Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4
Volume 1
Number 11 November, 1960 Article 16
1-1-1960
Bitter pit : a progress report on the use of calcium nitrate sprays Bitter pit : a progress report on the use of calcium nitrate sprays for its control
for its control
Frank Melville S. E. Hardisty
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Part of the Fruit Science Commons, Horticulture Commons, and the Plant Pathology Commons
Recommended Citation Recommended Citation
Melville, Frank and Hardisty, S. E. (1960) "Bitter pit : a progress report on the use of calcium nitrate sprays for its control," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 1: No. 11, Article 16.
Available at: https://library.dpird.wa.gov.au/journal_agriculture4/vol1/iss11/16
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BITTER PIT
A PROGRESS REPORT ON THE USE OF CALCIUM NITRATE SPRAYS FOR ITS CONTROL
by
F. MELVILLE, B.Sc. (Agric), Adviser (Fruit)
and
S. E. HARDISTY, B.Sc. (Agric), Adviser, Bridgetown
17REEDOM from serious pests a n d diseases such as Black Spot a n d Codling Moth
•*- a n d relative immunity from storage rots h a s greatly simplified apple growing in Western Australia. However, w h a t h a s been gained in this respect is often count- ered by p r e - h a r v e s t a n d post-harvest physiological troubles which are r a t h e r com- mon to apple growing in this S t a t e .
Over t h e years t h e disorder w h i c h h a s remained a problem a n d in some years caused widespread losses is Bitter Pit. T h e incidence of pit varies considerably from year to year, from o r c h a r d to o r c h a r d a n d from tree to tree b u t almost invariably it will show up in some degree on Cleopatras and in G r a n n y Smiths a n d Golden Delicious in light crops a n d on young trees.
Fruit of these varieties was particularly prone to pit during t h e p a s t season which was probably comparable with some of t h e worst years experienced in t h e p a s t .
Visible losses commence at harvest with rejections for tree pit i n t h e orchard, a n d continue on t h e sorting table, but probably t h e most serious economic loss is w h e n after handling, packing and cool storage charges h a v e been incurred, t h e fruit is rejected for export. R e t u r n s on t h e local market u n d e r such conditions often fail to cover t h e costs involved. Where susceptible fruit does get awav it creates an unfavourable impression overseas.
Although pit rejections for Cleos were high during the 1960 export season it is well to n o t e t h a t t h e allowable tolerance for pit was no different from previous years. Increased rejections of fruit destined for Scandanavia rpsulted from the compulsory storage of Cleos for one week before inspection, but by t h i s m e a n s fruit which could only have brought bad outturn reports was held back.
P I T LIABILITY
Growing conditions in Western Australia accentuate the pit problem. The summer is normally hot a n d dry with m a n y sunny days and hot drying winds which combine to produce p e r m a n e n t drought or t e m - porary physiological drought within the trees. T h a t is a situation develops in which t h e leaves are transpiring water a t a greater rate t h a n t h e roots can absorb it a n d a water deficit is developed within t h e tree.
The majority of Cleos are growing w i t h - out irrigation a n d this further accentuates t h e drought effects.
Pit develops as a result of localised water deficits in the m a t u r i n g fruit resulting in collapse of certain tissue which subse- quently discolours and forms the brown depressed areas we know as pit. Apart from surface pits t h e disorder often ex- tends in the form of small localised areas of brown tissue scattered t h r o u g h t h e flesh.
The water deficit m a y occur while the fruit is still on t h e tree as t h e result of excessive moisture loss from t h e foliage producing the tree pit seen a t harvest.
Some of the necrotic areas m a y n o t be readily visible a t this time but develop in t h e early storage period. Water shortage in certain tissue m a y also occur during ripening due to uneven conversion of s t a r c h to sugar. I n varieties which are pit liable the loss of s t a r c h from t h e tissue 1017
occurs very unevenly as t h e fruit m a t u r e s . Water is required for t h e process of c h a n g - ing s t a r c h t o sugar a n d a s t h e sugary tissue h a s a g r e a t e r a t t r a c t i o n for water, areas of a c u t e w a t e r s h o r t a g e will develop in t h e h i g h s t a r c h a r e a s . This condition results in t h e formation of storage pit, a series of d a r k brown depressed spots located t o w a r d s t h e calyx end of t h e fririt.
Low h u m i d i t y in cool store will accen- t u a t e pit a n d u n d e r Western Australian conditions low t e m p e r a t u r e s a p p e a r to i n - crease t h e disorder. By slowing down t h e r a t e of ripening, cool storage will increase pit a p p a r e n t l y by prolonging t h e period during w h i c h conditions for pit develop- m e n t a r e p r e s e n t .
Conditions i n t h e o r c h a r d which accen- t u a t e pit a r e periods of serious competition between leaves a n d fruit for moisture.
Anything which induces excessive growth such a s p r u n i n g , heavy n i t r o g e n usage, young trees or ideal s u m m e r growing con- ditions such as occurred last season a n d particularly if associated w i t h light crops, will r e n d e r t h e fruit pit liable. With trees c a r r y i n g good crops a d e q u a t e irrigation
appeared to greatly reduce pit in t h e p a s t season.
Storage pit is most likely to occur in fruit w i t h excessive s t a r c h , t h a t is fruit picked i m m a t u r e or w h e r e for some reason t h e conversion of s t a r c h to sugar is slow.
This is t h e case w i t h light crop fruit a n d m a y also h a v e been a factor in t h e prevalence of pit last season.
T h e only m e a n s available in t h e p a s t for r e d u c t i n g pit h a v e been t o limit exces- sive t r e e vigour, pick a t t h e correct stage of m a t u r i t y a n d only store fruit from good crops off m a t u r e trees. I r r i g a t i o n appears to h a v e a beneficial effect in reducing pit a n d t h i n n i n g out fruit clusters by h a n d or by t h e use of chemical t h i n n i n g sprays h a s proved worthwhile.
CALCIUM DEFICIENCY
Calcium is known t o be a n i m p o r t a n t element in cell wall construction a n d is necessary for n o r m a l cell functions.
Localised calcium deficiency in t h e cells of t h e fruit is t h o u g h t to be related to t h e cell collapse responsible for t h e develop- m e n t of pit. I t h a s been suggested t h a t moisture stress actually produces a local- ised calcium deficiency in t h e subsequently disease cell a r e a s .
The effect of calcium n i t r a t e foliage sprays in reducing blossom end rot in tomatoes, a somewhat comparable d i s - order, resulting from physiological d r o u g h t conditions in t h e t o m a t o p l a n t , a t t r a c t e d a t t e n t i o n to t h e use of t h i s m a t e r i a l for t h e control of bitter pit in apples. Field trials were therefore conducted w i t h Cleo- p a t r a s during t h e 1959-60 season i n c o r - porating suggestions m a d e by Dr. D. M a r t i n of T a s m a n i a who h a s h a d considerable success with these sprays.
CALCIUM NITRATE SPRAY TRIALS The south-west was selected as a s u i t - able area for t h i s work a n d blocks of Cleos were chosen on t h e properties of W. Delia Polina & Son, Bridgetown, a n d M. C. Fry
& Sons, Donnybrook.
Five trees were included in each t r e a t - m e n t a n d randomised.
T r e a t m e n t s were as follows:—
(1) Borax a t 1 lb. p e r 100 gallons of water applied a t full blossom.
(2) Calcium n i t r a t e a t 16 lbs. per 100 gallons of w a t e r applied at—
(a) Bridgetown on 15th Novem- ber, 1st J a n u a r y , 11th J a n u - ary.
(b) Donnybrook on 15th Novem- ber, 1st December, 1st J a n u - ary.
(c) Bridgetown on 1st J a n u a r y , 11th J a n u a r y , 25th J a n u a r y
—Triton a t t h e r a t e of 4 fl.
ozs. p e r 100 gallons of w a t e r was added.
(3) Borax 1 lb., Calcium n i t r a t e 16 lb.
per 100 gallons of w a t e r applied a s in 2 (a) a n d 2 (b).
(4) Control—unsprayed.
Boron was included as t h i s element is known to be associated w i t h t h e develop- ment of corkiness a n allied condition.
Trees a t Delia Polina's were old trees, poor to fair vigour a n d carrying a heavy crop. Trees a t M. C. Fry & Sons were large and vigorous a n d c a r r y i n g a very light crop. I n both i n s t a n c e s p a s t experience had shown pit to be severe in most years.
At Fry's i t h a s n o t been u n u s u a l for a high proportion of t h e fruit to be lost during t h e harvest, h a n d l i n g a n d early storage period.
1018
SPRAYING
A satisfactory solution of the calcium nitrate was only obtained by dissolving the salt in very hot water and then adding to the spray vat. At Bridgetown two-thirds to one gallon of spray was applied per tree by means of a power spray. At Donny- brook a knapsack was used.
Some leaf scorching occurred on weak foliage sprayed with calcium nitrate in late January. Fruit injury consisting of a greenish grey tear stain mark was also noted on fruit from one tree. It is felt that this could have resulted from inade- quate mixing in the spray vat.
HARVESTING AND STORAGE A sample of 200 fruits was harvested from each tree at Bridgetown on February 24th and at Donnybrook on February 29th.
The apples were sorted and a record made of tree pit. The remaining sound fruit was stored in experimental chambers at Robbs Jetty Cool Stores at 32° F. until May by which time storage pit was well developed.
Assessment of pit was made after a period of one week out of cool store.
RESULTS
Unfortunately as the result of an abnormally mild winter the trial trees at Donnybrook were very late blossoming, fruit set was erratic and very light and the resultant fruit was very off type. Pit was very severe and although some im- provement resulted from the sprays no commercial control was obtained. It should be noted that the last spray was January 1st. Sprays later in January may have been more effective.
The trial at Bridgetown was however, very successful. Borax gave no improve- ment but calcium nitrate sprays reduced total pit that is tree pit plus storage pit to almost one fifth. Fruit from unsprayed trees developed 24 per cent, pit as against 5 per cent, for the calcium nitrate treat- ment. The effect was, however, more spectacular than these figures indicate because of the much greater severity of pitting in individual apples in the u n - sprayed control. Prior to harvest sprayed trees could easily be picked out in the orchard because of the very pronounced reduction in tree pit.
Details of the variation in pit according to treatment are shown in the following table. Slight pit would include fruit show- ing some pitting but insufficient to prevent its sale. Severe pit would seriously reduce the commercial value of the fruit. It will be noted that practically no severe pitting occurred where calcium nitrate sprays were used.
CALCIUM NITRATE 8PB.AY TRIALS AT BRIDGETOWN
Treatment
1. Borax Spray
2. t alcium Nitrate Sprays, l o t h N o v . , 1st Jan., 11th Jan.
3. Calcium Nitrate sprays, 1st Jan., 11th J a n . , 25th Jan.
4. r n s n n t y e d
Tree
1 2 S 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
Tree Pit
at Har-
vest
8 12 3 23 24 2 1 2 5 0 0 6 2 1 3 6 10 5 0 23
Pit after Cool Storage
Slight 18 21 38 12 36 4 6 6 17
Severe 14 22 7 21 2 2 0 0 1 0
14 9 6 8 2 21 26 20 26 42
1 0 0 0 0 17 9 2 6 20
Total Fruit Pitted
Aver- age per 200 cent, f i o l t Pit sample]
40 55 48 66 81 6 7 9 22 6 16 15 8 9 5 43 45 2 7 41 8 5
28
5
5 - 2
2 4 1
While no firm recommendation can be made at this stage it is felt that calcium nitrate sprays are worth trying on an experimental basis by anyone who has trouble with Bitter Pit in Cleos.
From all information available it would appear that at least three sprays are re- quired and the best time would be during December and January. A suggested pro- gramme would be mid December, early and mid-late January. In view of the slight injury to leaves and fruit on odd trees it is not advisable to exceed 10 lb. of calcium nitrate per 100 gallons of water.
Calcium nitrate was not available in com- mercial form last season but it is antici- pated that supplies will be obtainable later this year.
This is the first promising lead for the control of pit and further work is planned for the coming season.
1019
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