Surfactant and cranberries

Kim Patten, The Cranberry Vine, 2017

Here are some general guidelines. New cranberry growth is very sensitive to adjuvants that are oil-based. Don’t use any adjuvant that is classified as a crop oil (COC) or methylated seed oil (MSO) from bud elongation to after fruit set. One of the reasons these surfactants work well is that they damage the waxy cuticle, allowing for better uptake of the herbicide. You won’t always get damage, but you could. For example, a COC adjuvant during dormancy and after the cranberry canopy has hardened off is fine, but could result in damage to tender new cranberry growth.

This is somewhat problematic for grass herbicides, as they are most effective when used with a COC (as per label recommendations). You can still get more than adequate efficacy with a non-ionic surfactant (NIS), just not as good as with a COC. For that reason, during times when the cranberries are not sensitive to an oil-based surfactant, consider using a 0.5% v/v COC surfactant to improve control. Use a 0.25% v/v NIS during sensitive time periods.

Even after bud set, I would still be cautious with a COC during hot sunny days. Overall, a NIS will not be as effective as a COC with grass herbicides, but will be good enough. The Callisto label states both a COC and NIS can be used. Therefore, stick with 0.25% NIS to be safe. Another popular type of adjuvant is the hybrid silicone-based surfactants. These are particularly effective in that they reduce surface tension enough to allow direct stomata uptake of the herbicide. I would be cautious using any silicon-based surfactant for foliar applications of herbicides on cranberries, but new data indicate that they are very effective in improving the efficacy of weed wiping with glyphosate.

Differences in efficacy between adjuvants of the same type are subtle and there are too many adjuvants, 632 labeled in WA, to make specific recommendations. Stick with those from major companies. A good adjuvant guideline to download for free is the “Compendium of Herbicide Adjuvants” (to find the download, google PPP-115.pdf).