Weed and Pest Update

Summer is rapidly coming to an end, bringing cooler temperatures and the feel of fall in the air. Although the summer is nearly over, Crook County Weed and Pest continues to stay busy into the fall months in the office and in the field.

To date, the district crew has treated over 620 acres of weeds in Crook County, covering and protecting over 16,000 acres of land. These numbers will continue to rise into the fall months as treatments will continue as long as the weather holds out.

Leafy spurge will continue to be treated by the district until snow flies and/or the leafy spurge stops growing. Fall treatments of leafy spurge are very effective, but the window of opportunity is limited due to the rapidly changing weather conditions.

Many different species of weeds can be controlled in the fall with excellent results. As growing conditions start to diminish, most plants will have seeded and growth is very minimal.

At this point, plants are cued by environmental factors such as shortened day length and cooler temperatures, and they begin to prepare for winter and continued growth and spread in the following spring.

As summer months and growing conditions diminish, perennial species will allocate their resources directly to root reserves rather than above ground growth, which makes for very effective herbicide treatments as the plants will pull the herbicide directly to the roots. Some species will sprout small seedlings while others remain green at the base of existing plants.

These green plants will photosynthesize and store all the resources and allocate them directly to the roots to ensure growth the following year, rather than use them for continued growth. A few examples of perennial species that can be effectively controlled in the fall are: leafy spurge, Canada thistle, Dalmatian toadflax.

Biennial species can also be controlled with favorable results during the fall. Some biennial species will be maturing in the fall months, and continue growth and seed set until winter.

These plants include: houndstongue, common mullein, spotted knapweed, musk thistle, Scotch thistle, and several others. Treating these more mature plants can prevent the spread of seeds, and if treated with residual herbicides, can prevent growth of new germination of seedling rosettes.

Many species complete their cycles faster and will have set seed in early summer. These seeds can germinate in the fall and emerge as a seedling vegetative “rosette” in the late summer and early fall where they prepare to continue growth the following spring. Treating seedling rosettes is very effective; however, treatments at either stage can be effective.

Winter annual species are a type of plant that germinate (start growth) in the late summer and early fall, and then overwinter as seedling plants where they will be the first green plants in the following spring. Winter annual plants include: field pennycress, dandelions, marestail, prickly lettuce and many others.

These plants can be controlled with great results in these fall months with herbicide treatments. Annual plants sprout a seedling directly from seed, and there are no roots available to re-grow, so killing this fall growth will help prevent any further spread. However, there still may be seeds in the soil that have not germinated, and plants may come up the following spring or fall.

Fall can also be a great time to treat winter annual grasses such as: cheat grass, jointed goat grass, wild rye, annual bluegrass. In the fall, most perennial grasses will have gone dormant; however, winter annual grasses will just be germinating and emerging – giving an excellent window of opportunity to kill them without harming beneficial grass species.

For control on any type of weed species in the fall, ensure there is green growth of the plant and watch carefully for small seedlings that may be hard to see. Additionally, ensure spray equipment is winterized or stored inside during the night to prevent any freezing issues. For any more questions about treating weeds in the fall, please stop by our office and visit with us.

Submitted by Andrew Litzel