Grapevine leafroll disease
Grapevine leafroll disease, Leafroll disease, and Grapevine leafroll-associated virus (GLRaVs)
Who am I?
Grapevine leafroll disease is actually a group of viruses found throughout the world. The disease is transmitted by the grapevine mealybug called planococcus ficus. Approximately one hour of feeding upon infected vines is enough for mealybugs to contract the virus.
Mealybugs lose the ability to infect new vines with grapevine leafroll disease after four days of contracting it. The virus does not transfer from the adult female to her offspring.
The movement of mealybugs in the vineyard is partially independent and partially passive (with the aid of ants), which could explain some of the spreading patterns. The virus tends to first spread from one infected vine to another vine in the same row. The introduction of the disease to different adjacent rows takes place later on. Introduction of the disease in healthy, virus-free vineyards is caused by the mealybug vector.
Vines infected with the disease exhibit a reduction in the quantity and quality of fruit that comes from an overall decrease in the contents and accumulation rates of sugars. Generally speaking, wine grape varieties are found to be less tolerant to the effects of the disease; therefore, wine grape varieties suffer significant yield losses.
The symptoms vary in red and white varieties. In red varieties, it is common to see interveinal reddening of the leaves, a state when leaves become red though the veins remain green. In white varieties, the symptoms are fewer and less defined such that it may include mild chlorosis and curling of leaf edges. In some cases, symptoms aren't clear enough.
Quick tip: It is easy to confuse symptoms of the virus with those of magnesium deficiency. There is no treatment for the virus; therefore, it is not possible to cure a diseased vine.
Ways of coping with the disease include preventing its arrival by working with virus free materials, slowing or preventing its distribution in the vineyard by fighting the mealybug vector and in some cases uprooting infected vines.
It is not an easy decision to uproot and destroy infected vines, but models have shown that displacement of moderately infected vines can significantly slow down the spread of the disease.
Using traps to monitor: Monitoring systems provide useful information regarding when to apply insecticides. Population levels can be reduced or controlled by mass trapping, mating disruption, and lure and kill.
Controlling ants: Other than assisting in the spread and establishment of mealybug colonies, ants can suppress natural mealybug enemies.
In vines, mealybug populations overwinter primarily under the bark of the trunk which keeps them relatively safe and protected from spraying applications. A common practice in vines is peeling up the bark along the stems - from cordon to bottom. This will expose mealybugs and make them more vulnerable to sprayable insecticides.
The following are a few generic names of products found throughout large parts of the world and frequently used against mealybugs: Imidacloprid, clothianidin, thiamethoxam, acetamiprid, thiachloprid, sulfoxaflor, Dichlorvos, Spirotetramat, Buprofezine, Chlorpyrifos, and Synthetic Terepenes extract of Chenopodium.
Oils such as neem, tea-tree, mineral oils, and detergents\soaps designed especially for agricultural usage are natural recommendations.
Commercially available, beneficial insects to manage this disease are the Anagyrus pseudococci, Leptomastix dactylopii, and the larval stage of the coccinellid predator Cryptolaemus montrouzieri.
Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides and Herbicides). It is the grower’s sole responsibility to keep track after the legal uses and permissions with respect to the laws in their country and destination markets. Always read the Instructions written on the label and in any case of contradiction work with accordance to the product label. Keep in mind that information written on the label usually apply only to local markets. Pests control products intended for organic farming are generally considered to be less effective in comparison to conventional product. And so one must keep in mind that when dealing with organic, biologic and, to some extent, small number of conventional chemical products, a complete eradication of a pest or a disease will often require several iterations of a specific treatment or combination of treatments.