Is euryops pectinatus allelopathic?

Can anyone tell me if /euryops pectinatus/ (bush daisy) is allelopathic, and if so, which other species are most affected? I have a Stanley plum tree planted close to some euryops, and here it is late April and the tree has no leaves on it; a couple of flowers that appear they won't set fruit. I planted the tree as a bare root in January 2006, and it grew fine that first year. I'm in Sunset climate zone 19, I think; can't seem to get a precise fix on the zone from the zone pages I can find on the map. Pasadena, CA if that helps.
Earlier, I had a comice pear (bare root) planted near the same europs bushes, and that tree didn't do anything for two years - no leaves in the spring, although it would eventually put out a little bit of foliage at the tail end of summer. I eventually moved the pear tree across the garden to a different location away from the euryops, and although it hasn't produced any flowers or fruit (probably not enough chilling hours), the tree does at least put out leaves and new shoots in the spring, as I would expect it to do.
I have a Santa Rosa plum tree a little farther, but not a lot, from the euryops, and that tree produces leaves, shoots, flowers and fruit seemingly normally.
I did considerable search on the web for "euryops pectinatus" + allelopathic/allelopathy, and I couldn't find anything definitive.
Any information appreciated.
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