Bitter Pit is recognised by the small brown speck on the skin of the fruit, in particular on the Russet type apples. Bitter Pit can also be a problem with Bramley Seedling Apple. It will also be seen that the flesh below the skin develops brown patches.
The unfortunate thing, is that it develops during the storage period. Any solution for Bitter Pit must be centred around prevention rather than cure. Once it shows up during storage, it is too late to do anything with that season's crop.
If you think you have a problem with Bitter Pit - the fruit will be inedible - then follow the tips bellow.
Bitter Pit is thought to be a problem of nutritional disorder - maybe a low Boron level in the soil. Certainly an annual dressing of domestic Borax will ease if not prevent he problem of Bitter Pit. It should be watered into the soil around the root zone at a rate of 30-40gms per 20 sq metres. A watering can is best for the application.
If you have this type of problem with any other fruit, then look for a different cause, for Bitter Pit is a disease only of apples!
Watering your 'suspect' fruit tree in the summer months also seems to help - maybe by helping to release some nutrients locked up in over-dry soils. Watering is particularly important during dry July and August months, and often overlooked as the trees normally look in good shape as far as foliage is concerned. Lack of soil moisture locks up nutrients..
In particular, calcium can become locked into dry soils, and is also thought to be a contributory factor. Together with this, mulch around the root zone of the apple tree. If there is a lack of calcium, then there will be competition between the fruits and leaf growths for the available calcium. Invariably, the foliage wins, and the end result can be Bitter Pit of the Apple fruit.
Fruit trees are often neglected insofar as feeding is concerned, so a simple general fertiliser application in the spring might also help prevent Bitter Pit, and in any case is desirable! make sure that it is a balanced fertiliser, for a too heavy application of Nitrogen can also be a cause.
Heavy pruning during the winter can also be a contributory factor. It is noticeable, that Bitter Pit is usually present during years with light crops. Light cropping is normally as a result of lack of feeding, winter damage, incorrect pruning, and poor water availability, which in turns reduces the amount of calcium available to the tree.
It will be seen, that good husbandry will go a long way in either reducing or preventing Bitter Pit in apples. Treat your fruit tree as a plant, rather than simply neglect it and hope for the best!