Correction of iron deficiency in trees by injection with ferric ammonium citrate solution

Abstract

Ferric ammonium citrate is more soluble than iron sulfate, and a very few ml. is all that is needed to supply Fe to trees when injected into trunks of the trees. Ten ml. of a solution with 8% Fe contains enough Fe to increase leaf concentration in 16 kg of leaves by 50 mg kg^‐1 expressed on a dry weight basis; this would be a moderately large tree. The technique used is to slant drill holes on two or more sides of a tree and at different elevations, and then add Fe with a syringe corresponding with size of tree. The tree is left to absorb the solution. Control is achieved in days for most species. A few species do not respond. Overtreatment is easy because of the high concentration of Fe. This ferric ammonium citrate method has been used on numerous trees with no injury. Regreening starts to take place within a week. A commercial product is available which has a balance of manganese with some nitrogen. The cost per very large tree for this product is about $0.25 USA. The method is rapid enough for a single operator to do several hundred trees a day. It is suggested that the hole be covered with an asphalt‐base tree‐sealing compound after the Fe solution has been applied. The sterilization of the drill bit, either by alcohol or flame, would be recommended in those areas where bacterial or viral diseases are problems. Since it has been reported that citrus trees absorb fluids poorly, citrus was selected for leaf tissue measurement before and after treatment. About 5 ml. of the ferric ammonium citrate increased the leaf Fe concentration by 50%. The trees used were mature, being about 20 years old. Zinc chelate was tested and found to be effective; DTPA was better than EDTA. Zinc sulfate was ineffective. As a consequence of the zinc treatment, it was found that phosphorus concentrations were elevated.

Key words:

• Iron
• zinc
• phosphorus
• iron chlorosis
• citrus

Notes

The Laboratory of Biomedical and Environmental Sciences is operated for the U.S. Department of Energy by the University of California under Contract No. DE‐ACO3–76‐SF00012.