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By: Maria Smith, HCS-OSU
This past week, I have received several questions on when, where, and what to shoot thin (ST), so now is the perfect time to highlight the importance of this practice. In 2017, I co-authored an in-depth article on shoot thinning with Dr. Michela Centinari at Penn State that can be used as a cited companion resource to this blog post.
Shoot thinning is the first important canopy management practice following dormant pruning, especially throughout Ohio and the Eastern US where high humidity, temperatures, and precipitation pose significant challenges to vigor control and disease management. This practice reduces the density of the canopy through the selective removal of excess shoots, in turn opening the canopy to increased sunlight exposure and airflow. The main benefits of ST include:
- Reduce excess yield and decrease fruit shading, thus improving fruit composition at harvest
- Improved winter bud cold hardiness through increased sunlight exposure during bud development
- Lower disease pressure due to a less humid, faster drying canopy environment and, again, more sunlight penetration through the canopy
ST is best performed when shoots are between approximately 6-12” in length and, if possible, following the last date of frost. However, as Hickey, 2021 noted, constraints for timing ST may be dependent on labor availability. Also, hybrid varieties can be thinned before Vinifera due to the highly fruitful nature of secondary and latent/basal buds in the event of a spring frost. Very early ST (< 4”) can reduce the practice benefits by inducing emergence of secondary and latent buds, while late ST (> 12”) can be difficult due to the lignification of the shoot base. Late thinning should be performed using pruning shears to reduce injury to the vine.
As of this week (5/16/22), we are approaching the start of the window for shoot thinning at Unit 2 in Wooster (Fig 1).
Fig 1. Shoot growth at E-L stage 12 on 5/14/22 on Marquette. At this stage, shoots are about 5 leaves unfolded and 4” in growth.
Density of shoots:
For the sake of speed, keep in mind that these are estimates and visual inspections are sufficient as you are thinning. Only in academia will we stand around precisely counting shoots!
- Vinifera: 3 to 5 shoots per foot of cordon (= 18 to 30 shoots per vine at 6’ spacing)
- Hybrids: 4 to 6 shoots per foot of cordon (= 24 to 36 shoots per vine at 6’ spacing)
- Native or Labrusca varieties: up to 15 shoots per foot of cordon (= up to 90 shoots per vine at 6’ spacing)
As Dr. Patty Skinkis mentioned at the OGWC in February, spur vs. cane pruning tends to shift labor demands in the vineyard: spur pruning, while quicker to perform during dormancy, often requires more labor for ST than cane pruning. This is because spurs from older cordons tend to produce latent shoots that require removal, while cane pruning will typically produce one, or occasionally two shoots depending on secondary bud break, at each node position along the cane (Fig 2, Fig 3).
Fig 2. Shoot density of 2-bud spur (left) vs. canes (right). Note: increased density often arises from latent buds of older cordon wood or on vines with excessive bud retention in spur-pruned vines. Photos from Unit 2, Wooster. 5/14/22
Fig 3. Ideal shoot density, representing approximately 4 shoots per 1’ of space in V. vinifera Chardonnay. Photo from Unit 2, Wooster. 5/14/22
What shoots to keep/remove?
In a spur-pruned vine, the fruitful primary shoots from count nodes 1-2 on each spur should be prioritized (Fig 4). If a spur is becoming stacked, one well-positioned healthy shoot closer to the cordon may be prioritized for spur renewal. Fruitless basal and latent, diseased, weak-growing, and poorly positioned shoots should be the first to go, especially in highly dense portions of the canopy (Fig 5).
Lastly, unless retaining a shoot for potential cordon or trunk renewal, vine trunks should be suckered to prevent dense growth from shading the fruitful shoots (Fig 6). This can be accomplished easily at the 6-12” shoot growth stage by simply running a hand down the trunk of the vine to remove excess shoots.
Fig 4. Shoot emergence on a 3-bud spur on V. vinifera Cabernet Franc. 5/14/22, Unit 2, Wooster. Note: shoots that emerge on “non-count” buds are often fruitless in Vinifera and can be thinned. Fruitful shoots from nodes 1 and 2 should be prioritized for retention due to proximity to the cordon.
Fig 5. Example of a weak, fruitless latent shoot that should be removed during thinning
Fig 6. Example of a vine with dense growth on the trunk that requires suckering to remove the excess shoots and prevent canopy shading. 5/14/22, Unit 2, Wooster
By: Maria Smith, HCS-OSU
Finally! In the past week, the sun’s come out and so have the growing degree days (GDD). In fact, we have added 80 GDD (base 50 F) in Wooster since Monday alone. We pay so much attention to GDD because it is the primary driver of phenological development for plants. But did you know that it also determines insect lifecycles as well?
…It does, and we can use it to take advantage of when to monitor and manage insect pests in the vineyard. And even if not in the vineyard yet, like Spotted Lanternfly (SLF), we should still be taking advantage of GDD to know when we need to look for various life stages on major host plants.
SLF Egg Hatch prediction map
As of today, SLF range anywhere between about 1% hatch through 100% hatch, depending on location in the state (Fig 1).
Fig 1. SLF Percent of predicted hatch, from https://tools.cei.psu.edu/slf/
What should you be on the lookout for?
Currently, Ohio has 3 known counties with SLF populations: Cuyahoga, Lorain, and Jefferson counties (Fig 2). We expect egg hatch to be further along in Jefferson County than in the more northern Lorain and Cuyahoga counties. It is not unreasonable to suspect that there are other populations out there yet to be identified, therefore it would be prudent to regularly scout for tree-of-heaven (Fig 3) and SLF (Fig 4, 5). At this early point in the season, if you find SLF, you're most likely to encounter older or hatched egg masses (Fig 4) or early instar nymphs (Fig 5). In contrast to egg masses (immobile) and adults (large, showy), newly hatched nymphs are small and mobile, and more difficult to find (Fig 5). At this stage, the first instar nymphs are approximately ¼” in length with black and white spots. They are easily confused with other small insects, but to me look most like ticks. If you have a regular tree-of-heaven that you scout and would like to capture nymphs, using circle traps is one of the preferred methods for catching early SLF nymphs. Circle traps can be purchased through Great Lakes IPM or can be made DIY.
Fig 2. Current SLF distribution map, March 28, 2022. From https://nysipm.cornell.edu
Fig 3. Tree-of-Heaven stand (left) and trunk (right), found near downtown Wooster, OH, October 2021. Tree-of-heaven has shallow-fissured, greenish-brown bark, large compound leaves with two terminal leaflets, and persistent, prolific number of seeds on female trees that develop mid-summer.
Fig 4. SLF egg masses at various ages and coverings. Photo from: https://extension.psu.edu/what-should-you-do-with-spotted-lanternfly-egg-masses
Fig 5. Early instar nymph, SLF, Photo: L. Barringer, PA Dept. of Agriculture, https://bugwood.org
Increasing the search beyond tree-of-heaven (republished from ODA):
Spotted Lanternfly (Lycorma delicatula) has been identified on 172 hosts, some of which were determined to not be hosts on which feeding occurred. Through survey and research observations, there are several hosts on which SLF life stages are seen in higher frequency. Listed below are the hosts which can be surveyed to increase the potential for detection of SLF. SLF population levels and life stage will affect visual survey efforts with lower populations and early instars being more challenging to detect even with the higher frequency hosts at the time of survey.
Egg mass hosts are not listed in terms of high frequency of occurrence as egg masses can be found on many different tree and plant species as well as inanimate objects.
Penn State Extension Spotted Lanternfly website, Spotted Lanternfly Management for Residents, Landscape Professionals, Vineyards
Houping Liu, Seasonal Development, Cumulative Growing Degree-Days, and Population Density of Spotted Lanternfly (Hemiptera: Fulgoridae) on Selected Hosts and Substrates, Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1171–118
Houping Liu, Richard Hartlieb, Spatial Distribution of Lycorma delicatula (Hemiptera: Fulgoridae) Egg Masses on Tree-of-Heaven, Black Walnut, and Siberian Elm in North America, Journal of Economic Entomology, Volume 113, Issue 2, December 2019, pages 1028-1032.
Joseph Keller, J. Rost, K. Hoover, J. Urban, H. Leach, M. Porras, B. Walsh, M. Bosold, and D. Calvin, Dispersion Patterns and Sample Size Estimates for Egg Masses of Spotted Lanternfly (Hemiptera: Fulgoridae), Environmental Entomology, Volume 49, Issue 6, October 2020, pages 1462-1472.
Lawrence Barringer, Claire M Ciafré, Worldwide Feeding Host Plants of Spotted Lanternfly, With Significant Additions From North America, Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 999–1011.
If you suspect presence of SLF, report your findings to the Ohio Department of Agriculture by calling 614-728-6400, emailing firstname.lastname@example.org, or filling out the online report. Sightings of all invasive species in Ohio can be reported using the Great Lakes Early Detection Network App, which can also be used to report repeated negative or positive findings of tree-of-heaven and SLF. Please take photos and exact locations (GPS, identifiable landmarks, etc.) to file with your report.