Background: Grapevine leafroll-associated viruses (GLRaV) are a significant problem for grape growing regions worldwide. They are the most common grapevine viruses present in Australia. Infected vines may not show immediate visual symptoms or yield loss and the virus infection can go unnoticed. This leads to more significant problems as the infected vines mature. Viruses are commonly spread through infected planting material and grafting, but some viruses are also spread within a vineyard through insect vectors such as scale, mealybug and mites. Ensure you monitor for vectors year round as you are walking or driving through your blocks, so you can gauge potential for vector spread of any viruses present.
Symptoms: One of the issues in identifying virus infection is the variability in symptom expression. The most obvious symptom of a GLRaV-infected vine is that the leaves roll downwards at the margins during late summer and autumn. Leaves can change colour, being red-purple for red and black varieties or yellow for white varieties, whilst the area around the veins remains green. Mature leaves (those lower on the shoots) are the first to show symptoms of infection. Late summer to autumn is the key time for symptom expression of leafroll viruses and therefore the best time to actively or passively survey your vineyards for signs of this and other viruses.
Viruses can also be mistaken for magnesium or phosphorous deficiencies resulting in potential misdiagnosis. It’s therefore important to validate your observations through diagnostic testing, and to ensure your testing includes both symptomatic and symptomless or asymptomatic vines.
Help: If you are unsure of your accuracy in identifying this virus, please contact Tony Hassall or your local DAFF officer to assist. If you have an iPhone, you can download the app “Leafroll3” to assist in the identification of the virus or use Google Lens as an alternative.