This is where it gets a little more sticky. The troubleshooting of diseases isn't fun at all. Thoughts like, "Can it still bear fruit even with disease?" or "Shouldn't the vine self-heal? Why am I responsible for the strains of virus that it catches along the way?" or "Why not just pull the vine and plant a new one?" (a.k.a. - divorce) All these questions and more flood my mind when it comes time for the vinedresser to treat the diseases that creep in along the way. I'm looking for a way to avoid this part of the husbandman's responsibility. Anyone else feel this way about Grapvine virus diseases?
Grapevine Virus Diseases
This virus group includes at least 13 different viruses that can cause disease in grapevines. They share in common transmission by nematodes and a polyhedral physical structure when purified and examined with an electron microscope. This is the source of the name “nepovirus”: “ne” for nematode, “po” for polyhedral. Fortunately, only a few of these viruses are reported to be of importance in grapes in the U.S.
Fanleaf Degeneration — Grapevine fanleaf virus — GFLV
GFLV is perhaps the best characterized virus of grapevines, causing fanleaf degeneration in affected plants. It is widely distributed throughout the world. Fanleaf disease is a major viticultural problem in California, causing reduced yields due to poor berry set. The reduction in yield can be over 80% in some varieties. Symptoms include fan-like distortions of leaves and chlorotic yellowing as ringspots, vein banding, and mottling or mosaic patterns. The virus is transmitted by the nematode Xiphinema index and can infect all Vitis species.
Yellow Vein — Tomato ringspot virus — ToRSV
ToRSV causes yellow vein disease. A similar disease is caused by tobacco ringspot virus. These viruses are transmitted by several species of nematodes including X. americanum, X. californicum and X. rivesi. Symptoms of both diseases include shot berries, shoot stunting, and devigoration of the vine. These diseases are common in vineyards in the eastern U.S. and in fruit trees, but are rarely seen in California vineyards. The symptoms of yellow vein resemble those described for fanleaf, and they can be easily confused.
Arabis mosaic virus — ArMV
This virus is widespread in grapevines in Europe. Although not found in California vineyards, it has recently been reported as common in Missouri and some infections have also been reported in Canada. Infected grapevines show symptoms similar to those of fanleaf, and ArMV can be present in a mixed infection with GFLV. Several nematode species can transmit ArMV to grapevines, the most common being Xiphinema diversicaudatum.
There are at least seven distinct viruses reported to be associated with leafroll disease. These viruses are collectively referred to as grapevine leafroll-associated viruses (GLRaVs) and are designated GLRaV 1 through GLRaV 7. ELISA tests are currently only available in commercial labs in the U.S. for GLRaV 1-5.
Symptoms of leafroll disease may include downward rolling of leaves, leaf reddening in the fall of red-fruited varieties, poor fruit color development, and delayed fruit maturation. Yield losses of 10 to 20% may occur. In cases of mixed infections with more than one virus, vines may be severely weakened and vine death may occur.
RUGOSE WOOD COMPLEX
Diseases in the rugose wood complex are characterized by trunk and stem disorders (pitting and grooving). Foliar symptoms similar to leafroll may also occur. Diseases in this complex include corky bark, Kober stem grooving and rupestris stem pitting. Their effects on grapevines vary from mild to severe. Disease severity is compounded when multiple infections of the rugose wood complex occur, or by the presence of other viruses such as leafroll.
In recent years, individual viruses have been discovered and characterized which has made the detection of these disease agents much easier. There are still some rugose wood diseases for which the agent has not yet been described, making it necessary to perform laborious and slow biological tests.
Rupestris stem pitting-associated virus — RSPaV
RSPaV is associated with rupestris stem pitting of grapevines. This disease is usually of little consequence. Decline due to rupestris stem pitting has been reported, but is not well-documented. RSPaV is widely distributed and is not targeted for elimination in most certification programs.
Vitiviruses — GVA, GVB, GVC, GVD
The vitiviruses are a group of viruses associated with the rugose wood disease complex. Four vitiviruses have been discovered in grapevines: grapevine vitivirus A (GVA), grapevine vitivirus B (GVB), grapevine vitivirus C (GVC), and grapevine vitivirus D (GVD).
GVA is associated with Kober Stem Grooving. Affected vines may show swelling at the graft union and fail to thrive. Ungrafted vines may be infected, but usually do not show symptoms.
GVB is associated with corky bark disease. The disease affects only grafted vines. The severity of corky bark is more pronounced in vines infected with other rugose wood complex viruses.
Neither GVC nor GVD have been proven to cause disease in grapevine but their structure and genetic profiles have shown that they belong to the vitivirus group.
Grapevine fleck virus —GFkV
GFkV is a graft-transmissible virus that causes symptoms of disease only in V. rupestris. Other Vitis species can be infected but remain asymptomatic. In infected V. rupestris, symptoms include localized clearings (flecks) in the veinlets of young leaves. In older leaves, the symptoms diffuse into a mosaic pattern and the leaves wrinkle and curl upward. Symptoms persist during mild weather and disappear with the onset of hot temperatures. Very little information is available about the economic importance of fleck virus.
Many other graft transmissible diseases, likely caused by viruses, can infect grapevines. These include asteroid mosaic, enations, vein necrosis, and vein mosaic, among others. These diseases have been studied to varying degrees, but have never been demonstrated to be common or severe.
Occasionally, new diseases appear that are significant. Recently, a new stem lesion virus disease was discovered in California (see California Agriculture, July-August 2001). Also known as Redglobe virus, this disease can kill vines on certain rootstocks. Continuing research is necessary to identify important new diseases like this and to develop diagnostic tools to help minimize their future impact.
I am struck by the nuanced nature of disease. You can't see it by just looking at the vines, sometimes it can only be seen by looking at the veins, those little darkened spiderwebs within the leaf that can only be seen by drawing close. It's like the difference between the tree and the twig. You can think the tree looks great all the while the twigs are speaking a different story.
And here's the skinny...until you get closer to your wife, you will keep seeing her as a tree instead of a collection of twigs. You will see the leaf (the vine), but miss the life (the vein). Some diseases can be seen from the watchtower within the vineyard. Discoloration is detected in a section of the vineyard that needs some attention. But often, the diseases can't be seen without walking through the vineyard, taking each vine in hand and feeling the texture of the the leaf's skin, looking at the changing colors within the vine's veins. Without this vine-dressing, without this botanic EKG, the wife-vine can begin to die a slow death and unknowingly be left for dead by her husband. She will even bear fruit during her diseased state, but the wine will start tasting sour, wild (but we will get into that another day).
Suffice it to say, that woman-wine comes forth when she is handled as a veined vine. The disease/dis-ease that can be avoided with early detection and early treatment is quite profound. I've found some viruses that have crept into my wife over the years that I've had to treat with Truth-pesticide. I call it truthicide.
- Insecurity stem virus (ISv)
- Replaceable anomoly (Rp A-2)
- Lonley bark syndrome (LBsyn)
- Significance vein strain (SgnVS) - this strain of disease can't be seen on the surface.
- Discoloration of Face/Joy Disorder - DF/JD
It's been good for me to see my responsibility in fighting these diseases that creep in along the way. I can't just hope the vine heals itself. I can't just say, "It's not my fault she has such a low immunity to viral infection." I'm the vinedresser. I'm the husbandman. I have to be protecting the vineyard that is my wife.
So I keep my eyes on the veins, not just the vine.