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"Take two aspirin and call me in the morning," is a phrase not often thought of as applicable to plant diseases. Recent research, however, has shown that acetylsalicylic acid, the ingredient in aspirin, has a surprising use in the protection of plants from infections. What is even more exciting is what this research revealed about the response of plants to pathogenic infection. . .
Fortuitous discovery
Years ago I came upon some original research that, at that time, was not widely publicized. The work concerned the use of acetylsalicylic acid (ASA) to treat plants with viral infections. Intrigued, I decided to give this a try for myself. I obtained some laboratory grade ASA and began an experiment, using it on a specimen of Alocasia that had begun throwing distorted viral-infected leaves. To my surprise and delight, the leaves emerging after treatment were perfect and virus free! The results I observed inspired me to write an article about it for the International Aroid Society newsletter, and started me on a quest to find out what was going on.
A little background history of aspirin is appropriate here. As far back as the fifth century B. C., chewing the bark of the Willow tree was known to relieve pain and fever. The active principle in the Willow turned out to be a compound called salicin, which is closely related to acetylsalicylic acid, or aspirin. In fact, the word "aspirin" comes from joining the "a" from acetyl with "spir" from the name of a plant, Spiraea, from which the Bayer Company got their salicin, and "in", a common ending in drug nomenclature. I share this bit of history as a way of demonstrating that the active principle is related to a naturally derived compound, salicylic acid, that plays a significant role in the response I observed in my experiment.
Resistance is not futile!
More years went by and the only times I thought about this discovery again was whenever one of my plants contracted a virus infection. I still had some of my acetylsalicylic acid left, so I would simply mix up a batch, spray my plant, and all would be well. That is, until about a year ago when, with modern access to information via the internet, I resolved to see what the current state of the art was in regards to this. To my immense surprise, a great deal of progress had been made in this area. A whole field of study had sprung up; the study of systemic acquired resistance to disease in plants, or SAR for short.
Scientists, studying the response of plants to infections by pathogens, observed that if one leaf got infected, other leaves nearby began to exhibit resistance to the infection. Much research has been performed to determine the active agent or mechanism for this heightened resistance, and significant strides have been made. Within the plant, certain biochemicals are produced, activating genes that confer resistance to the spread of the infection to uninfected plant parts. Interestingly, one biochemical that is considered to play a role in this is salicylic acid. Thus, my application of ASA externally acted to trigger the activation of the same genes that the internal, or endogenous, salicylic acid did. That explained why my plant responded to the ASA spray.
But it turns out that even more was going on here, as other biochemicals were involved. Furthermore, the question remained as to what from the pathogen was acting to stimulate this response in the plant. Research using Erwinia amylovora, the pathogen responsible for fire blight, revealed that a certain type of protein from the pathogen, called harpin protein, stimulated the SAR response in plants exposed to it. The next step was demonstrating that the protein alone, without the pathogen, would stimulate the response. This turned out to be the case, and the harpin protein is now available to gardeners as a product that can be applied as a spray to induce SAR.
Acquiring immunity
The bottom line is that both acetylsalicylic acid and harpin protein signal the plant to activate an internal immune system. Applying either of these to uninfected plants causes them to respond as though they have been compromised by a pathogen, but without the damage. This is surprisingly similar to the immune response in animals and humans, whereby exposure to a dead or weakened pathogen results in the production of antibodies that confer protection against fully functional disease organisms.
This is exciting research, to say the least. Instead of trying to kill off the pathogens by the use of toxic pesticides, the plant is stimulated to activate its own defense system to guard against attack before it happens. A bonus is that the plant becomes more vigorous and healthy in the process.
Do try this at home!
So now that you are enthralled with the possibility of protecting your plants this way, how do you do it? If you want to try the acetylsalicylic acid technique, all you need is three (3) aspirin tablets and four (4) gallons of water. This combo will make a 1:10000 solution, which is what was used in the research. Dissolve the aspirin tablets in the four gallons of water, then spray the mixture on the plants you'd like to stimulate. In my own work I've used an ounce of dimethyl sulfoxide (DMSO) as a solvent for the acetylsalicylic acid before adding it to the water. DMSO also acts as a powerful cell penetrating agent, so anyone using it should wear personal protective equipment, just as is recommended when working with any garden chemical.
If you choose to try out the harpin protein, you can obtain a product called Messenger, sold by Eden BioScience and designed for just this purpose. Messenger comes in pre-measured packets that mix with one gallon of water to make a final solution for spraying. Eden BioScience's website has plenty of helpful information about harpin protein and SAR, too, so it is worth your while to visit, even if only for the education.
Welcome to the promising new world of induced plant immunity!
Salix nigra line drawing from Britton and Brown (1913) and in the public domain.
About LariAnn Garner
LariAnn has been gardening and working with plants since her teenage years growing up in Maryland. Her intense interest in plants led her to college at the University of Florida, where she obtained her Bachelor's degree in Botany and Master of Agriculture in Plant Physiology. In the late 1970s she began hybridizing Alocasias, and that work has expanded to Philodendrons, Anthuriums, and Caladiums as well. She lives in south Florida with her partner and son and is research director at Aroidia Research, her privately funded organization devoted to the study and breeding of new, hardier, and more interesting aroid plants.
Posted by bethmacl (from Swannanoa, NC) on March 17, 2008 at 6:59 PM:
I'm currently doing my senior project on developing a method to extract Salicylic Acid from our garden's tomatoes. I've been doing a lot of reading trying to figure out all the latest developments with SA and SAR, but there is a lot out there and I'm not sure I'm finding it all. I'm doing this initial step of developing a method (that our college equipment can handle) so that eventually another student can do an experiment to see if a diseased tomato plant can induce SAR in a nearby healthy plant by the airbourne chemical MeSA (methyl salicylic acid). The idea is that the spray of SA on tomato plants might help fight disease. I was wondering what you thought about the idea of SA as a spray (especially with tomato plants) and if you knew of any research that's been done recently on this idea? After reading this message from you, I'm wondering if my experiment idea has already been done. Any other information you think might be beneficial, please share. Thanks.
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Posted by LariAnn (from Miami, FL) on March 17, 2008 at 7:08 PM:
The work I'm familiar with involved the use of acetylsalicylic acid, which does induce SAR. I have used it successfully as a spray treatment to induce SAR in aroids, specifically Alocasia symptomatic with viral infection. The result is a complete clearing up of the infection.
Research in the induction of SAR, as well as the biochemical mechanism, is fairly extensive. I mentioned the product, "Messenger" in my article; this is a commercial application of the discovery that a protein called harpin protein induces SAR. The product is intended specifically to spray on plants for induction of SAR. Current research has moved beyond the use of SA for induction of SAR and is focused on such things as why some plants exhibit the SAR response and others don't.
Posted by bethmacl (from Swannanoa, NC) on March 19, 2008 at 3:54 PM:
Thanks.
I read that SA is the only plant derived compound known to induce SAR. Do you know if this is true? I'm confused if also Jasmonic Acid induces SAR (seems not to?) or other phytohormones?
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Posted by LariAnn (from Miami, FL) on March 19, 2008 at 4:30 PM:
Salicylic acid (SA) and Jasmonic acid (JA) are both key signaling molecules in plants, but they signal different responses. In at least one study, researchers found that application of both to plants in the study caused a decrease in the JA response when compared to JA alone. Both compounds signal defense responses, but one (JA) signals physical defense (increase in new leaf trichome density to deter herbivores) and the other (SA), biochemicals against biotrophic pathogens.
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Subject: Well Done!
Posted by darius (from Marion, VA) on February 20, 2008 at 9:41 AM:
Thanks, great article. I knew aspirin works but not why... and I LOVE Messenger.
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Posted by Horseshoe (from Efland, NC) on February 20, 2008 at 1:30 PM:
Great explanation, LariAnn.
Great write-up, too!
Thanks!
Shoe
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Posted by Dea (from Frederick, MD) on February 20, 2008 at 7:51 PM:
Another wrinkle in my grey matter today - thanks - really nice article!
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Subject: Treatment only for viral disease?
Posted by pamsaplantin (from Morgantown, WV) on February 20, 2008 at 1:57 AM:
Very interesting article! I was wondering if the aspirin treatment is also effective against disease caused by fungi & bacteria. I am assuming that since it improves the plant's immune system it makes it more resistant to any infection? I had problems with anthracnose on cucumbers & peppers this year & am looking for preventative measures. In your opinion, would this be worth trying in my situation? Last year I tried Neem oil after the symptoms appeared. It slowed the progression but eventually I lost all my cucumbers & some peppers. I want to be more proactive this year. I followed the advice of the county extension office, disposing of all debris, etc. I know prevention will be my best hope. Thanks for any suggestions you can give.
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Posted by doccat5 (from Fredericksburg, VA) on February 20, 2008 at 4:12 AM:
This very interesting and informative. Thanks for sharing.
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Posted by LariAnn (from Miami, FL) on February 20, 2008 at 9:44 AM:
IMHO, the aspirin treatment, as well as the harpin protein treatment, should offer some protection from fungi and bacteria. I think you would need to apply the aspirin before any signs of infection show up for maximum benefit, and then reapply at, perhaps, a 4 to 6 week interval. This field of study is relatively new and so each different plant it is tried on will yield new information.
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Posted by pamsaplantin (from Morgantown, WV) on February 20, 2008 at 12:15 PM:
Thank you so much for replying. I felt so helpless watching my plants succumb to anthracnose last year. I worked hard to remove the infected areas & treat the remainder with Neem oil but once it started the battle was already lost for the most part. This seems like a safe, simple, proactive approach. I will experiment with part of my cucumber crop as a basis of comparison. Thanks again for the info!!!
Pam
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Posted by lcosden (from Pawling, NY) on February 20, 2008 at 1:19 PM:
I was wondering if I can just add it when watering the plants or do I have to spray it on the leaves?? Is there any harm in adding like half an asprin everytime I water??
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Posted by LariAnn (from Miami, FL) on February 20, 2008 at 2:13 PM:
I would not recommend adding it to regular watering because once the immune effect is initiated, the extra aspirin won't do anything. In fact, too much can be harmful to the plant; that's why the dosage is a 1:10000 solution. I would stick with the successful method, which is application via spray. IMHO, a root drench might work better if you are trying to protect against root diseases.
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Posted by lcosden (from Pawling, NY) on February 20, 2008 at 3:18 PM:
Got it.. Thank you! :)
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Posted by daylilydaddy (from morehead, KY) on February 20, 2008 at 11:56 PM:
This may be a stupid question, but what dosage of aspirin do you use? I take the 325 dose everyday due to heart problems. Is this the right dose or the 81 dose.
Geo
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Posted by Fitsy (from Hayesville, NC) on February 25, 2008 at 10:15 AM:
Stupid question #2 - I have a big bottle of outdated aspirin!!!??
Would it be just as good??
Thanks worlds for all of this very interesting info!!
Fitsy
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Posted by LariAnn (from Miami, FL) on February 25, 2008 at 12:04 PM:
I think that unless the aspirin got wet or is otherwise discolored or etc., it should be fine for this kind of use. If you decide to get new aspirin, I suggest that you get the "regular", not the low dose kind that people take for purposes other than headaches.
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Posted by lockej (from Portland, OR) on February 26, 2008 at 3:58 AM:
Wonderful information. Thanks very much. Now, speaking of drenches, do you think this might work on verticillum wilt? I have lost three or four Japanese maples to this disease and now must plant in containers. Or is wilt just with us like influenza?
Thanks, ej
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Posted by LariAnn (from Miami, FL) on February 26, 2008 at 9:36 AM:
The whole field of systemic acquired resistance is so new that a lot of what we try will be trailblazing. Remember that the treatment purpose is to stimulate the plant's own immune response. If the Japanese Maple is inducible, it's worth a try. I mention inducibility because apparently there are plants that do not exhibit SAR, or at least do not get induced by the aspirin treatment. There is no listing of which ones don't, so we just have to try and see what happens!
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Posted by pamsaplantin (from Morgantown, WV) on February 26, 2008 at 11:24 AM:
Is there any downside to this treatment, ie. adverse effects on certain plants? Or is it safe to try on anything at this concentration?
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Posted by LariAnn (from Miami, FL) on February 26, 2008 at 11:46 AM:
The only downside that I know of is that if you overdose the plants, they may show some phytotoxic damage. This is a case where using any more than the recommended amount can be harmful. Since this is a new field of study, some untested plants could turn out to be more sensitive than others, but at the concentration of 1:10000 as suggested, I believe you'll be fine.
The aspirin is just acting to turn on the immune response; it has no direct effect on any pathogenic organisms.
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Posted by lcosden (from Pawling, NY) on February 26, 2008 at 12:11 PM:
Is Messenger any safer to use than asprin for the plants?? Will it also cause OD if we're not careful in mixing the concentration?? And Messenger has a seed powder to coat the seeds before planting.. Are those any better??
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Posted by LariAnn (from Miami, FL) on February 26, 2008 at 12:36 PM:
I've gotten some Messenger to try out, but haven't tested it yet. Technical questions about Messenger are best addressed to Eden BioScience, as I don't have knowledge enough about using it yet to give reliable advice. Messenger does come in premeasured packets for 1 gallon of mix so, IMHO, you can't really go wrong with it. All of the formulations containing harpin protein will function in the same manner (i.e. stimulating the immune response), as far as I know.
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Posted by pamsaplantin (from Morgantown, WV) on February 26, 2008 at 2:00 PM:
However, the aspirin therapy is obviously much cheaper since the Messenger costs about $20 for 9 gallons if I'm not mistaken.
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Posted by LariAnn (from Miami, FL) on February 26, 2008 at 3:46 PM:
That is correct; however, the ingredient in Messenger (harpin protein) has been shown to do more for the plant than just activating the immune response. While aspirin will induce SAR, that is the extent of what aspirin does. Harpin protein activates this plus several other biological processes within the plant, leading to increased vigor and performance.
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Posted by lcosden (from Pawling, NY) on February 26, 2008 at 5:34 PM:
Interesting.. So the stuff I care more about, I'll use Messenger and other regular stuff, I'll use asparin.. Coolio.. Thanks!
