With the frost risks largely in the rear-view of April, we are starting to see new shoot growth bolt ahead under warming temperatures of the past week (Figure 1). Keep in mind, if you did have damage from those late-April freeze events, you may just be starting to see the emergence of secondary and tertiary shoots (Figure 2).
Figure 1. Shoot growth Chardonnay 4-May 2023 at E-L stages 3-4.
Figure 2. Primary and secondary shoot emergence from single node position
Cumulative GDD in Wooster is near the historic average for this time of year (Figure 3) as warm early- and mid-April temperaturs have been buffered with a cool down in late-April through early-May. As mentioned in the last post, we saw two late spring frost events that contributed to wide-spread injury to many vineyards in the northern portions of the state.
April precipitation (4.0”) was 0.6” above the 10-year average rainfall (3.4”), but we are currently on track for a drier than average May, with only 1.3” of accumulated rainfall in the first 2 weeks of the month.
Figure 3. Wooster, OH cumulative GDD (base 50F) as of May 16 = 372, historic GDD for May 16 = 383. Chart from CFAES Weather System (https://weather.cfaes.osu.edu)
Timely vineyard management:
Below are some considerations for cultural management of your vines at this early stage of the growing season:
- New vineyard plantings: Now through early June is when we need to get our new vineyard plantings completed. If dry weather persists, new vines should be irrigated. 1 and 2-yr-old vines should receive around 0.5” to 1” of water per weekthrough rainfall and irrigation while root systems are being established.
- 2 and 3-yr-old vines: retain the 2-3 shoots required for continued trunk and/or cordon establishment and remove the remaining shoots from the trunk. Remove inflorescences (flower clusters) from the remaining shoots. The goal of these tasks is to encourgage robust vegetative growth of young vines.
- Mature vines: Shoot thin vines when shoots are between 6-12” in growth. For details on shoot thinning and suckering mature vines, visit our blog post from May 2022 and review our video on canopy management here. *Note: shoot thinning for vines that were adjusted for bud counts following winter injury is critical, as canopies will be denser with greater bud retention.
- The process of de-hilling soil around grafted vines should be completed to prevent scion rooting
With the rapid rate of shoot growth along with the increase of average daily temperatures, it’s important to ensure your shoots stay protected against early season diseases, including Phomopsis, Anthracnose, Black Rot, Downy Mildew, and Powdery Mildew. Remember that disease management should be preventative beginning around 1” of shoot growth and combined with best canopy management practices.
For successful control, it’s important to understand the disease, cultivar susceptibility, and management options. There are several resources available for disease management such as the Midwest Fruit Pest Management Guide, Developing an Effective Fungicide Spray Program for Grapes in Ohio, and NY/PA Pest Management Guide. Fact sheets on important grape diseases can be found here. Read and follow all label guidelines and ensure proper fungicide rotation and sprayer coverage/calibration to reduce risks for fungicide resistance.
During the warm stretch of April, I was hearing from several growers about the prevalence of grape flea beetles in vineyards seen brazenly snacking on swollen buds. Adult beetle damage to newly developing buds can be economically damaging to yield if not adequately controlled. Flea beetles tend to be most concentrated along vineyard boarders in proximity to wood lines, so treatment may only need to be targeted in certain portions of the vineyard. Thresholds for spraying flea beetle have been suggested at 2 to 4% (or 2 to 4 injured buds per 100 buds checked), and broad-spectrum insecticides work well against flea beetles if necessary to use. Be aware that flea beetles go through one lifecycle per season and that their larvae can cause damage and skeletonization to leaves through June (though rarely in sufficient quantity to be considered economically important), and control of larvae may help reduce future populations of this insect.
Herbicide drift injury
Rapid shoot growth in vineyards generally coincides with planting time for row crops, and with that comes the risk for herbicide drift injury. The most effective way to reduce the risk for herbicide drift injury is to develop relationships with neighboring farmers and applicators and inform them about the proximity of your vineyard. However, drift injury may still happen, and it’s best to be prepared since drift events are sporadic and difficult to predict.
An early, subtle symptom of auxinic herbicide (2,4-D, dicamba, etc.) injury is shoot epinasty, which can be mistaken for other abiotic stresses like drought (Figure 4). Other symptoms including leaf cupping, curling, and chlorosis (leaf yellowing) may take additional time to develop and depend on the amount of herbicide exposure (Figure 5).
If you suspect your vineyard has experienced an herbicide drift event, document your evidence as soon as possible and consider taking action by contacting the Ohio Department of Agriculture to file a complaint. — By Maria Smith, HCS, OSU
Figure 4. Shoot epinasty, or the downward growth of shoot tips. 48-hrs following low-concentration herbicide exposure.
Figure 5. Leaf cupping patterns 48-hrs following high-concentration dicamba exposure.