The Mysterious Avocado Problem
Often in a session, questions around nutrition and diet arise. Once someone asked if there was anything she should not be eating. What came to me (as a medium) was avocados. When I further inquired as to ‘why avocados’, I received the word ‘pesticides’. I went back and asked again and all I received were the words avocados and pesticides. So going forward this person adopted the habit of buying organic avocados. This information was a bit puzzling because avocados have a thick outer covering and must be peeled before eating. Although pesticide content is easily measured when it is on the outside of a piece of fruit, it is technically difficult to get accurate lower limits of detection in the food or fruit itself due to interfering substances.
Later I investigated pesticide use to treat avocado trees and this is what I found.
From the session:
S: Yeah, yeah. I mean, I don't see anything wrong with... I'm not getting the message to not eat them, I'm just getting the message that there's some sort of issue with them and then pesticides came in. So, I would go ahead and eat them. I would just be careful to shop for organically grown avocados.
{Because I did not understand the avocado /pesticide connections as this fruit has a thick outer surface and is served with the peel removed, I looked up what could possibly be the problem and found the following publication. Thrips are insects that eat the leaves of avocado trees and can essentially wipe out entire orchards. To find a commercially viable method to control the thrips, insecticides were injected into the trunks of the trees. Although testing showed variable results, it was explained using lower limits of detection in leaves and fruit. No numbers were given as to what the lower limits of detection were. Furthermore, it is technically difficult to develop acceptable lower limits of detection directly in food, especially fruit. These insecticides were found in the fruit following injection into the trunk of the trees and were present after 4 months for two of the compounds. The one candidate thought viable by the authors came in below their lower limits of detection, but no numbers were provided, and technically viable methods were not able to show with any validity the absence of this compound in the fruit. I think this was Spirit’s way of giving us a head’s up as to what is going on the avocado production industry and a nudge to watch for further developments}.
From my investigation:
Pest Manag Sci. 2012 May;68(5):811-7. Online ( doi: 10.1002/ps.2337. Epub 2012 Mar 6. )
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Evaluation of neonicotinoid, organophosphate and avermectin trunk injections for the management of avocado thrips in California avocado groves
Frank J Byrne 1, Anthony A Urena, Lindsay J Robinson, Robert I Krieger, Joe Doccola, Joseph G Morse
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Abstract
Background: Trunk injections of systemic insecticides were evaluated for the management of avocado thrips. Insecticide residues were quantified in leaves to determine when after treatment, and for how long, toxic concentrations of the insecticides were present. Residues in fruit were quantified to determine whether trunk injection of insecticides might present a greater risk than traditional application methods for contaminating fruit.
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Results: Residues of imidacloprid and dinotefuran were at least tenfold higher in leaves when trees were treated via trunk injection compared with soil application. Dinotefuran uptake was more rapid than imidacloprid, and no residues were detected within fruit. Acephate was also mobilized very rapidly and gave good control of thrips in bioassays; however, residues of acephate and its insecticidal metabolite methamidophos were detected in the fruit for up to 4 weeks after injection. Avermectin uptake was very slow, and it was ineffective against avocado thrips.
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Conclusions: Trunk injections of acephate and dinotefuran permitted rapid uptake into avocados, and they are strong candidates as control methods for avocado thrips. However, residues of organophosphates in fruit could necessitate increased preharvest intervals. Residues of neonicotinoids were below detection limits in fruit, suggesting that neonicotinoids may be the more suitable control option of the two chemical classes.