Virus Decline of Strawberry

Symptoms of this virus disease resemble those of nutritional deficiencies and other abiotic disorders and can be difficult to diagnose and confirm in the field. Leaves of strawberry plants with virus decline turn purple to red in color. New growth may appear in the center of plants with young leaves that remain green. Plants affected early in their development are often stunted. Diseased plants have greatly reduced fruit production, and roots are brittle with reduced numbers of small absorptive rootlets.

Outbreaks of virus decline are usually associated with the presence of the greenhouse whitefly vector Trialeurodes vaporariorum, as well as aphids that can transmit most of the non-whitefly-transmitted viruses associated with this disease. Increased numbers of the greenhouse whitefly in the field have been correlated with increased disease incidence in coastal strawberry fields in recent years. The absence of vectors when symptoms are observed, however, does not rule out the possibility of strawberry decline. Young strawberry plants may be infected by either a whitefly- or aphid-transmitted virus but remain symptomless. Introduction of an additional virus at a later date by a different vector would lead to disease development. Strawberry plants are usually symptomless if infected with only SPaV or BPYV.

The presence of BPYV or SPaV alone or together will not cause this disease. For virus decline to occur, strawberry plants must be infected with either SPaV or BPYV as well as any of several viruses transmitted by aphids. Non-whitefly-transmitted viruses that have been found associated with strawberry decline include Strawberry crinkle virus, Strawberry vein banding virus, Strawberry mottle virus, and Strawberry mild yellow edge virus. Other viruses such as Strawberry latent ringspot and Fragaria chiloensis latent viruses were recently identified in California strawberry plantings. Their potential roles in virus decline are being examined.

SPaV and BPYV are members of the genus Crinivirus. SPaV has a narrow host range and is primarily limited to strawberry and related species but can also infect a few common weeds. BPYV has an extensive host range and infects many plants in addition to strawberry, including cucurbits and numerous weeds common in coastal production areas.

Confirmation of virus infection requires testing plant material with molecular or serological techniques.

• When available, use transplants that are not infected with SPaV or BPYV.
• Control the greenhouse whitefly and aphid vectors.
• Remove weeds and alternate crop hosts of BPYV and SPaV, which may be virus reservoirs, prior to planting strawberry to prevent movement of virus-carrying whiteflies into the strawberry crop.