   Common Sense Weed Control - September 12, 2001 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Keeping up with weeds can seem like a monumental task. No sooner than you pull out most of your warm season annual weeds, the cool season annuals start germinating. Perennial weeds are even more difficult to control. Gaining ground on the war on weeds requires patience. You also need to know you enemy: annual or perennial; warm season or cool season; and even how difficult one weed is to control vs. another within the same category. In this column, I will outline my personal philosophy on weed control. First, you must identify the weed or weeds that are interfering with your gardening objectives. Weeds are easier to identify when they are mature with flowers or seed heads. A good reference book is Weeds of the West by the Western Society of Weed Science. It costs $24.50 if you order from the University of Wyoming. This book has detailed descriptions of 900 weeds with color photos of mature and juvenile plants. I believe there are copies in several of our county libraries. If you have trouble identifying your weed(s), another option is to bring them to the Cooperative Extension office. Once identified, you can learn more about the weed's life cycle and what control measures are most appropriate. Annuals are easiest to control. Perennials are more difficult. Prioritize your weeds and start managing them. Don't try and solve all your weed problems at once. Hand pulling before seed production is a good strategy and can reduce annual weed populations significantly. Many annuals will continue to germinate in subsequent years after you have diligently pulled each one. Plants may not have brains, but they're not stupid. Weed seeds can lay dormant in the soil for several years waiting for the right environmental conditions. Annual weed seeds can also have a wide variation in the levels of seed dormancy within a given year's seed crop. For instance, seeds of yellow starthistle can take as long as seven to ten years to germinate. Of course, many will also germinate the next year. Think about it from the plant's perspective: if all seeds germinated the following year, would that be a good survival strategy? Not really. Diligence is the key: just keep after them until the seed bank is exhausted. You will have little or no success if you try to maintain bare ground. Nature abhors a vacuum. If resources are available (i.e. soil, sunlight, and some moisture), then some plant (usually a weed) is going to take advantage of the situation. A good goal is to out-compete the weed species and occupy the available habitat with a plant that is easier to control and less disruptive to your objectives. Cool season annual grasses such as rye or barley are effective at competing with cool season annuals. Warm season perennial grasses are good competitors for summer weeds. In my yard, I have targeted Dalmatian toadflax and ragweed for high priority control. Both are perennials. The toadflax is predominantly a cool season grower and the ragweed is warm season. I have had decent success by loosening the soil and digging out all the roots I can find. I try not to break the root as I dig and concentrate my efforts before they flower and produce seed. In addition to pulling these weeds, I gather and spread seed heads from nearby sand dropseed: a native warm season perennial grass. This has resulted in decreased habitat for the weeds and looks like a grassy meadow after the monsoons. Over time, sideoats grama (another native warm season perennial grass) has increased as well. Other options are landscape fabric or removing irrigation water, but I'll save that topic for a later article. After two years of this strategy, I still have a few Dalmatian toadflax plants and lots of ragweed. However, the grasses are increasing and seem to be slowly crowding out the ragweed. I may never completely rid my yard of these weeds, but at least I'm getting ahead of them. I'm in no hurry. I think patience is key to long-term weed control. It takes time for weed seed banks to become exhausted and landscapes to develop a balance between available resources and occupied space. Herbicides are always an option and I have nothing against them, but I have not resorted to using them in my landscape yet. If you use them, use them wisely and realize weeds always find bare ground and occupy it. I do not recommend the use of soil sterilants such as Dicamba or Triox. These products prevent plant growth for many years and are designed for use in industrial areas, not in home gardens landscapes. They can also result in damage to surrounding desirable landscape plants. Many other herbicide formulations are available and much more "landscape-friendly". The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |