Systematic Calcium Fertilization Reduces Bitter Rot in Apples
That calcium supply has a major influence on apple quality is a fact that has been known to fruit growers for a very long time.
Calcium, which is absorbed and transported by the plant as the divalent cation Ca2+, plays a major role in the metabolic processes within the plant cell:
Calcium, which is absorbed and transported by the plant as the divalent cation Ca
- Ca
2+ions bridge phosphate and carboxylate groups of proteins and phospholipids, thus stabilizing the cell membranes. - Ca
2+binds with pectin contained in the middle lamella of the cell wall, thus forming stable cross-links. - The polygalacturonase enzyme, which breaks down pectin, thus destablizing the cell walls, is checked by Ca
2+.
Known forms of quality degradation in apples attributable to a lack of calcium are, for example, bitter pits, water core, skin and flesh browning.
The susceptibility to bacterial disorders and fungi also increases if the calcium concentration in the fruit is too low.
The susceptibility to bacterial disorders and fungi also increases if the calcium concentration in the fruit is too low.
In the year of the experiment, 2007/2008, and based on trials carried out in the crop year 2006/2007, trials were carried out at the Kompetenzzentrum (Center of Expertise) in Ahrweiler to determine the potential effectiveness of various calcium leaf fertilizers - both on their own and in conjunction with the fungicide agent Captan (800 g/kg) - in combating Gloeosporium fruit rot, a fungicidal disorder found in apples which results from storage and is of major commercial importance.
Trial Design
The Pinova variety was used in the trials. The following 6 groups were tested:
The Pinova variety was used in the trials. The following 6 groups were tested:
| Group / Treatment | ||
| 1 | Control group, untreated | |
| 2 | Captan (0.75) | |
| 3 | Captan (0.75) + calcium chloride flakes (2.50) | |
| 4 | Captan (0.75) + formulated calcium formate (3.70) | |
| 5 | Calcium chloride flakes (2.50) | |
| 6 | Formulated calcium formate (3.70) | |
(Figures in brackets = Amount used in kg respectively L per ha and per meter canopy height
The leaf fertilizers used contained 49.3 % CaO (formulated calcium formate), respectively 78.5 % CaO (calcium chloride flakes), so that approx. 1.82 kg, respectively 1.96 kg, CaO were used during each fertilizer treatment.
The leaf fertilizers used contained 49.3 % CaO (formulated calcium formate), respectively 78.5 % CaO (calcium chloride flakes), so that approx. 1.82 kg, respectively 1.96 kg, CaO were used during each fertilizer treatment.
On 6 occasions during the period from mid August to mid September 2008, at intervals of 5 - 10 days (T1 - T6), the test groups were treated according to the following plan:
| Group | Treatment Dates |
|
| 1 | Control group | - no treatment - |
| 2 | Captan | T1 - T3 |
| 3 | Captan + calcium chloride flakes | T1 - T3 |
| 4 | Captan + formulated calcium formate | T1 - T3 |
| 5 | Calcium chloride flakes | T4 - T6 |
| 6 | Formulated calcium formate | T4 - T6 |
The mandatory 21-day waiting period for the Captan agent meant only using the first three treatment dates in August for groups 2, 3 and 4.
Calcium chloride and calcium formate have no obligatory waiting period so were only used in groups 5 and 6 on the last three dates in September - being the only two agents where this applied.
The apples were picked on 21.10.2007 (BBCH 87). The harvested apples were assessed on 12.03.2008 and on 09.04.2008.
Calcium chloride and calcium formate have no obligatory waiting period so were only used in groups 5 and 6 on the last three dates in September - being the only two agents where this applied.
The apples were picked on 21.10.2007 (BBCH 87). The harvested apples were assessed on 12.03.2008 and on 09.04.2008.
Results
Fruit analysis showed that the type of calcium bond in the leaf fertilizers used influences the calcium concentration in the fruits. According to the results of the analysis, the calcium contained in formulated calcium formate (groups 4 + 6) was more readily available to the fruits than in a chloride form (groups 3 + 5), although these groups actually received more calcium during each of the three treatments.
Fruit analysis showed that the type of calcium bond in the leaf fertilizers used influences the calcium concentration in the fruits. According to the results of the analysis, the calcium contained in formulated calcium formate (groups 4 + 6) was more readily available to the fruits than in a chloride form (groups 3 + 5), although these groups actually received more calcium during each of the three treatments.
Furthermore, both assessment sessions discovered a direct connection between the calcium concentration in the apples and Gloesporium infestation: The higher the calcium concentration found during analysis the lower the susceptibility to Gloesporium fruit rot.
A direct comparison of the calcium fertilizers that were administered on their own with the fertilizer/fungicide combinations showed that rating results comparable to those of the calcium formate Captan variants (group 4) could be achieved with the formulated calcium formate variant (group 6), when administered alone. Calcium chloride, when administered on its own (group 5), was unable to achieve the same effect. The level of infestation seen during initial assessment, and during the examination as a whole, was actually higher than in the untreated control group.
Conclusions
The following conclusions can be drawn from these trial results:
The following conclusions can be drawn from these trial results:
- Calcium leaf fertilizers - even when used at a more advanced stage - increase the calcium concentration in treated apples.
- Apples with a higher calcium concentration are more likely to be able to fend off disease penetration into the fruit (in this case Gloeosporium fruit rot) or keep the level of damage down once the fruit has been infiltrated.
- Despite not having examined the exact mechanism behind the outcome as part of this experiment, it can be assumed that Ca
2+ions stabilize the cell membranes, thus providing the physiological background. - Regarding bitter rot infestation in stored apples it can be said that leaf fertilization using formulated calcium formate (share of calcium formate in the product amounting to at least 70 %) can achieve results which are similarly positive to when using fungicides - and is also accompanied by a positive side effect, i.e. no waiting periods need to be observed after using a calcium leaf fertilizer, making fertilization possible right up to the point of harvest.
- Administering the standard calcium chloride flake variant on its own did not show any such desirable results.
The complete test report can be found in the Monatsschrift - Magazin für den Gartenbau-Profi (german magazine for the professional gardening; Edition 08/08)
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