A scary plant story

Phylloxera galls                                    Oklahoma State University

There are many creepy things in the garden — tomato hornworms, wolf spiders, slime molds. Things that give you the shivers and things that make you shriek. But when my friend George showed me a grape leaf, studded all over with warty coneheads of some kind, I knew I had a perfect subject for a Halloween column.

The entire upper surface of this grape leaf was colonized by weird abnormal growths of an unknown kind. Fixed, immobile, silent, they offered few clues. Were they alive? Was there something lurking inside them?

I was a little leery of bringing who-knows-what home with me, but I was on a mission to have this eerie phenomenon identified. What if they awoke while I was sleeping, infecting the houseplants, the foodstuffs, the dog? I secured the leaf inside a sealable plastic bag, tiny vase of water and all.

Next day, I took the specimen to my local office of the Rutgers Cooperative Extension Service. When I unveiled my find, most of the staff took a step back. One brave soul stepped up, though, and identified the mystery infestation as leaf galls produced by the practically microscopic plant louse known as grape phylloxera.

In grape-growing regions of the world, this pest is widely known — notorious, you might say. That’s because it had a devastating effect on the production of something very serious indeed: wine.

In the mid-1800s, a lively trade in grape stock had developed between France and America with vineyards swapping cultivars to see how they might perform. In 1865, a shipment of American vines arrived in Bordeaux. They shortly exhibited previously unknown leaf galls, went into decline and ultimately died.

Within a decade the infestation spread through France and the continent, wiping out vineyards that had been tended for centuries. Mon Dieu! This was a crisis, and France posted a reward for unraveling the pestilential mystery that today would be the equivalent of $1.5 million.

The solution to the Great Wine Blight came from the same location as the problem. American grapes, having evolved with the pest, are more resistant to its effects. Here’s where the French really do owe us a debt of gratitude. Their vineyard and others on continental Europe were replanted with grape vine varieties grafted to American rootstock. Violà!

The restoration of the vineyards began even before the culprit was identified as a tiny, sucking insect with a complicated life history.

Phases of the phylloxera mite

A female emerges in spring and travels to a leaf, where her feeding produces a gall by interfering with normal plant cells. She fills the gall with eggs and dies. Nymphs hatch from the eggs, migrate to other leaves and themselves produce egg-filled galls — and this can go on from six or seven generations before the really bad stuff begins to happen.

It’s not the leaf-feeding generations that are harmful, but the ones that hibernate over the winter on grape roots and, come spring, begin to feed on them. This produces root galls, warty abnormalities that interfere with the plant’s uptake of nutrients and moisture, eventually causing the plant to yellow, wither and die.

Notice that it is an entirely female clan that causes all the trouble so far. The leaf phase and root phase of the phylloxera can go on for a long time — years, even — until some of the root-dwellers lay eggs that become winged females.

These in turn travel from the roots to the stems where they lay two kinds of eggs: The big ones become females and the small ones become males, both lacking mouthparts. They don’t feed but they do mate. The female lays a single fertilized egg which hatches into the leaf-feeding generation — and the cycle continues.

For the home grower, phylloxera is generally no cause for panic. There are few effective controls for the gall-making critters on the leaves, since they abide in their little coneheads, safe from pesticides. The advice from Rutgers is to remove the gall-infested leaves, bag and discard them. Chances are the plant will survive and bear fruit just fine.

In the vineyards of California it’s a different story — winemaking there is critical to a multi-billion dollar industry. Huge populations of vine-destroying phylloxera, left unchecked, can destroy the vines on which all of this rests. This is big. So big that NASA has developed satellite-based infrared imagery that can detect infestations even before the above-ground portions of the plants show any symptoms.

When phylloxera reached the California wine country, many growers responded by using a rootstock for grafting called AXR#1 (others are called things like SO4, 5BB Kober and Teleki 8B, if you’re curious). It was thought to be phylloxera-resistant, but whether that belief was unwarranted or whether a new variant of the bug evolved, it no longer offers protection.

Ironically, the vine growers of California are doing exactly what their French counterparts in the 19th century did — replanting their vineyards, all the while arguing over the relative merits of “pre-phylloxera” and “post-phylloxera” wines.

You can keep your make-believe Halloween ghosts and goblins. The bug that ate the vineyards is a real-life nightmare. Just pray that we keep one step ahead of it. How could we go on in a world without wine?