- Fruits: grapes
- Pest Management: weed ecology
- Soil Management: soil analysis
This project investigates the problems of excessive canopy and weed control in a southern vineyard through soil analysis while employing a variety of ground covers. The shading as a result of canopy overgrowth has precluded harvest in this Traminette plot and has proven to be a regional challenge in other vineyards growing this and other varieties. Excessive canopy growth was attributed to excessive available nitrogen (N) in the soil, although no fertilizer additions have been applied in the past 5 years. The experimental approach was based on the hypothesis that excessive N was the main contributor to excessive canopy growth. The addition of high carbon materials (e.g. straw or wood mulch) will immobilize N into the organic N fraction of the soil, making it unavailable for plant use until this material is mineralized into a plant available form. The use of a cover crop will utilize available N in the soil that is incorporated into the plant biomass, rendering it unavailable until that material decomposes and goes through the mineralization process described above. Both mechanisms will reduce the amount of plant available N and would reduce N uptake by grape, to reduce the early season vigor experienced with this variety. Further, the use of ground cover (cover crop and mulch) can suppress weed pressure by shading, out competing, or creating a physical barrier to weed growth. After project initiation and first year data analysis, it was concluded that other factors such as Traminette vigor were more influential than native soil fertility levels, but the treatments established in 2012 remained in place for 2013 to confirm these results.
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2012 offered a major challenge to the study design consequent to minimal rainfall as affecting rye grass stands and the usual weed pressure. I consider this to be somewhat ironic as I had previously suspected the frequent summer rains to play a significant role in the genesis of excessive canopy (along with particular varietal characteristics and nitrogen availability). Obviously the rainfall threshold to allow excessive vigor falls below the offerings of even an historically dry southern climate. 2013 was also plagued with challenges, a late freeze after budbreak followed by excessive rainfall during the remainder of the growing season.
No difference in canopy density could be demonstrated between plots pruned more vigorously pre-budbreak and those pruned in routine fashion as guided by UK viticulture specialists. Consequent to this fact we propose to alter plot management as pertains to differential pruning. All plots will be pruned in identical fashion prior to budbreak. Mid-summer selective pruning and leaf-pulling will be employed in those plots previously pruned more vigorously in early spring. If nitrate availablility and the effects of various ground covers do not offer a solution to this ubiquitous problem, a second pruning may represent the only viable answer, despite its cost.