Soaking rains bring much-needed water to our desert environment, including plants. Rainwater is especially beneficial to plant material as rainwater is less alkaline than our irrigation water. While rain is a positive thing for our plants and irrigation water bills, it also helps weeds grow. For effective weed control in your yard, manual removal is the easiest way to get rid of a small number of weeds. To control weeds over a large area, herbicides are the most efficient tools available. There are two categories of herbicides for weed control: Pre-emergent and Post-emergent.
Post-emergent for winter weeds: Post-emergent herbicides kill weeds that have germinated and are visible in the landscape. To kill weeds in winter months, you need to use a herbicide containing Diquat. Spectracide products, which contain Diquat, are available for personal use at most home improvement stores or nurseries.
Pre-emergent herbicides: Pre-emergent herbicides are designed to prevent seeds from germinating in the soil. They are most effective when applied during the rainy season. In Arizona, that means either before the summer monsoon in June & July or from October through January to take advantage of the winter rains. A timely application of pre-emergent can greatly reduce the number of weeds that germinate since it inhibits the weeds’ roots and does not allow them to grow.