Monitor your vines for color change in the fall

By: Maria Smith, HCS-OSU

My favorite week of the year is here: peak fall color has finally arrived in Wooster. 

Like the maples, oaks, and hickories, grapevines are perennial woody plants that drop their leaves in the fall in a process called leaf senescence. This process is principally a response to hormonal cues (abscisic acid (ABA) and ethylene) and metabolism changes induced by shorter daylength and exposure to colder temperatures (32-50 F). However, several other factors influence the timing for leaf senescence, including stress factors (drought, disease), rootstock selection, and cropping decisions [1-4].

Leaf senescence plays a vital role in vine health through the reabsorption of nutrients that are stored overwinter and are used to support vine growth early in the growing season [5]. So, having an extended fall acclimation period has been nice in terms of seeing leaf yellowing in the post-harvest period prior to the first hard killing freeze (< 28 F) forecast for early next week. Typically, the first killing freeze on average in Wooster occurs during the last week of October, hastening leaf fall and dormancy. 

During this time, there are still plenty of post-harvest activities still ongoing in the vineyard, including soil hilling for graft union protection, taking down netting and clips, and managing undervine weeds. As part of these activities, we encourage you to look at the vine foliage for deviations and patterns in leaf color. 

In general, healthy grapevine foliage turns yellow in the fall (Fig. 1). This color is due to the breakdown of cell structures like chlorophyll that are in part responsible for reflection of green light. Some cultivars do characteristically have red leaves, therefore this is not universally true and why it’s important to know your cultivar traits (Fig. 2). However, conspicuous presence of red leaves in an otherwise sea of green and yellow, should elicit an eyebrow raise and further consideration for the overall vine health (Fig. 3), since red leaf coloration is related to stress response of the vine [6].

Figure 1. Typical leaf yellowing during grapvine acclimation in the post-harvest period at Hort Unit 2. Photo: Fernanda Cohoon. 

Figure 2. Naturally occurring red leaf coloring in a Vitis hybrid. August 2025 NE Italy. Photo: Maria Smith

The University of Maryland and Rutgers University have both put together great resources regarding four different reasons leaves may turn red, identification, and management: 

1) Nutrition deficiencies (potassium, magnesium) 
2) Virus infection (Grapevine leafroll associated virus, Red blotch virus) -- Fig. 3 
3) Crown Gall infection (Agrobacterium) -- Fig. 4
4) Canker and other trunk diseases (Eutypa, Botrysphaeria) 

Figure 3. Red leaf coloration with green veins and leaf margin curling associated Grapevine Leafroll Associated Virus. Photo: Maria Smith 

Figure 4. Red leaf coloration associated with Crown Gall infection (top) and gall formation on base of trunk that is leading to red leaf symptoms on only the right side of the vine (bottom). Photo: Maria Smith

Now that we’re moving into post-harvest, it’s time to take stock of the reason(s) you may be seeing red:

• Did your vine trunks experience winter injury that led to trunk infection (Crown gall, cankers)? 
• Did excessively wet (spring) or dry (summer/fall) conditions limit nutrient availability and uptake (potassium, magnesium)? This may be more noticeable in young vines with limited root system establishment
• Have you been noticing year-over-year declines in yield and fruit quality, particularly among older Vinifera plantings (leafroll virus) that are otherwise healthy? (Fig. 5)

Figure 5. Cluster architecture of leafroll infected Cabernet sauvignon vines (top) vs. cluster architecture of asymptomatic Cabernet sauvignon vines (bottom). Photos: Maria Smith and Diane Kinney

The reasons inform the response. It’s important to observe patterns of leaf coloration throughout the growing season (emergence date, leaf age, distribution changes in the canopy) and, where feasible, keep close records of yield, fruit maturity, send tissue samples for diagnostics, regularly monitor vine nutritional status, and possible injury events to make informed determinations. 

Citations:

[1] Poni et al. 1994. DOI: 10.5344/ajev.1994.45.2.252
[2] Peterson and Walker. 2017. DOI: 10.5344/catalyst.2017.16006
[3] Keller et al. 2014. DOI: 10.5344/ajev.2014.14042
[4] Edson et al. 1993. AJEV. 44:2. 139-147.
[5] Schreiner. 2016. DOI: 10.5344/ajev.2016.16019
[6] Espinoza et al. 2007. DOI: 10.1093/jxb/erm165