Do plant-plant interactions inhibit growth? Plants produce lots of compounds that inhibit (kill or irritate) microorganisms and insects. They have defenses against plant viruses and infections. What kinds of compounds or hormones to plants use to regulate the growth of other nearby plants? I have hear of ethylene, but I would like to hear about more specific compounds that might be known that work against specific species or kinds of plants?

The phenomenon you are asking about is allelopathy.

Remarkably, it has its own journal - Allelopathy Journal (ISSN: 0971-4693) published since 2009 and currently at volume 30, issue 1.

Here are the titles of the papers from the most recent issue:

> In-vitro assessment of allelopathic effects of wheat on potato.
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> Allelopathic effects of sunflower on seed germination and seedling growth of _Trianthema portulacastrum_.
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> Effects of simulated acid rain on the allelopathic potential of invasive weed _Wedelia trilobata_.
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> Allelopathic effects of _Brachiaria ruziziensis_ and aconitic acid on _Ipomoea triloba_ weed.
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> Effects of _Butia capitata_ pyrenes extracts on the germination of lettuce seeds.
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> Effects of root exudates from crop plants on the growth of _Fusarium oxysporum f.sp. niveum_.

So, if you have specific questions, this might be the place to look.