‘Morning all:
I have been out and about in the foothills area of GA (Cleveland/Dahlonega), but also up in the Yadkin Valley AVA in NC.
Depending on variety, bloom likely started mid- to late- this week in some warmer Yadkin Valley vineyards, and it will likely start sometime next week in the cooler Yadkin Valley vineyards with a bit more altitude.
In Cleveland and Dahlonega, Chardonnay is likely between 50-80% bloom – again depending on site. Cabernet franc and Merlot are roughly 30-50% into bloom in Cleveland (see Cabernet franc pictures from yesterday, below).
In northern and higher altitude GA regions (i.e. Tiger, Young Harris, Ellijay) trace bloom may already be observed in some earlier varieties, but these regions are likely going to see full on bloom in many varieties by late next week.
What does the fact that it is pre-bloom / bloom mean?
Several things really, but I’ll just focus on two with a particular emphasis on the latter – spraying and canopy management:
Spraying – I would encourage you to read the newest post on Dr. Mizuho Nita’s grape pathology blog(https://grapepathology.blogspot.com/).
There are MANY diseases to consider spraying for around this important time, and Mizuho elaborates on this. Further, his materials to the right side bar of his blog can offer further guidance. PLEASE USE THEM.
Canopy management – we had a well-attended workshop on May 4 about this very topic.
Remember that diseases can be managed by both chemical (spraying) and cultural (canopy management) methods. Fungal diseases of grape tissues are best managed culturally by reducing vine self-shading, and promoting an open canopy and fruit-zone.
Shoot thinning – If you have not finished shoot thinning, that should be a priority. As shoots grow and tendrils grab, shoot thinning just becomes more difficult. Recommendation for shoot density varies on training system, variety, and production goals, but 4-6 shoots per linear foot of row produces an economical crop without causing extreme canopy and cluster density.
Shoot positioning – it is best to position shoots so they are standing (or trailing) side-by-side like soldiers in a line. This maximizes functional (exposed) leaf area and limits leaf shading. Again, as tendrils grab and shoots grow, this becomes more difficult.
Leaf removal – here we go…
The question is always “how many leaves should I remove and when?” And, the answer is “it depends”. What are your goals? If you want to manage disease, any grape pathologist would agree that you should completely open the fruit-zone. However, if malic acid preservation is a goal, then a bit of shade may be warranted in some cases. It also depends on the labor situation in your vineyard – not all who want to pull leaves early in the season have time to do so because it is already a week after fruit set by the time shoot thinning and positioning are finished…
At this point, it is not too early to start thinking about removing a few leaves from the fruit-zone. While intensive (i.e. > 4 fruit-zone leaves) pre-bloom leaf removal can limit yields, results have been promising regarding early leaf removal effect on fruit composition and disease management. See picture, below, of a Cabernet Sauvignon cluster harvested from a shaded treatment up in Winchester, VA in the fall of 2015. I am going to go out on a limb and say that nobody wants to drink wine made from fruit that looks like this:
Some work that Tony Wolf and I have done up in VA (in this case, in Cabernet Sauvignon) has shown that removing 4 to 8 leaves before bloom can result in 38-66% crop yield reduction and 33-62% less compact clusters, compared to a no leaf removal-control. However, pre-bloom leaf removal also resulted in at least 78% less Botrytis incidence when compared to a no leaf removal-control. If you are going to remove leaves from the fruit-zone and don’t want looser clusters and reduced yields, I would recommend removing leaves immediately after fruit set, as leaf removal at this stage has no effect on fruit set and crop yield. However, if you want looser clusters and can afford some yield reduction, the pre-bloom and bloom stages may be a good time to remove leaves. The question becomes “will the reduced crop yield be offset by reduced disease incidence and increased wine quality potential?” That’s hard to say, but you have a great chance of reducing fungal disease incidence and late-season bunch rots by removing fruit-zone leaves. Further, I have seen many presentations and read many publications pointing to the fact that fruit exposure generally improves varietal character as well as increases the synthesis of positive sensory impact compounds. Besides crop yield reduction with intensive pre-bloom leaf removal, the only “risks” associated with generally intensive fruit-zone leaf removal are increased sunburn and reduced anthocyanins; see below comments on both items.
Anthocyanins: In the same, above-mentioned leaf removal work (in addition to similar work that was conducted in Petit Verdot and Cabernet franc): total berry anthocyanins were either maintained or increased with fruit-zone leaf removal in every year of the study – regardless of stage (pre-bloom, post-fruit set) or magnitude (4, 6, 8 leaves) of leaf removal. Why? Anthocyanins require light for their biosynthesis. But, light coupled with extreme (>35 deg. C) temperatures can result in reduced grape anthocyanins. It appears that the climate of the region in which this work was conducted (northern Shenandoah Valley of VA) did not result in enough radiant berry heating to reduce anthocyanins. This contrasts reports from the western US (San Joaquin, CA; Prosser, WA), where reduced anthocyanins were observed in well-exposed grapes.
Sunburn: Waiting until berries are marble sized to completely expose the fruit-zone may increase sunburn risk. However, we never saw sunburn over the four years (2012-2015) of the above-mentioned leaf removal work up in VA – regardless of stage (pre-bloom, post-fruit set) or magnitude (4, 6, and even 8 leaves) of leaf removal. Then again, some southeastern regions may be at high sunburn risk no matter what – however, I have never seen much, if any, data on this from NC and GA, but….
Research on fruit exposure: We are currently evaluating leaf removal at three different stages (pre-bloom, bloom, post-fruit set) to two different magnitudes (3 and 6 leaves) in a few varieties (Chardonnay, Merlot, Cabernet franc – see pictures below) in GA. We will evaluate radiation and berry temperature patterns, but also disease incidence, crop yield, and fruit composition. Further, we have leaf removal experiments underway in north-south oriented, vertically-shoot positioned Cabernet franc vineyards in GA, NC, and VA. In general – we are evaluating leaf removal effect on grape sunburn and anthocyanins in a very important vinifera grape that is widely planted across several east coast growing regions.
Looking forward to reporting on all of this.
That’s it (and that’s enough) for now. Give a holler if you need anything, and good luck with your pre-bloom and bloom stages.
Cain
