Blueberry producers have a fair selection of herbicide products to work with, and two additional products were recently labeled: Callisto (mesotrione, Syngenta Crop Protection) and Chateau (flumioxazin, Valent U.S.A.). Current herbicide recommendations are provided each year in Michigan State University Bulletin E-154, Fruit Management Guide. This is an important publication for commercial growers because it provides detailed instructions about how herbicides and other pesticides should be used.
Most growers have two general weed control questions. First is choosing the early season preemergent program. The goal here is to choose an herbicide or combination of products that are strong on the dominant weeds. An effective choice will control most annuals and some perennials through the summer.
The second consideration is how to manage established perennial weeds that are not effectively controlled by available preemergent products. This often requires careful use of glyphosate late in the season.
Preemergent programs Princep (simazine, Syngenta), Karmex (diuron, DuPont Crop Protection), Sinbar (terbacil, DuPont), and Solicam (norflurazon, Syngenta) are the work-horse preemergent herbicides in established blueberries. They control many germinating annual weeds for one to three months. These products can potentially injure blueberries, so be familiar with the label precautions regarding sandy soils and young plants. Princep and Karmex tend to be stronger on broadleaf weeds, whereas Sinbar and Solicam are effective on grasses. Combining broadleaf and grass materials controls a broader spectrum of annual weeds.
Callisto and Chateau were labeled for use on blueberries recently. Callisto provides preemergent and post-emergent control of several pigweed species, chickweeds, horsenettle, lambsquarters, marestail, eastern black nightshade, ragweed, and smartweed, but is weak on grasses. Apply Callisto before bloom, either in one 6 fluid ounce per acre application, or two 3-ounce applications at least 14 days apart. Crop oil concentrate (COC) improves postemergent activity, but Callisto with COC may injure blueberry leaves and young stems. Avoid plant contact as much as possible.
Callisto is labeled for young, non-bearing and bearing blueberries. Chateau is primarily a preemergent product with some postemergent activity if applied with surfactant or COC. Chickweeds, dandelion, common groundsel, lambsquarters, Eastern black nightshade, several pigweeds, ragweed, and most annual grasses are controlled. Apply Chateau before budbreak at 6- to 12-ounce product per acre. Bushes need to have been in the field for two years.
Growers should work with Callisto and Chateau to learn how they perform on their farms. These herbicides have different modes of action in plants 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.