Leaf Drop Streak

Leaf drop streak is a phase of rugose mosaic developing soon after infection and characterised by necrotic streaks on the stem and underside of the veins of some of the potato plant’s leaves. It leaves plants stunted or killed, sometimes causing almost a total loss of yield in plants affected by the disease.

Common Signs and Symptoms of Leaf Drop Streak

Symptoms of leaf drop streak vary between potato varieties and strains of virus. Some strains of Potato Virus Y (PVY), e.g. tobacco veinal necrosis strain (PVYn), can cause mild mosaic symptoms in the first and second years.

Symptoms During Year 1: Dark spots or streaks on veins, leaves shrivel and drop i.e. leaf drop streak. Some varieties. e.g. Estima, Pentland Squire and Wilja only show a mild mottle or mosaic. Leaf drop streak symptoms only appear on the stems of plants have been fed on by that virus infected aphids, so not all plant stems will necessarily be affected.

Symptoms During Year 2:  It is common to see plants become dwarfed and brittle, and with leaves showing severe mosaic and rugose or wrinkled surfaces. Leaves will appear mottled with flecks of varying shades of green.  By this point all stems of the plant will be affected.

Common Causes and Conditions of Leaf Drop Streak

Leaf drop streak is transmitted, like many potato diseases and viruses, by aphids. The virus is non-persistent in the aphid, meaning the spread is mainly localised, however it can spread very rapidly in some seasons, particularly in South East England during periods when winged aphids are high in numbers.

Vulnerable / Immune Varieites

Some potato varieties had a high resistance to leaf drop streak, including Brodick, Caesar, Claret, Donald, Pentland Crown, Picasso, Romano, Roscor and Sante.

Control of Leaf Drop Streak

Leaf drop streak can be controlled and prevented by the following steps:

Cultural and Methods:
Using only classified seed.

Any seed saved from ware crops should be isolated as far away as possible from other potatoes, particularly those that have already been grown once.

Chemicals:
Existing pesticides are fairly ineffective against leaf drop streak, because the infection occurs before insecticide have a chance to take effect.