Unlike other pathogens, a grower may diagnose Leafroll virus after watching the vine’s symptoms over several seasons. Virus-infected vines are less vigorous than those that are not infected, and may develop cupped leaves. In red varieties, the leaves of the infected vine can turn bright red, which does not occur in white varieties. Instead, white varieties show slight chlorosis. Because of its symptoms, leafroll is oftentimes confused with nutrient deficiency symptoms. This means that the virus may go untreated for a significant time while tests are done on nutrient deficiencies in the vine and soil.

Leafroll virus is considered to be the most significant virus affecting grapevines as the present time. It provides a significant threat to grapevine health but in a different way than the diseases mentioned previously. While control of fungal and oomycete pathogens can be done via fungicides in the vineyard, leafroll cannot be controlled. As such, it is necessary to completely remove the vine from the vineyard as the only method of control. Growers must be vigilant about the spread of the disease by testing even asymptomatic vines that surround the infected one. Roguing is a very costly move for growers, who aim to keep their vines planted for upwards of 25 years. Replanting means losing several growing seasons while the vine is reestablished.

Unlike the fungal pathogens, this virus is primarily transmitted through vegetative propagation of infected vines.  It can also be transmitted through mealy bugs and soft scales in the vineyard. Leafroll can result is significant reduction of crop yields, up to 30 to 50%. The transmission of Leafroll virus by mealybugs is understood to be semi-persistent, because while it may persist after molting, they soon lose the ability to transmit it after it is transferred. They usually obtain the virus in thirty minutes to 12 hours, and retain it for 12 hours to five days. Researchers have explored the control of mealybugs, but as yet, there are no effective techniques for control.

As with the other pathogens mentioned previously, the quality of the fruit on the grapevine is most important for selling to wineries and for using in wine production. It is, therefore, crucial to control those diseases which threaten the quality of the fruit growing on the vine. Leafroll threatens the grapevine canopy, which in turn will lead to decreased fruit quality due to the lack of photosynthetic machinery and photosynthates flowing in from the leaves.