Floor management systems to reduce vineyard inputs and improve grape quality

Abstract

This project investigated the effect of three distinct floor vegetation management treatments on vine performance, grape and wine quality, and plant, arthropod and soil microbial biodiversity in vineyards. The three floor vegetation management treatments applied were (1) unvegetated where the entire floor vegetation was sprayed with herbicide, (2) partially vegetated, which involved the spraying of the undervine area only, and managing the interrow vegetation by mowing, and (3) vegetated where floor vegetation was managed by mowing with no herbicides used. Increasing levels of ground vegetation led to decreased early-season soil moisture and petiole nutrient status, and strongly reduced vine vegetative growth. After three years, grape yield also became limited. Large treatment differences in vegetative growth, canopy structure and yield contributed to differences in berry weight and composition. Treatment differences in berry quality at harvest also gave rise to differences in sensory perception of wines made from the fruit. Large differences in vine vigour between the treatments were observed at Wagga Wagga whereas these differences were less pronounced in the milder climatic conditions at the Tumbarumba site. Some weed species resistant or tolerant to glyphosate such as annual ryegrass, mallows, stocksbill, wireweed, goosefoot, peppercress, shepherd’s purse and skeleton weed increased in dominance over time in the herbicide treatments and have the potential to develop herbicide resistance. In general, bacterial and fungal counts were significantly lower in the unvegetated treatment. Hot water extractable carbon (HWC) was positively correlated with fungal counts and with cellulolytic, pseudomonad, copiotrophic and oligotrophic bacterial counts in both the interrow and under-vine soil. HWC was also negatively correlated with soil bulk density. The grapevine rhizosphere bacterial population was dominated by cellulolytic bacteria, which were positively correlated with soil HWC and populations were significantly higher in the vegetated treatment. Beneficial nematodes, namely bacteria-feeders, omnivores, fungi-feeders and predators, were more abundant in the top 0-10 cm soil in the inter-row than in undervine positions. In contrast, higher population densities of plant parasitic nematodes were recorded in under-vine positions. There was no strong or consistent impact of any of the floor management treatments on arthropod richness, abundance or biodiversity in pitfall and sticky window traps. There was some evidence of increased springtail and ant abundance in unvegetated treatments, and increased abundance of natural enemies like ladybird and rove 10 beetles, lacewings and wasps in vegetated and partially vegetated treatments. Rutherglen bug was consistently more abundant in vegetated than unvegetated treatments at Wagga Wagga. Pilot biological control field trials showed that predation and parasitism rates of grapevine moth eggs were very low in both vegetated and unvegetated treatments. In contrast, high rates of predation of grapevine moth larvae by predatory shield bugs and green lacewing larvae were recorded but there was no significant difference between treatments.

Summary

Effect of three different ground cover treatments on the plant, insect and soil microbial diversity in two Chardonnay vineyards, and impact on grape and wine quality. Increasing ground cover decreased soil moisture and petiole nutrient status, and strongly reduced vine growth. After three years, grape yield also became limited, and after four years, the grape composition was also altered, all effects stronger under hot than mild climatic conditions. Reduced herbicide use increased soil organic matter and microbial diversity in the 0-10 cm soil layer. Slight increase of beneficial and decrease of parasitic nematodes with reduced herbicide use, and evidence of increased abundance of natural enemies like ladybird and rove beetles, lacewings and wasps. Some weed species, known to have the potential to develop herbicide resistance, became more abundant with increased herbicide application.