Mar 5, 2012

Michigan growers have access to new herbicides

Michigan blueberry growers have access to several new herbicides, though there is limited experience and information on their efficacy.

Chateau (flumioxazin) and Callisto (mesotrione) have been labeled for two seasons; Stinger (clopyralid) for one season; and Sandea (halosulfuron) was labeled in 2011.

These herbicides represent four new modes of action for blueberry growers, with the products varying widely in the weed spectrum they control. Efficacy depends on rate, timing and soil characteristics. The Michigan State Horticulture Society Trust provided funding for trials of some of these products.

Observations

Chateau is a pre-emergent product with some post-emergent activity, if applied with surfactant or crop oil concentrate (COC). Chateau controls a wide range of broadleaf and grass weeds, including chickweeds, dandelion, common groundsel, lambsquarters, eastern black nightshade, several pigweeds, ragweed and most annual grasses. Chateau needs to be applied before bud break in the spring, requiring 6 to 12 ounces of product per acre. Bushes need to have been in the field for two years.

Chateau seems to provide a longer period of control than most blueberry herbicides, so it is effective in the late fall as well as spring. Chateau will burn developing buds and young leaves if sprayed on the base of plants.

Callisto provides pre-emergent and post-emergent control of several pigweed species, chickweeds, horsenettle, lambsquarters, marestail, eastern black nightshade, ragweed and smartweed. Grass control is poor, so combine Callisto with a grass herbicide. Apply Callisto before bloom, either in one 6 fl. oz. per acre application, or two 3 oz. applications at least 14 days apart. Post-emergent activity is improved with COC, but Callisto with COC will also injure blueberry leaves and young stems that are contacted.

Callisto is labeled for young, non-bearing and bearing blueberries. For effective post-emergent activity, delay Callisto treatments until weeds have begun growing. Callisto will suppress some perennial weeds such as aster and goldenrod.

Sandea provides pre-emergent and post-emergent control of many broadleaf weeds such as pigweed, ragweed and smartweed. The primary value of Sandea is for yellow nutsedge control. Treat nutsedge when three to five leaves are present. Two applications with non-ionic surfactant are most effective. Rates are 0.5 to 1 oz. per acre, and no more than 2 oz. per year. Pre-harvest interval is 14 days.

Stinger has pre-emergent and post-emergent activity. Stinger is most active on weeds in the composite and legume families, such as thistle, asters, dandelion, goldenrod, ragweed and clovers. It also controls nightshades, smartweeds, wild buckwheat and plantain, as well as wild bean or groundnut.

Timing is somewhat complicated. Blueberries are most sensitive to Stinger near bloom, so it should not be applied from one week before to one week after bloom. PHI is 30 days. The best times for treatment appear to be before bloom when weeds are growing; shortly after bloom, but not within 30 days of harvest; and after harvest. Rates are 2.6 to 5.3 fl. oz. per acre, and not more that 10.6 oz. per season. Stinger is a residual material, so accurate rates per acre are important even if spot treating by hand.

SelectMax is a selective, post-emergent grass herbicide similar to Poast and Fusilade. Like the other grass herbicides, SelectMax needs to be applied when grass is growing actively early in the season. Use 9 to 16 fl. oz. per acre with a non-ionic surfactant for best effect.

Herbicide combinations are often needed for control of a broader range of weeds. Combining herbicides with different modes of action reduces the potential to develop resistant weed populations.

Growers should work with the newer products (Callisto, Chateau, Sandea, Stinger) to learn how they perform on their farms. These herbicides have different modes of action than the traditional blueberry herbicides such as Princep, Karmex and Sinbar. As a result, they should be helpful in discouraging development of herbicide-resistant weed populations.

By Eric Hanson, Michigan State University