Girdling the trunk a benefit in fruit trees

Garry Brockley

Whilst out in the big wide world web i found this article, does anyone else have information on this?

Trunk Girdling - A Useful Tree Manipulation Tool

Girdling and cincturing treatments have potential for managing tree vigour, enhancing fruit set in vigorous trees, stimulating return bloom, enhancing fruit colour and advancing fruit maturity. Effect varies with timing of the girdling cut.
Girdling at petal fall or soon after, increases fruit retention and offers strong vigour control, giving reductions of 50 % or more in annual extension growth. As girdling is delayed, the reduction in extension growth diminishes. Even so, with very vigourous trees December girdling can still result in a 20 to 30 % reduction in extension growth.

Stimulation of return bloom is strongest around petal fall, and again just after the natural fruit drop has occurred. In cropping trees, this later girdling is preferred because it allows fruit drop to occur, thereby reducing the hand thinning job. December girdling also allows shoot growth to give sunburn protection, and a more favourable leaf to shoot ratio.

Fruit colour enhancement and advance in fruit maturity can be obtained from girdling as close as three or four weeks from harvest.

Girdling treatments interrupt the translocation of photosynthates from the leaves to the roots. This increases carbohydrate levels in the upper tree at the expense of the carbohydrate supply to the roots. This gives a similar effect to planting on a dwarf rootstock. Girdling offers an alternative to dwarfing rootstocks for higher density plantings and there are a number of examples of intensively planted blocks on vigourous rootstocks being successfully held in check by regular girdling each year.

Because some root growth is necessary to keep the roots healthy and allow them to carry out the function of supplying the tree with nutrients and water girdling treatments should not completely cut off the sap flow to the roots. However, to be effective, girdling cuts must sever most of the phloem tissue which carries photosynthates down to the roots.

Girdling Techniques

Two girdling techniques are in general use. Double "C" overlapping cuts, one each side of the trunk, and spiral cuts which overlap. Experience has shown the Double "C" technique to be more reliable, however, the overlapping ring or spiral cut is useful for young trees.

For general purposes, the Double "C" technique using cuts 50 mm apart, with 50 mm cut overlap has been shown to give about the right amount of effect. The effect of girdling can be increased by either bringing the cuts closer together or increasing the amount of overlap. Conversely, the effect can be weakened by widening the gap between the cuts, or reducing overlap.

Girdling is a fairly precise technique, so needs to be carefully carried out and well supervised. Unsatisfactory results and failure have frequently occurred when girdling treatments have been poorly implemented.

For young trees up to about 50 to 60 mm trunk diameter, an ordinary knife or saw cut with bark removal done as an overlapping ring with 10 mm overlap and 5 mm separation between the cuts does a very good job.

Older trees need the double bladed girdling knife which removes a strip of bark. These knives come in a range of sizes, taking out bark strips from 3 mm to about 7 mm in width. The 3 mm knife is satisfactory for trees up to about 150 mm trunk diameter.

Larger trees need more aggressive treatment and because of tough, thick bark, may need a powered saw such as a chainsaw. On these bigger trees, some cutting into the wood beyond the phloem does not seem to matter too much.

Trees girdled correctly will show mild signs of leaf paling two to four weeks after treatment, then recover their normal leaf colour. Excessively severe treatments result in trees sulking for much longer periods, and sometimes the entire growing season.

Disease Problems

Three potential disease problems can develop as a result of girdling.

One of these is collar rot, Phytophthera cactorum which can enter the wound from soil splash. In general, little if any infection of this disease has occurred following girdling. It is considered a risk with highly susceptible varieties such as Cox's Orange Pippin.

Another disease is fireblight, Erwinia amylovara, which poses a serious risk in pears and certain very susceptible apple cultivars. Trees infected with active fireblight may carry systemic infection in their sap stream, so the infection can be transferred from one tree to the next on the girdling tool. In this situation, it is necessary to sterilize the knife between trees.

Also, in trees with active fireblight, we believe that rain or irrigation may wash fireblight bacteria down the trunk into the girdling wound. Great care needs to be taken in regard to managing the fireblight problem.

European canker is another disease which has potential to enter girdling wounds.

It is possible that wound treatments containing low concentration of copper fungicides may give protection against these diseases.

Girdling is a commonplace treatment in stonefruits to enhance fruit size and advance maturity. Although gumming often occurs following girdling, there is not a lot of evidence to suggest that blast infection is a big problem where trees are girdled.


Oct 2001

__________________

Eric Frei

Where's the source?

Is this it?

http://www.hortwatch.com/library/trunk-girdling.html

Nice find and topic.

__________________

Eric Frei

What they do for fruit production can be pretty full on. I read somewhere once that beside pruning the canopy mechanically (a topping and hat racking) they actually trenched to cut roots too and got much better fruit, it's all about fruit yield because it's a crop with a use by date.

I found this picture of grape vine girdled. (source)



Another of a peach called S girdling also showing the knife. (source)

Attached Thumbnails

     

__________________

Garry Brockley

it's incredible what they do to get a greater yeild from fruit trees, no wonder they are always re planting new trees all the time.

__________________

treeshaveneeds

I wonder if the same technique could be applied to stop a tree from coming to flower. I have a number of clients with crabapples, walnuts that are ok with the flowers, but don't want the fruit -- and if they could girdle the tree and stop the flower production, they would be thrilled.
Of course the treatment would have to be done every year.
And wouldn't that likely weaken the trunk enough to dramatically reduce its life? I know they are always replanting fruit trees - but could this be applied to shade trees?

Eric Frei

Jeez, I doubt it.

Bit risky for an amenity tree. Infection, dropping dead etc.

__________________

Garry Brockley

I would definitely say not to do it to shade trees these are techniques for the fruit growing industry and the odd home owners fruit tree if need be, but to do this to a large walnut or crab apple that they want to keep isnt something that should be done, they really do alot of rotating of trees and crops over the years, im going out next week to see how avacado growers massacre (i mean prune) for fruit production, should be an eye opener.

__________________

treeshaveneeds

Galbee

I look forward to your news about the avocado plantation, and how they prune to maximize fruit production.

dov

It would seem that the practice basically revolves around putting the tree under severe stress so it will go into 'species protection' mode and produce a stack of fruit, while delaying growth of structural timber etc.

It seems crazy. I know of fruit trees planted by my Great-great-Grandfather around 1850 that are still fruiting heavily in specimens where decent tree shape and health has been maintained. These girdled trees wouldn't last 10 years! Sheesh. If I want a smaller tree that fruits at a younger age, I just graft onto a Quince stock...

__________________

FlashD

I'll second the holding off of gridling trees for clients. Considering the fruit growers are doing it to increase fruit production, it certaintly would not decrease fruit production in a walnut tree, unless you'd like to decrease it peremenantly. The reason fruit growers do this is, as stated above, to initiate "species survival mode". The plant finds itself under stress and, in turn, produces more fruit.

If you simply want to keep crabapples and walnut trees from fruiting, might I suggest Snipper. It's an injectible hormone, available from Sherrilltree, that causes premature flower drop, essentially aborting fruit production in sweetgums, crabs, walnuts, maples, oaks, etc. Check it out.

PS. interesting article. Sorry to derail your thread for a minute there.

MCW

True to some extent but it isn't severe stress by any means however it is a technique that produces more stress hormones (auxins etc) that result in a heavier flower and fruit (berry) set. It is a technique mostly used in table grapes and is very effective in some varieties that are poor or inconsistent croppers. I am yet to see it used in other horticultural crops in our region but I'm sure it has been used elsewhere - the big issue in crops like Stonefruit would be the introduction of pathogens like Bacterial Gummosis etc. There are a number of table grape properties in Sunraysia (VIC) that use this technique and it is quite sustainable. There are vines that are decades old that have shown no decrease in vine health or yield by doing this although it isn't generally done on an annual basis. By the way the girdling knife pictured above has a set depth it cuts to so it won't ringbark the vine completely. Every time it is done it is at a different trunk height. The wound callouses over quickly.

I know it's an older thread but thought I'd jump in. My previous job was as a Horticultural Consultant and my current job is as the Senior Horticultural Agronomist (Tree and Vine crops) in my region for one of Australia's largest agriculture suppliers after being poached.

Garry Brockley

good info MCW! nice to have your expertise on the subject

__________________

MCW

No worries mate. Also noted that you were going out to see Avocado trees getting pruned. How did that go? You see some really good jobs but also some shockers - I've done a small amount of Avo pruning but a fair bit in Citrus and Almonds with Stihl 200T's etc. Most guys around here (Riverland, SA) have basically given up on Avocados, hence they've "pruned" them back to a stump! They get frosted - drop all their fruit. Get too hot - drop all their fruit. Good money to be made but that inconsistent that nearly everybody has left it to the tropical guys It's not unusual for guys to input massive amounts of fertiliser etc only to have their whole crop drop at the slightest hint of heat or cold. Very frustrating.
Girdling is quite interesting actually but most guys now use chemical/hormonal means to control croploads. Less labour intensive but most corporate properties find it more cost effective. Experienced girdlers are also hard to come by. You'd think it would be a simple job that any meathead could do but apparently not.
Matt.

P.S. I also find a lot of the Arborist guy's info on backyard trees etc here very interesting. It's amazing how many chemical actives are the same just sold under different trade names. Also some of your pathogens and insect pests are also quite interesting while some are the same For your info my previous job was the consulting offshoot of this company and many of the beneficial insects produced there were sold into backyards across the country although the main focus is commercial greenhouses and orchards http://www.biologicalservices.com.au/