An integrated approach, utilizing several methods, is the most economical and effective means of controlling weeds. Develop your weed management plan for landscapes before you plant by following these five basic steps:
Before soil preparation and when the weeds are visible, evaluate the soil, mulch, and slope of the site so problems can be corrected or future problems anticipated before planting. Site characteristics to look for include drainage, soil compaction, shading, and water infiltration rate. Identify the weed species in the area, with particular focus on perennial weeds (see References). The best time to look for winter annual weeds is mid- to late winter; perennials and summer annuals are easiest to identify in mid- to late summer.
The most often overlooked aspect of a landscape maintenance program is site preparation. Control existing weeds, especially perennials, before any grading and development are started. Glyphosate (Roundup, etc.) can be used to kill existing annual and perennial weeds. Preplant treatment with fumigants (available to licensed pesticide applicators only) or soil solarization can be used if time allows; however, 6 weeks are required for solarization and it is most effective when done during the time of highest sun radiationâ??from June to August in California (see References). Annual weeds can be reduced by irrigating the area after final grading, allowing the weeds to emerge. While the weeds are still small, a shallow cultivation (less than 1 inch), scraping the weeds off the soil, or spraying with a postemergent non-selective herbicide and then repeating this process of irrigation, emergence, and removal 2 or 3 times will greatly reduce annual weed competition and population.
There are more weed control options if the planting consists entirely of woody plants as opposed to herbaceous annuals or perennial plants, or a mixture of all three. If there is opportunity to do so, consider using mowing strips, planter beds, and borders to reduce weed encroachment and delineate planting types. Choosing drip irrigation and microsprinklers over conventional or flood sprinkler heads will also help in reducing weeds since the water is placed at or near your plants. Watering large areas where there are no plants will only encourage weeds to grow there.
Weeds are sometimes introduced in the soil brought to the landscape site either when amending the soil or in the potting mix of transplants.
Use the best management practices to get the plants established as quickly as possible so that they become competitive with weeds and more tolerant of herbicides applied to the site. Hand-weeding and keeping weeds from producing seeds in the landscape will greatly reduce overall weed populations.
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