Plant diseases are much more difficult to deal with than plant pests. Normally a plant disease has settled in with the plant before the effects are seen. This makes plant disease more difficult to treat, and in many cases the disease cannot actually be cured - simply controlled.
Plant diseases are not insects, though they can sometimes be caused and spread by insect activity.
Diseases normally consist of one of a group of three wide-ranging organisms. Fungi, Bacteria or Viruses! Some of these are invisible unless under a microscope, but the affects of the infection are soon to be seen.
Most plant diseases are either difficult or impossible to 'cure'! This fact above all else makes the prevention of diseases the more important.
The main diseases that attack plants are those caused by various fungi. Many fungi are harmless or even beneficial in the garden, but there are several fungus types that can cause diseases ranging from wilt to basic rots or just potentially lethal leaf discolorations.
One of the most common problems on specific plants is that of Rose Black Spot - a fungus. It is different, though similar to the Black Spot that materialises on Acers. However, the treatment is broadly similar.
Plant diseases are very difficult to positively identify, as there are many diseases that cause the same symptoms - as in the Rose and Acer black spot diseases. The good news is, that most 'similar' diseases can be treated in general terms. Absolute positive identification is not always necessary - unless of course you are rather deep into plant pathology! Theses pages are not for you!
'Damping off' of seedlings in the seed tray is caused by several different fungal pathogens. They can all be thwarted with the same good husbandry, or controlled with the same broad spectrum fungicides. There are only a handful of worthwhile fungicides on the market. A collection of two or three will normally deal with any fungal infection you are pestered with. Of that, more later.