PECAN ROSETTE, a nutritional disease, is caused by an inadequate amount of available zinc in the soil to provide the tree with its requirements for growth and nut production.

J. J. Skinner and J. B. Demaree, while conducting tests for rosette control in southern Georgia in 1922, were able to bring badly rosetted trees that were growing on soils low in organic matter back to normal by growing and turning under two green manure crops each year. Chemical fertilizers, as used in the experiment, had no influence in increasing or decreasing rosette. A decade later, several research men, working on pecans in Louisiana and Arizona and in California on apple, pear, peach, plum, cherry, and walnut trees and grape vines, discovered independently that zinc applied to the trees or vines by soil applications, dips, or sprays to the leaves, or by other means effected a control or cure of the disease known as rosette or littleleaf.

In its early stage, pecan rosette shows a yellow mottling and crinkling of leaves in the tops of the trees. As the disease progresses, the symptoms appear on the leaves of the lower branches. In advanced stages the leaves become dwarfed, the internodes Of the terminal shoots are shortened, and gradually the twigs and branches in the tops of the trees die.

Severely rosetted trees usually do not Produce and may become so weakened that they die from attacks of borers or from other causes. Rosette alone, however, has never been known to kill Pecan trees.

A varietal resistance or susceptibility seems to exist. Stuart is the most susceptible. In most localities Moneymaker usually is quite resistant.

Rosette may be corrected by applying a solution of zinc sulfate as a spray to the trees or the dry salt to the soil; the method of application is determined largely by soil conditions. Soil applications are not practical in orchards where trees are growing on neutral or alkaline soils; then spraying is necessary. Spraying is satisfactory regardless of the soil condition.

Three spray applications of a solution consisting of 2 pounds of zinc sulfate, analyzing approximately 36 percent zinc and added to 100 gallons of water, will overcome rosette if it is present in the mild form. The first application should be made as soon after pollination as possible. Two further applications should be made at intervals of 3 to 4 weeks. That schedule should be followed annually until all signs of the disease have been eliminated. Then observations should be made regularly for the first signs of its recurrence it is likely to reappear at any time.

On heavy calcareous soils, where spray applications are not practical, A. O. Alben and H. E. Hammer reported in 1944 that some compost comprising zinc sulfate, manure, and sulfur, and applied in furrows in rather large amounts and plowed under, would overcome rosette in about 2 years.

Zinc sulfate applied to the acid soil where pecans are growing will produce more satisfactory results than spray applications because its effect lasts longer. The zinc sulfate should be broadcast evenly from near the trunk to beyond the limb spread. The rate of application is determined largely by severity of the disease, nature of the soil, and size of the trees. The normal recommendation in Southeastern States is 10 pounds to a tree, applied annually until all signs of rosette have been eliminated from the tree.

Winter injury is usually found on young, vigorous, late-growing pecan trees or those that were defoliated in summer and put out a new crop of leaves late in the season. Older trees, especially those that have received heavy applications of nitrogen, which tends to keep them in a vegetative condition late in the season, may be severely injured by sudden freezes.

The symptoms are dead or dying trees in early summer. Vigorous sprouts grow up later from the roots. Close examination will show that the trunks of the trees have been damaged near the ground. The affected tree usually foliates and grows normally in the spring, but the leaves wither and the tree suddenly dies as soon as hot weather begins. Shot-hole borers and other insects are sometimes present, but their damage is of a secondary nature. A cut through the bark into the cambium layer near the ground discloses the "sour-sap" and discolored wood.

Young trees should be fertilized only in early spring and should not be cultivated later than midsummer, except at the time of planting winter cover crops in the fall when the trees are approaching dormancy.

Injury from sunscald is sometimes confused with winter injury. The symptoms are dead or cankerous areas, usually on the southwest side of the trees or on the tops of larger branches.

One of the best methods of control is to head the young trees as close to the ground as practicable. Lower limbs should not be pruned until the trees have advanced several growing seasons.

JOHN R. COLE, a plant pathologist, is in charge of pecan disease control at the United States Pecan Field Laboratory, Albany, Ga. He became affiliated with the Department in 1924 and began pecan disease control work at Thomasville, Ga. He was later transferred to Lafayette and Shreveport, La., where he was in charge of pecan disease investigations in the southwestern United States.