Until recently on many farms it was routine practice to treat apples prior to storage with specific fungicides in order to control infections of fruit by fungi such as Gloeosporium, Botrytis, Monilinia and Phytophthora (see 'Disorders of the Flesh' section for illustrations and descriptions of the various types of rot).
At the present time this method of applying fungicides is no longer possible due to the lack of products registered for use in this way. However, chemical antioxidants, such as diphenylamine (DPA), continue to be used routinely for the control of superficial scald on Bramley’s Seedling and products containing calcium are used frequently to increase the calcium concentration in the fruit and thereby reduce the development of calcium-deficiency disorders such as bitter pit.
Previous recommendations for the post-harvest chemical treatment of apples were concerned primarily with achieving control of particular disorders and enabling growers to save chemical and time by avoiding unnecessary emptying and refilling of dipping or drenching tanks.
Today the major consideration in the minds of growers when deciding their strategy for post-harvest chemical treatments should be the public perception of those treatments.
Apples have always had a healthy image and this provides a very strong marketing tool for fresh apples and apple products. In their book, ‘Super Foods’, Michael Van Straten and Barbara Griggs list apples as one of ‘The Four-Star Super Foods’. They claim that apples are a bonus for the heart: the pectin and vitamin C in apples helps to keep cholesterol levels stable.
- Pectin has been shown to bind to heavy metals such as lead or mercury and carry them safely out of the body.
- Malic and tartaric acids in apples help neutralize the acid by-products of indigestion and helps the body cope with excess protein or rich fatty foods.
- The authors conclude “because of these qualities, apples are great detoxifiers, and those suffering from arthritis, rheumatism or gout should eat raw apples regularly”.
In recent years the consumer has become more concerned about the use of pesticides and residues on the food they eat. Nearly every week the words ‘apples and pesticides’ appear in the same article or broadcast.
- The Government’s residue testing of food programme has highlighted and quantified this concern.
- The results are published annually together with the source of the sample, the so-called ‘name and shame’ policy.
- Where any pesticide is found above the level of detection the results are published.
- Maximum residue levels (MRLs) have been set as a measure of concentrations that can be expected with normal use of the pesticide and are safe for human health.
- Post-harvest treatments by their very mode of action are always going to leave a residue on the apple.
- The cold, dark environment of fruit stores slows chemical degradation. Thus, any residue will remain on the apple and is not easily washed off.
Although the economic benefit of using post-harvest chemicals is clear, in today’s consumer-driven climate, their use should be considered very carefully.