No abstract

This study set out to establish concentrations of ethephon sprays that could reliably thin alternate cropping orange trees in a heavy set year to improve fruit quality for fresh marketing. An optimum concentration of ethephon as a thinning agent was identified for the practical control of alternate cropping in Late Valencia oranges. A single, high volume spray of ethephon (as Ethrel, 42-60 mL/100 L water), applied in a heavy-set year at 6-8 weeks post bloom when fruitlet size was 10-15 mm diameter, induced a 15-20% reduction in fruit number. This resulted in significantly improved fruit size and marketable outturn with negligible yield penalty. In the 2 successive harvests following spray treatment, the cropping pattern remained uniform and a 14% improvement in packout (marketable fruit size <100 counts per carton) was maintained. Internal fruit quality was unaffected. Control of alternate bearing was carried forward for at least 2 seasons with relatively stable yields following a single spray treatment.

Three field experiments, in successive seasons from 1981 to 1983, tested the effect of six sowing dates, at c. 3-week intervals from early May, on maturity, yield, and quality of the onion cultivars, Allium cepa L. 'Pukekohe Longkeeper' (PLK) and 'Early Longkeeper' (ELK). Sowing date had little effect on crop maturity date, which was about 22 days earlier for ELK than for PLK. Maximum total yield was recorded for the third sowing date for PLK (95 t/ha) and for the second sowing date for ELK (82 t/ha), and declined steadily with later sowing dates. The earlier sowing dates resulted in a high proportion of bulbs that bolted for both cultivars and severely reduced marketable yield. Reduction in total yield at the later sowing dates was caused by a reduction in average bulb size. The yield of marketable bulbs of > 57 mm diameter declined from 75 t/ha and 57 t/ha for PLK and ELK at the third and second sowing dates respectively, to 30 t/ha and 14 t/ha at the sixth sowing date. The effect of sowing date on the balance between quantity and quality of yield suggests that the optimum time to sow onions at Pukekohe is early June for ELK and late June for PLK.

Juice quality, yield performance, and cropping efficiency of 6 midseason orange varieties (Hamlin, Parramatta, Pineapple, Joppa, White Siletta, and Mediterranean Sweet), together with Seedless Valencia on 4 rootstocks [Troyer citrange, Poncirus trifoliata, rough lemon, and either Benton citrange (coastal) or sweet orange (inland)], were studied for their suitability for both processed and fresh orange juice production. Promising midseason varieties for processed orange juice were Parramatta and Hamlin on Troyer citrange, and Parramatta on P. trifoliata, when grown in coastal districts. Debittered juice of Joppa on Troyer citrange could also be used for processing by early September on the coast. Preferred inland varieties for production of processed orange juice were Mediterranean Sweet and Harnlin on Troyer citrange. Midseason oranges grown inland had higher citric acid levels than the same variety grown on the coast. This resulted in inland fruit having lower ratios of total soluble solids (TSS) to acid, and later maturities, than fruit grown on the coast. Acceptable fresh orange juice was produced from fruit of Parramatta, Hamlin, White Siletta, and Mediterranean Sweet varieties grown on Troyer citrange rootstock in coastal districts; inland, fruit of Mediterranean Sweet, Joppa, Parramatta, and White Siletta varieties on Troyer citrange rootstock produced good quality, fresh orange juice. Hamlin can also be marketed as fresh fruit. In coastal production areas, harvesting can commence from mid July for Hamlin, from mid to late August for Parramata, and from early September for White Siletta and Mediterranean Sweet. Harvest in inland districts for processed juice should commence in mid July for Hamlin and in early September for Mediterranean Sweet, whilst harvest for fresh juice and/or fruit should proceed in early September for Mediterranean Sweet, and in late September for Parramatta, White Siletta, and Joppa. Highest fruit yields and large trees were produced by Parramatta and Joppa on Troyer citrange and rough lemon rootstocks. Most quality characteristics were better for fruit produced on Troyer citrange than on rough lemon. Both Benton citrange and sweet orange performed poorly and are not recommended as rootstocks for midseason oranges. All varieties on Troyer citrange had better yield and TSS/ha than those on P. trifoliata rootstock, which produced smaller but highly cropping efficient trees.

Cherries sprayed with 500, 1000, 1500 and 2000 mg/l daminozide solution were analysed for daminozide residues 7, 14, 21 and 28 d after the spray. The residues decreased with time and the difference between the first and fourth week residues was significant (P< 0.05) for each treatment. The residues in peaches were measured 18 weeks after the spray and were not significantly different for each treatment. There was a strong correlation (r=0.98) between the residues in cherries and the daminozide concentration in spray. The recommended concentration of darninozide spray (1000 mg/l) for cherries and peaches resulted in residues below the National Health and Medical Research Council limit of 30 mg/kg for pome fruit.