I got a call yesterday about yellowing avocados. They are on Dusa rootstock which is very tough when it comes to root rot, but cannot handle wet feet. It turns out that this area is one where the grower cannot order water on demand, but must take it when the water company will deliver. So the poor trees get drowned and then go through drought. This sensitive rootstock is not the right one for this area. Many of the root rot resistant rootstocks have some sensitivity to salt, wet, crown rot, whatever, which brings up the question, if we have phosphites, what about the old rootstocks? Barr-Duke, Duke 7 and Borchard have some very attractive qualities: they are tough and can handle things like salinity and drought and are good producers in the absence of root rot. With phosphites now, they can muscle through root rot. Should we reconsider them? Of course, if you are an organic grower, you need to stick with the most root rot resistant selections. And it is also important to remember that the best line of defense against root rot is proper irrigation, which is the leading problem for root rot.
Aug 14, 2013
