Virus diseases, mainly transmitted by aphids are a particularly serious problem reducing cropping in many parts of the world. It is critical to only plant virus free plants, and to control aphis to prevent health plants from becoming infected. Don't get flower buds or petals wet. It can cause markings. Flowers which develop at lower temperatures have a tendency to split.
Flowers developing at higher temperatures develop faster and tend to have weaker stems.
Aphis and Mites can be very serious pests. Aphids spread virus and cause distorted growth. Mites cause mottling of the leaves and eventually drying of the foliage. Thrip and caterpillars can also become a problem. For single flowering varieties the flowers are harvested when the bud has opened fully so that the outer petals are at right angles to the stem and the inner petals are still tightly bunched.