Various methods of budding, beginning with the patch-bud, have been tried at different times, but shield-budding (Fig. 11) is the only one which has proved altogether satisfactory for nursery purposes. The method is the same as that used with citrus fruits and the avocado. Having been less extensively practiced, however, mango budding is less thoroughly understood, and it is not a simple matter to judge the condition of the stock plants and the bud wood without experience.
The best season for budding the mango in Florida is generally considered to be May and June, but the work is done successfully all through the summer. It is necessary to bud in warm weather, when the stock plants are in active growth.
When seedlings have attained the diameter of a lead-pencil they can be budded, although they are commonly allowed to grow a little larger than this. The proper time for inserting the buds is when the plants are coming into flush, i.e., commencing to push out wine-colored new growth. When they are in this stage, the bark separates readily from the wood; after the new growth has developed further and is beginning to lose its reddish color, the bark does not separate so easily and budding is less successful. .
The budwood should be taken from the ends of young branches, but usually not from the ultimate or last growth; the two preceding growths are better. It is considered important that budwood and stock plant be closely similar, in so far as size and maturity of wood are concerned. If possible, branchlets from which the leaves have fallen should be chosen. In any event, the budwood should be fairly well ripened, and the end of the branchlet from which it is taken should not be in active growth.
The incision is made in the stock plant in the form of a T or an inverted T, exactly as in budding avocados or citrus trees. The bud should be rather large, preferably 1 1/2 inches in length. After it is inserted it should be wrapped with waxed tape or other suitable material. A formula for use in preparing waxed tape will be found under the head of avocado budding.
After three to four weeks the bud is examined, and if it is green and seems to have formed a union, the top of the stock plant is cut back several inches to force the bud into growth. A few weeks later the top can be cut back still farther, and eventually it may be trimmed off close above the bud, - this after the bud has made a growth of 8 or 10 inches.
J. E. Higgins1 describes a method of shield-budding which has been successful in the Hawaiian Islands. So far as known, it has not been used on the mainland of the United States. Higgins says, "Budding by this method has been successfully performed on stocks from an inch to three inches in diameter. . . . Wood of this size, in seedling trees, may be from two to five years old. It is essential that the stocks be in thrifty condition, and still more essential that they should be in ' flush.' If not in this condition, the bark will not readily separate from the stock. It has been found that the best time is when the terminal buds are just opening. . . . The budwood which has been most successfully used is that which has lost most of its leaves and is turning brown or gray in color. Such wood is usually about an inch in diameter. It is not necessary in this method of budding that the budwood shall be in a flushing condition, although it may be of advantage to have it so. . . . The incision should be made in the stock about six inches in length. . . . The bud shield should be three to three and a half inches long, with the bud in the center." After-treatment of the buds is the same as with the Florida method which has been described: in fact the Hawaiian method seems distinct only in the size of stock plant and budwood, and the consequent larger size of the bud.
1 Bull. 20, Hawaii Agr. Exp. Sta.
Crown-grafting (Fig. 12) is not commonly practiced in Florida, but it has been successful in Porto Rico. It has also been employed with good results by H. A. Van Hermann of Santiago de las Vegas, Cuba, and it is said to have proved satisfactory in Hawaii and in India. W. E. Hess, formerly expert gardener of the Porto Rico Agricultural Experiment Station, who has had much experience with the method, says that it has proved more successful in Porto Rico than budding, and is at the same time superior to inarching because of the greater rapidity with which trees can be produced in large quantities. As in budding, success seems to depend mainly on the condition of stock and cion at the time the graft is made. Provided the stock is in flush, the work can be done at any season of the year. For cions, tip ends of branchlets are used. They should be of about the diameter of a lead-pencil; of grayish, fully matured, dormant wood; and from 3 to 5 inches in length. A slanting cut 1 to 2 inches long is made on one side, tapering to a point at the lower end of the cion. The stock may be of almost any size. When young plants are used they are cut back to 1 foot above the ground, and a slit about 1 inch long is made through the bark, extending downward from the top of the stump. The cion is then forced in, with its cut surface next to the wood, and is tied in place with soft cotton string. No wax is used. The graft is inclosed in three or four thicknesses of oiled paper which is wound around the stock and tied firmly above and below. This is left on for twelve to twenty days, when it is untied at the lower end to admit air. Fifteen or twenty days later the cions will have begun to grow and the paper can be removed entirely.
Fig. 12. Crown-grafting the mango. On the left, two cions of proper size and character; in the center, a cion inserted and another tied in place; and on the right, the covering of waxed paper which protects the cion while it is forming a union with the stock.
This method is applicable not only to nursery stock but also to old trees which it is desired to topwork. In this case about half of the main branches of the tree should be cut off at three or four feet from their union with the trunk. It is necessary to leave several branches to keep the tree in active growth; this also has a beneficial effect on the grafts by protecting them from the sun. When the cions are well established, these branches may be removed or they also may be grafted if more limbs are necessary to give the tree a good crown. The cions are inserted under the bark at the cut ends of the limbs, exactly as described for young stocks, but larger cions may be used.
In Florida many large trees have been topworked by cutting off several of the main branches, close to their union with the trunk, and allowing a number of sprouts to come out. When these have reached the proper size, they are budded in the same manner as seedlings.
Throughout the tropics there are many thousands of seedling mango trees which are producing fruit of inferior quality. By topworking, these trees could be made to yield mangos of the choicest Indian varieties. The work is not difficult and the value of the tree is increased enormously. Perhaps no other field in tropical horticulture offers such opportunities for immediate results as this.