Blueberry weed control updates for 2014

Review some of the newer materials and label changes in blueberries found in the 2014 Fruit Management Guide.

Several new herbicides have been labeled on blueberries in the last few years. This is great news because more choices are available, but it also takes time to learn about new products and understand how they are best used. Changes are updated each year in the Michigan State University Extension Bulletin E-154 “Fruit Management Guide,” so consult this publication for details. Below is a review of some of the newer materials and label changes for 2014.

New for 2014

Zeus XC (sulfentrazone) is labeled for blueberries that have been in the field for three years or longer. Zeus is a preemergent herbicide that should be applied before weeds emerge in the spring or tank-mixed with a post-emergent herbicide such as Gramoxone or Aim. Apply 8-12 fluid ounces per acre and no more than 12 ounces per acre during any 12 month period. Do not apply after petal fall unless a shielded sprayer is used.

Zeus controls selected broadleaf weeds and grasses as well as sedges. Some common blueberry weeds that are controlled by Zeus include most annual grasses, several pigweeds, smartweeds, black nightshade and yellow nutsedge. Weed control may be reduced in soils with very low pH or high contents of organic matter and clay. Best control is achieved if 0.5 inches of rain or irrigation is received after application. Pre-harvest interval (PHI) is three days.

Surflan XL 2G is a new formulation of the old herbicide oryzalin that is labeled for use on non-bearing blueberries. It will likely have limited value in blueberries because few growers have appropriate equipment to accurately spread granular products. Surflan XL is not degraded by sunlight as quickly as older oryzalin formulations, so it is not as critical to incorporate the product with irrigation soon after application. However, rain or irrigation is still needed to activate the product. Oryzalin only controls weeds as they germinate and has no effect on emerged weeds or established perennials. It controls most annual grasses and a few annual broadleaves.

Trellis (isoxaben) is labeled for non-bearing blueberries only and replaces the older isoxaben product, Gallery. Trellis will be most useful in new plantings for control of annual broadleaf weeds such as common lambsquarters, ragweed, black nightshade and smartweed. It does not control grasses.

Apply Trellis at 0.7 to 1.3 pounds per acre before weeds emerge. Trellis does not control established perennials or any emerged weeds. If applied after planting, wait until the soil is settled by rain or irrigation. Maximum annual rate is 1.3 pounds. Wait 60 days between applications.

Labeled in the last few years

Chateau has been labeled on blueberries for a few years and the PHI was shortened to seven days last year. Chateau controls many broadleaf and grass weeds, including chickweeds, dandelion, common groundsel, lambsquarters, eastern black nightshade, several pigweeds, ragweed and most annual grasses. Chateau also provides some burndown of small weeds if combined with surfactant or crop oil concentrate (COC). Apply 6 to 12 ounces of product per acre to bushes that have been in the field for two years or more.

Sandea provides preemergent and post-emergent control of many broadleaf weeds such as pigweed, ragweed, smartweed and even 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. Rates are 0.5 to 1 ounce per acre and no more than 2 ounces per year. Do not use on ‘Elliott’ bushes less than three years in the field. PHI is 14 days.

Dual Magnum is another effective herbicide on nutsedge, but has a 28-day PHI. Use only on bushes established at least one year. Use 0.67 pints on young bushes on sandy soils and 1.33 pints on large bushes on heavier soils. Only one application is allowed per season.

Stinger is a preemergent and post-emergent herbicide that is strong on weeds in the composite and legume families, such as thistle, asters, dandelion, goldenrod, ragweed, clovers and wild bean or groundnut. It also controls nightshades, smartweeds, wild buckwheat and plantain. Stinger has some odd timing restrictions (see chart). Stinger is a growth regulator type herbicide and is most effective when weeds are up and growing. Rates are 2.6 to 5.3 fluid ounces per acre and not more than 10.6 ounces per season.

Matrix 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 4 ounces per acre once per year with 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. PHI is 21 days.

Devrinol XT is a new formulation that protects the chemical from photo-breakdown, so it provides longer control than the older product. Devrinol is safe on new plants and provides good control of annual grasses and some broadleaves if applied to a clean soil surface before weeds germinate. Apply 2 gallons per acre. Do not repeat in the same growing season.

Application timing

Most herbicide labels include specific application times. Some are less specific. Best timings for weed control and PHI vary and are not always specified. The following table was developed to help describe when herbicides should be applied.

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Herbicides kill weeds by disrupting specific plant processes and they are classified based on these modes of action. If herbicides with the same mode of action are used repeatedly, resistant weed populations may develop. The table below groups the common blueberry herbicides by their modes of action. To avoid resistance, rotate between or use combinations with different modes

Modes of action of blueberry herbicides.

Herbicide

Mode of action

Karmex, Princep, Sinbar, Velpar

Inhibit photosystem II

Casoron, Trellis

Inhibit cellulose synthesis

Sandea, Matrix

ALS inhibitor

Solicam

Disrupt carotenoid synthesis

Stinger

Synthetic Auxin growth regulator

Surflan

Inhibit microtubules (cell division)

Devrinol, Dual Magnum, Kerb

Inhibit VLCFAs (cell division)

Callisto

HPPD inhibitor (pigments)

Aim, Chateau, Zeus

PPO inhibitor (disrupts membranes)

Poast, SelectMax

Lipid synthesis inhibitors

Gramoxone

Photosystem I electron diverters

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