Root Rot, Chlorosis, and other deficiencies
Root rot in trees is a common disease that is often overlooked or attributed to another disease or mistaken as tree mortality. There are two distinctive root rot pathogens, Phytophthora and Cotton(Phymatotrichum). Phytophthora spp. is a soil-borne pathogen called an oomycete or “water mold”. Once thought to be a fungus, it is now known to be a separate species, ranging in the hundreds, responsible for considerable destruction to all types of plants and trees. Most are host specific like Sudden Oak Death (SOD) which is caused by Phytophthora ramorum. Phytophthora cinnamomi can infect thousands of species of plants and is found in 70 countries. Cotton Root rot is a fungal pathogen that affects crops and trees(fruit, nut, and shade) and can cause rapid death if not addressed as soon as possible.
Potassium phosphite is an effective fungicide for treating root rots. Product names such as Phostrol, ArborFos, or Reliant are available. Only a few are listed for trunk injection on the label so be sure to read it before you purchase. Although the percentage of the chemical is similar, it is the “inactive” ingredients that may have adverse effects when trunk injecting. I tend to stick with those products that are listed but it is up to you.
A maximum of 5 ml of product for every 2″ of diameter is what I recommend regardless of the mixing instructions on the label. I say this from experience having had tree leaves burn from too high a potency. By the way, the percentage of potassium can range from 45.8% to 53.6% which is a rather large range in the world of injecting. Also, If the tree has been pruned or trimmed or the canopy is diminished then use fewer injectors or you could damage the leaves as well.