Post-emergent blueberry weed control options for 2013

Now that the 2013 blueberry season in underway, post-emergent herbicides can be helpful to manage some weeds that have escaped earlier treatments.

Post-emergent herbicides are applied directly to weeds for control and have no effect on weeds emerging after applications. Below is a review of post-emergent herbicides labeled for blueberries. With all herbicides, be sure to follow all label directions, particularly the pre-harvest interval (PHI). Additional information is available in Michigan State University Extension bulletin E-154, 2013 Michigan Fruit Management Guide.

Post-emergent herbicides

SelectMax (PHI 14 days), Poast 1.5E (PHI 30 days) and Fusilade DX2E (non-bearing bushes) control only grasses. They control annual grasses and can suppress quackgrass and other perennial grasses. They are less effective against grasses taller than 4 to 6 inches, so summer applications need to be timed according to PHIs and the grass growth stage.

These grass killers are sometimes useful for controlling late season grasses such as crabgrass and fall panicum in new plantings. Remember that sedges and rushes are not grasses and are unaffected by these products. Include non-ionic surfactant (NIS) or crop oil concentrate with Poast and Fusilade, and NIS with SelecMax.

Rates: 1 to 2 pints per acre (Fusilade and Poast); 9 to 16 fluid ounces per acre (SelectMax)

Aim 2EC (PHI 0 days) provides burndown of small broadleaf weed seedlings. It is most useful when applied with a preemergent herbicide or to burn down seedlings in new plantings. Avoid contact with blueberry leaves or new shoots. Add NIS or COC for best results.

Rate: 1 to 2 fluid ounces per acre

Gramoxone SL should not be applied after new blueberry shoots emerge because treated blueberry leaves and green bark will be injured. Annual weeds are effectively killed, but established perennials may re-grow. Burndown occurs rapidly, within a few hours or days.

Rate: 2 to 4 pints per acre

Rely 280 (PHI 14 days) provides effective burndown of most annual grasses and broadleaf plants. Rely seems to provide slightly better control of some perennials than Gramoxone, suggesting there may be some movement within treated plants. Weeds treated with Rely take longer to show injury than those treated with Gramoxone. Do not contact blueberry leaves or green bark. Rely supplies may be limited this year.

Rate: 3 to 4 pints per acre

Roundup Ultra 4L and Touchdown 4L (PHI 14 days) provide control of most annual and perennial weeds if applied at the right time. This chemical can move in plants. If perennial weeds are treated after mid-summer, movement into the roots occurs so weeds are killed. Treating perennials early in the summer may only injure the top of plants. Annuals are usually controlled at any time. Weeds die gradually over several days or weeks. Use extreme care to avoid all contact with blueberries, particularly late in the season when translocation occurs.

Rate: 1 to 2 quarts per acre

Stinger 3L (PHI 30 days) is a post-emergent herbicide that is strong on weeds in the composite, legume and nightshade families, such as thistle, asters, dandelion, goldenrod, ragweed, clovers and wild bean or groundnut. Although it is too late to apply Stinger before harvest, consider using Stinger after harvest on these annual and perennial weeds.

Rate: 2.6 to 5.3 fluid ounces per acre. Stinger has some pre-emergent activity, so make sure rates per treated area are as recommended.

Preemergent herbicides with burndown (post-emergent) activity

Preemergent herbicides generally persist in the soil to control weeds as they emerge, but some also burn down small weeds present when applied. These can still be used during the growing season with two cautions. First, follow the PHI on the label. Second, adjust nozzles to avoid hitting the base of bushes; burndown herbicides generally also damage treated blueberry leaves and branches.

Chateau SW (PHI 7 days) controls many broadleaf and grass weeds, including chickweeds, dandelions, common groundsel, lambsquarters, eastern black nightshade, several pigweeds, ragweeds and most annual grasses. Chateau also provides some burndown of small weeds if combined with surfactant or crop oil concentrate (COC).

Rate: 6 to 12 ounces per acre

Sandea (PHI 14 days) provides preemergent and post-emergent control of many broadleaf weeds such as pigweeds, ragweeds, smartweeds and yellow nutsedge. Treat nutsedge when three to five leaves are present. Two applications with non-ionic surfactant are most effective. The second application may need to be after harvest. Young Elliott plants may be sensitive to Sandea, so don’t treat plants during the first three years

Rate: 0.5 to 1 ounce per acre

Matrix SG (PHI 21 days) controls a broad spectrum of annual grasses and broadleaf weeds. Do not use Matrix on sandy soils or on bushes less than a year in the field. Apply with a non-ionic surfactant. Avoid contact with growing shoots and leaves. This product has the same mode of action as Sandea, so don’t use these products together or sequentially.

Rate: 4 ounces per acre

Dr. Zandstra's work is funded in part by MSU's AgBioResearch.

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