The control of bitter pit in apples

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Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4

Volume 5

Number 12 December, 1964 Article 2

1-1-1964

The control of bitter pit in apples The control of bitter pit in apples

Frank Melville S. E. Hardisty N. S. Shorter

Follow this and additional works at: https://library.dpird.wa.gov.au/journal_agriculture4

Part of the Horticulture Commons, Other Physiology Commons, and the Plant Pathology Commons

Recommended Citation Recommended Citation

Melville, Frank; Hardisty, S. E.; and Shorter, N. S. (1964) "The control of bitter pit in apples," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 5: No. 12, Article 2.

Available at: https://library.dpird.wa.gov.au/journal_agriculture4/vol5/iss12/2

This article is brought to you for free and open access by the Agriculture at Digital Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 4 by an authorized administrator of Digital Library. For more information, please contact [email protected].

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The control of bitter pit in apples The control of bitter pit in apples

Cover Page Footnote Cover Page Footnote

The authors wish to acknowledge the invaluable assistance given by many growers, the W.A. Fruit

Growers Association, the W.A. Meat Export Works, Robbs Jetty, Westralian Farmers Ltd. (Bridgetown) and various Horticultural Officers who collectively made this work possible.

This article is available in Journal of the Department of Agriculture, Western Australia, Series 4:

https://library.dpird.wa.gov.au/journal_agriculture4/vol5/iss12/2

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By F. M E L V I L L E , Senior A d v i s o r (Fruit), S. E. H A R D I S T Y and N . S. SHORTER, H o r t i c u l t u r a l Advisers

Bitter p i t is a physiological disorder of apples w h i c h causes considerable wastage of otherwise sound f r u i t . I t is a p r o b l e m o f world-wide occurrence and in Western Australia g r o w i n g conditions appear particularly favourable f o r its development.

I n recent years a practical means of control by c a l c i u m sprays has been developed.

BITTER PIT has been a major problem w i t h the Cleopatra variety in W e s t e r n Australia f o r many years and Golden Delicious is also susceptible.

Recently, b i t t e r p i t has become prevalent in Granny Smiths. T h i s is a serious development because more than a m i l l i o n bushels of Granny Smiths have been exported in a single season and the quantity w i l l increase.

Factors which may have been respon- sible for the increase in pit in Granny Smiths include:—

• An increasing quantity of fruit coming from young, vigorous trees.

• Improved vigour and better fruit growth as the result of irrigation and changing management prac- tices.

• The overseas demand for larger, greener fruit and market incen- tives to harvest earlier for export.

Fortunately means are now available to the orchardist for coping with the problem. Scientific investigations have shown that pit is related to a deficiency of calcium in the fruit and that commercial control of the disorder can be obtained by the use of calcium sprays during the growing period.

Forms o f Pit

The main forms of the bitter pit com- plex seen in this State are termed "tree pit" and "storage pit." Tree pit is the

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form which develops on apples on the tree before harvest and occurs as small irregular sunken areas, olive green to brown in colour, with brown areas deeper in the flesh. Storage pit develops only during cold storage and appears as a series of regular brown spots on the skin.

These do not penetrate below the surface tissue.

Although the two forms differ con- siderably in appearance they are both symptoms of the one disorder which

C A L C I U M SPRAYS A M U S T

In view of the reaction in recent years by overseas countries it is i m - portant t h a t c a l c i u m sprays should be applied annually as a w o r t h w h i l e i n - surance against p i t troubles.

Calcium sprays are inexpensive and are easily applied. Growers of susceptible varieties cannot a f f o r d t o take the risk o f p i t in t h e i r export f r u i t .

Journal of Agriculture Vol 5 No 12 1964

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results from internal water stress in the fruit on the tree. Both forms of pit are controlled by calcium sprays.

Varietal Susceptibility

Pit is confined to the early and mid- season varieties. Cleopatra and Golden Delicious are susceptible to tree and storage pit and they are probably the varieties most prone to pit. Granny Smiths are rarely affected with tree pit but may be subject to considerable storage pit. Jonathan and Delicious will develop both forms although they are usually only mildly affected.

Late varieties such as Yates and Doughertys do not appear to be susceptible.

LOCAL INVESTIGATIONS

Since the earlier work reported in 1960, investigations into the control of bitter pit of the Cleopatra and Granny Smith varieties have been carried out on fruit from all the major apple growing areas of Western Australia and as a result of this work the disorder is now better under- stood and recommendations can be made for its control. This article gives the main results of these investigations and suggests ways of dealing with the problem.

Pit is associated with a number of in- terrelated factors including seasonal conditions, tree vigour, harvest maturity, fruit size and crop size. Although the various factors are considered separately it should be remembered that pit liability depends on the combination of them all.

The Effect of Harvest Maturity

Tree pit of such varieties as Cleopatra and Golden Delicious develops before

harvest and is therefore not affected by picking maturity.

Storage pit on the other hand is greatly increased by early picking, but although much of the pit could be avoided if harvesting was sufficiently delayed, this method of control is generally impractic- able because of marketing requirements.

A study of storage pit development in the Granny Smith variety was made by harvesting the fruit at different periods and cold storing until maximum pit was produced. This showed that although pit susceptibility is high at the earliest period of harvest it does increase as harvesting proceeds to reach a peak before the optimum picking period and then falls off again. In 1964, a year of early maturity, the peak was reached for Granny Smiths just before mid March. In 1963, a late year, it was about the end of March.

Results of the 1964 trials are shown in Table 1.

The trend is the same in trees sprayed with calcium nitrate as in unsprayed trees but the amount of pit is greatly reduced by calcium sprays. The effect of harvest maturity on subsequent pit development is illustrated in Fig. 1.

90 •

g3°r

u

5z°t

Q- 10 ' 28 4

•t> Mar

12 16 20 2 * 28 1 5 DATE OF HARVEST *Pr

13

Fig. 1.—The relationship of pit to harvest maturity. (Results with unsprayed Granny Smiths given in Table I.)

Table 1 . — T h e development of storage pit in Granny Smiths—Donnybrook, 1 9 6 4

Treatment

Unsprayed

2 early calcium sprays ....

3 early calcium sprays 4 calcium sprays

3rd March

%

36 6 3 0

13fh March

%

52 19 14 4

Harvest Date 23rd March

%

23 4 0 0

2nd April

%

15 2 0 0

12th April

%

17 3 0 0

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Table 2.—Rainfall and temperature records for Donnybrook.

Rainfall (points)—

1962-63 ...

1963-64 ....

Average Maximum Tempe rature—

1962-63 ...

1963-64 ....

Oct.

410 239

73.1 °F 67°F

Nov.

282 82

78.8°F 75.5°F

Dec.

84 1

Jan.

101 1

Feb.

26 17

Total Rainfall

11.03 (in.) 3.40 (in.)

Seasonal Susceptibility

It is well known that the incidence of pit varies between seasons. Seasonal conditions which affect tree growth, fruit size and maturity have a definite bearing on pit susceptibility.

In years of insufficient winter chilling the main apple blossoming is delayed so that if fruit is harvested according to calendar dates irrespective of date of blossoming or seasonal conditions then it will be picked in some seasons at a less mature stage. Severe pit occurred in the 1960 and 1963 harvests which followed the delayed foliation years of 1959 and 1962. Comparatively higher rainfall, especially in the early part of the growing season and lower temperatures in this period were also features of these two pit- susceptible seasons.

A comparison of climatic data in a bad pit year (1963) and a light pit year (1964) is made in Table 2.

More rain and lower late spring temperatures were a feature of the 1962-63 pit year. These growing conditions could be expected to produce more vigorous shoot growth and to increase fruit size,

both of which increase pit. On the other hand drier spring and early summer conditions usually mean higher maximum temperatures which promote fruit growth more than shoot growth, and also advance fruit maturity. Seasonal variations are illustrated in Fig. 2.

Foliage growth, which can also be en- couraged by heavy pruning and irrigation, is an important factor and, in fact, pit liability has been related to the ratio of leaves to fruit. As foliage in relation to fruit increases so liability to pit increases.

6 0 • - 5 0 • 2 4 0 - LI U a.

2 0 - 10

16 2 0 24 2 8 4 8 12 16 2 0 24 2 8 DATE O F HARVEST

Fig. 2.—Seasonal variation in pit. (a) Donnybrook Granny Smiths 1 9 6 3 — a late season w i t h summer rains; (b) Granny Smiths from the same property in 1 9 6 4 — a n early season with

dry summer

Cleopatra apples affected with tree pit

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Fruit Size

Susceptibility to pit also increases with fruit size. For instance pit is of little consequence on small sized Granny Smith apples as compared with larger fruit.

Tree pit on Cleopatras is nearly always confined to the larger fruit. Storage pit in Cleopatras will, however, develop on the smaller sizes but to a lesser degree than on larger fruit.

CONTROL W I T H CALCIUM SPRAYS The most extensive work on pit has been carried out with calcium sprays. Calcium nitrate and calcium chloride applications have invariably reduced pit, but other calcium salts have not been very success- ful.

Calcium nitrate has performed better than calcium chloride in most instances and has not proved as toxic to foliage Relatively inexpensive supplies of calcium nitrate are available and as Western Aus- tralian growers are primarily concerned with pit control in green varieties investigations and subsequent recommendations have been centred on the nitrate form.

Elsewhere the chloride is used on red varieties as the nitrate tends to delay colouring.

Spray Concentration

It could be expected that improved pit control would follow increasing concentration of the mixture. However, trials using 5, 10 and 15 lb. of calcium nitrate

per 100 gallons failed to produce any great difference in pit control but the highest concentration resulted in considerable leaf burn and therefore was unsatisfactory.

A suitable concentration is 10 lb. per 100 gallons but where previous experience has indicated liability to leaf injury this could be dropped to 8 lb.

It would appear that the number of sprays applied is more important than the spray concentration.

Frequency and Spacing of Sprays

A trial conducted in 1963-64 showed quite clearly that as the sprays increase in number so the pit is reduced. This is illustrated in Fig. 3, using details given in Table 1.

Under average conditions three sprays would be considered satisfactory but where pit is expected to be prominent either due to seasonal conditions or to the

60 50

[40>

§30

10-

CONTROL 2 3 4 5 (not sprayed)

NUMBER OF SPRAYS

Fig. 3.—The effect of number of sprays on pit control.

Granny Smiths, harvested March 13, 1964. There was virtu- ally no pit when five sprays were given

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Calcium spraying is inexpensive and effective against pit

susceptibility of the orchard then four or more sprays would be worthwhile. Up to six sprays have proved beneficial under experimental conditions on very susceptible trees.

Where pit is likely to be a problem, less than three sprays gives inadequate control.

Many combinations of spacing spray applications during the growing season were investigated in 1961-62. Using three sprays, more efficient control was obtained by spreading them evenly over the period from early December to early February than by applying them either as three early or three late sprays. One or two sprays, although they reduced pit, were not very satisfactory.

The effectiveness of spacing the calcium spray applications can be seen in Table 4, in which the control of pit with

variously spaced sprays of 10 lb. calcium nitrate per 100 gallons of water is shown.

It will be seen that by suitable timing of the three sprays, pit was reduced from 10.6 per cent, where sprays were applied from mid January to early February, to 6.2 per cent, when applied in December and to 3.7 per cent, when spread over the full December-early February period. Un- sorayed fruit developed 31 per cent. pit.

Three calcium nitrate sprays will reduce pit to within commercial requirements but complete control is not always possible.

Spray Burn

A slight marginal scorch on the foliage can, in some cases, follow the application of calcium nitrate sprays but it is not considered to be of any consequence in

Table 4.—Percentage of pit developing in cold store on Cleopatras from a non-irrigated Bridgetown orchard, 1 9 6 1 - 6 2

C a l c i u m nitrate spray schedule

December 15 December 21 January 3 January 10 January 2 4 February 5

Percentage of pit ....

SA

SA SA

3 . 7

SA SA SA

6 . 2

SA SA SA

1 0 . 6

SA SA

, 4 . 7

SA

19.5

Unsprayed

3 1 SA = spray applied

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relation to the benefits obtained from such treatments.

Spray burn on the fruit which takes the form of small brown spots on the skin has also occurred in a few instances both in trial work and in growers' spray pro- grammes, but in five years of trials this damage has been insignificant. However the damage has assumed serious proportions where growers have mixed calcium nitrate with either oil sprays, insecticide emulsions or, in one instance, water with 130 g.p.g. of salinity.

Calcium nitrate is not compatible with spraying oils or pesticides in emulsion form and is not recommended for mixing with any other sprays.

Pruning

The association of increased pit follow- ing severe pruning has long been known to growers of Cleopatra apples. For some decades now, very little pruning has been carried out on this variety with the result that much of the fruiting wood is crowded and skin blemish has been correspond- ingly high. With the application of calcium sprays, thinning out of the fruiting wood is now possible without increasing the pit hazard.

Chemical Thinning

There is no evidence to date to indicate that chemical thinning sprays will increase liability to pit.

Pit Development During Storage

A study of pit formation during storage showed that in susceptible apples storage pit started to form shortly after the fruit went into store and continued at a fairly constant rate. In Cleopatras a maximum was reached after about two months. A delay of one week before cold storage had no material effect on the amount of pit finally produced.

The important point is that if apples develop some pit during the first few weeks of cold storage then the disorder can be expected to reach fairly serious proportions if the fruit is held in cold store for any length of time.

The rate of pit development in cold store measured by regular sampling of Cleopatras from unsprayed trees is shown in Table 4.

RECOMMENDATIONS

(1) The varieties to be sprayed with calcium nitrate for pit control in Western Australia are Granny Smith, Cleopatra, and Golden Delicious.

(2) Use 10 lb. of calcium nitrate per 100 gallons of water with the addition of 2 fl. oz. of wetting agent.

(3) Do not mix with other spray material.

(4) The minimum requirement for calcium nitrate applications is three sprays, applied in early De- cember, early January and early February. Under conditions where severe pit is likely more sprays should be used.

(5) Thoroughly wet the foliage and fruit. Avoid spraying too late in the day for the spray to dry before nightfall.

(6) Notwithstanding the use of pro- tective sprays, early picking should be avoided and the main harvest delayed if possible until the period of greatest pit hazard is over.

(7) Pit susceptibility is directly affected by fruit size; large fruit is more prone to pit. Fruit from young trees should be disposed of quickly on the local market and not exported or held for long storage.

ACKNOWLEDGMENTS

The authors wish to acknowledge the invaluable assistance given by many growers, the W.A. Fruit Growers Associa- tion, the W.A. Meat Export Works, Robbs Jetty, Westralian Farmers Ltd. (Bridge- town) and various Horticultural Officers who collectively made this work possible.

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