With the impending withdrawal of Carbaryl in Europe, scientists have been seeking alternative fruitlet thinners for apples.
- One product that has shown some promise in trials conducted mainly in the USA is benzyl adenine (BA). Approval has been gained in some European countries.
- Trials conducted at East Malling have produced variable results with BA, as shown below.
Thinning Royal Gala with BA
In trials conducted in 1995 and 1996 at HRI-East Malling and funded by APRC (Webster and Spencer, 2000), sprays of benzyl adenine (BA, Paturyl formulation) at concentrations ranging from 50 ppm to 200 ppm reduced percentage final set on Royal Gala trees.
- However, the sprays, which were applied at the 12 mm fruitlet diameter stage, had only small and insignificant effects on fruit size and grade out.
- On this preliminary evidence BA appeared not to hold much potential as a fruitlet thinner for Gala.
- However, trials in 1998, comparing sprays of three different formulations of BA (Paturyl, Accel and Perlan), showed that all three formulations of BA, applied at high volume (100 ppm), improved the proportion of Class I fruits in the >65 mm category without reducing total yields.
Effects of sprays of BA (Paturyl, Accel or Perlan) on the fruit set, yield and fruit size of Royal Gala (sprays at 12 mm stage –100 ppm in 1000litres/ha)
| Treatment | Final set/100 floral buds | Total yield/tree (kg) | % Class 1 >65 | Mean fruit wt. (g) |
|---|---|---|---|---|
| Unthinned | 146 | 24.5 | 11.5 | 94 |
| Paturyl | 140 | 25.2 | 39.7 | 111 |
| Accel | 132 | 26.5 | 30.8 | 101 |
| Perlan | 126 | 28.1 | 29.7 | 109 |
- Further research is needed on Gala clones to find strategies for reducing this inconsistent thinning response to BA.
Thinning Queen Cox with BA
Sprays of BA applied at the 12 mm fruitlet diameter stage to Queen Cox trees in 1995 reduced final fruit set/100 floral buds and increased mean fruit size and grade out of the larger Class I fruits (Webster and Spencer, 2000).
- The most effective spray concentration was 100 ppm applied in high volumes of water.
- The sprays caused no significant reduction in total yields/tree.
Effects of BA sprays on the fruit set and yields of Queen Cox in 1995
| Treatment | Final set/100 floral buds | Total yield/tree (kg) | Mean fruit wt (g) | Class 1 (%) | |
|---|---|---|---|---|---|
| >70 mm | 65-70 mm | ||||
| Unthinned | 105 | 13.0 | 84.3 | 9.6 | 12.5 |
| BA 50 ppm | 75 | 11.8 | 105.0 | 17.0 | 25.3 |
| BA 100 ppm | 66 | 11.0 | 107.6 | 13.6 | 37.1 |
| BA 200 ppm | 68 | 11.4 | 116.2 | 38.3 | 29.9 |
| Carbaryl 750 ppm | 54 | 9.8 | 117.9 | 20.1 | 52.9 |
- Although the BA sprays reduced fruit numbers/100 floral buds, when applied for the second year (1996) to the same trees, this thinning was insufficient and failed to compensate for the much increased blossom abundance stimulated by the sprays applied in 1995.
- Consequently, fruit sizes were not improved in 1996.
- Further trials using BA as a fruitlet thinner for Queen Cox are warranted.
Thinning Jonagold with BA
- Sprays of BA (100 ppm) applied at the 12 mm stage to ‘Jonagored’ trees in 1998, improved fruit size and grade out, although the benefits were less than those achieved with hand thinning.
Effects of BA (Paturyl, Accel or Perlan) sprays on the fruit set, yield and fruit size of Jonagold in 1998 (sprays applied at 100 ppm in 1000 litres/ha at the 12 mm fruitlet diameter stage)
| Treatment | Final set/100 floral buds | Total yield/tree (kg) | Mean fruit weight (g) | % Class 1 >90 mm |
|---|---|---|---|---|
| Unthinned | 62 | 39.2 | 186 | 0.1 |
| Hand thinned | 34 | 29.2 | 262 | 27.8 |
| Paturyl | 51 | 37.4 | 223 | 15.5 |
| Accel | 43 | 31.8 | 238 | 24.1 |
| Perlan | 52 | 37.2 | 219 | 11.3 |
Trials in continental Europe with BA
- In trials conducted in mainland Europe, sprays of 100 ppm proved ineffective in thinning the early ripening variety Summered in Norwegian trials.
- However, in Swiss trials, sprays of the same concentration increased the mean size of Boskoop fruits at harvest.
- Results on the variety Golden Delicious have been variable with no benefits reported in Switzerland but improved fruit size reported in Spain.
- In trials conducted in Slovenia, mixtures of BA and NAA have proved effective in thinning Gala.
- In German trials BA has also proved an effective thinner for the varieties Delbard Estivale and Pinova.
- In Italy, BA, which is known under the trade name of ‘Expander’, has proved effective in thinning Royal Gala when applied at 100 ppm at the 10 mm fruitlet diameter stage and trials on the variety Fuji have also shown good thinning responses from BA at 200 ppm.
- On the variety Pink Lady, trials in France show that BA (150 ppm) was an effective thinner applied at the 15 mm fruitlet diameter stage.
- Recent work conducted in Poland indicates that thinning with BA increases with increasing concentrations up to 200 ppm and that it is improved by use of high spray volumes.
BA has shown promise in thinning apple fruitlets in trials conducted in several countries.
- More work is needed on this thinner if the inconsistencies of response are to be understood and overcome.
- BA is not approved currently for use as a thinner in UK orchards.