Brown Spotting Of Apricots

New Zealand Journal of Agriculture, Volume 59, Issue 3, 15 September 1939, Page 229

Brown Spotting Of Apricots

Experiments Reveal Boron Deficiency

H. O. ASKEW,

Cawthron Institute, Nelson, and

W. R. LLOYD WILLIAMS,

Instructor in Horticulture, Alexandra.

IN CERTAIN orchards at Alexandra, Central Otago, boron deficiency of apples has been definitely established as a result of the co-operative investigations of the Department of Agriculture and the Cawthron Institute.! The success obtained with borax in the »J»II— Illi—Illi——1111——Illi——Illi——Illi—Illi—Illi—Illi——Illi— ♦F

I . j I A browning of the flesh of | j apricots, more particularly in | j the stem end of the fruit, has 1 j been shown to be due to boron i = deficiency. This ailment may be j I controlled by the use of hy- j 1 drated borax, either as a soil j I topdressing or as a spray. The ? j marked increase in boron con- = j tent of the fruit following borax i j treatment is correlated posi- I | tively with freedom from | I browning of the flesh. | IHl— Illi— Illi—llli—llli—HU—-Illi———Uli—UM— tje

control of internal cork suggested the possibility that defects in certain stone fruits grown in the same locality might likewise be due to boron deficiency.

Apricots on certain light-textured schist soils on the banks of the Clutha River develop a brown spotting of the flesh which superficially resembles lesions caused by boron deficiency in apples. Interest attaches to this ailment as McLarty and Wilcox have stated that a disease “drought spot” of apricots in British Columbia is amenable to boron therapy.* The authors are however unaware of any published description of the symptoms of the Canadian disease.

Arrangements were made through the willing co-operation of Mr. G. S. Harvey for. a field trial on a part of his orchard. The field work was done by officers of the Department of Agriculture, and. the chemical analyses were carried out at the Cawthron Institute as part of the boron investigations which have been proceeding there during the past few years.

Symptoms of Disease

Affected fruits show a browning of the flesh, often definite lesions of several millimetres diameter. In mild cases only the stem end is effected, but in more severe cases this browning or spotting may extend almost the whole length of the fruit, being most obvious near the stone. A dry spongy condition of the flesh near the stone is also seen. “Brown spotting” appears to be a suitable name for this ailment. Whether it is identical with

the “drought spot” of McLarty and Wilcox* is not known. Fig. 1 shows affected and healthy fruits, the latter being in the top row. As the photograph shows a constriction in the flesh of the fruit often occurs near the stem end in seriouslyaffected fruits, which are valueless in the market. Field Experiment In the experiment the trees, variety Newcastle (an early variety), were arranged in plots of four trees. Three replications of each treatment were provided, with suitable guard rows between the plots. Two treatments with hydrated borax were used: (1) Spray 0.1 per cent.; applied on October 20 and November 10, 1938. For the twelve trees treated a total of llg gallons and 10| gallons of spray were used on the respective dates. Both days were bright with a light breze.

(2) Soil topdressing; jib per tree,

applied on October 20, 1938. The borax was applied over a circle of radius about sft from the tree trunk and lightly hoed in. (3) Control (untreated) plots were provided. - An inspection of the trees made by Mr. I. L. Nottage of the Department of Agriculture on November 10. showed no damage to foliage from the first spray. - There was no sign of browning in the flesh of the fruit on this date.. Oh December 14 the owner reported that he had noticed brown spots on the flesh of the fruit about a week previously. The fruit was now advancing rapidly to picking maturity on the untreated trees, 1 but was more backward on the treated trees. No affected fruit was found on the treated trees, but much badly-affected fruit was present on the untreated trees. Samples of leaves and fruit for chemical analysis were collected at this stage. Untreated Trees Suffer On December 21 fruit was commencing to drop badly on the untreated trees in the experimental block, and on other untreated trees in the body of the orchard. From the experimental blocks 100 fruits were collected from each unit of four trees except that on some of the untreated trees no fruit was available so that extra fruits were taken from those trees carrying fruit. These samples were used to obtain counts of healthy or affected fruits. In the examination of the fruits three grades were used: —(a) Free from browning, (b) slightly affected, and (c) moderately to badly affected. Table 1 shows the results of these counts.

From the three control plots an average of only 2 per cent, of fruit free from spotting of the flesh was obtained. The remainder of the fruit was slightly to badly affected. On the other hand the fruits from the borax-treated plots were very free from ailment, 94 per cent, and 98 per cent, of clean fruit being obtained on the sprayed and topdressed plots respectively. In both these cases the affected fruit showed only slight blemish.

ing with the stage of maturity, the control fruit being nearly mature with the sprayed fruit a few days Behind. On the topdressed plots, however, the fruit was very markedly retarded, and therefore much smaller. The weight of 100 fruits from the topdressed plots was only 41b 12oz. Maturing of Fruit An interesting observation made by Mr. Harvey during the harvesting was that although, as stated above, the fruit on borax-treated trees was less mature than that on the control trees when picking began, all the fruit on treated trees had matured and were harvested before the (picking could be completed on the control trees. Thus the treated trees matured their fruit very rapidly. Mr. Harvey also considered that the fruit from the topdressed trees when harvested was slightly larger than that from the untreated or borax-sprayed trees. Samples of leaves and fruit from the experimental blocks were analysed for boron content, the results being given in Table 2.

Weights of 100 fruits are also given in Table 1. The fruits from the control and borax-sprayed plots are comparable in weight, being 61b 2oz and 61b Boz respectively for the number of fruits specified. These weights are in keep-

The figures for the control show a very low boron content for both leaves

NOTE. —Slightly affected fruits were those showing browning in the flesh just below the stem but not sufficiently advanced to show- throughout an - appreciable part of the flesh. '

and fruit, correlating well with corresponding data for internal cork of apples.t On the other hand fruit from the two series of borax-treated plots showed 34.5 p.p.m. and 46.5 p.p.m. on the dry basis. These data indicate that the borax applications have been readily taken up by the trees and used in the production of healthy fruit, since, as shown in Table 1, clean fruit was obtained on the two series of borax-treated plots. A very good correlation is shown between boron content and healthiness of the fruit, high boron content being associated with freedom from browning of the flesh. Observations on other varieties in this orchard showed that on December 21, Roxburgh Red and Ouillins were rather badly affected, but not so severely as Newcastle variety. Moorpark, the latest to mature of the varieties present in the orchard, appeared to be free of the complaint. The results of the investigation therefore indicate that in orchards where the particular type of internal browning of the flesh of apricots occurs excellent control of the disease may be obtained either by the use of 0.5 pound of hydrated borax per tree as a topdressing or by the use of a 0.1 per cent, borax spray. The latter treatment would almost certainly require to be an annual one, while the former one application at the rate specified should last for several seasons. It is proposed to continue observations on this point in future seasons. REFERENCES. * McLarty, H. R., and Wilcox, J. C. (1936); Country Life in 8.C., Vol. 20, Dec. P. 7, t Askew, H. 0., and Thomson, R. H. K.; (1937), N.Z., J.Sci. & Tech., 18, 661.

Treatment. Plot. Free from spotting per cent. Slightly affected, per cent. Moderately to badly affected per cent. Weight of 100 fruits. Control A 4 62 34 5 lb. 14 oz. (No borax) B 1 . 37 62 6 lb. 9 oz. C 1 56 43 6 lb. 0 oz. Average 2 52 46 6 lb. 2 oz. 0.1 per cent. D 94 6 .— 6 lb. 4 oz. borax spray E 95 5 — 6 lb. 15 oz. F 93 7 . 6 lb. . 5 oz. Average 94 6 — . 6 lb. 8 oz. 0.5 lb. borax Gr 99 1 .— 4 lb. 12 oz. topdressing . H 100 — • • • —— 4 lb. 8 oz. 4 lb. 8 oz. : I 95 5 • 4 lb. 15 oz. 4 lb. 15 oz. Average 98 . -2 - ■ •— 4 lb. 12 oz.

TABLE 1. Showing Percentages of Healthy and Affected Apricots together with Weights of 100 Fruits.

Treatment. Boron (B) p.p.m. Leaves. | Bruit. Control (no borax) . . 12.5 | 5.7 0.1 per cent, borax spray 32.0 1 34.5 0.5 lb. borax per tree: topdressed . 40.5 1 46.5

TABLE 2. Boron Content, in Parts per Million (p.p.m.) on the Dry Basis of Apricot Leaves and Fruit.