Blueberry weed management

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Many growers have already applied their preemergent herbicides, but some fields have been too wet or growers are waiting a little longer before making applications. In most situations, the traditional preemergent herbicides such as Princep, Karmex, Sinbar, and Solicam will provide good control through the harvest period. If applications are delayed somewhat, control is extended later into the summer. This can be helpful if late-germinating annual weeds (pigweeds, crabgrass, fall pannicum) are troublesome.

The new preemergent herbicide Callisto can be applied up until bloom, so there is still time to try this product on some fields. Callisto provides preemergent and postemergent control of several broadleaf weeds that are troublesome in blueberries, including several pigweed species, chickweeds, horsenettle, lambsquarters, marestail, eastern black nightshade, ragweed and smartweed. Callisto has limited effect on grasses. Apply Callisto before bloom at up to 6 fl. oz. per acre. This amount may be split into two 3 oz. applications at least 14 days apart (too late for two applications in 2009). The addition of crop oil concentrate (COC) will improve postemergent activity, but Callisto with COC may injure blueberry leaves and young stems. Callisto can be used on young, non-bearing and bearing bushes. Avoid plant contact as much as possible.

If preemergent herbicides are applied later in the spring to try to prolong control later in the summer, they can be combined in some cases with postemergent materials to control weeds that have already emerged. The postemergent
herbicides labeled for blueberries, their rates and typical costs are summarized in Table 1. Aim, Gramoxone, Rely and Roundup all cause injury if they contact blueberry leaves and young, green stems. If nozzles are oriented so that the base of bushes is sprayed, injury will result. Although injury can be minimized by directing spray away from the base of bushes, it is a good idea only to use these products on larger vigorous bushes with abundant renewal canes, since a little injury can be tolerated. Also keep in mind that these postemergent herbicides do no good unless weeds are present when they are applied, and these weeds will not be controlled by your preemergent materials alone.

Lastly, this is about the time to use Fusilate (non-bearing bushes only) or Poast for control of quackgrass. These materials must be applied to actively growing grass that is less than eight inches tall to achieve good control. If shoots are taller (older), control is reduced. Fusilade and Poast are selective grass herbicides; then do not harm blueberries or any other broadleaf plants.

 Table 1. Rates and general costs of post-emergent herbicides for  blueberries.
Product Common name Rates (product/acre) Price ($) $/treated acre2
Aim DF carfentrazone 1-2 fl oz 210/qt 7-14
Fusilade DX 2E fluazifop-butyl 1-2 pt 140/gal 17-35
Gramoxone MAX 3L paraquat 1.7-2.7 pt 35/gal 7-12
Poast 1.5E sethoxydim 1-2 pt 77/gal 10-20
Rely glufosinate 3-5 qt 34/gal 26-42
Roundup Ultra 4L glyphosate 1-2 qt 38/gal 10-20
1Costs approximated from dealer quotes, January 2009. Actual costs will vary with source.2Product costs for treating an acre of ground. If band-applying under blueberry rows so half the ground surface is treated, costs would be half of those listed.

Dr. Hanson’s work is funded in part by MSU‘s AgBioResearch.

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