Have a question for those forum members in California. I seem to have issues with pummelos where I live in N. San Diego county. All my other citrus have established well - mandarins, oranges, lemons (they grow like weeds here), limes, and grapefruit/grapefruit hybrids. But, anything with pummelo in it's genetic background, either full pummelo or a cross seems to really struggle. It looks like something at the root. I have had one person suggest my soil pH, which I seriously doubt, since Oro Blancos and Melogolds were specifically developed to grow here in our coastal S. California area, and I've seen plenty of well established Oro Blancos everywhere here. My soil pH is pretty neutral, about 6.9 to 7.1, and same with my water. Not like I'm dealing with something very alkaline. So, that leaves me with maybe phytophthora?? I'm wondering if the rootstock perhaps used with pummelo hybrids propagated here in California are different than mandarins, lemons, oranges, etc., and possibly more susceptible to phytophthora? I am going to have a chat with the guys at Clausen's Nursery to see what their opinion might be. I've replaced one Oro Blanco already, and when I dug it up, it was pretty moist down in the root area, so I might have some clay pockets in my pretty much all DG soil (there are clay deposits here and there in my general area). Any thoughts on this? The trees just look like they're having major root issues - no new growth, poor looking leaves, and some in the death throes will set out a bunch of blossoms before they expire. And, it's not just me. My two neighbors, one of which is a very experienced and knowledgeable gardener, are also experiencing the exact same thing with their pummelo/pummelo hybrids. Any thoughts from my fellow Californians would be much appreciated.

Hi !

I am not from California. but maybe I can help with an idea ...

Since you think it is the root stock, why not find out which root stocks your successful plants have and then try to get a pumello grafted on them, or graft them yourself ?

I may have to resort to that. I couldn't find out what the rootstock was on my pummelos. I've bought them from several sources. I know for sure the Tahitian pummelo was grown by Monterey Bay Nursery, but not sure if they actually did the grafting. But, they will know what the rootstock is, so I'm going to try to contact them, and see what it was. I'll try to ask Clausen's in Vista, too, which is where I got my Melogold and my Oro Blanco. If they're all the same rootstock, I'm going to get more suspicious this is the issue. Especially if it's different than my mandarins and oranges. But, I think it may pretty much be all the same - Carizzo or Troyer is what I think Clausen uses for their semi-dwarf citrus (except lemons). ? they are either one in the same, or very difficult to distinguish. Does do well in clay, and suspeptible to blight. So, if it was Carizzo/Troyer, and I happeend to be planting these trees in clay pockets? Grasping a bit here, I know. Don't think it's blight, but I'll have to check that out. I would think I'd have more affected trees if it were blight. The mystery thickens.

Many in CA use Cuban Shaddock for dwarfing rootstock.

Yes, that's what Four Winds uses almost exclusively. I will probably not choose something quite so dwarfing. Probably will use C35 if I graft. I'll probably have a chat with the folks at Citrus Treesource. They are great about helping to decide what rootstock to use. We'll see how my replacements do with some changes in watering, fertilizing, pH adjustments, etc. Getting them through the wet mild winters is the key. That's when things go downhill for me, which is why I was suspicious of something fungal or quasi-fungal in the soil.

Good Luck !

Your problem, in all likelihood, might not be phytophthora, but who knows. The rootstocks that are susceptible to phytophthora foot and root rot, are probably rootstocks that you don't have. Of the more or less common rootstocks that are susceptible to phytophthora are:
Sweet Orange
Rough Lemon
Cleopatra (you might have this one)
Sun Chu Sha Mandarin
Shekwasha Mandarin

Volkomer Lemon and Carrizo are just intermediately susceptible to phytophthora.

If any of your trees are on Smooth Flat Seville, Kinkoji, or most any of the Citranges, these rootstocks are tolerant of phytophthora, while C35, Swingle and trifoliate are very tolerant.

Find out what your pummelos are growing on and hopefully the above list will help you.- Millet

Thanks, Millet. I was reading through the article from Dr. Bitters on the UCR Citrus Variety web site. I'm pretty sure they're on either Carrizo or Troyer. If I decide to graft, I'm going to go with C35. Best all around for my area. I've dug up the poor Tahitian pummelo and I'm going to repot it in a container and see if I can save it. Highly unlikely, and more unlikely to get a replacement, which is sad. Again, appreciate the info.