GIRDLING PEACHES FOR PROFIT - A REVIEW OF THE PRACTICE
Girdling (removal of a strip of bark tissue) is a practice that has been used on fruit plants for centuries. California as well as the countries of Israel and South Africa utilize girdling as a regular part of their cultural program on peaches and nectarines. Following years of experience, growers in California have ably mastered the art of girdling to accomplish two primary goals, namely to increase fruit size and earliness of harvest. They presently girdle practically all early peach varieties through the Coronet season. Their early nectarine varieties are handled in a similar fashion. California's Marketing Order usually imposes a minimum 2 1/4 inch (88 count) size (for shipping) on their earliest peach varieties. Girdling is one of the main tools that enables California growers to ship such a large minimum size so early in the season.
Before 1979 no girdling was being done in the Southeast. As a result of some preliminary studies we conducted in 1978 and 1979 in south Georgia and north Florida, girdling became a recommended practice (on trial basis) in commercial plantings in Alabama, Florida, Georgia and South Carolina.
To further determine how well girdling would work under southeastern conditions, studies were conducted in commercial plantings in Alabama from 1979 through 1984. The results of these studies were very promising and indicated that girdling of early peach varieties could prove safe and quite profitable for growers when the practice is properly used. After several years of girdling trees in commercial plantings (especially in Georgia and Alabama) during the early 80's, this practice has become well accepted and utilized across the southeastern peach belt.
Although an increase in fruit size (by 1/8 to 1/4 inch in diameter) and greater earliness of harvest are two of the most important benefits of girdling, several other valuable benefits may be gained from this practice. Among the most noteworthy are: (1) an increase in yield by 1/4 to 1/2 bushel per tree, (2) fewer pickings (usually 2 to 4 compared to the normal 3 to 5) and a greater percentage of crop is harvested during the first picking (an enhanced concentration of ripening), (3) an increase in red skin color (helps in meeting USDA color standards), (4) use of an outstanding variety to partially or completely replace (by moving harvest season forward) an earlier poorer performing variety, (5) where desirable, the harvesting period for a large block of a single variety may be split, and (6) provides a fruit sizing benefit generally equal or superior to that realized from extensive and costly bloom thinning of early varieties. This permits the grower to adequately size early peaches without risking an increased crop loss from freeze damage following bloom thinning. But with all practices, the bottom line is profit, and our demonstration studies in Alabama have shown that girdling can increase gross income per acre by several hundred dollars (about $250 to $800 per acre).
Girdling has primary value for early varieties which characteristically have smaller fruit size and lower yields than mid and late-season varieties. Varieties vary somewhat in their response to girdling (some give more fruit size and yield increase than others, etc.). However, all of the early varieties we have studied thus far have responded quite well to the treatment.
Earliness of harvest is very important to growers because prices usually
start high at the beginning of the season and steadily fall until they
"bottom out" in early to mid July. Some recovery in price usually occurs
after this date. Through the use of girdling we have been able to consistently
advance the first harvest date of very early varieties such as Camden and
Springold by at least 3 to 4 days, Rubired by 7 days, while harvest of
the later maturing Redhaven is advanced by nearly 10 days. It should be
obvious that the harvest dates of later maturing varieties are advanced
much more than for early varieties. In general, the following chart applies
to how much the harvest date can be advanced by girdling:
|Days Variety Ripens Before Elberta||Number of Days1 Ripening is Advanced|
|50 to 60||3 to 5|
|35 to 45||6 to 8|
|30 and earlier||9 to 12|
Definition of terms is very important in understanding the difference between girdling and scoring. Both of these practices have been evaluated in our demonstration work. Girdling refers to the cutting and removal of a strip of bark tissue from the trunk or scaffold branch (Figure 1). This is achieved with a specially designed girding knife (Figure 2). Scoring involves the severing of bark tissue (to the wood) with a knife, but no bark tissue is removed (Figure 3). A large-bladed knife of any type is satisfactory for scoring but a tile knife is ideal (Figure 4). For optimum results with the least detrimental effect, girdling (or scoring) must be done correctly. The following are suggestions for growers who wish to use the practice in their orchards:
Type of Trees and Varieties to Girdle
Generally only early season varieties need girdling (those ripening 30 or more days ahead of Elberta). This includes varieties ripening as early as Goldcrest and Camden and as late as the Maygold-Sentinel season. Girdling will work quite well on later maturing varieties but generally is not needed for adequate sizing. An exception would be a variety like Redhaven which has a sizing problem. Also, if there is a need to ripen part of a block of trees earlier, girdling could be used.
Girdle trees in their 5th leaf or older. Trees in 4th leaf may be girdled if they have attained good size and base of scaffold branches are at least 2 inches in diameter. Please note that trees in their 3rd and 4th leaf may be scored (preferably branches only) to enhance fruit size and earliness. Scoring is as good as girdling on some varieties but not as good on others. One of the main limiting factors in using scoring is the problem of growers being able to inspect trees to make certain cuts are being properly made (very difficult to see cuts and also know if they are deep enough).
Use only vigorous, healthy trees for girdling. Avoid girdling trees which appear weak and are under stress of any kind. This includes trees with gummosis or insect damage.
Only girdle trees which have full fruit crops. Girdling trees which have reduced crops because of poor set or damage by freezes and hail is not advisable. This could result in excessive sizing in some varieties and increased fractured or split pit problems.
Description of the Girdling/Scoring Process
There are at least three sizes of girdling knives available based on the width of cut, 1/8 inch, 3/16 inch and 1/4 inch. The 1/8 inch knife is recommended for younger, thinner barked trees (4th to 8th leaf) because complete healing of the cut area is realized quicker and with less difficulty. However, if properly used the 3/16 inch knife also works well. The use of a 3/16 inch knife should be restricted to 9th leaf trees and older having large scaffold limbs with thicker bark. It is easier to cut thicker bark with a wider blade. The wider the cut, the longer the time required for healing. In the case of very vigorous varieties such as Bicentennial and Springcrest, a wider cut might prove of value in allowing for more time for sizing of fruit. It is suggested, however, that growers learn the "art" of girdling first using the 1/8 inch knife. The 1/4 inch knife as used in California is not recommended.
Girdle the lower portions of the primary scaffold branches (Figure 5). Do not girdle trunks. Only girdle branches 2 inches in diameter and larger. The greater the diameter of the branch generally the more rapid and complete is the recovery process. Girdling of small branches can result in limited recovery and death. Girdling of trunks is not recommended.
Use an "S" (spiral) girdle rather than a complete girdle. A complete girdle is one in which the beginning and ending portions of the cut are brought together at the same point. An "S" girdle involves starting the cut at one point on the branch and ending the cut in line with the beginning cut but 1 to 2 inches above or below it (Figure 1). Thus the two ends of the cut forming the "S" girdle are separated by 1 to 2 inches of bark. Both types of girdling give the same results in terms of fruit size increase, etc., but the "S" girdle provides a higher degree of safety and recovery of the tree.
If scoring is used, it should be done at the recommended time for girdling. Two parallel cuts should be made about 1 inch apart on each scaffold branch with a tile knife (or equivalent) that has about 1/16 inch blade. Each of the two cuts should connect making a complete circle (Figures 3 & 4). It seems that the effectiveness of scoring may vary among varieties more so than girdling (scoring effect may not be as pronounced as girdling). For example, scoring has worked equally as well as girdling in sizing JuneGold fruits, but not quite as good as girdling with the Camden variety.
Proper Timing of Girdling
Girdling should be done approximately 4 to 8 weeks before normal harvest time. The final 10 to 20 days just ahead of complete pit hardening is ideal. For very early varieties such as Springold and Camden, this means girdling should be done about 4 weeks after bloom, which is about 4 weeks ahead of normal harvest. Where necessary these varieties may be girdled 2 1/2 to 3 weeks after bloom.
It is important that fruit thinning and girdling not be done at the same time because of the excessive shock to the tree and remaining fruit. This could cause an undesirable increase in the number of fruits with split pits. Ideally, trees should be thinned and then girdled several days later (allow at least 4 to 5 days between thinning and girdling). However, if it becomes necessary, trees may be girdled first and fruit thinning completed several days later. If a little follow up thinning is needed (after bulk of thinning is completed) this may be done within 2 days after girdling with no problem.
Girdling trees twice during the same season is not advised. Some growers have tried this approach because of serious problems in sizing fruits of certain varieties. Reportedly, some growers in California utilize this practice on one or more extremely vigorous varieties.
If a particular orchard is being girdled it is generally not necessary to bloom thin in order to produce adequate fruit size. However, with a real problem variety both practices could be combined to maximize fruit size. If this approach is followed the grower may observe some increase (though usually tolerable) in the level of visible split pits as compared to a tree that was bloom thinned only.
Callousing and complete healing of wounds normally takes only 3 to 4 weeks but may require another week or two in some cases (Figure 7). During the healing period, the girdling wounds are sometimes infested by lesser peach tree borer. Thus, during the period from girdling until harvest (4 to 7 weeks) attention should be given to directing the normal cover sprays to provide reasonable control of borers during this period. Once harvest is completed, a borer spray should be applied to lower portions of branches and trunk for season long control. This spray will normally be applied during June.
Trees under drought stress will fail to size their fruit adequately even if girdled. Irrigation (or rainfall) is essential in realizing the maximum effect from girdling. Where only periodic irrigation is being used, try to complete final irrigation no closer than 8 to 10 days before harvest.
Girdling does not replace the need for proper fruit thinning. Both practices are essential for developing optimum fruit size of early varieties.
Girdling places trees under considerable stress while they are maturing their crop. Therefore, it is recommended that mature, bearing trees receive at least 60 to 75 pounds of nitrogen per acre (such as 600 to 750 pounds of 10-0-10) during late January- February. Following harvest, girdled trees should receive an additional 20 to 40 pounds of nitrogen per acre such as 200 lbs./acre of calcium nitrate or 100 lbs./acre of ammonium nitrate (or other equivalent nitrogen source). A postharvest application of nitrogen is a part of the ten-point program for managing peach tree short life. The above fertilizer rates are provided as general guidelines and may be adjusted upward or downward based on previous fertilization experience, tree size, crop load and type soil involved. Maintaining good vigor is especially important for varieties susceptible to bacterial spot.
In result demonstration studies conducted since 1979, no problems with girdling the same trees in successive years were observed so long as good tree vigor was maintained and lesser borers were controlled. Thus, where proper nutrition and pest management are maintained, annual girdling of the same blocks works well.
Because of potential disease problems in all peach orchards, girdling knives should be dipped in a chlorine solution (9 parts water plus 1 part liquid chlorox) between blocks or rows of trees as conditions dictate. Although diseased trees should not be girdled, there is always the possibility a given block may have some diseased trees that are cut. If an area is free of gummosis, be certain all tools are treated before use in that block to avoid introducing the problem. After chlorine treatment, spray with an oil (such as WD-40 or equivalent) and wipe clean, otherwise the blade will corrode.
For growers who are interested in girdling but have never used the practice, it is suggested that only small blocks of trees of early varieties be used in initial testing. Only after having gained experience and confidence in using girdling on a few trees should growers consider extensive use of this practice.
Special Considerations at Harvest Time
Special attention should be paid to harvesting of blocks which have been girdled. Ripening of fruits on girdled trees occurs appreciably faster and must be more closely monitored by the grower. This greater speed of ripening is not as obvious in extremely early varieties such as Camden. However, it is definitely more noticeable with later ripening varieties such as Rubired and Redhaven (Figure 6).
The key in maintaining good firmness in fruit on girdled trees is to harvest at normal shipping maturity. Don't allow fruit to hang too long. Fruits do not have to be harvested every day but the grower should never allow more than one or two days between individual pickings. The grower who has a roadside market and wants to sell only tree-ripened fruit will have to harvest at least every other day.
Costs of Girdling Trees
Custom girdling costs usually vary from $.20 to $.75 per tree depending on difficulty of job. Young trees with only 3 to 5 properly arranged scaffold branches may only cost $.20 to $.30 per tree (Figure 8). Experienced workers can girdle about 100 trees or nearly an acre per 8-hour day. However, in some orchards workers may double this rate. Older, poorly trained trees are more difficult and costly to girdle (may cost $.50 to $.75 per tree).
Sources For Girdling Knives
The best and most economical source of girdling knives is VACA Shears, Fresno CA. This used to be part of Malaga Maid Manufacturing, the company that supplied knives in the past. Other companies such as Farmer's Buying Service, Fresno CA, Growers Supply, Reedley, CA and Michigan Orchard Supply Co., South Haven, MI, sell girdling knives to growers which they apparently purchase from VACA or other sources. For obvious reasons it is usually more economical for growers to obtain knives from a basic manufacturer than from a retailer, although they may be purchased from any of these companies.
It is recommended that growers purchase girdling knives without a scraper. These knives retail for around $24.00 each, but growers may be able to order them directly from the company at about a 40% discount. To order, growers should phone the company and ask about the shipping charge. Once this is determined they may forward their check for the total amount and the shipment should be received in a few days. The other method of ordering is to call the company, place the order and pay for the shipment C.O.D.