Ken Schackelton: Fall weed control


Spraying season isn't over yet. The best control of perennial weeds is in the fall when the plants are going dormant for the winter. At this stage, the plant is taking the nutrients from the foliage into the roots for the winter and will take the herbicide with it. This particularly is effective for perennials with extensive root systems such as Canada thistle, leafy spurge, Dalmation and yellow toadflaxes and others. Waiting until after the first frost up until the foliage turns brown is the general recommendation. But with some species that can leave a short window of opportunity to work into a busy schedule. Starting after the temperatures cool down, especially with some rain showers will produce good results. Canada thistle responds particularly well to fall treatment. The roots can grow as deep as 30 feet, making root kill very important. It is also much easier to spot in the fall when the thistle is at full height and as tall, or taller, than the grass. Canada thistle is one of the last weeds to go dormant, usually around the middle of October in Routt County, giving a lot of time for spraying.

Biennial plants also respond well to control in the fall. Biennials take two years to go to seed. The first year they grow as rosettes with leaves close to the ground. The second year they flower, go to seed and then die. The seeds from these plants can germinate throughout the summer after a rain. Spraying in the fall kills the rosettes after they have germinated for the year and destroys the seed production for the next year. It also provides a chance to catch any missed plants the next summer. Some common biennials found in Routt County are houndstongue, common mullein, musk thistle and bull thistle.

There are resources available to aid in control of noxious weeds. The Routt County Conservation District has rental equipment for weed control and pasture management. This includes a John Deere Gator ATV with an 80-gallon sprayer, tractor mounted sprayers, a grass drill and other equipment. Call the Conservation District at 879-3225, ext. 3, for information. Backpack sprayers are available at the Routt County Extension Office. Call 879-0825.

The extension office personnel and the Routt County weed supervisor can help with identification and control recommendations. They can provide handouts on specific noxious weeds, general information and keep a list of commercial sprayers that work in Routt County.

A critical but often ignored step in proper spraying is calibrating the sprayer. This holds true for field sprayer, hose guns and hand-held or backpack sprayers. Using too little herbicide reduces or eliminates control, too much is too expensive and can cause damage to desirable species or the environment. Some labels recommend a percent solution for spot spraying. Otherwise, the recommended rate is based on the amount of pesticide per acre or per thousand square feet for turf. The important part is to know how much water is being sprayed per acre or thousand square feet. The process is more intimidating than difficult. The process needs to be done with just water in the sprayer. For boom sprayers, water is caught from one nozzle for a specified time and measured. Formulas that can be found online or at the extension office are used from here to determine the amount of water sprayed per acre. Changing the ground speed or sprayer pressure will change the rate.

Hand-held sprayers and hose guns on a larger sprayer are easier to calibrate. Consistency in spraying style keeps the rate the same. Measure and mark an area 18 1/2 feet by 18 1/2 feet. Time how long it takes to spray the square, using only water. Do this three times and take the average of the three times. Then spray into a bucket for that amount of the average time and measure the amount collected in ounces. The number of ounces collected will equal the number of gallons of water sprayed per acre.


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