Girdling is a readily used practice in citrus and stone fruit orchards where it is typically used as a technique to increase fruit size.

Biennial bearing can be a serious problem in olive trees which can result in heavy crop losses to producers.  Under non-irrigated conditions, yields can fall substantially or drop to zero making the production year uneconomical to harvest.  Girdling may be a practice if done under the right conditions and timing could increase the production of an olive tree.

What does Girdling or cincturing involve?

Girdling also known as cincturing which is a horticultural practice involving eliminating up to a 1.5cm strip of bark around the trunk to stop the translocation of photosynthates to the root system.  A girdling knife or cincturing tool is used to cut the bark of the olive tree.

Researchers in Israel*  found that 15mm scaffolds covered with CaCO3 mineral oil and wax or PVC cover were most effective in facilitating wound healing.  PVC treatment was more rapid in wound healing.   During the first prevailing year after girdling found a 40% in increase yield.  Another study from Spain~ that looked into optimal widths and timing found that removing a 15mm band of bark 30 days before full bloom increased the fruit weight from 3.9g in the ungirdled trial to 4.7g.

Wounds with untreated scaffolds in the Israel study saw a drop in yield.

The width of the scaffold and healing duration as well as the time of year in which the girdling was carried out all had bearing on an increase or decrease in production.  The Israel study found that girdling olive trees increased the yield in the season following treatment with later girdling causing an increase in fruit set only.

Several scaffolds were used in the studies from 30mm to 5mm where the 5mm girdles were reported to heal too quickly and had no effect on increased production.

It was also noted that trees that were about to produce a high yield did not respond to girdling and in some cases actually reduced the yield.  Long-term studies need to be conducted to ascertain if alternate scaffold girdling should be considered.

The studies were interesting because there is potential that girdling practiced correctly in an olive grove may have a positive outcome for increased yield output however, the width of the girdle, healing timing, and time of year need to be taken into account when considering employing this technique in a commercial grove and can also have a positive effect on production in the alternate bearing years.

* STUDY

ABSTRACT

The effect of scaffold girdling on the productivity of olive trees was studied on four cultivars grown under intensive irrigated conditions. Girdling increased the yield when done in midwinter (December-February) and to a lesser extent in April. A girdling width of 10-15 mm covered with PVC tape was most effective and promoted rapid healing. Uncovered girdling wounds healed very slowly, with a resultant decline of the scaffold. Girdling increased both inflorescence formation and fruit set. With cv Manzanillo young scaffolds were more responsive than old ones. The responses of different scaffolds on the same tree to girdling were independent of each other. The degree of response of a scaffold to girdling depended on the potential yield of the scaffold in the year of treatment. No direct prevailing effect of the girdling on of the following year's yield was noted.  

Read the full study:  Girdling olive trees, a partial solution to biennial bearing. I. Methods, timing and direct tree response: Journal of Horticultural Science: Vol 58, No 2

~ STUDY

Olive tree girdling: optimum timing and width

López-Rivares, E. P. ;  Suárez-García, M. P.

Escuela Universitaria de Ingeniería Técnica Agrícola, Seville, Spain.

ABSTRACT

Six-year-old multi-trunk olive trees (cv. Manzanilla) growing under controlled irrigation in an 'off' year were girdled at monthly intervals from 15 Dec. to 15 Apr., removing 10 mm-wide rings of bark. In a separate trial, trees of the same cultivar growing under similar conditions were girdled by removing a 5-, 10- or 15-mm-wide ring of bark in Apr., i.e. a month before full bloom. Ungirdled trees served as controls. Girdling date had no significant effect on either flowering or fruit set. Removing a 15-mm-band of bark at 30 days before full bloom increased individual fruit weight from 3.9 g in the ungirdled control to 4.7 g.

Read the full study:  Olive tree girdling: optimum timing and widths.

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What is the problem?

Hi Amanda,

Please help, we are based in the Hunter Valley and it appears that where moisture runs through the tree is where the problem is ?(see pictures). ?It doesn't look like sooty mould but we had scale and olive lace bug issues. ?The trees are in urgent need of care. ?What is the black on the trunks and what do I do? ?P NSW

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So, what is going on and how do I fix this??

I have spoken with plant pathologist, Dr Len Tesoriero from DPI NSW and he has the following suggestion:

"There appears to be dead wood running up the stem on one side. This is probably from a wood rotting fungus (Botryosphaeria or even one of the basidiomycetes) although the damage looks to be quite old and it may no longer be active. Again if it's possible I'd cut the limb off and use copper or lime sulphur on the wound. If the conclusion is that the fungus is no longer active - the tree can sometimes partition infected wood and the fungus may die out - or if it is on the main trunk and it would be difficult to excise then leave it or just treat it with copper or ?lime sulphur"

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