A grower who makes the decision to topwork a citrus orchard to change variety is looking for a way out of an unprofitable situation.
However, the grower may find himself only jumping out of a frying pan into a fire unless he counts the cost of a good topworking job.
It is not inexpensive or simple to topwork citrus, according to a panel of experts at a recent grower meeting in Dinuba, Calif., sponsored by the Citrus Research Board and the University of California Cooperative Extension offices in Tulare and Fresno counties.
Plan to invest at least 18 months or more in changing over a grove. This begins with the collection of certified budwood from a nursery six months before the budding or grafting begins in May and June and then plan on investing a year with a grafter to ensure that the work is successful, according to Orange Grove, Calif., grower Tom Mulholland; Exeter, Calif., grafter Eddie Mendez of Exeter, Calif., and nurseryman Roger Smith of Tree Source Citrus Nursery, also in Exeter.
“Topworking is more difficult than it sounds, and you can spend money needlessly if you do not plan it right,” said Smith.
Mendez said he and his father have successfully top-worked citrus groves as old as 40 years old, although experts say topworking is generally recommended on much younger trees.
The trees must be healthy to successfully graft or bud. If they are not, it is best to push out old, unwanted trees and start over.
There is more to consider in topworking citrus than simply changing variety, said Mulholland. One is that a grower cannot change orchard spacing nor can an irrigation system be modified when changing a variety via topworking. The only way to do that is to replant and that may be a better choice than topworking, if spacing needs to be changed to increase production per acre.
A variety may be changed by grafting to a scaffold or a trunk. If the trunk is used, it eliminates any unwanted influence from the older variety. However, there is only one shot at successfully grafting onto a stump. On topworked scaffolds, another graft can be made if the initial one fails.
Mulholland recommends hiring professional grafters rather than training a grower's workers to graft trees.
“You have to have flowing sap to successfully complete a graft,” said Rogers, meaning that the earliest a grower should graft is May 15. And sometimes even then a cold snap can slow or stop fluid flow in trees.
And check the compatibility of the new scion to the existing tree.
For example, UC experts do not recommend grafting lemons to any other citrus. There are also compatibility issues with Mandarin and Tangelo grafted to several other varieties.
The three also recommend that the professional grafters manage the grafted trees for at least a year after the grafting job is complete.
“The grower is responsible for irrigation and pest control, but the grafter should be responsible for managing the grafted trees,” said Mendez.
Here are some of the recommendations offered by nurseries to successfully topwork citrus:
Prune to accommodate budding at least a month prior to budding to allow trees to recover from the shock of severe pruning. All brush must be shredded.
The number of buds required per trees depends on the age of the trees. Buds cost about 35 cents apiece.
Once the grafting tape is removed and the bud begins to grow, pest control becomes very important. Prevent damage from snails, ants, aphids and other damaging insects. Economic thresholds are low for these emerging buds since injury can stop development of new shoots.
Trees must be whitewashed prior to grafting from the ground level to the point above bud insertion locations.
After tape on the graft is removed and girdling by the grafter, all successfully budded branches except the nurse limb are to be lopped off completely, eight inches above the point of bud insertion. Nurse limbs should be removed after one or two years.
Sprouts must be removed, but be sure to identify correctly the sprouts and the leaves of the new graft. Valencia and navel foliage looks almost identical and workers should be trained to recognize the difference between unwanted suckers and growth from new buds.
Girdle above grafts as required.
Bud shoots should be allowed to grow to about 15 inches and then pruned back to eight to nine inches for strengthening. As secondary shoots elongate to 12 to 15 inches, they, too, should be shortened to eight to nine inches.
Carefully manage irrigation because foliage will vary greatly during the topworking process.
Newly grafted trees are more susceptible to frost.
Even under the best situations, it is uncommon to have 100 percent bud take in topworking. Ninety percent is considered good and 70 to 80 percent is common.