Nov 17, 2017Washington state apple pesticide residue study released
Since 2011, the Washington Tree Fruit Research Commission (WTFRC) has conducted annual trials to evaluate pesticide residues on Gala apples.
This year, researchers applied seven insecticide/acaricides and five fungicides with a Rears airblast sprayer according to either an “aggressive” protocol intended to generate the highest possible residues while observing label guidelines (maximum label rates at minimum retreatment and pre-harvest intervals) or a “standard” protocol following more typical industry use patterns for rates and timings.
Each treatment protocol was sprayed at both 100 (concentrate) and 200 (dilute) gallons of water per acre with a Rears Pak-Blast sprayer while holding the rate of pesticide per acre constant. Fruit samples were collected at commercial maturity on September 6 and delivered the next day to Pacific Agricultural Labs in Sherwood, Oregon, for chemical residue analysis.
“We found no residue level for any pesticide in 2017 that was close to tolerances set by EPA; this result has been consistent throughout seven years of trials and clearly affirms that residues produced by any grower following label instructions should be fully compliant for domestic markets.
Several products we tested produced residues which exceed maximumresidue levels (MRLs) set in important export markets for Washington apples including Danitol, Inspire Super, Ziram, and Merivon. These findings generally have less to do with risk associated with any of these products than the fact that some foreign markets have established very low tolerances for those particular active ingredients.
“In our first year of comparing effects of concentrate vs. dilute spraying (100 vs. 200 gal/acre) of the same rate per acre of pesticides, the results indicate that concentrate applications generally produce higher residues, perhaps because extra water in the spray mix encouraged excessive rinsing and/or runoff of pesticides from fruit surfaces. This trend may not have been as clear in older, denser orchard canopies where additional water volume may be needed to provide adequate spray coverage.
“In contrast, preliminary results in a 2016 cherry study showed that dilute applications (400 gal/acre) tended to produce slightly higher residues than concentrated applications (200 gal/acre) in large, open-center Bing/Mazzard trees with dense canopy structures. Further study is warranted in both cases before drawing firm conclusions regarding carrier volume effects on pesticide residue levels.”
Reports from previous pesticide residue studies on apple and cherry that provide a broader context for these results are available on the WTFRC website at www.treefruitresearch.com.
“We encourage growers and consultants to stay abreast of current information on international MRLs, which often change in response to trade negotiations and/or political developments,” the research report stated.
For more information, visit the Northwest Horticultural Council website, www.nwhort.org.