CRANBERRIES

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• Cranberries are highly tolerant of Callisto’s active ingredient (mesotrione) [and no long-term cranberry damage has yet to be seen in Washington or Oregon after 3 years] – Cranberry is highly tolerant because it is capable of rapidly metabolizing the mesotrione, but some growers out west have reported ‘some’ cranberry blossom damage as a result of the particular surfactant that might be used in conjunction with it, if used during bloom. Mostly, it was the surfactant known as Silicon Hybrid that was the more phytotoxic one—to cranberry—of the six that were studied out west.
• 88% of the applied herbicide is absorbed within just 3 hours, and the dry-time is QUICK (also a matter of hours);
• It has pre and post-emergent activity on a wide range of weed species.  Unfortunately for us, it isn’t as effective as I was hoping against Yellow Loosestrife, one of our very stubborn weeds, but it will stunt the loosestrife and weaken it.  So with enough years of application of Callisto®, the battle against yellow loosestrife could theoretically be won!  This is true, too, of any perennial weeds in general, in terms of “permanent” control using Callisto®.
• Callisto® is absorbed by roots, stems AND leaves, so it is translocated throughout the plant.
• It is being said that Callisto® is arguably a better overall choice than Casoron®, though there would be times when Casoron® might still be a good choice, but due to known root-inhibition and subsequent yield-reducing nature of prolonged annual use of Casoron® (and gradual but steady decline of vine health), Dr. Patten feels that switching over to Callisto® should help to increase growers’ yields!  He had photo slides of side-by-side plots, with one plot having had Casoron used on it for 3 years, compared to the other plot that received Callisto® instead, for 3 years, and the cranberry plants in the Callisto® plots (there were 2 plots of each treatment) definitely looked healthier and denser.  I believe he used the word “sparse” to describe the number of cranberry uprights in the two Casoron® plots as compared with the two Callisto® plots.

Activity.  Callisto® is a bleaching type herbicide, comprised of the active ingredient, mesotrione, which is a naturally-derived compound produced by a plant called Callistemon.  Mesotrione inhibits the building of a yellow plant carotenoid (pigment) which functions as a sun-screen to protect a plant's chlorophyll -- so without that sun-screen protection, susceptible plants treated with Callisto® will turn white or yellow. Callisto® has both pre-emergent and post-emergent weed control activity. When applied before germination of annual weeds the seedlings take up the herbicide from the soil resulting in death. The Section 18 exemption for Wisconsin indicated that Callisto® should not be applied if growers anticipate rainfall or sprinkling for frost protection within 48 hours of application, so check the new label to see what is recommended regarding this.

When applied post-emergent the herbicide is taken up through the foliage. Thus, irrigation immediately following a post-emergent application is not recommended. In bearing beds, Callisto® can be applied after the bud break stage but before the fruit set stage. In non-bearing beds, Callisto® can be applied after the bud break stage but not less than 45 days before flooding in fall or winter, according to the rules established for the Wisconsin label.  Now that the full label is available, some of these time and rate rules could be different, so that label will need to be examined thoroughly before using the product.

Weeds controlled. Under Wisconsin’s Section 18 Exemption Callisto® application could only be made to control four specific weeds: Birdsfoot trefoil, Violet, Marsh St. Johnswort, and Buttercup. However, Callisto® is effective against many more weeds than these according to its label for corn, including smartweed (ladysthumb), carpetweed, ragweed and pigweed, to name but a few.  And, on the Section 18 label for Washington State, the "cranberry application directions" paragraph includes rushes, sedges and yellow loosestrife as some of its target weeds, suggesting that the material must have some noteworthy activity against those plants! Yellow loosestrife is one that has been particularly problematic on cranberry beds in Maine in recent years, and for which there has been a shortage of materials to use against it. According to Dr. Kim Patten, at Washington State University Extension, Callisto® will not kill yellow loosestrife outright, but will weaken it and stunt it, so perhaps after continued annual use of Callisto® the loosestrife could be eliminated.

Rates (under the Wisconsin Section 18 label). The maximum application rate for Callisto® for the Wisconsin label was set at 8 oz/acre/application with no more than two applications per season. Thus, the maximum annual application was 16 oz/acre. Split applications had to be at least 14 days apart. Research plots in Wisconsin had single application rates of 4 oz/a to 8 oz/a.

Application. Because Callisto® is a very active herbicide it is critical that application be made with a carefully calibrated sprayer. Also, because Callisto® is expensive, many of the applications are going to be spot applications with a backpack or hand-held sprayer. These sprayers must also be calibrated. Calibration of hand sprayers is determined by the walking speed of the applicator and the discharge rate from the nozzle along with the concentration of the material in the tank. Use great care in spot-treating. The difference between an 8-oz application and an 80-oz application is only seconds on the trigger. Spot treatments made to runoff will exceed the maximum application rate.

Worker Protection Standards. These are not listed on the various state Section 18 Exemptions (Wisconsin's and Washington's, for example). That is one reason why it is critically important to read the package label. Callisto® has a 12-hour re-entry interval and a 45 day pre-harvest interval under the Wisconsin label. Applicators and handlers must wear at least:

• Long-sleeved shirt and long pants.
• Shoes plus socks.
• Chemical resistant gloves (Category A).

Pesticide interactions. Wisconsin’s Section 18 exemption did not mention tank-mixing Callisto® with any other pesticides. In addition, the recommendation from Syngenta was that Callisto® not be applied within 7 days (either before or after) of an organophosphate or carbamate insecticide such as Lorsban.

Research plots in Wisconsin (and in Washington State) showed Callisto® to be a safe and effective herbicide for control of weeds in cranberry plantings. In those test trials, researchers did not observe a reduction of cranberry yield from Callisto® application. However, as with any new pesticide, it would be advisable to test this product in a small area first, given that research plots cannot account for all climatic conditions, management practices, cranberry varieties and bed age, and other variables that differ greatly among beds.

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