The information provided on this pamphlet is based on the unpublished results of a series of bioassays on replant soils from Pennsylvania vineyards from 2002-2003. Results are summarized and recommendations for the testing of vineyard replant soils are provided below. This reference is not for citation.

Introduction:

Replanting of grape in existing vineyard sites is a common viticultural practice in Pennsylvania. Young vines often show symptoms of mature vine decline, such as delayed and weak vine growth, sparse yellow foliage, shortened internodes, uneven wood maturity, root rot and reduced feeder roots. Grape replant disorders have been associated with both biotic and abiotic factors. Bioassays were conducted to determine the role of biological factors in young vine decline in Pennsylvania and the effects of compost on vine growth and soil microbial activity. Growth parameters of French-American hybrid winegrape cultivar Vidal Blanc and rootstock Couderc 3309 were examined in heat sterilized, compost amended and untreated soils from six replant sites. Based on the results of the greenhouse bioassays, four of the six sites showed characteristics commonly observed with grape replant disorder in the field. Significant decreases in soil microbial activity resulting from the heat treatments were associated with increased vine biomass. Diseased plants often had fewer roots and larger proportions of dark colored roots than those planted in heated vineyard soils or soils adjacent to the replant disorder where grapes had never been planted. Alterations in mineral nutrition of the soil, especially ammonium and manganese, resulted from the heat treatment although plant tissue analysis confirmed that increased growth of vines was not attributed to plant nutrition. Soil amendments with poultry manure and municipal yard waste composts increased vine biomass in two of three sites tested and decreased mass in the third. The growth benefits of the compost were accredited to a temporary decrease in microbial activity of the soils and increased soil nutrient levels.

Biotic and Abiotic Soil Factors to Consider Prior to Replanting of Grapevines:

I. Soil pH and Mineral Nutrition

Analysis of soil pH and nutrient content is not only necessary prior to the initial planting of a vineyard but also prior to replanting grapes in an existing vineyard site. Changes in pH may occur over time with the addition of fertilizers. Some nitrogen-containing fertilizers (e.g., sulfate of ammonia, ammonium nitrate, urea) can be acidifying to the soil if applications of lime (calcium and magnesium carbonates) are not applied in neutralizing quantities (1). Compost or other organic amendments should also be tested for pH and nutrient content. The addition of basic compost (pH >7) to replant soil slightly increased soil pH in potted vine bioassays in this study. An additional analysis of pH may be desired after fertilizers or compost are added to soil.

II. Nematode Analysis

Presence of the dagger nematode, Xiphinema spp., contributes to replant disorder in vineyard soils of the northeastern US. Dagger nematodes vector tomato ringspot virus (ToRSV), a common pathogen associated with vine decline of several grape cultivars in Pennsylvania (4). Presence of grape roots in the replant soils in this study were associated with increased populations of the dagger nematode genus Xiphinema, suggesting an association between grape roots and survival of the genus Xiphinema in Pennsylvania. To determine nematode populations, soil samples from the root zone of replant sites may be submitted to Dr. John Halbrendt, Nematologist at the Fruit Research and Extension Center, The Pennsylvania State University, Biglerville, PA. The number of plant pathogenic genera Xiphinema, Pratylenchus, Hoplolaimus, Helicotylenchus and Criconemella are determined per 100cc of soil. Cover cropping with up to 2 green manure crops of brassicas (e.g., rapeseed, mustard) for a season prior to replanting can reduce nematode populations. As an additional measure, replants can be established in the row middles of the previous planting if the removal and reestablishment of post and wires is an option. Action is recommended when a population of Xiphinema exceeds 6 per 100cc of soil (5).

III. Herbicide Phytotoxicity

Herbicide injury to grapevines may occur from either direct contact with leaves during application or absorption by roots (3). A simple bioassay to determine high rates of herbicides residing in replant soil may be conducted by germinating vegetable seeds in the soil. Four replicates of lettuce (Lactuca sativa cv. "Buttercrunch") and cucumber (Cucumis sp cv. "Marketmore") were germinated in pots containing replant soil. Symptoms of herbicide toxicity were not expressed in vegetable seedlings grown in the six major sites evaluated, although in a preliminary survey of replant disorder, vegetable seedlings expressed toxic foliar symptoms characteristic of the pre-emergent Simazine when grown in several replant disorder soils. Symptoms observed on vegetable seedlings after three weeks included stunted growth and chlorosis of cotyledons and true leaves (Figures 1-4). Similar foliar symptoms were observed in vineyard weed species at those sites, such as purslane (Portulaca oleracea L.).

IV. Site Evaluation for Biological Replant Disorder

Heat sterilization of vineyard soils is not a practical pre-treatment for eliminating soil-borne microorganisms in the field; however, a bioassay may be conducted in pots by comparing the growth of vineyard cuttings in heat treated versus untreated vineyard soil provided from the replant site. Such bioassays are useful for evaluating the 1st year growth of replanted vines prior to replanting. A small-scale trial may be conducted as follows:

Collect 5-10 samples of soil from the rooting zone (10-30cm depth) of the replant site and combine the samples. Scrape the top inch of soil away prior to sampling to remove surface litter and remove large rocks from the samples when mixing. Collect enough soil to fill 20 pots (approximately 3" wide x 6" tall).

Divide the sample into two equal parts. Store one portion in a cool dark place (35-55oF). Air-dry the other portion and then place it into a pre-heated oven at 180oF for one hour.

Obtain rooted cuttings of the desired replant cultivar/rootstock and place one in each pot (10 pots containing heated soil and 10 containing untreated soil). Water the potted vines as necessary and observe the root and vine growth after 8-12 weeks.

If root and vine growth are visually reduced in the untreated soil then a biological soil-borne factor (e.g., fungal, bacterial or nematode) may be inhibiting young vine growth in your site. A soil sample can also be submitted for nutrient analysis to determine if mineral deficiencies contributed to the replant disorder. It is important to note here that soil sterilization techniques are non-selective and will also result in the reduction of beneficial microorganisms.

V. Compost Additions to Replant Soils

Numerous studies have demonstrated disease suppression of specific root and foliar pathogens on agricultural crops by use of compost. The mechanisms of biological control associated with compost treatment of soils include: the addition of microorganisms that compete for nutrition and for spatial occupation with the general soil microflora, production of antibiotics, and the induction of systemic acquired resistance (SAR) in the plant leading to resistance to root and foliar diseases (2). An objective in this study was to determine if compost had an effect on replant disorder of grape. Mixing compost with soils diagnosed with biological disorders increased root and vine mass and reduced discoloration of roots in this study. Both composted manure and composted yard trimmings produced similar results when applied to potted vineyard soil at a rate of 15% total volume. More information regarding compost applications in commercial vineyards can be reviewed at http://fpath.cas.psu.edu/.

VI. Summary

Not all grape replant disorders in Pennsylvania were caused by interactions of soil-borne microorganisms with roots. Replant disorders may be the result of a complex of both biotic and abiotic factors. Abiotic factors to consider in replant disorder of grape include; nutrient deficiencies or toxicities, residual herbicide in surface soil, competition by weeds, water logged soil, drought, and cold injury to young vines. Damage from wind and road salts were also observed in vines on end rows of vineyards near open fields or roadsides respectively. Greenhouse pot bioassays provide useful information regarding herbicide residue and the effects of soil amendments in grape replant sites. Young vines have less developed root systems and appear more sensitive to many of the above stress factors. Further research on the long-term effects of compost and green manure amendments in grape replant situations in the field would benefit the grape industry in Pennsylvania by improving recommendations for grape growers.

VII. References

1. Bates, T. R., Dunst, R. M., Taft, T. and Vercant, M. 2002. The vegetative response of 'Concord' grapevines to soil pH. Hort. Sci. 37(6):890-893

2. Hoitink, H. A. J., Stone, A. G., and D.Y. Han. 1997. Suppression of plant diseases by composts. Hort. Sci. 32:184-187.

3. Pearson, R. C., Pool, R.M., Jubb, Jr., G.L. 1998. Disorders caused by abiotic factors. Pages 65-71 in: Compendium of Grape Diseases. R. C. Pearson and A. C. Goheen, eds. APS Press, St. Paul, Minnesota.

4. Stewart E. L., Wenner, N. G. 2004. Grapevine decline in Pennsylvania and New York. Wine East. 32(2):12-21, 51-53.

5. Travis, J. W. 2004. Personal communication. The Pennsylvania State University, Department of Plant Pathology, Fruit Research and Extension Center, Biglerville, PA.