Hail netting changes to spray droplets and patterns in grape canopies

Abstract

While hail netting in vineyards provides effective protection to wine grapes (Vitis vinifera L.) from hail, pests, and bird damage, it may also affect the spray efficacy. This study tested the interaction between hail netting and location within the canopy in determining spray droplet characteristics. Two grape cultivars (Petite Sirah FPS 04 and Touriga Nacional FPS 05) grafted onto 1103P rootstock were examined to assess spray coverage, droplet size distribution, and deposition within grapevine canopies under netted and unnetted conditions. Spray droplets were measured using spray cards placed at five locations within the canopy. Significant interactions were observed primarily at the base of the canopy directly above the cordon, where grape clusters are most concentrated. Unnetted Touriga Nacional exhibited higher spray coverage compared to Petite Sirah, attributed to its looser cluster structure. Hail netting standardized all parameters across both cultivars, mitigating the influence of canopy and cluster differences. Hail netting created smaller, uniformly distributed droplets within the canopy, an essential characteristic of effective pest and disease control. Conversely, without netting, larger droplets were unevenly distributed, predominantly settling on the outer and lower canopy sections. Hail netting also maintained deposit densities within recommended ranges, supporting effective pest and disease management without compromising spray coverage. The consistent spray coverage achieved with hail netting across all canopy locations highlights its role in improving application uniformity and grapevine health, leading to evenly ripened, high-quality fruit. Contrary to the perceived risk of reducing spray efficacy, hail netting appears to enhance vineyard spraying outcomes, potentially offsetting netting costs.