Orchard crowding in the macadamia industry is common and there has been concern that it reduces yield and quality. To investigate this we monitored yield, nut quality, tree volume, and light interception in macadamia orchards (Macadamia integrifolia Maiden and Betche) that represented a range in crowding. The predicted rate of change in yield/ha with time remained positive, i.e. yield increased over time, for orchards with crowding levels up to a tree volume of 43 500 m3/ha and light interception of 94%. There was a trend for the rate of yield change to decrease with increasing tree volume/ha. For orchards with tree volume >43 500 m3/ha the rate was negative, indicating a slight decline in yield over time. There was no evidence of a detrimental effect of orchard crowding on percentage kernel recovery, unsound kernel, or grade 1 kernel. It appears that macadamia, unlike many other orchard crops, can maintain yield and quality up to a high level of orchard crowding. The implication of this is that timing of canopy management and optimum canopy dimensions will be dictated by management requirements for machinery access and effective spray coverage before yield decline becomes an issue.
Hedging and 25% tree removal were investigated in a 6-year study as strategies to manage tree crowding in mature macadamia orchards. The trial orchard comprised 9-year-old macadamia (Macadamia integrifolia Maiden and Betche) trees, cultivar Kau (HAES 344), planted at 7 × 3.5 m and which had formed a hedgerow. In the hedged treatment, both sides of the hedgerow were lightly pruned annually with a mechanical hedger. In the tree removal treatment, 25% of trees were thinned out by removing every second tree in every second row. Hedging reduced yield in years 5 and 6 after the start of hedging, by 14 and 21%, respectively. Over 6 years, average yield reduction due to hedging was only 4%. Tree removal reduced yield/ha by 17% in the year immediately after thinning and this effect gradually reduced to 11% over the next 5 years as trees grew into the available space. Over 6 years, average yield reduction due to tree removal was 15%. The economic implications of the different patterns of yield reduction are discussed. Nuts dropped earlier in the tree removal treatment but there were no effects of hedging or tree removal on kernel recovery, unsound kernel or grade 1 kernel.
Trials were conducted in three successive years to test the response of Granny Smith, Jonathan, and Delicious apple varieties to Alar (succinic acid 2, 2-dimethyl hydrazide) applied at various times and concentrations. The results confirmed overseas reports of reduced shoot growth, increased fruit set, reduced fruit size, reduced pre-harvest drop, and, in some cases, increased blossoming the following spring. The Jonathan variety was less responsive to the growth retardant than Delicious, which was, in turn, less responsive than Granny Smith.
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