Viral diseases of roses in a greenhouse and methods for their control

Viral diseases of roses in greenhouse conditions

Several viral diseases develop on greenhouse roses, although data on their harmfulness is scarce. Strawberry latent ringspot virus affects plantations of the cultivars Vassaga, Sago!, Ziregsz{ag, and PshK Zepsaiop. Diseased plants show stunted growth, young leaves become wrinkled and grey-green, and a mild yellow mottling develops. Loss of color is particularly noticeable on the Vassaga cultivar.

Like the arabis mosaic virus, also found on roses, the pathogen is transmitted by nematodes. The only effective control methods are:

• removal of diseased plants;
• suppression of nematodes.

However, it is not possible to completely eradicate nematodes, and as a result, the disease reappears in the second or third year after planting.

Rose mosaic is perhaps the most common viral disease. Apparently, its causative agent may be one or more viruses, including the prunus necrotic ringspot virus, arabis mosaic virus, and tobacco streak virus. Symptoms of infection include bright yellow mosaic, streaking, and typical oak-leaf patterns. In spring, leaves of the cultivar Mem Worker show signs of oak-leaf patterns, accompanied by necrosis on the flowering shoot and some bud abortion. In summer, diseased plants bloom normally, with only mild signs of mosaic appearing on the leaves.

All infected rose bushes must be removed. Selection of propagation material should be carried out very carefully, discarding all specimens with symptoms of mosaic.

Non-pathogenic disorders and chlorosis

On some rose cultivars, in particular on Vasa, sharp signs of leaf drop appear in the spring, and sometimes in autumn. The symptoms of affected aging leaves are almost impossible to distinguish from the symptoms of downy mildew. The cause of the disease has not been established, but it develops particularly severely during a sharp rise in temperatures in the greenhouse. When soil temperature increases, it is necessary to stimulate the growth of shoots to ensure normal root growth and water absorption by them, thereby balancing the water loss by leaves.

Fig. 15.9. Symptoms of viral diseases of rose:

a — leaf chlorosis with symptoms of etching and oak-leaf pattern due to infection with Prunus necrotic ringspot virus (cultivar Mem Yorker); b — light green angular mottling, especially noticeable on newly opened leaves, due to infection with Strawberry latent ringspot virus (cultivar Vasa); c — change in leaflet width (sign of narrow-leaf) due to infection with Strawberry latent ringspot virus (cultivar Sinu o0Ё 1.ee4$); d — severe vein yellowing as a result of mixed infection with Arabis mosaic virus and Prunus necrotic ringspot virus on Rosa multiflora; e — yellow mosaic and severe chlorosis due to infection with Arabis mosaic virus on Rosa rugosa.

Chlorosis: when grown in soil with an alkaline reaction, roses often suffer from iron deficiency. A distinct interveinal chlorosis appears on young leaves, gradually covering the entire blade. As a rule, the development of chlorosis can be prevented by adding peat or sulfur to the soil or by applying iron chelate.

Further reading

Forsberg, J. L. (1975) Diseases of Ornamental Plants. University of Illinois Press, Urbana, IL...

Griffin, M. W. and Paceper W. T. (1981) Control of Diseases of Protected crops: (Publications), Mon House, Withbury Lane, Anwick, Northumberland.

Mastalerz, J. W. and Langhans, R. W. (1969) Roses. Pennsylvania Flower Growers Association; New York Flower Growers Association inc. CHAPTER 16. ROD