By Barry Tickes, UA area agriculture agent

Kerb SC is registered for use in lettuce at rates between 2.5-5 pints per acre. These rates do not vary for weed species or soil type but for the irrigation method.

It is important that all three preemergent herbicides used in lettuce be at the right place at the right time to be effective. The right place is around the germinating weed seeds. The right time is during germination.

Unlike Prefar (Bensulide) or Balan (Benefin), Kerb moves readily with high amounts of irrigation water. Prefar and Balan adhere better to the soil.

When lettuce germinates with furrow irrigation and Kerb is applied after planting and before the first irrigation, water moves laterally and upward (subbed) and dissolves, but does not move the herbicide downward.

Higher rates are required for effective weed control since much of the herbicide stays on the surface.

When the herbicide is applied after planting before the first irrigation and sprinkler irrigation is used, Kerb is moved with the overhead water further into the soil. Less herbicide is needed and rates drop by about one third.

Depending upon the weed species and timing, some of the herbicide can move deeply into the soil and below the germinating weed seeds. This is why delayed applications by chemigation are often used with Kerb.

Chemigation is the most efficient means of concentrating Kerb where and when a grower needs it. The rates are therefore half of the recommended rates for furrow irrigated lettuce.

Unfortunately, the most effective techniques to concentrate Kerb around weed seeds also concentrate it around the lettuce seed. For this reason, do not use higher rates than necessary for good weed control.

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Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.

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