Rate of application of zinc sulfate: Mildly rosetted trees—apply 5 pounds zinc sulfate (36 percent) annually for 2 to 3 years. Severely rosetted trees—apply 5 to 10 pounds zinc sulfate (36 percent) annually until rosette symptoms disappear.
Time and method of application: Apply zinc sulfate to the soil around trees in late February or early March. Broadcast zinc sulfate under the tree from the trunk to several feet beyond the limb canopy. Disking, harrowing, or any operation that mixes the zinc sulfate with the soil, is desirable to prevent washing away and surface soil fixing of zinc.
LICHENS
Lichens commonly are found growing on the branches and trunks of pecan trees, especially in humid areas and river bottom orchards having poor air drainage.
Lichens are nonparasitic to the pecan tree, but merely attach themselves to the bark surfaces. Lichens grow equally well on rocks, fence posts, bricks and other objects. There are several types of lichens that occur on pecan trees, none of which are damaging except perhaps in appearance to the trees in cases of extremely heavy infestations, [Figure 5].
Figure 5. Lichens commonly found on the bark of pecan trees. Left, a fan-shaped type. Right, an erect-branched type.
Control.—The occurrence of lichens in trees regularly sprayed with copper-containing fungicides is rare.
ARTICULARIA LEAF MOLD
Articularia leaf mold caused by the fungus Articularia quercina (PK) Hoehn is a disease of minor occurrence and importance. The disease occurs most commonly following rainy periods and in areas of high relative humidity in the leaves of trees of poor vigor.