During the period of AHDB funding (2019-2022) the aims were to demonstrate ‘best practice’ in plum production, ‘best practice’ in crop and environment management and to compare different production techniques.
Results of experimental plantings
Results of experimental plantings and demonstration plots between 2019-2022
In 2019, three experimental plantings and demonstration plots were assessed and recorded.
Performance of Victoria on four different rootstocks
The experimental planting comprises four replicated 5-tree plots of Victoria on the following four rootstocks of varying vigour:
- VVA1
- Wageningen
- Wavit
- St. Julien A
The planting allows replicated comparisons of the performance of Victoria including:
- Tree size/vigour
- Flowering time
- Ripening time/season
- Disease susceptibility
- Productivity
- Fruit size and quality
Replicated demonstration plots of Victoria planted on four different rootstocks with four different tree architecture systems
The experimental planting established in 2016 comprises two replicated plots of 16 rootstock/tree architecture combinations. The rootstocks and training systems used are:
| VVA1 | Narrow A-frame |
| Pixy | NarrowTable-top |
| Wavit | Super spindle |
| St Julien A | S system |
Replicated comparison of the two new East Malling varieties P6-19 and P7-38 on Wavit versus St. Julien A rootstock
The experimental planting (planted spring 2017) comprises four replicate 6-tree plots of each of the variety/rootstock combinations.
Key results from 2019
Yields
- The Oblique and Super Spindle systems on the dwarfing rootstock VVA1 produced the highest yields in 2019.
- The Narrow Table-Top and Super Spindle systems on Wavit rootstock also performed well.
- Over the past three years, the Super Spindle has produced the highest yields.
Gross margins
- The average gross margin for UK plums has been estimated at £250/ha/year.
- Other tree fruit crops make considerably more.
- The Oblique and Super Spindle systems on VVA1 rootstock and the Narrow Table-Top on Wavit have produced a higher gross margin in 2019 than an average cherry crop.
Fruit quality
- The training system x rootstock combination appears to have an impact on fruit quality.
- Information needs to be gathered over several seasons before any firm conclusions can be drawn, but information will be presented every year on this website.
Key results in 2020
Yields
- The Oblique Spindle on VVA1 rootstock produced the highest yields in 2020.
- Second highest yields in 2020 were recorded on the Narrow A Frame training system on Wavit rootstock.
Fruit quality
- Between the training systems or rootstocks in 2020, there were no significant differences in Brix levels or fruit size.
- Highest firmness and individual fruit weight were recorded on the Candelabra and Fan training systems and Wavit and St. Julian A rootstocks
Key results in 2021
The spring followed a mild winter in 2020/21 which advanced the timing of bud break and the blossom period. This spring period coincided with some of the lowest temperatures and frost events that had been experienced in Kent for the past 50 years leading to almost complete loss of flowers and developing fruits from all parts of the Centre. Plans are now under way to install overhead mist irrigation at the Centre to avoid such severe damage occurring in future.
As a result of this crop loss, virtually no fruit was picked at the Centre in 2021, so no useful records of yield or fruit quality could be collected. The complete loss of flowers and fruits, triggered the trees into vigorous vegetative growth and it is because of this growth that the consortium determined to work in 2022 to return the trees to a more balanced growth between flower and shoot production.
Drawing conclusions so far
At this stage in the Centre’s life, it is still too early to draw firm conclusions, but the trends are showing favourable results for VVA1 and Wavit rootstocks and the Super Spindle and Oblique Spindle training systems. The performance of these demonstration plantings will be assessed and recorded again in 2021, although at the time of writing, some flowers have been damaged by frost and yields are likely to be affected.
It is also worth noting that a proportion of trees planted on the VVA1 have died from canker whilst a proportion of the trees on Wageningen rootstocks did not establish well. These trees are being replaced.
Previous research
Protected cropping
There is a dedicated area for demonstrating the difference in performance of Victoria grown under polythene clad multi-bay tunnels vs unprotected.
Demonstration of mechanical thinning and weed control aids
Several mechanical aids for thinning flowers and controlling weeds in the crop row are available to growers in the UK. These and other machines were demonstrated in open events for growers to view their performance.
Demonstrating the use of root-pruning for vigour control
Root pruning was demonstrated by assessing half a row of root pruned versus half a row without, with the effects on tree vigour recorded. This took place in fan-trained plums during July.
Comparision of the use of organic mulches
Many commercial growers now use organic mulches in the tree row to suppress weeds, conserve soil moisture and improve soil texture and soil structure in the root zone. A long-term comparison will be made of trees treated with organic mulch and those not treated.
Earwig-safe spray programmes and conservation biocontrol
Results of AHDB-funded research projects on preservation of earwigs in orchards and conservation biocontrol are being implemented at the Centre. This includes implementing ‘earwig-safe’ spray programmes, deploying earwig refuges, employing wildflower strips around the centre and between crop rows (in certain areas) and the use of beetle banks. The numbers of earwigs and pollinators are being assessed and recorded. Comparisons of earthworm numbers are also being made between bare soils, grass strips and wildflower areas.
Survey of pollinators and beneficial insects
NIAB led a study on hastening the influx of beneficial insects into newly planted apple orchards, through the provision of wildflower strips in alleyways, earwig refuges (Wignests), and hoverfly attractants.
In general, these interventions had a positive impact over the two years of the project, by increasing numbers of beneficial insects including hoverflies, predatory spiders and anthocorids, whilst reducing numbers of pest species including aphid numbers in the Spring, and codling moth later in the season. To find out about the impact of these interventions in the Plum Demonstration Centre, see the survey results page.