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By: Maria Smith, HCS-OSU

A few weeks ago (April 22), we officially hit the starting line of the 2025 growing season. Despite some late pruning in our cold-hardy hybrid block, we are now finally at greater than 50% bud break in all cultivars at Hort Unit 2 in Wooster (Table 1). 

The good news is that this is one of the most “normal” starts to the growing season that we’ve had in years. Despite the polar vortex events of late January, bud injury was limited to less than 10-15% in most cultivars, including cold-sensitive Vinifera, and we narrowly avoided widespread freeze on 27 April, even if some vineyards had frost formation. There is another frost advisory forecast for tomorrow morning (8 May) in Ashtabula County, however, actual temperatures are only expected to reach the low-40s to upper-30s F, so we should still be safe from widespread freeze. 

Table 1. 50% bud break date of key trial cultivars at Hort Unit 2, Wooster, OH and GDD at bud break (base 50°F, 1 Jan to bud break date)

Cultivar	50% Bud break date	GDD (Base 50F)
Clarion	4/22	209
Frontenac blanc	4/23	220
Petite Pearl	4/25	252
Crimson Pearl	4/25	252
Itasca	4/21	203
Marquette	4/23	220
La Crescent	4/23	220
Aromella	4/25	252
Jupiter	4/21	203
Neptune	4/28	269
Cab Franc FPS 11	4/21	203
Chardonnay FPS 37	4/23	220
Albarino	4/23	220
Regent	4/23	220
San Marco	4/28	269

Management considerations for the early season

Many growers have reached out over the past couple of weeks pertaining to management questions regarding cultural, pest, and weed management. The following information should help answer some of those questions.  

Cultural management

Each growing season has a list of in-season canopy management tasks that should be completed in accordance with best grape growing practices. These include:

1. Shoot thinning, trunk suckering (6-12” shoot growth)
2. Leaf removal (fruit-set)
3. Cluster thinning (pea-size to bunch closure, when appropriate)
4. Shoot positioning (bunch closure to lag phase)
5. Shoot hedging/skirting (shoot tips folding over the trellis top, shoots on the ground)

We’ve finally reached the point in several cultivars at Hort Unit 2 are ready to be thinned/suckered (Figure 1). Keep in mind the priorities of shoot density, spacing, fruitfulness, and positioning (conformation to the trellis system, trunk/cordon replacement, and proximity to the fruiting wire). Even in cane-pruned vineyards, vines may require some, albeit minimal, shoot thinning to remove secondary and tertiary shoot emergence.

For more information on shoot thinning, see: Best viticulture practices: Shoot thinning  

  

Figure 1. (1) Shoot thinning (5/7/2025), (2) and (3) pre-thinning vs. post thinning spur position (NY 06), thinned cordon to 7 shoots per foot of cordon length (Frontenac blanc), (4) trunk suckering in Cabernet Franc (vertical shoot positioned) and thinned (left cordon) vs. unthinned cordon (right cordon) 

Pest Management

Disease

With shoots rapidly growing and the weather producing so much rain over the past few weeks, Phomopsis has started to pop up in susceptible cultivars (Figure 2). For context, we have had measurable rainfall in Wooster every day since 1 May, with a cumulative precipitation of 2.56”, 3.66” since 22 April. 

At the Hort 2 vineyard, we are shortening our spray intervals to every 7 days of Mancozeb and JMS Stylet oil (we have sulfur-sensitive cultivars planted) while we are stuck in what feels like an infinite loop of precipitation. To be more precise, I recently learned that it’s called an “Omega Block” and is the cause of this weather pattern. Once we reach the pre-bloom stage, we will begin to incorporate systemic fungicides into our spray program and will reconsider our intervals at that time.  

To note, mancozeb has not had a final decision made regarding its registration status and can still be used for the 2025 growing season. We will provide an update on mancozeb guidance when it becomes available. 

Because we’re rapidly approaching the critical period for disease management, I wanted to share some wisdom on practices for fungicide resistance management from Katie Gold’s article from the latest Finger Lakes Newsletter:

Fungicide resistance stewardship practices for commonly used products

• SDHI products (FRAC 7) such as the Luna family, Aprovia, Miravis Prime, Pristine, and Endura, no more than 3x/season and never twice in a row
• QOI products (FRAC 11) such as Abound, Azaka, Reason, Sovran, Topguard EQ, Flint Extra, Intuity, Pristine, and Quadris no more than 3x/season & never twice in a row– with caution, PM & DM resistance is well documented
• DMI products (FRAC 3) such as difenoconazole (the “Top” in common combos), Cevya, Inspire Super, Mettle, Rally, Procure, Rhyme, tebuconazole, and Topguard EQ no more than 3x/season & never twice in a row
• Revus and Zampro (FRAC 40) no more than 3x/season & never twice in a row – with caution, as resistance is well documented
• Vivando and Prolivo no more than 2x/season and never twice in a row
• Gatten, Torino, or Quintec no more than 2x/season each and never twice in a row
• Ridomil NEVER more than once per season

Figure 2. Phomopsis lesions developing on Clarion (MN1220) at Hort Unit 2, Wooster, OH. Photo taken May 6, 2025. Notice the small black lesions with a surrounding yellow halo. 

Insects

For the most part, when growers have sent in images of perceived pests they have, for the most part, been benign or friends. There are, however, instances of pests to watch out for early in the growing season. These include rose chafers, cutworms, and flea beetles. These pests cause damage through feeding on young buds and shoots. Flea beetle larvae can also cause damage to foliage (Figure 3). The threshold for control is low for these insects because of their ability to significantly reduce vineyard productivity and yield, but scouting is paramount for insect signs and injury symptoms prior to using insecticides.  

For those who have cultivars that are highly susceptible to foliar phylloxera (e.g., cold-hardy Riparia hybrids), control can be timed using growing degree days (GDD) or via incorporation of insecticides at key stages of vine growth. For more information on foliar phylloxera, visit Practical Tips for Managing Grape Phylloxera in Minnesota. 

Since GDD coincides with insect lifecycles, we can use them in conjunction with vine growth stages as well. Key insecticide timings for managing grape foliar phylloxera are summed up from Dr. Ashley Leach’s 2024 Ohio Grape and Wine Conference presentation here:

• Danitol (restricted use):
  • Application 1: Pre-bloom
  • Application 2: 10-14 days later
• Movento: 
  • Application 1: 4-10” shoot growth
  • Application 2: 30 days later 

 

Figure 3. Flea beetle adult (left) and larvae (right) feeding on grape foliage

Weed management 

With the vines having growth initiated, RoundUp (Glyphosate) is not recommended for use until later in the fall after the first killing frost. However, several contact options remain available for use during the growing season, including Rely 280, Aim, Gramoxone (restricted use), and Venue (original and Max formulations). These can also be tank-mixed with registered pre-emergent herbicides to provide residual control of weeds throughout the remainder of the season.

Similar to insects, scouting and identifying the weed population is a critical component to the success of an herbicide program. 

With all pesticides, read the label before use. Some pre-emergent herbicides have restrictions with vine age and the yield-bearing status of the vines. For more information on vineyard herbicides, refer to the herbicide section of the Midwest Fruit Pest Management Guide.   

Of course, there are non-chemical management options, as well. These include mechanical tillage, mowing, ground cover use, and integrated livestock (sheep! Figure 4). I will be reviewing options for alternative weed management in the coming months. 

Figure 4. Sheep grazing the vineyard floor (January 2025)

Herbicide Drift

Yes, it is that time of year again, and yes, I do expect this to be a long-term, ongoing annual problem. I have been seeing yellowing weeds around Wooster lately, which means that fields are being prepped with herbicide use. It is important to keep very close watch for neighboring applications, onsite weather conditions, and any symptoms of herbicide drift injury over the next 6-8 weeks. Please see the OSU factsheet series on preparing for and responding to herbicide drift injury. Working cooperatively with neighboring applicators is the best solution to avoiding drift injury.

We encourage all grape growers who experience herbicide drift injury to report to ODA. I fully understand and empathize with frustrations and anxieties over both the issue and process. However, the only formal way to document and quantify incidences of drift injury in Ohio is to report it.  Remember: anecdotes are not evidence. 

Wishing all of us fair weather and a trouble-free, productive growing season.