by Fred Roundstone
(Angmering, West Sussex, UK)
Disease is one of the most annoying and most serious of all the problems in growing seasonal fruit trees, whether at home or on a commercial venture. It is a significant factor that limits productivity, and worse, kills the tree.
Plant diseases are caused by fungi, bacteria, viruses, nematodes, and mycoplasmas (protozoans).
There are disorders, however, that mimics the symptoms of diseases. Their symptoms look like diseases themselves but actually are caused by weather imbalances or by deficiencies or overdosing of nutrients.
Proper identification and preventative management should be implemented at once. Toxicity caused by the chemical boron or blossom-end rots cannot be cured by fungicides, as it usually is misdiagnosed.
There are books and websites that can identify these disorders. A book like “Organic Tree Fruit Management” includes detailed descriptions of diseases of fruit crops, including hosts, status (potential impact), symptoms, life cycles, monitoring and thresholds for treatment, and organic management strategies.
In established orchards, growers can initiate and practice good sanitation. This includes cleaning up debris, pruning, and removing diseased plants and parts.
Some plants act as alternate hosts for some diseases until they find their ideal hosts. Eastern red cedars are alternate hosts for cedar-apple rust. Wild plums can harbor peach brown rot. There are many other examples.
Maintaining your crops in excellent health and with sufficient soil nutrients is a good defense against plant diseases. Many of these fruit crop diseases affect only a particular species and variety of fruit.
Some diseases and prevention
There are, however, some diseases that are common to almost all fruit crops. Fruit rots are common because of the high sugar content of most mature fruits.
The grower can help by allowing good air circulation and sunlight penetration into the plant’s interior. Sunlight dries up leaf and fruit surfaces, thereby limiting fungal and bacterial infections.
Proper pruning and training also help. Aeration and sunning plus a well-timed fungicide application can control fruit rot.
Another common problem is root rot. Prunus species (peaches, plums, cherries, etc.) are very intolerant to poorly-drained soils. In turn, they are susceptible to root-rotting organisms common in such soils.
Adding significant amounts of organic matter to the soil makes it “disease-suppressive.”
In Australia, they added adding lime and a combination of chicken manure, cereal straw, wed residues, etc. to control root rots in avocados.
This strategy, known as the “Ashburner system,” is now adopted and is commonly practiced in many areas where avocados are grown. However, in humid New York, mulching apple trees increased root rot incidence.
Like all other aspects in planting and raising seasonal fruit trees, prevention is still the key to avoid having your crops catchingdiseases.
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