Foliar chlorosis rating (0 = healthy, 5 = dead branches) of 15 red oaks (Quercus rubra) prior to (year 0) and after trunk injection with a combination of ferric ammonium citrate and urea.
Years after treatment
Number of trees
Mean foliar rating
0
15
3.3
1
15
0.8*
2
8
1.4*
3
7
1.6*
4
5
1.0*
↵* Significantly different from the pretreatment foliar rating using a paired sample T-test (P < 0.05).