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Fall is an excellent time to control perennial weeds, those troublesome ones that return year after year. When perennials first emerge in the spring, they have so much energy stored in their root systems that herbicides have little effect. The top may die back, but the weed will emerge again. Perennial weeds are most vulnerable at two specific points in their life cycle: in the bud or early flowering stage, and in the fall. When the plants are just beginning to flower, they have used a considerable amount of the energy that was stored in their roots and are therefore vulnerable. During the summer, many weeds are not very metabolically active, and therefore herbicides have only moderate effect.
In the fall, however, the weeds are drawing their energy back into their roots in preparation for winter. Plants store this energy in the form of sugars and starches. Herbicides applied now will move through the plant readily, and be drawn down into the root system along with the carbohydrates. Even if treatments applied at this time don't kill the weeds, they will severely weaken them and make them easier to control in the spring.
For herbicides to be effective, the target plant must be metabolically active. If the plant has already gone into dormancy, the herbicide will not work. Bermuda grass, for example, which is a warm-season grass, will not respond to treatments now. Fall applications need to be made while the weeds are still green. Dandelion, bindweed, and Russian knapweed are examples of perennial weeds that can be successfully treated now.
Biennial weeds, which complete their life cycles in a two year period, form a dense cluster of leaves in the first year called a rosette. These weeds also store their energy in their roots following their first year, in order to flower and set seed the following season. Many biennials can be successfully treated in the fall. Most of the troublesome thistles are biennial weeds.
The third category of weeds that can be controlled now is the winter annuals. These are plants that germinate in late summer or early fall, go dormant over the winter, and set seed in spring, completing their life cycles. Cheatgrass (downy brome) is a winter annual, as are storksbill and flixweed. Look for these plants to be emerging now, in areas where they have been a problem in the past. Cheatgrass is particularly a pest, as it is both a fire hazard and a nuisance to pets when it dries out in the spring. It is very common along alleys and waste areas.
Most herbicides are effective within specific temperature ranges. The common broadleaf herbicide 2,4-D, for example, needs to be applied when the temperature is between 50E and 80EF. Below this, it will not work well; at warmer temperatures the risk of drift to non-target plants is increased. The information about appropriate temperatures is on the herbicide label. All yard and garden chemicals need to be properly stored over the winter; again, please consult the label for specific information. This week with our high temperatures predicted to stay in the 50's will be a perfect time to treat weeds as long as it isn't windy. Windy conditions greatly increase the chance that herbicides will come into contact with our desirable plants (or our neighbors') so please don't spray if it's breezy.
Timing herbicide treatments to correspond to the vulnerable stages of the target plants saves time, money, and aggravation, and minimizes the impact of these chemicals on the environment. It makes good sense to take the time to properly identify your problem weeds and learn about their life cycles. Bring samples to the Colorado State University Cooperative Extension office at the Mesa County fairgrounds if you'd like help with identification, or give us a call at 244-1836. Although we will never be free of weeds, getting a jump on them this fall will make management a lot easier next spring.
In the fall, however, the weeds are drawing their energy back into their roots in preparation for winter. Plants store this energy in the form of sugars and starches. Herbicides applied now will move through the plant readily, and be drawn down into the root system along with the carbohydrates. Even if treatments applied at this time don't kill the weeds, they will severely weaken them and make them easier to control in the spring.
For herbicides to be effective, the target plant must be metabolically active. If the plant has already gone into dormancy, the herbicide will not work. Bermuda grass, for example, which is a warm-season grass, will not respond to treatments now. Fall applications need to be made while the weeds are still green. Dandelion, bindweed, and Russian knapweed are examples of perennial weeds that can be successfully treated now.
Biennial weeds, which complete their life cycles in a two year period, form a dense cluster of leaves in the first year called a rosette. These weeds also store their energy in their roots following their first year, in order to flower and set seed the following season. Many biennials can be successfully treated in the fall. Most of the troublesome thistles are biennial weeds.
The third category of weeds that can be controlled now is the winter annuals. These are plants that germinate in late summer or early fall, go dormant over the winter, and set seed in spring, completing their life cycles. Cheatgrass (downy brome) is a winter annual, as are storksbill and flixweed. Look for these plants to be emerging now, in areas where they have been a problem in the past. Cheatgrass is particularly a pest, as it is both a fire hazard and a nuisance to pets when it dries out in the spring. It is very common along alleys and waste areas.
Most herbicides are effective within specific temperature ranges. The common broadleaf herbicide 2,4-D, for example, needs to be applied when the temperature is between 50E and 80EF. Below this, it will not work well; at warmer temperatures the risk of drift to non-target plants is increased. The information about appropriate temperatures is on the herbicide label. All yard and garden chemicals need to be properly stored over the winter; again, please consult the label for specific information. This week with our high temperatures predicted to stay in the 50's will be a perfect time to treat weeds as long as it isn't windy. Windy conditions greatly increase the chance that herbicides will come into contact with our desirable plants (or our neighbors') so please don't spray if it's breezy.
Timing herbicide treatments to correspond to the vulnerable stages of the target plants saves time, money, and aggravation, and minimizes the impact of these chemicals on the environment. It makes good sense to take the time to properly identify your problem weeds and learn about their life cycles. Bring samples to the Colorado State University Cooperative Extension office at the Mesa County fairgrounds if you'd like help with identification, or give us a call at 244-1836. Although we will never be free of weeds, getting a jump on them this fall will make management a lot easier next spring.
