Winegrape growers are continually faced with balancing acts, regardless of where they farm.
Too much canopy can be a detriment to berry quality, disease management and ripening.
Too little canopy, and the fruit can be sunburned.
Like many growers elsewhere, Michigan grape growers pull leaves to create microclimates around the clusters, according to a news release.
But Paolo Sabbatini, a Michigan State University horticulture assistant professor specializing in viticulture, could find no standard timing as he talked to growers.
If you pull too many leaves, you remove the plant's powerhouse responsible for converting sunlight and nutrients into carbohydrates. You also remove the cluster's natural shade, setting the fruit up for sunburn.
Remove too few and you create a humid microclimate conducive to disease.
Complicating the entire equation is Michgan's shortened growing season, which is 120 to 140 days, compared with California's longer season.
Sabbatini chose to conduct trials with pinot noir, a finicky variety prone to bunch rot because of tight clusters and thin skin.
When he pulled leaves at bloom, he found that plants set less berries, making clusters looser.
That's actually a benefit, since looser clusters are less susceptible to bunch rot.
He also looked at leaf pulling durig ripening. If they were pulled too early, there was no effect.
Leaves pulled at veraison helped ripening as does cluster thinning at the same time.
But pull leaves too late, and growers can see negative effects.
In trials with chardonnay, Sabbitini found leaf removal before bloom did not affect cluster set.
But when he pulled leaves at bloom, Sabbitini noticed the number of berries per cluster was reduced. There also was better skin to pulp ratio, which is desirable.