Apples turning brown on the tree before ripening, or falling to the ground as rotten fruit, are classic signs of the fungal disease Monilinia fructigena.
Let's forget the scientific name for now, and use the common name of brown rot. It is a name that accurately describes how the fruit seems to be suffering.
If healthy apples are falling, this is probably fruit drop. Here in this article, we are talking of apples turning brown whilst still on the tree in the ripening stage. Fruit drop normally happens in early summer, brown rot of apples appears in late summer.
Brown rot of apples is the of the most annoying of all apple tree diseases and problems, though rarely fatal if dealt with.
The climatic changes from year to year also play an important part in natural control of this disease. Humid or wet spring flowering times are ideal incubation triggers, whereas dry springs tend to augur well in reducing the incidence.
An added sign to go with the rotten brown fruit, is the tell tale sign of white or cream 'blisters' in concentric rings around the affected fruit appear. These blisters are the actual fungal growths but the damage is on the inside if the fruit as well.
Monilina is a widespread fungus that also affects the apple tree flowers in spring. Then it is known as Blossom Wilt. Typical signs are the flowers wilting together with nearby young foliage, and turning brown. It is a sure sign that the fruit will also be affected - normally in late summer.
The fungal spores find their way into developing fruit through all manner of damage to the outer skin caused by birds, insects and the codling moth.
It is not unusual to find that the affected fruits remain on the tree. All tree fruit are susceptible to this brown rot, though Apples tend to be affected more than other fruit.
The main control measure, is to remove the affected fruit as soon as seen and dispose of by burning. You will need to form a fire from old garden rubbish or an incinerator because the apples do not actually make good fuel!
There is little point in spraying at the visible infection stage, neither is there a chemical spray that will stop this particular fungus rot directly. However, a regime of fungicide sprays with a general fruit fungicide throughout the year seems to give some protection in also preventing damage to the fruit skin by scab and the like.
The first annoying signs for the gardener are generally when the apples - or other fruit - start to rot on the tree. The fungus which causes this rot has probably been on the tree for some considerable time. The same brown apple rot fungus disease firstly appears in spring flowering time, affecting flowers and leaves. This is particularly so in damp weather at the flowering season.
Wilting and browning of the flowers and young leaves are the visual symptoms. (This should not be confused with the natural process of the flower dying and its place being taken by the small emerging fruitlets.) Fungus spores at this time are normally deposited into crevices on nearby bark and remain on the tree until the opportunity of maturing fruit period arrives. Small cankers can appear on spur growths. These are the home for the resting spores of the brown rot fungus. The fungus spores will re emerge as the fruit matures and provides them with their next home - hoping to over-winter on fallen fruit!
The spores enter the fruit from damaged areas of the apple. Small holes left by insects, birds, scab, or even bruising against other fruit or spurs, are all entry points for the spores.
If the rotting apple fruit is left on the tree or allowed to lay on the ground, then this will be a continuation process for the fungus to over-winter and reappear again the following spring. A blustery summer can also be the cause of skin damage.
Brown rot fungus is not an easy disease to control and needs proactive methods from the gardener to prevent its spread and continuing annoyance.
The most effective, but time consuming action, is that of general crop cleanliness and removal of all diseased material as soon as seen. This will include pruning the affected spurs ir even branches as soon as cankers are seen. These should be burned and not shredded or otherwise left to rot. Affected flowers and foliage should also be removed and burned.
Developing fruit should be protected from insect and bird damage, even to the extent of of netting the tree.
Chemical control is mainly centered upon preventing apple scab and preventative fungicide spraying is tne best way forward. This may not directly deal with the brown rot fungus, but will go some to stop providing a home for the fungus spores - damaged fruit!
All affected apples should be removed as soon as seen, and certainly not left on the tree or allowed to lie on the ground. The affected fruit should be burned, or at least buried some 30cm in the ground.