Collecting Pecan Graftwood
By Dr. George Ray McEachern, Extension Horticulturist
Texas A&M University, College Station, TX 77843-2134
The Texas inlay bark graft method has become the standard top working technique for pecans throughout the irrigated southwest. Heat, drought, high light intensity, wind and other factors common to the southwest make grafting very difficult. Classic grafting systems used in Europe, California, New York and Georgia for other fruit crops fail in Texas because of these limitations. Along the Gulf Coast many of these other grafts are effective; however, once one moves 200 miles from the humid conditions grafting becomes very difficult.
The four-flap graft has also become popular in Texas because of its easy technique and very high percent of success, even by beginners. Commercial nurseries use the patch-bud graft in the spring, but more commonly in the late summer.
Spring patch-buds will require budwood collected late in the winter just before bud break. Most graftwood is collected in February and early March while the wood is very dormant.
When to Collect Graftwood and Budwood?
The longer one waits to collect wood, the shorter the period of time before bud break after grafting. Ideally, one would like to have three to five weeks after grafting and before the buds begin to grow. This long period will give the cambium tissue of the graft and cambium tissue of the rootstock sufficient time for each to generate new bark and wood which are connected. Once the tissues are connected, water can move from the rootstock wood up into the new graft and success follows. On the other hand, if conditions are not ideal or if there is not sufficient time for the graft/rootstock cambium tissues to generate a connection, the graft or bud will die. Therefore, the time at which you collect graftwood or budwood is very important.
Collect pecan graftwood from February l to March 15. This is the wood which will be used for the Texas inlay bark graft method or the four-flap graft.
Collect pecan budwood from March 15 until primary bud swell. This is the wood which will be used for patch budding. Graftwood will not allow the patch to slip or pop off the graft stick because it is too tight or too dormant. Patch budding in the summer, starting in mid July through August is done with fresh budwood collected the same day you graft. These patches are on current season wood and will pop off and separate from the wood very easily.
Where Do You Collect Graftwood and Budwood?
Strong, rapidly growing one year old wood is ideal for grafting or budding. This is easy to find on young, fast growing trees or in the tops of trees which have just begun to bear. Old trees or slow growing trees should be avoided. If a large number of grafts will be needed, older trees can be dehorned to stimulate compensatory growth. These straight, round, one year old shoots are perfect for grafting or budding.
Drought, freeze or herbicide damaged trees should not be used for graftwood. Trees which are not positively identified also should not be used. All too often, growers will think a tree is a certain variety when it is not. Variety identification is a very important part of graftwood collection. Waterproof ink and metal tags should always be used.
Two year old wood can be used, but it is not as good as current season growth.
How to Process Graftwood and Budwood?
Once the wood is cut from the tree, it should be moved out of the sun to a cool, moist location to wait for processing. The graftwood should be processed for storage the same day it is collected. Cut the graft sticks into 6", 12", or 18" lengths which will give one, two or three grafts per stick.
Process only one variety at a time to prevent mixing the varieties.
Dip the freshly cut ends in orange shellac, grafting wax, paraffin or pruning compound. Orange shellac is ideal because it never dries and new growth from the graft will move over it without delay.
Make sure the primary buds are not damaged or knocked off while processing the wood. This primary bud, or insurance bud as it is sometimes called, has the best chance for growth after the two cambium tissues connect, so caution needs to be practiced to prevent losing it.
A very small amount of moisture should be maintained near the graftwood while it is stored. In the old days this was in wooden boxes with moist wood shavings. Today, paper towels and polyethylene bags are used. Avoid colored plastic bags because they may not breathe. The respiration rate of the dormant grafts in refrigeration is very slow; therefore, the bags should allow carbon dioxide to exit, and oxygen to enter the bag. The paper towels used for maintaining moisture should be squeezed to near dryness. This is accomplished by soaking the towels in water, squeezing the water out with a very strong grip of the hand, and finally stepping on the towels with your foot. Then, take the towel up, shake it out and it is ready to wrap five graft sticks. This will prevent the collection of too much water and the formation of mold on the graftwood. Dr. Loy Shreve always said, "It is better to have no moisture source than wet graftwood." This is very true. So, when you squeeze the wet paper towels, they need to be squeezed dry.
How To Store Graftwood and Budwood?
Once sealed in polyethylene bags with variety and year identification using waterproof ink, the graftwood needs to be stored at 35 to 45 degrees F. until used. Make sure the graftwood does not freeze. The refrigerator needs to be monitored frequently to prevent freezing. A high/low thermometer is good insurance against freezing.
Graftwood can be used only on the year it is collected. Make sure the label is marked for the year and the variety.
Take the graftwood out of refrigeration only as needed. A cool, then warm, then cool cycling of the temperature is not good. Also, move the graftwood to the orchard grafting site in a cooler with ice to keep it from getting hot.
If the graftwood or budwood is collected from strong, fast growing trees and if it is processed and stored properly, grafters should obtain at least 90% survival with the Texas inlay bark graft method or the four-flap graft. Grafting should not be attempted before the sap is moving; there are small leaves on the tree and the bark is slipping. This is usually in early April and grafting can continue until mid to late May, depending on how fast the season becomes hot.
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