FACTORS RELATING TO THE CONTROL OF SOFT-SCALD IN JONATHAN APPLES.

New Zealand Journal of Agriculture, Volume 53, Issue 3, 21 September 1936, Page 161

FACTORS RELATING TO THE CONTROL OF SOFT-SCALD IN JONATHAN APPLES.

R. Sutherland,

Cool Storage Officer, Department of Agriculture,

Wellington.

During the past four years cold-storage experiments have been carried out in co-operation with the Department of Scientific and Industrial Research and the New Zealand Fruit-export Control Board with a view to determining the causal factors over a wide range of circumstances and conditions contributing to wastage in Jonathan apples.

Overseas surveys (i), (2) have produced evidence that although the various types of wastage may be very slight when the apples are discharged at the docks, there may be a rapid development during the marketing period. The longer the marketing period, the larger and more mature the fruit at the time of discharge, the greater the amount of wastage. The Jonathans concerned in the experiments were forwarded to cool storage in the Dominion through the usual channels as obtaining in export, and the examinations were conducted at such times as to

reproduce conditions comparable with a shipment arriving at its overseas destination and marketing of the apples subsequent to discharge. Diseases causing Wastage in Jonathans. Soft-scald. Although soft-scald varies in its incidence from season to season, and in some seasons it is entirely absent, it is often the cause of more or less serious loss. The disease, which usually makes its appearance comparatively early in the storage life of Jonathan apples, or shortly after their removal to atmospheric temperatures, is recognized by a browning of skin and underlying flesh, and, while in the early stages only a small area or a mere spot on the apples may be affected with scald, it spreads in an irregular formation and eventually covers the whole surface to varying depths into the flesh of the fruit. Fungal Rotting and Internal Breakdown. — In our experiments with Jonathans very rarely have these two types of wastage been very serious when the samples were removed from cold storage, but they have developed in varying amounts as the fruit ripened. The results have indicated that soft-scald is a very serious storage disease in Jonathans, and, while it varies in its incidence from season to season, susceptibility to the disease may likewise vary in fruit from different localities and orchards in the same locality. .

The variation in wastage in Jonathans from season to season and from different localities is well marked. There was clearly an association between soft-scald and fungal rotting. Plagge, Maney, and Pickett(3) believe that the disease is identical with soggy breakdown, the chief differences between soggy breakdown and soft-scald being in appearance only. Although our results are in agreement that both diseases are due to low storage temperatures, and influenced by time of picking and undue delay before storing, the suggestion that the development of the disease stops when the fruit is removed from storage is contrary to our findings, for while, as with internal breakdown, soft-scald may have made very little or no development when the apples are removed from storage, it may increase very rapidly on exposure to atmospheric temperatures.

This result indicates that although soft-scald varies in its incidence —during some seasons it is entirely absent (Table i)(4) —it constitutes the greatest amount of wastage in Jonathan apples ; and therefore, as the figures show, the disease may be reduced to a minimum by storage or transport at a relatively high temperature. To show (Table 3) a further result of the influence of relatively high temperatures in the control of soft-scald in Jonathan apples in 1933 — regarded as a susceptible season —comparable samples of counts 198, 180, and 163 were obtained from three localities and stored under three sets of temperature conditions —viz., 34°F., . 37 0 F., and at temperatures as obtaining in a precooler where large quantities of fruit were being loaded in and out daily, the temperatures varying from 42 0 F. to 32 0 F., the higher generally prevailing.

Although the effect of relatively high temperatures (5) has been pronounced in scald control, susceptibility to the disease may be increased by prestorage factors. . Delayed Storage. Delaying storage for ten days after gathering increased the disease and reduced the general storage life of Jonathans. In this experiment the samples were gathered from the same trees at two stages of maturity. The second picking was made ten days later than the first, and, while half of the samples was placed in cold storage immediately, the other half was held in a packing-shed for ten days before being cold-stored under the same conditions as the first lot. The experiment was carried on for four seasons, and, although each year the samples varied in susceptibility to soft-scald, the disease was always greater in its incidence in the delayed-storage samples from both the first and second stage of maturity.

The influence of placing Jonathans in cold storage with as little delay as possible was significant in reducing the amount of soft-scald, and, while there was very little difference in the amount of scald in the samples picked at an interval of ten days and stored immediately, the evidence indicated in both samples that delayed storage renders the apples less resistant to the disease. In addition to scald these samples were over-ripe, showing a tendency to breakdown and fungal rotting, and decidedly past their best marketing-condition. Oiled Wrappers. The effect of oiled wrappers in the control of soft-scald gave discouraging results. In the experiments, wrapping Jonathans in oiled wrappers as against comparable samples without wraps or in standard wraps did not - give any appreciable control of scald. The writer is of the opinion expressed (6) that the term “ soft-scald ” is misleading in that it is not related to the trouble generally known as superficial scald, but rather to a form of external breakdown. Packing-wraps. Following the introduction of the one-piece-all-round corrugated wrapper for lining apple-cases and the unexpected development of soft-scald in Jonathans packed in the all-round wrapper, an investigation was undertaken to test the suggestion that the disease may be due to the same cause as superficial scald (7) —the accumulation of volatile substance brought about by the wraps restricting ventilation. The experiments were arranged with Jonathans from a number of localities. These were packed in cases lined with the one-piece corrugated wraps, and the results subjected to comparison with comparable samples packed with strips of the corrugated wraps at the top and bottom only, and also no case lining. As with oiled apple-wraps, the corrugated wrap treatments under review gave negative results in so far as the incidence and control of soft-scald is concerned.

As this result is the average percentage of soft-scald for six cases ■of Jonathans in each experiment, the i per cent, less scald in the no - wraps treatment is not significant, and does not warrant any suggestion that the one-piece wrap is a factor in the development of the disease. Fertilizer Treatment. Over a period of four years an examination of Jonathans from plots which received a combination of fertilizer treatments* in addition to the commercial application gave inconsistent, and discouraging results with regard to overcoming susceptibility to soft-scald. ■ The influence of fertilizer treatments was most pronounced in cropproduction, the trees yielding from five to. eight cases of large-sized fruit 2| in. to, 3 in. each year, and there was some evidence that the additional manurial application resulted in the Jonathans being of a rather soft nature. Rainfall. The results secured indicated that heavy rain towards the end of the growing-season rendered the apples more susceptible to soft-scald. During the seasons 1930 and 1933, when the rainfall for the two months preceding picking amounted to 11 in. and 9-5 in. respectively, the disease was more serious than in other seasons when the rainfall was not so great. The influence of heavy as against light soils was not significant with regard to the development of the disease, and contrary results were obtained ; some seasons scald occurred in the samples from heavy soils, and the following season, while the samples from the heavy soils were almost free from the disease, those grown on light soils were affected. Summary. (A) Jonathan apples vary in susceptibility to soft-scald from different localities and from season to season. (B) Storage of Jonathans at low temperatures increases susceptibility to soft-scald. (C) Delayed storage or cooling of mid-season and late-season more mature Jonathans increases susceptibility. (D) Wrapping the fruit in oiled as against standard and without wraps did not appreciably control the development of soft-scald. (E) Fertilizer treatments of the soil gave inconsistent and discouraging results in overcoming susceptibility to the disease. (F) An increased amount of rainfall towards the end of the growing-season renders the apples more susceptible to soft-scald. Control Measures. Jonathans picked when they are mature (not immature or overmature) are the least liable to soft scald. Immediate cooling after gathering is recommended as a . control measure. Cold storage at relatively high temperatures (36° F. to 38° F.) provides a maximum of control.

References. (1) Report of Investigation by the Economic Section of the Empire Marketing Board in the Deterioration in Transit of Australian and New Zealand Fruit, No. 46, 1931. (2) The Prevention of Wastage in New Zealand Apples. Food Investigation Special Report No. 39. (3) Plagge, Maney, and Pickett : Functional Diseases of the Apple in Storage. Bulletin No. 329, 1925. (4) Tindale, G. B. : Cool Storage Investigation, Jour, of Agric., Victoria, February, 1932. (5) Harrison, J. E. : The Jonathan Apple in Cold Storage, Jour, of Agric., Victoria, January, 1926. (6) Plagge, Maney, and Pickett : Functional Diseases of the Apples in Storage. Bulletin No. 329. (7) Plagge, Maney, and Pickett. Bulletin No. 329.

* Commercial application applied to all the experimental trees : Basic superphosphate, 7 1 lb. ; sulphate ammonia, jib.; sulphate potash, ijlb. ; bonedust, i lb. Plot additions : (i) Sulphate ammonia, 2 lb. ; sulphate potash, 2 lb. (2) Sulphate ammonia, 2 lb. ; superphosphate, 2 lb. (3) Sulphate potash, 4 lb. (4) Superphosphate, 3 lb. (5) Sulphate ammonia, 4 lb.

Locality. Soft-scald. Internal Breakdown. Fungal Rots. Season 1933Season 1934Season 1935. Season 1933Season 1934Season 1935Season 1933. Season 1934- , Season 1935. % • % ■ 0/ zo /o o/- 0/ /o /o 0/ 0/ /o /o % 7o • • 0/ % 0/ /o /o ■ °/ % /o % % 5 6 Nil I 5 3 6 Nil 8 I . Nil I 2 Nil 5 7 • • '• • 8 12 4 Nil 6 3 8 8 i I Nil Nil Nil I 9 Nil » 10 IO 2 2 2’ 2 4 ,, 4

Table 1. —Showing Seasonable and Locality Variations in the Occurrence of Soft-scald, Internal Breakdown, and Fungal Rotting Fourteen Days subsequent to Removal from Cold Storage at 37° F.

Soft-scald. Internal Breakdown. Fungal Rots. Temperature 34° F. Temperature 37° F. Temperature 34° F. Temperature 37° F. Temperature 34° F. Temperature 37° F. % ■' « /o 0/ /o /o 0/ /o /o 0/ /o /o 0/ /o /o % % 8 3 2-5 2-5 i-5 i-5

Table 2.—Showing the Influence of Temperatures of Storage on the Development of Wastage in Jonathan Apples Fourteen Days subsequent to Removal from Storage. (The figures give the average wastage for three seasons in apples which were sound on removal from storage at 34 º F. and 37 º F. respectively.)

Soft-scald. 34° F. 37° F. 42-32 0 F. 0/ /o 0/ /o IO 0/ /o 2-4 Nil

Table 3.

First Picking. Second Picking. Immediate Storage. Delayed. Storage. Immediate Storage. Delayed Storage. 0/ 0/ 0/ 0/ /o /o /o /o 2 5 3 8

Table 4.-Showing the Effect of Immediate and Delayed Cold Storage in the Control of Soft-scald.

Experiment No. Storage Temperature. All-round Wraps. Soft-scald. Top and Bottom Pads. Soft-scald. No Wraps. Soft-scald. °F. % 0/ /o % I 37° 5 5 4 2 37° i i No test.

Table 5.— Showing the Influence of Wrap Treatments on the Development of Softscald.