Summer Annual Weed Emergence (February 4, 2015)

It is not too early to consider applying herbicides for summer annual grasses. Preemergence herbicides are available and effective for us in many summer annual crops. They are only effective however when applied before weeds emerge and it is better to be a month early than a minute late. The graph above is based on a trial we did in Yuma several years to determine when summer annual grasses emerge. Weeds seed germination varies by species and will be affected by temperature, soil type, depth in the soil and other factors. This chart is a general guideline. Summer weeds began to germinate in March, reached a peak in June but continued to germinate through October. Pre-emergence herbicides should be applied, when possible, starting in late February and may need to be reapplied in June or July. The herbicide label should be checked to see what is allowed.

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To contact Barry Tickes go to: btickes@ag.arizona.edu.