Most sprays applied to cherries to control spotted wing drosophila and powdery mildew leave residues that are within the tolerances for export markets, a field test in Washington shows. But there are some exceptions when the products are used at maximum label rates.

The test was conducted by the Washington Tree Fruit Research Commission this year to help Washington growers make informed choices about their spray programs.

In a mature Bing orchard near Orondo, Washington, 8 pesticides and 7 fungicides were applied at maximum rates and minimum preharvest and retreatment intervals to simulate the worst-case scenario. The scientists applied most of the pesticides twice, as allowed by product labels, whether or not commercial growers would typically do so. Fyfanon ULV (malathion) was applied by air, while the rest of the products were applied by airblast sprayer at a volume of 400 gallons per acre. Half the plot was treated twice with RainGard to find out how that affected residues.

The fruit was tested immediately after harvest and again after hydrocooling. All residues were below U.S. maximum residue levels but some exceeded the acceptable levels in certain export markets.

In field-run fruit not treated with RainGard:

Mustang MAX (zeta-cypermethrin) applications resulted in residues of 0.24 parts per million, which is above the 0.01 ppm tolerance in Australia.

Entrust (spinosad) applications resulted in residues of 0.095 ppm, exceeding the 0.05 MRL in Korea.

Danitol (fenpropathrin) residues of 1.8 ppm exceeded the European MRL of 0.01 ppm.

Carbaryl residues of 3.5 ppm were well above the 0.05 ppm MRL in Europe.

Applications of the fungicide Orbit (propiconazole) resulted in residues of 0.27 ppm, which exceed the 0.05 ppm MRL in Europe.

Rain in early June could have reduced the residues from the first applications of the products, reports Tory Schmidt, research associate with the commission.

When RainGard was applied, residues were slightly higher in most cases so that two additional products left residues above the lowest export MRL. Residues of boscalid, one of the active ingredients in the fungicide Pristine, slightly exceeded the Korean MRL of 1.0 ppm in field-run fruit. Belt (fenpropathrin) residues slightly exceeded the 0.7 ppm MRL in Korea for that fungicide. Schmidt recommends that growers using waxy products like RainGard consider using less aggressive spray programs to minimize potential residues. Hydrocooling reduced residues of some products but not all, and cannot be relied upon as a strategy to bring fruit into compliance with tolerances, he reports.

Products leaving residues within acceptable levels were: Diazinon, Warrior II (lambda-cyhalothrin), Nuprid 2SC (imidacloprid), Quintec (quinoxyfen), Abound (azoxystrobin), Procure (triflumizole), GEM 500SC (trifloxystrobin), and Fyfanon (malathion).

Schmidt said growers should bear in mind that this was an unreplicated study done at one site under specific conditions. The trees were planted on a 10- by 20-foot spacing and trained to a multiple leader open vase system. Growers using identical spray programs with different tree architectures in different weather conditions might not see exactly the same results.

See full results of the study. Results of a similar study on Gala apples should be available in early September. Reports from pesticide residue studies on apples and cherries conducted in 2011 are on the Washington Tree Fruit Research Commission’s Web site. The Northwest Horticultural Council has more information on MRLs in cherry export markets.

For more information contact Schmidt at (509) 669-3903 or by email.