Cucurbit yellow stunting disorder virus

Cucurbit yellow stunting disorder virus infection visible over the whole production field.

The yellow cucurbit leaves with the veins remaining green is a typical symptom of Cucurbit yellow stunting disorder virus.

Over the last couple of years, Cucurbit yellow stunting disorder virus (CYSDV) has become an increasingly big problem in certain parts of Limpopo, with some growers reporting up to 100% crop losses on different cucurbit crops grown. CYSDV can infect most members of the Cucurbitaceae family, including melon, watermelon, squash and pumpkins – with watermelon and melons being the hardest hit by the disease.

Symptoms first become visible on the older leaves and show a chlorotic (yellow) spotting and eventually it develops into a distinct interveinal chlorosis (yellowing). The veins remain relatively green, with the rest of the leaf turning yellow. With age, the symptoms intensify and become systemic throughout the plant.

Symptoms can often be confused with other yellowing viruses or nutrient deficiencies. Depending on when infection occurs, the fruit on infected plants may appear normal but are usually smaller in size and have reduced sugar levels, which will lead to the fruit being unmarketable.

The vector for the disease is the silverleaf whitefly, Bemisia tabaci (biotypes B and Q). The spread of the disease from plant to plant in and between fields happens exclusively through this vector. The virus cannot be transmitted mechanically (by touch) and it is not seed-borne and can therefore not be transmitted by seed.

The virus can also be spread over long distances by the movement of infected plant material or by virus-carrying whiteflies accompanying plant material that is being moved between different locations. High winds can also contribute to the movement of Bemisia tabaci over long distances.

Control

Due to the very high infestations of the whitefly in the affected areas, farmers have struggled to control the spread of the disease. With these high infestations, the application of insecticides for whitefly control has not proven effective in controlling the spread of the virus in the fields. The following guidelines could help in trying to manage the disease. • Control weeds to eliminate potential sources of inoculum; • avoid planting new fields close to older fields, especially

fields that have been known to be infected with the virus; • in open-field production, early-season exclusion of the vector, using mesh tunnels, may delay virus infection; and • after the growing season, sanitation is very important. Remove old crops/volunteers by ploughing or physical removal.

DISCLAIMER: This information is based on Sakata Seed’s observations and/or information from other sources. As crop performance depends on the interaction between the genetic potential of the seed, its physiological characteristics and the environment, including management, Sakata Seed give no warranty express or implied, for the performance of crops relative to the information given nor do Sakata Seed accept any liability for any loss, direct or consequential, that may arise from whatsoever cause. Please read the Sakata Seed Southern Africa (Pty) Ltd Conditions of Sale before ordering seed.