Study Shows Residue Levels Mostly Acceptable
A three-year study analyzing pesticide residue levels in blueberries at six different intervals after treatment has found that in most cases, if label directions are followed, levels are acceptable in the U.S. and most foreign markets. In some cases, however, delaying harvest beyond a label’s pre-harvest interval is necessary to meet maximum residue levels (MRLs) of different foreign markets.
In the study, conducted by Joe DeFrancesco, a senior researcher in Oregon State University’s Department of Horticulture, it was found that in nearly all cases, when following label directions, residue levels in the study met U.S. tolerance levels.
However, meeting standards in the European Union, Hong Kong and Korea sometimes require using a longer pre-harvest interval than the labels specify.
“E.U., Hong Kong and Korea are difficult markets to ship to,” wrote DeFrancesco in a summary of the study. “MRLs don’t exist for certain insecticides and fungicides in these countries or the MRL is so low that they are not possible to achieve unless fruit harvest is delayed past the U.S. pre-harvest interval.”
DeFrancesco also found that some insecticides, such as Malathion, spinosad (Entrust) and spinetoram (Delegate), degrade rapidly in the field, while others, such as esfenvalerate (Asana) and methomyl (Lannate LV), degrade slowly.
In the study DeFrancesco analyzed degradation properties of 13 commonly used insecticides, including Admire, Brigade, Sevin and Imidan, and two fungicides, Switch and Pristine. The field trials, conducted at the Lewis-Brown Research Farm in Corvallis, were replicated four times and conducted over three years.
Similar studies, using the same field research protocol and that included the same 13 insecticides, rates, number of applications and spray intervals, were conducted in Washington and Michigan.
Fruit was sampled for residue levels at intervals ranging from one day to 21 days after applications.
DeFrancesco’s final report provides details on which markets require longer PHIs than U.S. labels specify and how many days prior to harvest a product can be applied and still meet that country’s MRL.
In some cases, the study points out, particular markets do not have established MRLs for certain products and a grower should either avoid shipping to that market if using a particular product or avoid using that product if planning to ship to that market.
The full report and other berry and registration topics can be found at the North Willamette Research and Extension Center website. Click here to view the report as a pdf.
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