Tobacco Mosaic
Agent: Solanum virus
Symptoms
The most resistant of viruses - can survive up to 100 years in dry conditions. Most often infected by human contact (smokers can transmit it), infected seeds also occur. Forms variegated dark and light green spots on the leaves. Fruits are not affected, but weakened leaves impact the yield.
Control and prevention
Difficult to cure - the plant must be destroyed. Regularly disinfect inventory, greenhouses, equipment. Many resistant varieties have been developed for this virus.
Related problems
Similar symptoms might indicate a different cause — compare them.
Cucumber Mosaic
Cucumis virus
Transmitted by aphids, does not survive winter in soil or plants. The first symptom is leaves with raised stripe-shaped spots, which later appear on the stem and fruits.
Aphids
These are small green (sometimes reddish, brown) flies that usually attack in swarms. They suck the sap from leaves or stems, but do not touch the fruits. A tomato plant can withstand significant aphid attacks, but they should not be neglected, as too many can weaken the plant. These flies can also be carriers of viral diseases. A similar species is whiteflies; they act similarly, but are half the size. Aphids are protected by ants: contrary to popular belief, ants do not destroy aphids, but help them thrive.
Spider mites
A creature the size of a salt crystal with two black spots on its back. They usually weave webs on the underside of the leaf, causing the most problems during the hottest and driest summer months. They suck plant sap — yellow spots develop in the affected areas, which later turn brown and die.