DR. Paul's Research Update
Deciphering decline in grape vineyards

More problems in monoculture-land

By Paul Hepperly

August 31, 2004: All over the world, grape growers and scientists are becoming increasingly aware of decline in fruit productivity and quality with prolonged perennial production and with replanting in un-rotated fields.

In a recent issue of Wine East: News of Grapes and Wine in Eastern North America, Dr. Elwin Smith and Nancy Wenner of Pennsylvania State University detail some of the pathological agents associated with grapes in decline. These include: fungal root diseases, crown gall bacterium, tomato ringspot virus (TRSV) and dagger nematodes. (Dagger nematodes are both parasitic on grape roots and transmit TRSV to roots and vines.)

The decline of grape vineyards depends on the age of the grape vines and on the variety planted. Vine decline appears to affect all grape varieties, but American grapes are much more tolerant of the condition than French American or French varietal types. Within each class of grapes there is much variation in susceptibility as well. In terms of TRSV, for example, 37 percent of French American Hybrids, 23 percent of American and 18 percent of French varieties showed susceptibility.

Vineyards over 10 years old are particularly affected by decline. For organic and conventional vineyards, the selection of grape varieties should include their ability to withstand over time and not just short term quality considerations. The type of grapes and variety selection within the grape class are very important in this regard.

In another study focusing on grape decline after re-planting, master's student Fritz Westover and Dr. Jim Travis, also of PSU, investigated biological and non-biological causes of this malady. Results presented at a recent field day sponsored by Pennsylvania Association of Wine Growers showed that by pasteurizing soil and comparing growth to non-pasteurized soil, Westover and Travis found that 4 out of 6 farmer re-plant problems could be significantly helped by heat treatments. Soil amended with compost effectively increased vine growth in 2 out of 3 test situations. Mixing soil with compost reduced root discoloration and increased grape root mass.

Although soil from around the vines was associated with poor growth and showed improvement after pasteurization, taking soil from adjacent grassy areas showed no poor growth, and pasteurization decreased grape performance. This indicates that grass strips have a grape-positive microflora that is inhibited by pasteurization.

Besides the buildup of pathogens in soil, Westover and Travis found that herbicide injury to grapevines is common. Bioassays with lettuce and cucumber seedlings showed that simazine, a triazine herbicide related to atrazine, can persist in soils and cause subsequent replanting problems.

Paul Reed Hepperly, Ph.D., is research and training manager at The Rodale Institute.