Winegrowers have set their canopy density by this time of season by shoot thinning where needed (shoot thinning should occur before bloom). In the time period from bloom to fruit set, grapevine shoots should be about 24 to 36 inches long or greater, and the first round of shoot positioning has ideally be completed. Many growers sent petiole samples to the lab at bloom and should be receiving the results shortly and fine tuning seasonal fertilization (see Bloom Petiole Sampling post).
Most vineyards in Texas that survived the late spring frost are experiencing good fruit set, with berry size ranging from “bb” to “pea” size, and vineyards a bit farther north in Georgia are just now entering bloom. The best time to make the first round of leaf pulling (selective leaf removal) is within the 2 to 4 week period after bloom. Not all varieties or training systems will need the same level of leaf thinning (if any), but below are some general tips:
- Leaf pulling early after fruit set allows young berries to adapt to sunlight. Leaf pulling late in the summer increases sunburn risk and is generally avoided in hot climates.
- Leaf pulling within 4 weeks of fruit set can reduce vegetative flavors in red winegrapes at harvest (reduced levels of methoxypyrazines).
- Leaf pulling after fruit set will allow better spray penetration for fungicides at the critical time of disease susceptibility.
- Leaf pulling after fruit set allows better cluster coverage of insecticides for grape berry moth
- Leaf pulling on the side of the canopy receiving early morning sunlight will reduce moisture and morning dew on clusters, reducing potential disease pressure.
- Leaf pulling more selectively, or not at all on the side of the canopy receiving afternoon sunlight will reduce the incidence of sunburn on fruit in hot climates.
- The amount of leaf pulling (if any) will differ based on grape variety and grapevine training system
Growers with less than 10 acres of grapes are most likely pulling leaves selectively by hand. Once a worker is used to the task of leaf removal, it can be done quickly and without stopping between vines. Check out the video tutorials page to learn more about leaf pulling.