Mealybug, You Put The Leaf Roll Into My Vine

Date December 30, 2008

Learn About Grapevine Diseases

Only someone fascinated by the music genre of the 1980s would even remotely gather what song I parodied in the title of this post, but after doing the piece on Phylloxera last time I decided to take a moment to reflect on other vine nuisances that can cripple a vineyard and that’s the title that came to mind. I am by no means a ’80s music fan, just an unfortunate soul caught in the riptide of the 80s that hasn’t ebbed since my teens. I remember when “Video Killed The Radio Star” came out. MTV was to intelligence what Phylloxera was to the world’s vineyards. Neither has fully recovered since.

Let’s look at some of the vine diseases caused by invading pests and organisms.

Viral Diseases

  • Leaf Roll Virus: A colorful display of gold and red leaves with a curling downward leaf blade. Mealybugs deposit a sugary excretion as they feed called honeydew, a sticky mess that resembles soft candle wax and supports mold that grows on the leaves. This causes the pigment that would normally transfer to the grapes to remain in the leaves resulting in defoliation, bunch rots and spur and cane death. The only way to stop the spread of leaf roll is to remove the damaged vines.
  • Grapevine Fan Leaf Virus (GFLV): Spread by nematodes (roundworms) or by grafting infected vines, GFLV causes shortened internodes (the segment of cane between buds), zigzag branching, fasciation or crested shoots (which normally become canes), malformed, yellowed, fan-shaped leaves, a shoddy fruit set, small bunches and often times half the normal yield. Vines with untreated GFLV have a shortened lifespan. Treatment is expensive and time consuming and consists of heating the vines to kill the virus.

Bacterial Diseases

  • Pierce’s Disease: Another insect, a leafhopper called the Glassy Winged Sharpshooter prevalent from the West Coast of the U.S. down to Central America, causes premature leaf fall and eventually vine death. Leaves quickly become yellow or “scorched” in appearance. This cuts off nutrients to the vine killing it within one to five years.
  • Crown Gall: A root and stem disease caused by bacterium in soils where large tumor-like growths appear on the trunk of the vine that by strangling causes the vine to wither and die. You must uproot the infected plant to prevent spread.

Fungal Diseases

  • Black Measles: or Esca is the most destructive diseases of woody tissues in grapevines in hotter climates. It causes rapid leaf deterioration expressed by large veiny yellow patterns. The leaves eventually die, grapes never reach maturity and the only remedy to stop Black Measles is by using sodium arsenite on the plant during the dormant winter months, however as this is extremely toxic it has since been banned. The cause is not yet understood but believed to be by multiple fungi attacking the vine.
  • Eutypa Dieback/Dead Arm: A toxic fungus that enters fresh pruning wounds usually after a rain. It causes stunted shoots, kills canes, hence the name “dead arm” and makes new leaves cup and appear scorched. In severe cases part or all of the vine dies. Symptoms can take up to three years to emerge.
  • Oidium: Or Powdery Mildew resembles cobwebs on vines, leaves and berries. Grapes may shape irregularly, they will crack and will not reach full size and they will also have undesirable flavors. Canes will develop black spots. Leaves become discolored and distorted appearing withered. While this mildew is native to North America and native vines are immune, it wreaks havoc on Vitis vinifera.
  • Peronospera: Or Downy Mildew is another N. America native. It attacks the green parts of the vine. Leaves look like they are covered in oil spots. Cottony filaments spread out from these spots eventually causing leaves to drop off. Grapes harden and will shrivel up to look mummified in late stages. A spray of copper-sulfate called “Bordeaux Mixture” will curtail an outbreak.
  • Noble Rot: Or Botrytis Cinerea [boh-TRI-tihs sihn-EHR-ee-uh], Edelfäule [ay-duhl-FOY-luh], Pourriture Noble [poo-ree-TYUR NOH-bl] attacks healthy white grapes. While it is a harmless mold that has produced some of the finest dessert wines in the world, it can degenerate into Gray Rot and will kill the berry.

I was going to post some pics with these diseases but I just couldn’t find any with a similar style. Also, I just wanted to touch briefly on them as they aren’t as necessary for your basic wine knowledge unless you attempt to start a vineyard. If that’s the case, this site is not what you need to be reading. If you want to delve further into learning about grapevine diseases, most of them are covered on Wikipedia, with nice shiny photos to boot. Cheers.

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