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Sampling Vines to Confirm the Presence of Phylloxera

Additional Fact Sheets on Phylloxera:

Contributing List of Authors: Ed Hellman. Oregon State University. This fact sheet and others on grape phylloxera were produced as a set by a phylloxera task force at Oregon State University: Bernadine Strik, Extension Berry Crops Specialist; M. Carmo Candolfi-Vasconcelos, Extension Viticulture Specialist; Glenn Fisher, Extension Entomologist; Edward Hellman, Extension Horticulture Agent; Steven Price, Post-doctoral Research Associate, viticulture; Anne Connelly, Master’s student, horticulture; and Paula Stonerod, Research Aide, horticulture. The authors of this fact sheet acknowledge the help and guidance of others on this task force.

Grape phylloxera are small, root-feeding, aphid-like insects that spend most of their life cycle below ground. Their feeding weakens the root system and vine causing above-ground symptoms of weakened vine growth (see Phylloxera: What is it?). These above-ground symptoms usually first appear as a lens-shaped, weakened area in the vineyard. However, if phylloxera were brought in on self-rooted (non-grafted) planting material, then the whole vineyard block might appear generally weakened. As the phylloxera spread, the lens-shaped weak areas increase in size and other areas of infestation may “pop up”.

Finding grape phylloxera on infested roots is very difficult, especially in the early stages of an infestation. We have sampled weak areas in vineyards for two consecutive years without finding phylloxera, only to find them in the third year. Therefore, you should dig roots in suspected weak areas over repeated years. It may take from two to five years from initial infestation, depending on vine vigor and how the vineyard was infested, for the above-ground symptoms to show.

Keep in mind that there may be other causes for weak areas in a vineyard: shallow soil or drought (usually a weak area that doesn’t spread annually); Armillaria or oak root fungus (circular weak area related to an oak tree on site prior to planting or adjacent to vineyard block); nematodes (weak area not necessarily circular; sample for nematodes); and gophers (damage more random).

Sampling time

The best time to sample for phylloxera is when populations are at their peak in late summer/fall (see Phylloxera: What is it?). Sampling from late-July through harvest increases your chances of finding phylloxera if they’re present.

Where to sample

Phylloxera reproduce most successfully on healthy root systems; dead and weakened vines will often have very low populations on the roots. When you sample a suspected phylloxera infestation in your vineyard, it’s best to look for the pest at the border of the damaged area, on vines just showing the first signs of decline.

Carefully dig up a number of roots. Inspect new fleshy growth on fine, feeder roots for nodosities (small swellings), symptoms of phylloxera feeding. Root tips infested with phylloxera are club-shaped or form hooks. Nodosities may be white or yellow, turning brown later on. After root death, they will wither and decay, becoming indiscernible. Be aware that swellings on feeder roots may also be caused by nematodes; however, to a trained eye these look different than those caused by phylloxera.

Often tuberosities (large swellings) can be seen on older, larger diameter roots. However, phylloxera are often difficult to detect in the advanced stages of an infestation, as roots become dry or spongy and bark begins sloughing off.

Most phylloxera are present on roots in the upper one to four feet of the soil, so this is the best place to sample. We have had the greatest success collecting root samples within 1 feet of the trunk.

Samples should include a larger portion of root (about inch in diameter) as well as feeder roots. The feeder roots often show nodosities, but actual colonies of phylloxera are more prevalent on larger diameter roots. If these colonies contain numerous phylloxera, they appear as “yellow spots” on the root. Magnification (10X hand lens or greater) is essential to verifying presence of phylloxera. Often phylloxera are found under sloughing bark or in cracks of the root.

A “sample” consists of a pint to a quart of roots and associated soil (soil stuck to the roots) per vine. Sample as many “suspect” vines as possible. Remove roots and associated soil from the vine sampled carefully, immediately putting them in a sealed container.

Identification

Because phylloxera are extremely small, use a 10X hand lens or, preferably, a dissecting scope to identify this pest. If you need help, please contact your local County Extension Agent. Finding one phylloxera when sampling is verification of an infestation.