ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
FRUIT THINNING WITH CARBARYL |
| Author: | J.N. Knight |
| Abstract:
Over recent years there has been increasing pressure on the UK fruit grower to produce larger apples, and today size is certainly one of the major components of fruit quality. Small fruit is not easily marketed and so for the majority of orchards fruit thinning is essential. Of the various chemicals used throughout the world for thinning fruits, carbaryl is the only one used on apple in the UK. Although its mode-of-action is not fully understood, directions for its use have been carefully defined, and it is now used widely because it is very effective and reliable as a fruit thinning agent for the major cultivars grown in the UK. Thinning within the cluster is more beneficial to both fruit size and flowering in the following year than simple whole-cluster removal. Carbaryl selectively thins within the cluster, reducing the proportion of clusters that carry more than one fruit, as well as increasing the proportion of clusters that lose all their fruit. It therefore thins the crop in a way most advantageous to the production of large fruits. In addition, carbaryl removes lateral fruitlets from a cluster in preference to the 'king' fruit. In years when 'king' flowers set fruit, this inevitably results in an increased proportion of 'king' fruits in the harvested crop. With some cultivars this is of little consequence, whereas with others, e.g. Cox, this is detrimental to grade-out and is, therefore, an undesirable consequence of using carbaryl. Under UK conditions carbaryl has proved to be a safe chemical thinner as it is most effective when fruit set is high, and vice versa. In practice, this allows it to be used on a routine basis each year with minimal risk. Under-thinning may occasionally occur but the reasons for this are not clear. Historically, the timing of application of carbaryl has been regarded as critical in order to achieve effective thinning. For many cultivars, e.g. Bramley, Spartan and Discovery, the response to carbaryl does not, in general, vary from mid-May (petal-fall) to mid-June. Not unexpectedly, however, the greatest improvement in fruit size comes from the earlier thinning. In contrast, Cox does not follow this pattern but exhibits a peak response when the average fruitlet diameter is of the order of 12 mm. Thus, application at this stage produces the best grade-out for Cox. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
