Soil Analysis Directed Ground Cover Approaches to Excessive Canopy and Weed Control in Southern Vineyards

Soil Analysis Directed Ground Cover Approaches to Excessive Canopy and Weed Control in Southern Vineyards

Summary

Introduction

This project investigates the problems of excessive canopy and weed control in a southern vineyard through soil analysis by 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 alternate varieties.

Objectives/Performance Targets

The approach consists of initial soil analysis followed by various multiple plot applications (four replications of 5 vine groups) of woodchip mulch, wheat straw, rye, Gramoxone/Chateau herbicide combination, and additional pruning treatments. Soil samples were collected - nutrients, nitrate samples twice (April 2012 and February 2013), tissue samples (petiole), and soil organic matter. Weed pressure was visually rated and canopy density quantitated.

Accomplishments/Milestones

Initial Results and Observations

1. Soil nitrate (NO3) levels were near baseline for Kentucky soils. (Anything less than 10 ppm would be considered normal baseline for this region.)
2. NO3 samples were lower in 2013 than 2012, but at these levels probably a function of sampling time more than treatment effects.
3. Tissue samples low in nitrogen and phosphorus.
4. Pruning demonstration conducted by University of Kentucky viticulture staff to address appropriate spring pruning of this variety on a Geneva Double Curtain trellis system
5. Driest early spring and summer in more than 30 years (documentation to follow) resulted in poor rye grass stand precluding valid assessment of those plots in terms of both weed control and soil nitrate impact
6. Weed pressure somewhat reduced in 2012 as consequence of dry conditions
7. In terms of weed suppression, method effectiveness in decreasing order as follows: Gramoxone/Chateau (fortunately had rainfall 3 days after application), wood mulch, straw, and lastly rye grass (poor stand)
8. No difference in canopy density could be demonstrated between either different ground cover plots or between different pre-bud break pruning
9. No commercial crop could be harvested because of poor quality (low brix) and diseased (invariable consequence of shading/poor air circulation) fruit

Impacts and Contributions/Outcomes

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.

No difference in canopy density could be demonstrated between plots pruned more vigorously pre-bud break 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 bud break. Mid-summer selective pruning and leaf pulling will be employed in those plots previously pruned more vigorously in early spring. If nitrate availability 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.