pesticides – The Garden Professors™

The Dirty Truth Behind the “Dirty Dozen”

By: Abi Saeed

Pesticide residues and risk assessments have been a major topic of interest and inquiry for me for over a decade, and something that I wanted to write about on the Blog for quite some time. Over the past couple of months, I have had several inquiries from people regarding the “Dirty Dozen” list, so I thought this was the perfect time to organize the evidence-based data on this topic. To see a prior post on this topic, you should also check out Jeff Gillman’s post on the Dirty Dozen from 2010 and a follow up post from 2011.

Before diving too deeply, I wanted to acknowledge some of the articles and resources that I leaned heavily on while putting this post together. These include an excellent article by University of California Davis Extension Food Toxicologist Dr. Carl Winter on pesticidefacts.org, and an article authored by multiple experts from University of Arkansas Division of Agriculture Research & Extension (Dr. Amanda McWhirt, Dr. Jackie Lee, and Ples Spradley). Since both of these articles are over 5 years old, I have updated some of the information in my post to reflect any changes in the science and methodology since the time their articles were published. I also want to acknowledge that much of the regulatory information that I will be sharing within this post will pertain to agriculture in the United States, and for more detailed information on this topic pertaining to other countries, I strongly encourage you to seek out evidence-based resources and/or reach out to knowledgeable experts.

What is the ‘Dirty Dozen’

Aside from being a great World War II film from the late 1960’s, the term ‘Dirty Dozen’ also refers to a consumer-focused publication put together by an environmental advocacy group based in the United States. The Dirty Dozen is a list of 12 produce items (fruits and veggies) that allegedly contain the highest pesticide residue levels (dubbing them to be the ‘dirtiest’). This list is developed annually by the Environmental Working Group (EWG) with rankings that are based on United States Department of Agriculture’s (USDA) Pesticide Data Program (PDP) report. Although this sounds important and valuable to share with consumers, the information contained in these lists is derived through problematic methodology, disseminated using a lack of complete and evidence-based data, and results in unnecessary fear and uncertainty surrounding the consumption of fruits and vegetables that can have significant negative ramifications for growers and consumers alike.

The EWG’s “Shopper’s Guide to Pesticides in Produce” deters people from buying conventionally grown produce on the “Dirty Dozen” list, encouraging them to only purchase organic versions of these items. This annual guide also contains a “Clean Fifteen” list which includes produce items with the “lowest amounts of pesticide residues”. Neither list goes into detail regarding what these residues actually are, and whether they are even harmful to the consumer, and are therefore continually challenged by many scientists as lacking in scientific credibility.

The 2025 Dirty Dozen list is as follows:

Spinach
Strawberries
Kale, Collard, and Mustard Greens
Grapes
Peaches
Cherries
Nectarines
Pears
Apples
Blackberries
Blueberries
Potatoes

Recently harvested strawberries. Photo: **Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org**

EWG’s Dirty Dozen and Clean Fifteen methodology

Prior to 2025 EWG’s Dirty Dozen list was formulated primarily using percentages of samples with detectible pesticides and the number and amount of pesticides detected (with absolutely no information regarding the relative toxicity of these pesticides). As of this year, they have included the metric “overall toxicity of pesticides on a crop” as part of their screening criteria. Although this is a step in the right direction, it is still arguably incomplete information to share with consumers (especially since the most important component, whether these residue amounts are actually harmful to consumers, is still not addressed by any of their metrics, nor clearly communicated in their publications and marketing). This glaring omission is a big red flag in the credibility of this publication, and one of the main reasons why I have such a problem with it. As many of you avid Garden Professors Blog readers know from the many great science-based posts that have been shared (including Linda’s article on Recognizing Bad Science), we need to look carefully at the information being shared, regardless of the source, and make sure that it is evidence-based, credible, and complete.

Understanding Pesticide Safety

I want to caveat this section by stating that this is covering the science pertaining to pesticides and human health based on the research we have on this topic to date (which is subject to change as more evidence-based information comes to light). The scope of this Blog post does not cover environmental/ecological/economic/etc. impacts of pesticides in general nor the overarching impacts of various types of agriculture and food production systems (both of these are very complex topics which will require much more time and research to cover).

Although the term ‘pesticide’ is synonymously used with insecticides by many, pesticides are actually a broad category that includes all substances used to control or eliminate pests (including weeds, arthropods, vertebrate pests, pathogens, etc.). Therefore herbicides, insecticides, miticides, rodenticides, fungicides, bactericides, etc. all fall within the category of ‘pesticides’. Humans have been using ‘pesticides’ for thousands of years, though much of the innovation in pesticides (especially synthetic formulations) has occurred over the past 100 years. We have also greatly expanded our understanding and implementation of safety protocols and consideration for human and environmental health especially over the past 50 years (since Rachel Carson’s ‘Silent Spring’ and the formation of the U.S. Environmental Protection Agency (EPA) in 1970). Thankfully we have come a long way from the ‘DDT is good for ME-E-E’ era (and still have quite a long way to go). Although we are not perfect, pesticides in general are continuing to become safer and more effective, and products with higher toxicity and non-target effects are continually being phased out in support of better chemistries with fewer human health and environmental impacts (though the latter has much more knowledge gaps than the former, and we still have a LOT more work to do on this front). As we learn more about these products with scientific studies, we continue to update our protocols pertaining to them, though there are still knowledge gaps which continue to be explored by researchers. As Extension and IPM (Integrated Pest Management) professionals, we continue to educate people on the importance of pesticide safety, and urge people to think of the environmental impacts of these products, using them only after other IPM strategies (such as cultural, mechanical, and biological controls) have been unsuccessful. Anyone who uses pesticide products (whether Restricted Use Pesticides applied by Certified Pesticide Applicators and those under their direct supervision, or readily available general use pesticides such as Neem Oil, Insecticidal Soaps, etc.) should do so responsibly and in accordance with the label (the label is the LAW!), only when needed, and minimize negative environmental impacts when possible. The history of pesticides and formation of current regulatory protocols is a fascinating topic that I encourage all of you to read up on if you are interested (and may be an interesting topic for a Blog post in the future).

Home garden pesticides on a retail shelf from 1997. Photo: **Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org**

Now that we have covered pesticide basics, let’s get into pesticides and food safety in Organic and Conventional agriculture. First and foremost, if you are purchasing organic produce, that does not mean it is pesticide-free. In the United States, Certified Organic produce refers to food items that are grown utilizing a specific set of principles governed by the National Organic Program. Furthermore, there could be several conventional operations that still follow some of these principles, though may not be Certified Organic. An organic pesticide is basically a pesticide that is approved by the USDA for use in organic agriculture. Although pesticides used in organic agriculture are usually naturally derived, there are also synthetic pesticides that meet the criteria and are allowed in organic agriculture (just as there may be organic pesticides used in conventional agriculture). All pesticides utilized in the U.S. (with the exception of minimum risk pesticides) are registered with and regulated by the EPA. Any of the aforementioned pesticides that are used and sold within the U.S. have rigorous testing surrounding their safety for humans (and maximum allowable concentrations which are set at levels significantly below [10-1000 times lower] those that caused no adverse effects during testing), labeled according to these appropriate evidence-based safety guidelines, and off-label use is prohibited, routinely investigated, and enforced. Regardless of organic/conventional designation: just because something is naturally derived does not mean that it is safer than synthetically derived products. There are many natural substances that are extremely toxic (eg. Botulinum toxin, Ricin, Cyanide, Arsenic, Asbestos, etc.) and many synthetic ones that are relatively benign in comparison. In summary: Organic does not mean pesticide free, and natural/naturally derived does not mean safe.

For any of us that have taken a toxicology class, one of the most memorable take home messages was “The dose makes the poison”. Credited to a Swiss physician named Paracelsus in 1538, this statement applies to any chemicals (including water, salt, oxygen, caffeine, Aspirin, etc.) that are consumed or absorbed by us, forming the foundation of health and safety guidelines that determine the maximum allowable concentrations (tolerance levels) of these substances in our food, water, and the environment.

One of the most useful and illuminating courses I have ever taken in my career was Environmental Risk Assessment, which covered important topics including toxicology, pesticide risks, and invasive species (among other concepts). This course also detailed how Risk Assessments are conducted, the rigorous regulatory processes and evaluations required before products are even available for use, and the evidence-based tools used to determine whether a substance is hazardous and at what level (dose). A great summary of the Risk Analyses pertaining to pesticides and food safety have been summarized by Alejandro Fernández, Agronomist and Director of Hygiene and Safety of Products of Plant Origin SENASA (Argentine Food Safety and Quality Service), on the Pesticide Facts website (link in resources). These Risk Assessments and Analyses are the foundation of how we go about making determinations regarding any substances that we may be exposed to (including food and medicine).

The Issues with the ‘Dirty Dozen’

One of the biggest issues with the Dirty Dozen list is the fact that they do not communicate what having the highest (and lowest) pesticide residue levels even means. They do not conduct an accurate Risk Assessment to be able to support their message for avoiding conventional produce on this list. Although they do talk about the hazards (substances that have a potential to cause harm to us), they omit the crucial component of actual risk (likelihood of that substance causing harm to us), which incorporates another critical component of Risk Assessments: Exposure (how much of the hazard we are exposed to over a given period of time). If we looked at actual risk from the residues (incorporating hazard and exposure) we would find that the residues found on these produce items on the Dirty Dozen list are extremely low, and far below the threshold of having any risk associated with them, especially if we account for exposure (how many we consume on a daily basis, and over an extended period of time). A peer-reviewed Risk Assessment on pesticide residues published in the Journal of Toxicology by Winter and Katz (2011) in response to EWG’s 2010 Dirty Dozen list found just that (link in resources). Their conclusions were: (1) exposures to commonly detected pesticides in the 12 Dirty Dozen commodities had negligible risks for consumers, (2) substituting organic commodities for these conventionally grown ones did not result in any significant reduction of risk, (3) the EWG methodology for determining risk of these 12 products lacks scientific credibility (Winter and Katz, 2011).

Based on this cool pesticide residue calculator (link in resources), a woman of average height and weight could consume 774 servings of spinach or 453 servings of strawberries (the #1 and #2 produce items on the Dirty Dozen list) in a day without any effects. This calculator utilizes the highest possible amount of pesticide residue recorded by the USDA in these produce items, and not the average amount. Now I don’t know about you, but I would personally struggle to consume even 10 cups of strawberries in a day (every day), let alone over 450 cups. This is a great illustration of how dose/risk works, and why these produce items are considered safe for human consumption in conventional agriculture.

Pesticide residue calculator results. https://www.safefruitsandveggies.com/pesticide-residue-calculator/

In summary: the EWG fails to mention that these residue levels are still safe, and far below the thresholds that can begin to have an impact on the consumer. This can have negative ramifications for farmers that grow the produce on these lists, especially if they grow conventionally as opposed to organically. Concerns that people may opt to avoid conventionally grown produce, or avoid those specific produce items altogether is an added hurdle for growers to worry about. Both conventional and organic farmers care about what they produce, and also want our food to be safe (for their families and ours). Our regulatory processes further monitor this safety in both conventional and organic production systems, and as the science is updated, so are these processes. Although many lack access to this, if you have access: reach out to local growers and get to know what their practices are to get a better understanding, and support local farmers when possible.

Furthermore, marketing and messaging like EWG’s Dirty Dozen list discourages people from consuming certain produce, and with only 1 in 10 Americans eating enough fruits and vegetables in their diet, the cons far outweigh the pros for this messaging. An article from the Alliance of Food and Farming details some of these negative impacts (see Resources). This type of fear-mongering disproportionately impacts consumers in lower income brackets, and those that lack access to certain produce. A 2016 consumer survey showed 15% of lower income shoppers surveyed would opt to eat less fruits and vegetables after hearing about the ‘Dirty Dozen’ (Huang et al., 2016).

The take home message should be: the produce that you purchase, whether conventional or organic, is safe to be consumed (and backed by rigorous testing that determines this). Do not be deterred from eating the produce of your choice. Choose produce that is enjoyable, affordable, and accessible to you. And whether conventional, organic, or home-grown: eat more fruits and veggies!

Delicious strawberries. Photo: **Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org**

Resources:

Pesticide Facts: ‘Dirty Dozen’ List Contaminated with Non-Science:
https://pesticidefacts.org/perspectives/dirty-dozen-list-contaminated-with-non-science/

What is the “Dirty Dozen” list and should you be worried about it:
https://www.uaex.uada.edu/farm-ranch/crops-commercial-horticulture/horticulture/ar-fruit-veg-nut-update-blog/posts/dirtydozen.aspx

Organic vs. Conventional Pesticides:
https://www.pubs.ext.vt.edu/ENTO/ENTO-384/ENTO-384.html

Pesticide Facts: Pesticide Risk Analysis Ensures Food Safety:
https://pesticidefacts.org/perspectives/risk-analysis-ensures-food-safety/

USDA PDP Report (2024):
https://www.ams.usda.gov/sites/default/files/media/PDPLABOPSOP.pdf

Pesticide Residue Calculator:
https://www.safefruitsandveggies.com/pesticide-residue-calculator/

Alliance for Food and Farming: Consumer Impacts
https://foodandfarming.info/alliance-for-food-and-farming-dirty-dozen-list-scientifically-unsupportable-hurts-consumers/

Washing fresh fruits and vegetables safely:
https://extension.umn.edu/preserving-and-preparing/wash-fresh-fruits-and-vegetables

Carl K. Winter and Josh M. Katz, 2011. Dietary exposure to pesticide residues from commodities alleged to contain the highest contamination levels. Journal of Toxicology, Article ID 589674, doi:10.1155/2011/589674.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3135239/

Yancui Huang, Indika Edirisinghe, and Britt M. Burton-Freeman, 2016. Low-income shoppers and fruit and vegetables: What do they think? Nutrition Today 51(5): 242-250.
https://journals.lww.com/nutritiontodayonline/fulltext/2016/09000/low_income_shoppers_and_fruit_and_vegetables__what.6.aspx

Dear big box store: please make up your mind.

Report from the Center for Food Safety, April, 2015:

My photo from July, 2015:

Yes, sometimes folks want or need to kill bees, wasps, etc. But given the current hullabaloo, this particular sales display was too ironic for words.

Read and follow label directions…

Every extension specialist or educator that mentions any kind of pesticide in a talk or article always includes the disclaimer ‘Read and follow all label directions.” However that caveat ranks somewhere between “Your seat cushion may be used as a flotation device” and “Do not remove tag under penalty of law” as the most ignored phrase in the English language. While we can probably rationalize ignoring the last two (If a jetliner ditches in the middle of the Atlantic is a seat cushion really going to save you? And when was the last time you saw someone led away in handcuffs for pulling the tag off a mattress?); failing to pay attention to pesticide labels can have some real and immediate consequences.

I got called recently to inspect some tree and shrub damage at an industrial park in suburban Detroit. (Because the case potentially involves some legal issues, I won’t mention names of any parties). The industrial park included several hundred acres, much of it turf and landscape beds of trees and shrubs. The park had its own groundskeeper but contracted out its spray applications. A couple summer’s ago the staff groundskeeper complained several times to the contractor that they weren’t doing a sufficient job of keeping up with the weeds in the landscape beds. The typical vegetation management tools of choice on this site were spot applications of Round-up (glyphosate) and hand-weeding. For reasons that are not completely clear, this time the contract applicator reached for a jug of Sahara. Even if you don’t know what Sahara is; what image does the name conjure up? Parched. Barren. Lifeless. Sahara is a combination of two herbicides (Diuron and Imazapyr) designed for complete vegetation control in non-cropland areas such as parking lots and rights of way. And, unlike Round-up, Sahara provides foliar and root activity. This is a product you use when you want complete burn-down and you don’t want anything growing there for a long time.

A hedge maple 2 years after herbicide application

Unfortunately, that was not the desired result in this location. Within a week of the application, dozens of trees and shrubs all over the industrial park were either dead or wishing they were dead. The smoking gun was not too hard to find. The applicators had duly noted the herbicide application in their logbook and presence of active ingredient was confirmed in soil samples. Although the parties are still working a settlement, the bids for replacing the affected trees and shrubs are well into six figures.

The unkindest cut of all. These green ash were regularly treated with imidacloprid to protect against emerald ash borer. An herbicide ap took them out instead.

Two years after application there are still bare zones where Sahara ran off from mulch rings and landscape beds.

Of course, all of this death and destruction (and legal wrangling) could have been avoided simply by… Reading and following the label directions. The Sahara label notes in several places that contact with roots can damage trees and other plants, including this explicit statement under a heading in all bold letters, PRECAUTIONS FOR AVOIDING INJURY TO NONTARGET PLANTS: “Injury or loss or desirable trees may result if Sahara is applied on or near desirable trees or on areas where their roots extend.” Sounds pretty clear to me folks – don’t use this stuff near plants unless you want them to die.

So, next time you or someone working for you has any question about what a pesticide does: Read and follow label directions….

Bordeaux Mix

One of my favorite stories about pesticides is the story of Bordeaux mix. It’s a story of France in the 1800s (so it must be pretty romantic, right?) and how they were suffering from a shortage of grapes. Don’t feel sorry for them — it was really their own doing. Over the course of the 19^th century grape vines were brought from the United States to test their merits against European grapes. It was quickly discovered that, for the most part, American grapes were not the equal of European grapes for winemaking. Unfortunately for the French, however, along with the grapes came a disease: downy mildew. This mildew absolutely ravaged grape vines across Europe, and particularly France from the time that it was introduced, around 1878.

Meanwhile there was another problem for grapes growing in France. People. People like to eat grapes beside the side of the road and so, throughout France’s grape growing regions, grapes on the sides of the road were typically bare. Unlike downy mildew, however, grape growers had a pretty good idea what to do about people. They sprayed nasty stuff on the grapes. This nasty stuff took many forms, but the one which was most effective was a mixture of copper sulfate (basically you dissolve copper in sulfuric acid) mixed with lime. Brushed on a plant’s foliage, it was darn ugly.

Then came 1882; a terrible year for downy mildew. Grape vines were losing their leaves all over Europe, except for those vines beside the sides of the road. There the grape vines were doing just fine. The reason was the copper in the lime/copper sulfate mixture which was eventually dubbed Bordeaux mixture because of where it was first used. Bordeaux mixture is still available today, and is one of the most important tools in the organic grower’s pesticide arsenal. Unfortunately it’s nasty stuff – it builds up in the soil and it’s toxic to earthworms and a wide variety of different plants and aquatic organisms. Using this stuff once in a while – such as once a year – isn’t terrible, but regular use is a good way to ruin your plot of land.

One final thought – Those American vines which originally brought in mildew? They eventually became very important to French wines because of another introduced pest, phylloxera. They were used as rootstocks because they were resistant to this pest — unlike European grapes.

Bee studies, blogs, and biases

My original posting last Wednesday (“Ignorance and the so-called “bogus” bee study“) has generated some vigorous discussion, which is exactly what I hoped it would do. At some point, one of our readers posted the link on the original blog site, where it generated the following response:

“The issue on CCD and these studies that point to “causes” other than pesticides comes down to a question: What came first? The pesticides or the problem. Farmers almost always have the gut answer correct. In this case the farmers are the hundreds if not thousands of beekeepers who are certain that neonicotines are root cause of colony collapse disorder. I’m not a PhD, admittedly, but I’ve yet to read anything that points to an answer other than the pesticides.

“And for Linda to suggest that science can’t be “bought” at universities is an incredibly naive statement. I’m not saying Jerry was bought out, not at all. But I do think, overall, there’s a ton of pressure from the chemical industry for scientists to find an answer, any answer, that doesn’t point back directly to pesticides.”

I responded to this posting on the blog this morning, where it sat waiting for approval by the moderator:

“There are dozens of peer-reviewed studies on colony collapse disorder that can be easily accessed by anyone who is really interested in the science. Here’s a quote from a 2009 article:

“Of 61 quantified variables (including adult bee physiology, pathogen loads, and pesticide levels), no single measure emerged as a most-likely cause of CCD.”

From “Colony collapse disorder: a descriptive study.”

Authors: Engelsdorp, D. van; Evans, J. D.; Saegerman, C.; Mullin, C.; Haubruge, E.; Bach Kim Nguyen; Frazier, M.; Frazier, J.; Cox-Foster, D.; Chen, Y. P.; Underwood, R.; Tarpy, D. R.; Pettis, J. S.

Available at: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0006481.”

Then….it was deleted.

For whatever reason, the moderator of this blog didn’t want to post my response. So I’ve reposted it above, and have a couple of other observations:

1) “Gut answers” aren’t science. Sure, gut feelings can convince researchers to explore some particular question, but they are inspirations – not necessarily answers. As my husband pointed out, people once had “gut feelings” that the earth was flat and that the sun orbited around the earth. Enlightenment happens.

2) Let’s see some specific examples where science has been “bought” at universities. I’m sure there are a few bad apples (especially in pomology – HA!), but to my knowledge none of my colleagues have pandered to chemical companies and falsified data for publication. This is a serious charge – and if it’s true, we all deserve to see hard evidence.

As always, feel free to post YOUR comment. We won’t censor you, even if you don’t agree with us.

Dirty Dozen?

Nobody in their right mind considers pesticides safe. They are, after all, poisons which we have created to kill things, be those things plants, insects, fungi, rats, or whatever. The idea that we could have foods with no pesticides on them is attractive. Now I’ve got to admit that, as a general rule, I don’t think that the levels at which most pesticides are found on foods is concerning. Our methods of detecting poisons are just too sensitive today and so we end up saying that a poison is “present” on a tomato or whatever even if it’s there at a harmless parts-per-trillion level. Still, I won’t deny that I’d prefer it if there were no synthetic pesticides on any food.

A couple of days ago a report came out from CNN about the “dirty-dozen.” http://www.cnn.com/2010/HEALTH/06/01/dirty.dozen.produce.pesticide/index.html This is a list of the twelve fruits and vegetables which are most likely to have detectible levels of synthetic pesticide residues. Along with this list there is a suggestion that, when purchasing these fruits and veggies, you should select those that are organically produced whenever possible. I don’t have a problem with this list being reported. In fact, I think it’s a good idea to give people all of the information that we can about pesticides. While I, personally, am not particularly afraid of conventionally produced fruits and veggies because of the synthetic chemicals which they may contain I appreciate the fact that others might be. I do, however, have a major problem with the idea that organically produced fruits and veggies are necessarily safer than those produced with synthetics. You see, organically produced food is not tested for residues of potentially damaging organic pesticides, and those same foods that are slathered by synthetic pesticides in non-organic growing systems are typically slathered by organic pesticides in organic systems, particularly if you’re dealing with foods produced using what has become known as “industrial organic production” which fill most of our large grocery stores with USDA Certified Organic Produce nowadays. These organic pesticides may be present at higher concentrations than synthetic pesticides and may have similar effects on humans, and even worse effects on the environment than synthetics (though it depends on the exact pesticides used and how often they are used of course).

The myth that organic foods don’t have pesticides used on them is one that really needs to die. No farmer, organic or non-organic, wants to use pesticides, and sometimes they can get away without using them. Certain crops are rarely sprayed regardless of whether they’re produced organically or not. Pesticides cost money and are dangerous, but when faced with the potential loss of a crop producers will do what they need to do to avoid losing their crop, and if that means applying pesticides then so be it. Organic farmers may choose to use different pesticides, and they might wait longer before they spray (although often they spray sooner because the relative efficacy of their sprays are inferior to synthetic sprays) but let’s not say that organically produced foods are free of pesticide reside. Just because we’re not testing for it doesn’t mean it isn’t there.

Do Organophosphates cause ADHD?

Ever since Monday’s post I’ve been preoccupied thinking about that article which was mentioned in the comments section by Daniel http://www.cnn.com/2010/HEALTH/05/17/pesticides.adhd/index.html?iref=allsearch . This article basically summarized a study that seemed to show that ADHD in children was related to exposure to organophosphate insecticides.

Articles like this appear all of the time in mainstream media and they scare the bejezus out of us because, after reading them, we end up thinking “Holy crap! We’re killing ourselves and ruining our society with these insane chemicals!” Most of the time, however, this just isn’t the case. Look, if everything that the papers reported about the negative effects of pesticides and other chemicals was true we’d all have cancer, mental illness, or we’d just be dead.

After the above you’re probably telling yourself that I’m some kind of maniacal chemical apologist. Maybe I am, but I don’t think so. I’ve spent a lot of time reading the actual articles from which these media pieces are written and I like to think I have a relatively balanced view of these chemicals – maybe I’m deluding myself though – I’ve been known to do that on occasion. In any regard, what I’m going to do with this blog post is to take a look at the media article and let you know some of the questions that I want answered before I get very concerned about the research, and by answered I mean answered by the scientific article from which the media piece was derived. Now, to be fair, I have not read the actual scientific article from which this media piece was derived. It isn’t online as I’m writing this (at least nowhere that I can find it), though I have no doubt that it will be soon. I suppose that I could have waited to write this until it came out, in fact I considered that idea carefully, but instead I thought that I would tell you about the things that I’m wondering about the article; In other words, the things that I’ll be looking for when I finally get to read it. Media people want POW! Scientists want to know what’s actually going on.

Before we begin I should tell you that I’m no fan of organophosphates. They include a wide range of chemicals (though they are, obviously, all related in that they’re organic chemicals with phosphorus), some worse than others – from the relatively tame orthene and malathion to the scary-as-hell disulfoton (aka disyston). Right now, as an extension specialist who works with growers, I can tell you that organophosphate chemicals are, in general, not a preferred choice for most growers simply because there are so many safer and more effective choices out there. My feelings about organophosphates can best be summed up by what I wrote in my book The Truth About Organic Gardening “[Organophosphates] are an old class of insecticides that has served its purpose and for the most part should probably go the way of the dodo, with the possible exception of orthene and one or two others.”

So here we go, the things that I will be looking for when I read the actual scientific article:

1. What’s the confidence interval? In the media article it was stated that children with higher levels of organophosphates were about two times more likely to have ADHD, but no confidence interval was given. In epidemiological studies such as this the likelihood of a given outcome is usually expressed as an odds ratio. In this case the odds ratio that a child would develop ADHD given a high level of organophosphate exposure would be about 2 (because it would be 2 times as likely that a child would develop ADHD as it would be if the child weren’t exposed to the organophosphates). But in a scientific article the odds ratio will always be coupled with a confidence interval. A confidence interval tells you how confident you are in your odds ratio. If you’re very confident then you’ll have a narrow confidence interval – maybe 1.8-2.2 — which means that it is 95% certain that the odds ratio is between 1.8 and 2.2 (the 2.0 odds ratio is basically just the most likely point on the confidence interval for the odds ratio to sit. It’s kind of like, but not exactly the same as, an average). For an epidemiological study that’s darn good. If that’s the confidence interval present in the article then I’ll be impressed. What we might find though is a confidence interval of something like 0.2 to 22. That stinks and you’re deluding yourself if you think that a confidence interval like this “proves” anything – unfortunately I have seen plenty of media articles use research with confidence intervals such as this because of the POW! factor. They ignore the confidence interval and just look at the odds ratio. My guess is that this article has something in between the two confidence intervals which I listed above – we’ll see.

2. I want to know how often urine was sampled.
Organophosphates move through the body very quickly. In fact, I was recently reading a paper which showed that you can’t predict from one test time to the next what organophosphate readings will be because there’s so little consistency. If you’re exposed to an organophosphate one day you may test high that day, but two days later you’ll be testing low again, so, I want to know if a single sample was done – which I would consider to be almost useless in terms of telling us actual organophosphate exposure – or if multiple samples were taken over time which I would consider to be much more useful.

3. Did the organophosphate really come from food? The implication that these organophosphates which, in theory, contributed to the onset of ADHD came from food bugs me. I want to see if the author actually draws this conclusion in the paper or if it was made up by the media. There are lots of places that organophosphates are and have been used, the singling out of fruits, vegetables, or any food seems ridiculous to me. The author of the media article points out that organophosphates are not used around homes much – but that really isn’t the case and it certainly wasn’t the case just a few short years ago. There are still plenty of organophosphates being used quite regularly around homes. I just did a search for orthene and malathion and found that I could buy them quite easily online. Diazinon and chlorpyrifos are two others that shouldn’t be used by homeowners but which I know of people using – sometimes in heavily trafficked areas.

4. I’d like to know about how the other potential contributors to ADHD were controlled. There are other things that have been correlated with ADHD, how were these controlled so we know they weren’t the cause of the ADHD measured in this experiment? For example, abused or neglected children seem to have a higher rate of ADHD, how was this taken into account in the study? Was it taken into account? A theory would be (and I’m totally making this up) what if abused children are fed more food with higher rates of organophosphates while non-abused children are fed more organic food. Then the results would show that the neglected kids had higher ADHD and higher organophosphates – but was it the poor parenting or the organophosphates which caused the ADHD?

So, those are the four questions that I’ll be asking right off – and there are more that I’ll think of once I actually read the article. All of these questions don’t mean that I think the article is bad though – regardless of what their answers are. This research was probably well conducted and will enlighten scientists and lead to new avenues of research. But, I’m willing to bet that the POW! from the media article (ADHD is caused by eating organophosphates on food) isn’t quite as powerful when the whole article is read with a more critical eye.

Dandelions and clover

It was fun to read all of your comments last week about your opinions on lawn care. To follow up on it I’m going to talk a little bit about why I’m not fond of companies which apply herbicides multiple times throughout the year. But first I think I’ll mention why I apply herbicides at all — aesthetics. That’s it — the whole reason. Could I go the no-lawn route? Yes, but I like having a yard to run in. Not a huge yard, but a little yard to play tag with the kids.

What I long for though is the yard from the house that I grew up in. Our house in southeastern PA (About an hour west of Philly and an hour east of Lancaster) was set back about 800 feet from the road and was on old agricultural land. The area around the house was planted in grass in the mid 70s and then it was left alone. Fertilized once the first year I think, but that’s it. Dandelions invaded quickly as did clover. Over the years the clover began to dominate the grass, but not to the point that the grass disappeared, and the lawn actually appeared relatively homogeneous. Dandelions never left, but their numbers declined. The clover grew low and the grass never shot up like it does in a heavily fertilized lawn and so mowings only happened once every two weeks or so (well, OK, sometimes more often depending on the weather and where on the lawn you were — the spot over the septic tank needed mowing every 48 hours or so). The grass did go dormant most summers, but 800 feet from the road there wasn’t anyone to complain, and besides, the clover kept the lawn from appearing completely scorched. The lawn looked good for well over 30 years (until my parents remodeled the house and the yard was torn up).

The typical suburbanite might not have liked this lawn, but to me this lawn looked great, and, besides, it was low maintenance. The reason I’m bothering to tell you about this lawn though is because it illustrates so well what lawn care companies make impossible. They say (and by “they” I mean professors like myself) that pesticides beget pesticides and fertilizers beget fertilizers, and nowhere is that as true as in a well manicured lawn. The herbicide of choice is 2,4 D (though there are many others that are used) which lawn care companies apply multiple times over the the course of a year. This pesticide does a great job of killing dandelions, but it also kills clover. It rarely hurts grass unless it’s grossly over-applied. The problem with killing clover is that this clover is the stuff that fed the grass in the house where I grew up. Clover takes nitrogen out of the air and makes it available to grass every time the lawn is mowed (the clipped off pieces of clover degrade and the nitrogen in them feeds whatever plants are around). Without the clover you need to add fertilizers. So, because the lawn care company is keeping the lawn free of weeds they also need to fertilize because they’re killing all of the natural fertilizer. Here’s the thing, the weed that most people in the suburbs like least, dandelions, is actually very sensitive to low potassium. The lower the potassium in the soil the worse it does. In fact, dandelions can easily be out-competed by grass and clover if potassium is low — just as happened in the yard of the house where I grew up. But do lawn care companies pay attention to this (by using high nitrogen, low potassium fertilizers?) What do you think?

My guess is that many of you thought that I’d cite all kinds of scary side effects of the pesticides used on lawns. Nope. In general I think that, if used properly, they’re pretty safe for humans (with a few notable exceptions). I’ve spent a lot of time reviewing epidemiological and toxicology studies and I can think of many worse things. I am somewhat fearful of what 2,4 D may do to dogs in particular — they can’t excrete this poison like we can. Don’t think for a minute that I’m calling these poisons perfectly safe — I just think there are plenty of other better established reasons to avoid lawn care company pesticide schedules.

Thieves purr

Today I found a cool website – it’s an anagram generator (http://wordsmith.org/anagram/). The title of today’s post is the first of the 553 anagrams generated from the word SUPERthrive.

I’ve been getting free samples of SUPERthrive for a long, long time. For those of you living on a remote desert island, SUPERthrive is a product invented and sold by “Dr. John A. A. Thomson (in 27 different title Who’s Who Directories),” according to one of the promotional flyers. The same flyer features Nick Federoff (“ ‘Most Listened-to’ Radio Garden Expert”), who says of Dr. Thomson “he has saved far more trees than anyone else in the world.”

Space constraints and my patience limit how many of the product claims I can include. Here’s one from the package: “Dozens of the world’s science miracles in each drop!” Well, what are these science miracles? The only identified compounds on the label are Vitamin B-1 (which plants make themselves, and which I’ve written about here), and NAA, an artificial auxin used as a rooting hormone. The rest are mysteriously referred to as “crystalline compounds of C, H, O.”

Since this product has been around since 1940, there should be plenty of documented research on its efficacy. But thorough searches of the plant science databases turned up only two: one on growing hydroponic orchids (where SUPERthrive is used as part of the experimental protocol but not as a treatment) and one on rooting stem cuttings of Intsia bijuga, an Indo-Pacific tree in the pea family. Sadly, SUPERthrive was not as effective in promoting rooting as were traditional rooting hormones (IBA and NAA). An online research report from TAMU found SUPERthrive to have no effect on cotton. Even California Science Fair participant Chingiz R. Bigalimov was disappointed that SUPERthrive did not enhance rooting of narcissus bulbs.

Why would Dr. Thomson, who “by 1979 had received a Ph.D in biochemistry and nutrition, and a Doctor of Arts in biochemistry and horticulture,” claim that SUPERthrive is a “billions-proven extra-life-maker” without the science to back this up? I tried to find more information on Dr. Thomson’s doctoral research at Columbia Pacific University (an unaccredited distance learning school in California), but it had been closed by court order in 2000 for, among other things, failing to employ duly qualified faculty and failing to meet various requirements for issuing PhD degrees.

I think all of us GPs would agree that if you like a product and it causes no harm, more power to you. But please consider these last few caveats, especially if you are a Master Gardener or garden professional:

There is no established science supporting the use of SUPERthrive;
NAA is an artificial rooting hormone classified by the EPA as a pesticide, making SUPERthrive an unregistered pesticide. Some states ban the sale of this product.

Think I’ll go play with the anagram maker some more…

Disappointment

Yesterday evening I took my older daughter to dance class while my wife stayed home. While she was entertaining our younger daughter, the TruGreen guy came to the door to tell us that we had weeds in the yard (Damn, I had no idea!). He went on to tell my wife that we really needed to use his company to get rid of them. I was so disappointed that I missed him because I wanted to know all about what he had planned for our yard. Many of our neighbors use TruGreen and I have to say that I’m not particularly impressed. It’s not that they’re not professional — they certainly are. It’s not that they don’t do things by the book — they certainly do. It’s just that the book that we use is getting a bit outdated. When I read TruGreens online FAQ it looked like they actually plan six applications of chemicals per year. I’m assuming (I don’t know this for sure), that at least four of those include herbicides to one extent or another. It looks like people who have no tolerance for weeds should love TruGreen. But really, how many weeds should people allow in their yards? Is it one per square foot? Two? Five dozen? And what are weeds? Is clover a weed? At what point do we say enough is enough and that we’d rather just cope with a few weeds than hose down our whole yard with herbicides.

After reading my own words I feel like some kind of radical. In my job I tend to see two types of people, those who can’t stand pesticides and those who can’t stand weeds. One group is happy to spray five times a year if it means that their lawn will be weed free, and one won’t touch an herbicide. I’m not sure that either group is correct. I tend to handle weeds in my yard the same way I handle haircuts – I hate having my hair cut so I don’t go to the barber that often, but I do go to the barber eventually because my hair looks pretty ridiculous if it grows too long. I feel the same way about weeds (specifically dandelions) which infest the grass in my yard. I prefer not to add herbicides, but there’s a big weed bank in the area and so I end up needing to apply once every two years or so because otherwise it looks pretty bad. Rather than making either the making the weed-free lawn or the no-chemical group happy though I think that it just pisses them both off. They see my unwillingness to commit to one way or the other as a cop-out rather than reasonable moderation. What do you think?