# Bad Plant Combinations



## BHTX936 (Jan 15, 2010)

I was wondering if any of you know of bad combinations of trees or other types of plants there are that may lead to diseases, etc. I am familiar with cedar-apple rust in that it needs both a juniper plant and a plant in the rose family. But I don't know of many others. Any information would be appreciated, thanks.


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## Urban Forester (Jan 16, 2010)

Look into broadleaf evergreens and some conifers in close proximity to Black Walnuts. Black Walnuts produce juglone from their roots inhibiting root development of certain plants. There are very few fungal organisms, other than rusts (there are MULTIPLE rust families) that need an alternate host to complete their life cycle. One of the most complex alternate/host fungal life cycles on earth is the life cycle of white pine blister rust. It uses the plant ribes to complete its life cycle. It is perennnial on pines and annual on ribes, a truly amazing life cycle...


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## BHTX936 (Jan 16, 2010)

Thanks for the info, I'm aware of the alleopathic effects of Black Walnut, but not about any other plants, though I know there is more. Also, any info on what other plants are used as hosts for rust fungi?


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## Urban Forester (Jan 17, 2010)

Labrador Tea is the host for spruce needle rust in thje U.S. but in Europe rhododendrons are the host. It is a very complex disease with over 5,000 separate fungi, each having their own host alternate. Barberry and buckthorn can be the host for cereal rust. The list is almost endless. The University of Purdue has one of the largest collections of "rusts" in the world. If you can go the the Arthur Herbarium it is one of the longest running reasearch stations for rust in the world.


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## BHTX936 (Jan 20, 2010)

Thanks for the great information.


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