, Hubbard/Becker County Extension Educator at 1-218-732-3391, 1-218-846-7328 or by cell at 1-218-252-1042, or by email at ylini003@umn.edu. Source: Mark Loux, Ohio State Extension C.O.R.N. Newsletter.

Note: On recent field scouting trips and plot work in Becker and Hubbard counties, I have noticed what I believe is an increase is the number of corn plants that did not tolerate glyphosate applications. The seed industry indicates that this should only be about 1 percent, but in some fields it appears to be more like 2-4 percent, and maybe more. Check your fields after your applications of glyphosate and do some mortality counts.

Tags: