JAPANESE PLUMS (P. SALICINA L.) IN HIGH-DENSITY PLANTINGS

A number of varieties, giving good conditions for cross-pollination were grown. Tree height was limited to 1.5–2.5 m. The spacing varied from single rows to 4–5 row bed systems with 3333, 4000, 5000 and 6666 trees/ha (at spacings of 2 m x 1.5, 1.25, 1.0 and 0.75 m).

Most of the plum trees were propagated from hardwood cuttings, stratified in sand during the winter and transferred to plastic containers. These maiden plants on their own roots were ready for planting in autumn when they were comparable with those produced in nurseries and budded on rootstocks.

The high-density orchard plots were drip irrigated and fertilised.

The vigorous varieties (Methley, Cardinal and Golden-Japan) required relatively wide spacing, forming multishoot trees with an alternate pruning system or free palmette trellises (for Golden King). On the other hand Santa Rosa, Wickson, Laroda and Nubiana could be trained as bush-like pyramids at the narrower spacings. The first group of cultivars also had to have summer pruning or growth-retardant treatments (PP333) during the growing season. The dates of planting (from 1979 to 1981) and the training and management treatments for each variety are shown, together with yields, in Tables 1 and 2.

Wickson, Nubiana and Golden King were the most precocious varieties; Methley, Premier (S.E.), Santa Rosa and Golden Japan being later to come into bearing.

Paclobutrazol (PP333) applied to the soil or to the canopy reduced shoot growth and increased the number of fruits per tree (Table 3).

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