TESTS WITH UNFRUITFUL PLUM-TREES.

New Zealand Journal of Agriculture, Volume XVIII, Issue 3, 20 March 1919, Page 162

TESTS WITH UNFRUITFUL PLUM-TREES.

THE CROSS-POLLINATION FACTOR PROMINENT.

By

GORDON ESAM

Orchard Instructor, Hastings.

On some of the heavier lands in Hawke’s Bay difficulty is experienced in getting greengages and a few other varieties of plums to bear fair crops of fruit. The trees grow splendidly, and usually; blossom well, but the fruit falls when it is about the size of a pea. With a view of elucidating this-matter, the Department i was recently requested by the Hawke’s Bay Fruitgrowers’ Association to carry out an experiment in one of the local orchards. Mr. E. F. Sibeth, of Clive Grange, very kindly placed his orchard at the Department’s disposal for this purpose.

This orchard consists of a block of 133 plum-trees, made up of 92 greengages, 36 silver-prunes, and' 5 giant prunes. The greengages are planted in a block. A poplar shelter-belt borders' both ends of the plum block, pear-trees are on one side, and the silver-prunes on the other. The giant prunes are next the silver-prunes and farthest away from the greengages. The trees, although lacking proper training, are exceptionally well-grown specimens, as shown in the photograph on page 164. The greengages, particularly, have never cropped, the best average yield being not more than a half-case per tree.' The silver-prunes have cropped a little better than the greengages. The giant prunes are by far the most consistent bearers. The trees have not been pruned-for at least two —possibly longer. The spurdevelopment was splendid, especially on the two-year-old woodin fact, the trees gave the impression of being overspurred.

This season three hives of bees were brought into the orchard ; these were formerly situated at a distance of about 500 yards.

The property offered very favourable opportunities for investigation, and the following tests were established on defined plots for the purpose of ascertaining whether cultural methods were to any extent responsible or whether the trouble was wholly due to faulty pollination : —

Nd. 1 : Centre of trees opened by cutting out large limbs - no other pruning.

No. 2 : Centre of trees opened up and leading limbs well spaced by taking out at least one out of three leading limbs.

No.- 3 : Systematic reduction of spurs over the whole tree. For example, where there were six fruit-buds at least two were cut off. To carry this out most of the tree was cut back on to the previous season’s wood.

No. 4 : Centres opened up and limbs spaced, and similar spur reduction to No. 3.

No. 5 : Ring-barked around trunk, 1st August. Piece of bark ully | in. wide removed below limbs.

No. 6 : Each individual limb ring-barked in a similar. manner to No. 5. :

No. 7 : Two limbs only ring-barked similar to No. 6 ; the remaining limbs not treated.

No. 8 : Ring-barked, 1st August ; similar to No. 5, but saw-cut only.

No. 9 : Ring-barked, 1st August ; similar to No. 6, but saw-cut only.

No. 10: Ring-barked, 1st August; similar to No. 7, but saw-cut only.

No. 11 : Ring-barked similar to No. 8, but done when sap com menced to flow, 25th September. . b ’ ■

No. 12 : Ring-barked similar to No. 9, but done when sap com menced to flow, 25th September.

No. 13 : Bound wire tightly around trunk, 1st August. No. 14 :■ Bound wire tightly around each individual limb, 1st August. No. 15 : Dug trench around tree about 8 ft. in diameter and 18 in. deep, allowing this to stand open all summer. No. 16 : Untreated trees. - z No. 17 : A portion were sprayed with bordeaux, 6-4-50, on 25th September, when in cluster-bud. ’ About sixteen trees were sprayed in the winter with lime-sulphur, 1-15 ; the remainder were sprayed with oil, 1-15. All the trees blossomed abundantly. The giant prunes were the first out, the silver-prunes next, and then the greengages. A good deal of the late bloom on the silver-prunes was out at the same time as the early greengage blossoms, but the giant prunes were about over at the time the greengages blossomed.

The following report is from notes taken on 6th November, 18th November, and nth December.

. No. 1 : Crop about equal to untreated trees. No. 2 : Crop not the equal of plot 1. Nos.' 3 and 4 : Crop not as good as unpruned rows alongside. : Nos. 5, 6, and 7 : Crop no improvement on untreated trees alongside. The treated arms on the same tree were no better or worse than the untreated arms. '

Nos. 8, 9, 10, 11, and 12 : Saw-cuts, both in dormant season and at sap-movement; no improvement on untreated trees.

Nos. 13 and 14 : Wiring no improvement on untreated trees. The crop on greengages was consistently heavier with all treatments, and even more so on the untreated trees, the closer they were situated to the silver-prunes—those immediately alongside the latter carrving the heaviest crops. The variation in the crop harvested ranged in the proportion of eight cases to one. Again, the silver-prunes next the giant prunes were the heaviest, while those alongside the greengages were slightly lighter in crop. The silver-prunes were also consistently lighter the greater the distance from each of the other varieties'.

CONCLUSIONS.

It is evident from the great variation in the crops of the individual trees that both greengages and silver-prunes will set much better when

cross-pollinated. The giant prune proved a slightly better pollinator

for the silver-prune than the greengage. I placed some branches, of Pond’s Seedling in some of the trees at flowering-time;; but it'; was apparent that these were not sufficient to determine the influence of cross-pollination. ,

I think it advisable that at least two more hives of bees should be taken into the orchard. • It is very probable that the bees this season had a good influence. The crop is very much better than previously.

The tests will be carried on next season to note the behaviour of the trees under the various treatments. It is also proposed to further test the value of cross-pollination, and transplant in the winter some of the bearing silver-prunes to the centre of the greengage block.-