Science into practice: Optimising defoliation in young trees

The milder autumns of recent years have been causing problems for nurserymen as natural leaf abscission on field-grown trees is occurring later each year. Consequently, tree lifting is delayed and nurseries can fail to meet early demand from landscapers.

Alternatively, nurseries are being forced to lift trees while the foliage is still attached in order to meet orders. The only answer is to use chemical defoliants but HDC project HNS 157 seeks to find if the effectiveness of existing products can be enhanced or if they can be replaced with other chemicals or even an alternative mechanism for defoliation.

Field trials and experiments in controlled conditions to help determine the relationship between potential defoliants and the physiological stage of the crop at the time of application have so far demonstrated that Leaf Fall, a commercial product containing Copper EDTA, remains the most effective chemical for defoliating young trees. Feasible alternative defoliants to Leaf Fall (including Iron-EDTA) evaluated in the project to date appeared to be no more cost effective than Leaf Fall.

Wetting agents may improve the action of Leaf Fall by up to 100 per cent when both products are used in late autumn at the recommended rate. However, a half rate of Leaf Fall with wetter may be worth trying for those cultivars that appear more responsive to defoliants. Growers should note that the effectiveness of Leaf Fall remains variable depending on crop type and time of application (eg 60-80 per cent defoliation in Crategus compared to only 15-33 per cent in Malus Bramley). Applying mild drought stress during late-summer/autumn may encourage defoliation.

 


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