[John J]

I have just returned from a recce of a new herb garden here in Cyprus with a view to arranging a Branch visit. One of the sections is designated as a Pest Control Garden and on reading the info leaflet more closely I see that a claim is made for Oregano oil being an effective pesticide. A few drops diluted in water and sprayed on plants protecting them from aphids and beetles. Also claimed is that planting chamomile next to veggies deters harmful insects, while spraying cold chamomile tea is effective against aphids, brown rot and mildew.
I will of course follow this up on the day of the actual visit but in the meantime has anyone else come across similar claims for these herbs?

[Jill S]

Both could be really useful. As bees visit both plants they would obviously not be harmfull, just a deterent effect and fungicide?

[David Bracey]

The book"Science and the Garden" reviewed by the very same JohnJ in a recent TMG, on page 245 quotes "Companion planting---------------certain plant combinations are said to be beneficial because of volatile chemicals produced ...........they go on to quote the following examples onions and carrots to repel onion fly and carrot fly, African marigold to repel whitefly from tomatoes (in a greenhouse), garlic to protect against diseases such as peach leaf curl and rose blackspot (must be a hit with mediterranean gardeners).  They go onto say that the claims are based largely on anecdotal evidence.  Scientific trials have failed to show worthwhile protection."

I have searched the literature and frankly their is a lack of trials data to show that companion planting works. I think it is another case of mirrors and wishful thinking .

[John J]

David, I agree with you that the concept of companion planting has been with us for a long time without any solid scientific evidence that I know of to back it up. However, I think this is the first time that I have come across anyone claiming pesticide qualities for Oregano oil and cold Chamomile tea. Personally I find the said beverage so bitter and horrible that throwing it at aphids is probably the best thing that can be done with it. I look forward to possibly finding out more on our return visit next month.

[JTh]

I agree that there are not many scientific reports on the efficacy of companion planting and plant extracts used as pesticides, but I found at least one on oregano oil: Oregano Oil Works As Well As Synthetic Insecticides To Tackle Common Beetle Pest (http://www.sciencedaily.com/releases/2008/05/080522072339.htm), which was published in Journal of the Science of Food and Agriculture in 2008.

The listed benefits of oregano seems seem to be nearly endless:

'Analgesic, anthelminthic, antibacterial, antifungal, antimicrobial, antiseptic, antispasmodic, carminative, cholagogue, diuretic, emmenagogue, expectorant, fungicidal, tonic.
It’s Benefits: Acne, bronchitis, colds, congestion, flu, infections, insect bites and stings, muscular aches and pains. Well diluted, oregano oil can be added to ointments and balms for skin abrasions.' (http://www.pestreport.info/bacteria/antimicrobial-cytotoxic-activities-oregano-essential-oils/), but no further references to scientific reports verifying this.

[David Bracey]

Similar claims are made for argan oil.........mainly I would add by the marketers.

I thought that making false claims is illegal in thre EU? Are we returning to the good olde days of snake oil?

[David Dickinson]

Shall we extend this to "spices for pest control"? Take one kitchen shelf infested with ants looking for goodies. Add one jam jar lid filled with cloves. Hey presto! No more ants. Theory, experiment, thesis and results all in one 

[Jill S]

Thanks for the tip. Maybe not scientifically proven, but if it works then much, much better than having to place poison among food items. Will definetely try it.

[yvesans]

Ants hate cinnamon powder too

[Isabel]

I will set scientific proof aside for good old tried-and-tested proof. A student coleague of mine at the Botanics in Edinburgh placed Chai teabags on her vegetable plot and used chilli powder as a deterrent on her seeds and seedlings. Mind you, this was to deter mice, not insects. But there is something to be said for this method. She had no problems with mice while the rest of us all did!

[JTh]

I just read something that seems to fit in this thread, there are scientific investigations showing that some spices are more than ‘snake oils’.

A recent article (Control of Gardenia Leaf Spot and Bud Rot Diseases Using Some Natural Plant Oils) showed that among twenty plant essential oils tested in vitro, cumin (Cuminum cyminum) oil was the most effective one, it completely inhibited the mycelial growth of the tested fungi on gardenias at 500 ppm concentration.

Many of the other ones showed efficacy as well, such as clove, anise, thyme, peppermint, basil, geranium, clove, coriander and French basil oils. Interestingly, celery, parsley, chamomile, eucalyptus, tagets oils were showing the lowest antifungal activity. This was presented in Journal of Microbiology Research (2013; 3(5): 185-196), the link to the whole manuscript is: http://article.sapub.org/10.5923.j.microbiology.20130305.04.html

[David Bracey]

In vitro tests are notorious for giving positive results.  I expect snake oil would give good results as well.

[JTh]

Yes, but if you read the paper carefully, you'll see that the results are from both in vitro experiments and in vivo (greenhouse conditions), with significant results also for the latter category.

[David Bracey]

I did read the article but a greenhouse is not the real world.  I cannot see cumin oil being sprayed that,s assuming it,s available and enviromentally OK. 

I fail to see the justification for this research especially since resources must be limited in Egypt etc. There are many other areas for  research.