Jul 26, 2016

WTFRC completes cherry pesticide residue study

For the sixth consecutive year, the Washington Tree Fruit Research Commission conducted a study of residues of commonly used pesticides on cherry fruit at harvest. The study included 16 insecticides/acaricides, nine fungicides, and a potash & phosphite foliar fertilizer, as well as considering the effects on residues from spraying those materials dilute (400 gal water/acre) or concentrate (200 gal water/acre).

This study simulates a worst case scenario for residues of legally applied pesticides using aggressive rates, timings, and spray intervals. Most materials were applied twice as allowed by product labels, whether or not commercial use patterns would do the same. With that approach, all residues complied with domestic tolerances but some exceeded some foreign tolerances, whether from published MRLs or national default values:

• Insectides/acaricides: Centaur, Bexar, Mustang MAX, Assail 70WP, Baythroid, Danitol 2.4EC, Perm-Up 3.2EC, Carbaryl 4L, Onager
• Fungicides: TopGuard, Orbit, Topsin 4.5FL, Merivon
• Fertilizer: 19 percent potash + 33 percent phosphite foliar fertilizer

MRLs are known to change frequently and cherry producers should routinely monitor the most current information to facilitate compliance with dynamic foreign standards. Differences in residues between dilute (400 gal/acre) and concentrate (200 gal/acre) sprays were generally modest with the higher carrier volume tending to increase residue concentration by 10 percent to 20 percent. While fruit from this study were not rinsed prior to analysis, similar studies in 2011 and 2012 found no clear evidence of consistent residue reduction from commercial hydrocooler cycles.

For the first time, our 2016 study included a potash/phosphite fertilizer applied 3 times at 14 day intervals starting around shuck fall; these programs are used by some Northwest cherry growers for nutritional value and to promote overall tree health. While the U.S. EPA does not regulate residues of foliar fertilizers, phosphite residues are regulated by the European Union (EU) as part of its residue definition for fosetyl-Al (Aliette), which is not registered for use on bearing cherry trees in the U.S. The EU has set a tolerance for fosetyl-Al residues which includes phosphonic acid and all of its salts at 2 ppm; while our samples did not carry any measurable traces of actual fosetyl-Al, they did contain levels of phosphite well in excess of the EU standard. Growers hoping to ship cherries to Europe should avoid use of any phosphite products pending further study and/or relaxation of that MRL.

Digital versions of this report and similar studies on apple and cherry are available on the Washington Tree Fruit Research Commission website. For current information on maximum residues levels (MRLs) and other regulatory issues, please consult the Northwest Horticultural Council website. For more information, contact Tory Schmidt by phone at 509-669-3903 or by email at [email protected].

Source: Washington Tree Fruit Research Commission