The hybrid has been around since 1927 (bred at Placerville, CA). Stronger-growing than P. attenuata, but not as vigorous or productive as straight P. radiata (though it is hardier). The ones I've seen have shared P. attenuata's rather slender trunk, compared to the massive diameters P. radiata can produce.

Likely to be susceptible to pine pitch canker.

Resin

Resin's right, originally named Pinus X attenuradiata this was the first hybrid pine produced through artificial pollination, and the first produced on a large scale. It's growth is slower than radiata, but if the hardier sources of knobcone are used in the cross, the hybrid is more cold-resistant than radiata.

In doing more research I've read that this hybrid might be more susceptible to red band needle blight in wet areas, and I'm in the wettest of wet areas here. Maybe I'll stick to straight radiata.

I have KMX pine cones available for sale. I have experienced excellent growth rate in my forest in Oregon- without problems from disease or insect infestation. Text me if interested : 541- 570-5669, Amber Lacy