Rather than repetitive and likely costly injections, I'd suggest you investigate why the tree is displaying manganese deficiency (if, in fact, it is) and address the cause rather than just treating the symptoms. Manganese becomes bound in the soil if it is not sufficiently acidic and is fairly common in instances of poor drainage. I'd recommed testing the soil to determine a) its pH and b) current manganese levels and adjust as necessary. Aeration or improving the soil structure is also advised. Manganese sulfate is typically recommended in these cases, as a soil application (you can do now) combined with a foliar spray (in the spring, after leafout). Exercise caution, as excessive Mn in the soil will induce an iron deficiency with its associated chlorosis.