These are problems caused by unfavourable environmental or cultural conditions, and not by disease organisms. Cordon trained sweet peas are much more susceptible than those allowed to grow naturally.
Sometimes the growing points of cordon trained sweet peas may go 'blind' in the middle of the season. Some varieties are particularly prone to this problem, which is often due to the plant having suffered a very cold spell over winter. To overcome this, avoid being too efficient when removing side shoots - always have one held in reserve for such eventualities.
This is one of the great scourges of sweet peas. It is most severe on cordon grown Spencer varieties, and can be caused by a wide range of factors. The most common are dull weather when the plants are growing vigorously, and erratic watering. The problem will often resolve itself with a change of weather conditions.
Bud drop can also be due to ethylene pollution. Ethylene is often a byproduct of combustion, and is present in bonfire smoke and car exhaust gasses. Sweet peas are among the most sensitive of plants to traces of ethylene.
Also spelt Chimera. A minor genetic oddity of no real significance. Causes variegation with clearly defined edges, thus differing from most disease symptoms. Stems and petioles are similarly affected. May safely be ignored as it does no harm and cannot spread to other plants.