Plant Defence

[Jester]

Hi there crazy kids..........

I'm curious, is it true that, generally speaking, a pest will more readily attack a sick tree than a healthy one?? If the answer is yes, why? What does the healthy tree have to stave off attack that the sick tree does'nt. Joel I'm guessing this is probably one for you mate!!!

[Greth]

Yes it is generally true. One mechanism might be that damaged leaves can deliberately produce pest deterrent chemicals if they start getting attacked, this may be more efficient when the tree is really healthy. They also produce substances which induce the same changes in leaves not yet affected by pests.
One study showed a really mind boggling extension of this - some of the chemicals are volatile, and can travel via air to other trees of the same species nearby, and induce the same changes, even if the other trees are not under attack. I think it was a species of elm in which this was observed, happy to be corrected, but it was a genuine scientific study.

Your trees may be talking to each other..

[Joel]

Hi Greth. I have also read that a few years ago. I found these after searching google:
http://www.gi.alaska.edu/ScienceForum/ASF7/762.html In willows.
http://news.softpedia.com/news/Do-Trees ... 5806.shtml in willows and poplars with and without physical seperation.
http://sciencenetlinks.com/sci_update.php?DocID=361 Very interesting.

And yes Jester, it is due to the oils and chemicals inside the leaves. There is a surprisingly large variety of chemicals present within a leaf. Check out this wikipedia page on Acacia species. Look at some of the chemicals found in their leaves. http://en.wikipedia.org/wiki/Acacia#Phy ... _of_Acacia

Joel

[Jamie]

i have always beleived a healthy tree is more resistant to pests and disease joel and greths information seems to back this up too
i always pride myself on healthy trees and i get quite frustrated when they do get an issue whch i try to resolve quickly when it happens, 99% of the time i dont use and systemic, fungicides or insecticides either, i have lost a few trees but not a great deal but i think it is more to the fact that they dont like my climate more than anything else.


good question John


jamie

[Jester]

Thanks for all the help guys. I will be sure to read those articles Joel

Thanks again

John