A good home gardener recognizes symptoms of plant diseases quickly and takes steps to prevent or control them. Diseased plants do not grow normally. Foliage symptoms on plants infected with a bacterium or fungus will normally develop first on the older leaves. Virus symptoms develop on the younger leaves.
Viruses are very simple forms of life.
They are often spread to healthy plants by insects or on one's hands during normal gardening practices. Bacterial cells are much larger than virus particles, but they are still too small to see with the naked eye. Bacterial cells move in the water film on the leaf surface or in the water surrounding plant roots or soil particles. They are most often spread by splashing water. Fungal spores are larger than bacterial cells but are not visible without a microscope.