Pressing on when nature is against you: a grafting successResearch & Extension
AgFirst’s Jesse Reader explains how grafting was used to successfully rework an orchard in response to the drought – resulting in substantial yield improvements.
Between 2007 and 2010, when many Victorian apple growers were feeling the brunt of the drought, some chose to push out poor performing blocks and focus water and other resources into a smaller planted area, while others chose to keep the blocks alive (with minimal input), but take the radical action of chemically thinning the entire crop one season at a time in the hope that the dry spell would be short lived. In short, there was no water and desperate people do desperate things. I remember this period vividly and it lasts as a kind reminder of the power of nature.
During the drought some farms could access water at a cost, at times $1,000 per ML plus $300 transfer, making it a $1,300 per ML investment – if you could get it! It was not uncommon to hear of growers operating on 1.5-2.0ML/ha/year. Furthermore, many bores and dams became quite saline due to low water levels and infrequent fresh flows – further adding to the daily challenges of growing fruit.
Post drought, those who received decent recharge began replanting or cropping again. However, in several cases where blocks were retained and crops chemically removed, the years following would still see significant reductions in water allocations, a ‘salty hangover’ and significantly reduced cash flow from small crops and big water bills. Cost effective strategies needed to be developed that would allow these farms to press on with the objective of increasing crop load again on existing blocks, being part of the ‘colour upgrade race’ that was happening across the country, whilst still managing their compromised financial position.
The most common response I witnessed was the initiation of heavy reworking programs in the form of grafting. During these times when cash flow was limited, the ability to undertake major new plantings, for most, was off the table. Planting was high risk and the potential to maximise that investment was low. Grafting would tick several boxes:
Cost effective – No need for fumigation, ground preparation, new trees or modified irrigation.
Less water – Grafted trees require minimal water in the first two seasons as they leverage off a highly established root zone, small leaf area and minimal crop. This approach would also buy more time to increase water storage without the fear that would come with managing the water requirements of a new block of dwarfing rootstocks.
Colour upgrade – Grafting can be a highly effective way of changing varieties or strains in a very short period of time, thus decreasing the time out of production.
Early production – Rapid canopy establishment and early production is always the goal and through grafting this could be achieved in a shorter period of time under the existing management constraints and it was production of good quality fruit that would help drive these businesses out of a very tough situation.
Key features of a successfully grafted block
Let’s take a look at a real life example of a farm and how grafting led the resurgence back to profitability for this business.
Density: 4.5 x 2.0m (1,111 trees/ha)
This block was chosen due to its poor performance as a Cripps Pink block prior to the drought and suitability for grafting based on access to adequately positioned nurse limbs and reasonable trunk diameter. We know from experience and all that we have learnt from Future Orchards® that optimum planting densities are at least double this, however we weren’t in an ‘optimum situation’. Nevertheless, we still felt confident that a full canopy (at around 1:1 row width to tree height) would have this block paying its way as part of a transition the farm was going through.
*This may have been a good candidate for a Twin-Stem conversion – increasing the block to 2,200 stems per ha. Noted for next time.
Growing system: This block was previously grown in an informal type central leader without support, with 4-5 steep wings coming outwards and upwards from the base. It was slow to grow and failed to fill its allotted space and failed to produce the tree row volume that a 4.5 x 2m spacing needed in order to produce consistently high yields of high quality fruit. The new system will be a large, tall spindle system.
Tree height: Was 2.8-3.2m as a Cripps Pink block, currently 3.8m and aiming for 4.4m.
Tree height will be critical in this block in order to produce the Tree Row Volume required to grow a commercially viable crop.
Age (pre graft): 17yrs
It’s an old block but with no signs of replant issues, die back or other disorders that may further compromise this block. We were confident any arising issues could be managed. Furthermore, the low vigour from this block in the past meant that the trunk would still be suitable for grafting.
Grafted date: Spring 2011
This was the first opportunity after three bad years of drought.
Grafted area: 2ha
Grafted variety: Rosy Glow®
At the time of grafting, this property had 50 per cent Cripps Pink, 10 per cent Rosy Glow, 20 per cent Buckeye Gala, 5 per cent standard Fuji and 15 per cent Sundowner. This variety was chosen off the back of its ability to colour efficiently, meet/exceed market specification and for its standalone $/kg return at the time.
Irrigation was already in place and didn’t require any modification. This block was also set up for fertigation.
Rootstock: MM.111 (Collar rot and woolly aphid resistant). More vigorous than MM.106
This was our main concern – grafting what can be a very vigorous rootstock is far from desirable. However it has positive attributes and only really lost traction across the industry when we shifted to closer plantings where it was less suitable. Again, we would need to make do with the situation presented to us and maximise what we had. We also figured that if needed there are now a number of tools in the toolbox to manage vigour apart from rootstock.
As with any major change or re-development on the farm, there needs to be a plan and goals set. The grower set the following goals with their advisor prior to grafting:
- To build a canopy as quickly as possible off the graft and furnish it with long, pendant branches to achieve high early yields and sustain a productive crop in the long term.
- Use branch training and crop to control vigour as much as possible.
- Exceed the best performing Rosy Glow block on the farm – 48 t/ha.
- Hit Pink Lady™ industry average at the end of the third crop – 49 t/ha (upper quartile achieving 83 t/ha on average).
- To learn as much about grafted trees as possible during the process to determine future suitability of this process.
- The block had major timber removed in winter to ensure the stump was accessible for grafting and that the scion wood would not be in danger of any damage. Trunks were cut 1m off the ground with the intention of cutting a further 100mm off prior to grafting.
- Sap draw limb/s were left to absorb excess energy during the early months/year resulting in an extremely high strike rate. This is arguably one of the most critical components to successful spring grafting and if ignored can result in an extremely poor take and inconsistent block from day one.
- The stump was re-cut on the day of grafting ahead of the grafting gang to ensure the surface and cambium layers were primed for grafting. Trunk diameter was around 80-100mm. This process may seem like extra work but again will be one of the key factors to a high strike and block consistency.
- The scion wood (two pieces) were bark grafted into the sides and immediately waxed with BZ Mastic, secured with electrical tape (not grafting tape) right around the trunk and sealed with a Bacseal/Green Seal type product – a rubber-like acrylic resin to ensure the wound was sealed as soon as possible. Avoiding drying out of the scion wood and keeping water out were our primary objectives. We applied this process to both the stump and tips of the scion wood.
- A quick pass over the block the next day to ensure there are no missed spots when applying the prune wound dressing is an important step as the paint can shrink as it dries exposing fresh wood.
It is important to remember a grafted block is still a block of trees and a certain level of management is still required. They were irrigated semi-frequently, good pest and disease control still applied and weed control as per standard practice was endorsed. There was enough natural vigour from the stump that fertigation requirements to promote growth were minimal. Some magnesium to assist in counteracting blind wood and a small amount of calcium nitrate were applied in season.
Essentially there was minimal tree training in year one, just a focus on growing as much tree as possible. During the post-harvest window we treated this block in a similar manner to the cropping blocks with a good feed of calcium nitrate plus boron and foliar applications of lo-biuret urea. Nutrition played a key role in the development of early crops in this block.
After leaf fall we could see that there were a good selection of nice flat branches to choose from so strong wood or limbs with steep crotch angles were selectively removed and tree training began in the bottom half of the tree to begin setting up
calm, pendant fruiting units. This was a critical investment of time and money and without it the trees would have been overly vigorous and lacking in good quality bud for the following season. We would adhere to previous lessons learnt and point all limbs downwards in the direction of the tractor wheel marks in the inter row.
Winter also provided the opportunity to put in more posts and wires to support the future tree and its training needs. Remember a graft doesn’t always behave like a nursery tree and there is now another potential point of weakness at the graft union so support the tree well and support it early.
Heading into the first decent cropping season, the objective was to set as much fruit as possible to help calm the tree, whilst still developing the tree to its full potential. This phase is always quite challenging and debated by many across the world. We know that fruit quality will likely be compromised due to large fruit size, potentially excessive nitrogen levels and in some instances poor colour from vigour in the tops. Managing the tree in two halves becomes the name of the game and early applications of Regalis® in the bottoms is often a nice way to keep the bottom calm and productive whilst still punching the tops.
This block experienced quite a strong growing year. The tops actually ended up being quite punchy and would require intervention going forward. By the end of that season however the canopy was around 80 per cent complete and really taking shape – a stunning result.
The grower learnt a lesson that year on managing fruitfulness and vigour and noted the requirement for tree training in the tops and also to keep consistency within tree. Winter would be used to set up the tree for maximum light distribution noting that fruit quality would need to be a focus the next year.
Winter 2014 highlighted the unmanaged wood in the middle/top third of the tree quite clearly and being Pink Lady branches, they turn to the sky by preference and ultimately required heavy manipulation and in some cases removal. Whilst this mismanagement has cost the block yield coming into this season the tree is looking calmer and more and more productive each year, which is a great sign. Some steep uprights were chunk pruned out and a small amount of detail in the bottom scaffold to simplify the crop was all that was required.
Spring 2014 was excellent, reasonably mild, not too windy and provided ideal conditions for fruit set. The tree architecture is now really taking shape in its fourth leaf and this conversion is setting up for a great return on investment. Fruit set was high and these trees would be hand thinned to 250 apples per tree.
By spring, the block was performing in a way more suitable for the old, wide rows at 4.5m. Another 15-20 per cent canopy as mentioned in this block and the 65-70 t/ha target yields will be achievable. A fantastic outcome for a 1,111 tree/ha block grafted three seasons ago after drought.
We are yet to confirm the performance off this block as it wasn’t harvested when this article went to print, however what we can do is look at the performance of the old block prior to grafting and look at this block year to date to see if we are on track.
The first three cropping years in the original free standing block totalled 43 t/ha of production and maxed out at 37 t/ha after 10 years in the ground. The grafted block on the other hand has had more impressive results and after three cropping seasons has a cumulative yield of 104 t/ha and should hit 50 t/ha quite comfortably this season.
|Year||Yield – t/ha||Accumulated yield||Seasonal notes|
|1998||3||3||Help settle the tree.|
|2002||33||109||Canopy started growing.|
|2006||37||229||Largest crop achieved.|
|2007-2010 crop chemically removed due to severe drought conditions and inability to crop.|
|2011||0||Grafted to Rosy Glow winter 2011.|
|2013||12||12||First crop, second leaf. Stored surprisingly well/ Full colour.|
|2014||42||54||Second crop, big fruit, high colour. Returned good money back to the farm.|
|2015||50||104||Unmanaged vigour in previous season resulted in the forced removal of wood in the top third of the tree – thus impacting total crop load.|
|2016||60?||164||Very achievable after assessing this season’s canopy development.|
|2017||70?||234||At 1,100 trees/ha this may be our limit based on canopy and density.|
Summary of success factors
Whilst this block and its development is far from done, we can attribute several factors to its success and resultant production gains.
- The careful selection and management of an appropriate nurse limb at the time of grafting ensured that this block would have a high strike rate and the best possible chance of obtaining the goals set out in the beginning.
- The early management and training of the developing limbs in the tree to ensure we promoted cropping not vigour. This is critical and if ignored would have resulted in an overly vigorous block of MM111 and minimal fruit to show for it.
- The extra support provided to the tree in this block in the form of posts and wires was an excellent decision. Keeping the graft straight and well attached to the wire has been a major contributing factor to the consistency in this block.
- Having goals, a plan and reviewing them regularly has meant that this block never strayed too far from the middle stump. The constant analysis and data gathering on fruit size and bud counts allowed for fine tuning along the way.