The use of chemical sprays designed to provide some protection from frost and winds

Sprays of plant growth regulators, antitranspirants and other compounds

Although sprays of plant growth regulators have been reported to influence the winter hardiness of trees, these treatments have very little direct effect on the frost tolerance of apple flowers.

In research conducted in Washington State and Australia, the dodecyl ether of polyethylene glycol (DEPEG) has been shown to have cryoprotectant activity on the flowers of both apples and blackcurrants.

• The chemical was tested at a range of concentrations (0.5-8% w/v).
• Another product extensively tested on blackcurrants as a cryoprotectant is Teric 12A23B (ethylene oxide condensate).

Damage from frost occurs when the water within the floral tissues forms crystals as it freezes. This is enhanced if the water contains ice nucleation proteins.

• A number of bacteria, such as Pseudomonas syringae, P. fluorescens, Erwinia herbicola and Xanthomonas campestirs pv translucens, which are often common on plant tissues in large populations, are known to produce these ice nucleation proteins.
• Attempts have been made to reduce these populations on plant tissues in order to reduce frost injury.
• However, to date these attempts have met with little success.

None of the other chemicals or bacteria species listed above are currently approved for use in UK orchards.

Applying sprays to alleviate frost damage, to induce parthenocarpic fruit set and to aid fruitlet retention

Sprays of gibberellins, auxins and cytokinins

In the 1970s and 1980s, research conducted by scientists at Wye College in Kent on Cox and its clones showed that sprays of a mixture of gibberellic acid, an auxin and a compound exhibiting cytokinin-type activity could induce parthenocarpic fruit set and increase yields of apples (Kotob and Schwabe, 1971; Goldwin, 1978; Goldwin, 1981).