Viticulture & EnologyNewsExtensionViticulture & Enology Extension News – Spring 2026

Viticulture & Enology Extension News – Spring 2026

April 13, 2026

Vineyard Idling: Part 2

Author: Michelle Moyer, Washington State University

As promised in the Fall 2025 Issue of VEEN, we have created additional recommendations on how to plan for vineyard idling during the growing season. The information below is a quick summary of things to consider — full recommendations and details on how to approach idling can now be found in our official WSU Extension publication titled Idling Vineyards in the Pacific Northwest.

Irrigation and Nutrition in the Growing Season

If a vine is not being managed for crop production, than irrigation can be reduced accordingly. While it is still important to maintain vine water access for long-term survival, irrigation can be significantly reduced. Current recommendations include refilling the soil moisture profile in the spring, but then witholding water through fruit set. This will help reduce berry set and limit crop size. It will also help limit canopy growth. After fruit set, a modified irrigation schedule can be adopted to help keep the canopy functional.

Only minimal nutrient regimes are needed in idled vineyards. This includes nitrogen at low rates to help replace what was removed during vineyard pruning. Other nutrients are not needed in an idled program unless foliar deficiency symptoms are seen.

Canopy and Pest Management

With minimal irrigation and fertilization, canopy growth should be naturally reduced in an idled vineyard. If canopy management is still needed, mechanical approaches will assist in labor cost-savings.

Pest management approaches can also be reduced, especially for diseases like grapevine powdery mildew. Reduced fruit set and a smaller canopy will naturally reduce disease pressure. Maintenance programs, such as sulfur, can be used to help keep canopy disease development at a minimum. However, some powdery mildew should be expected in an idled block.

Diseases like grapevine leafroll and red blotch, and their associated insect vectors, should still be actively managed in an idled vineyard. This will help ensure the long-term health of the vineyard, and any neighboring vineyards. Trunk diseases should also be addressed through aggressive pruning tactics in an idled vineyard to allow for a successful return-to-production.

Insect (leafhoppers, cutworms) and mite pests may not need active management, as a reduced spray program will likely allow the build-up of beneficial insects. Management should only be considered if there are concerns of insect movement to adjacent, non-idled blocks.

Weed management in an idled vineyard block an be significantly reduced. Reduction in irrigation will naturally reduce weed growth. Sucker management might also be naturally reduced in an idled vineyard scenario due to lack of irrigation, however, sucker development may still occur. The vineyard manager can choose whether to spend money during the vineyard idle period to manage suckers, thus making return-to-productivity easier when that comes, or to delay the incursion of those costs until the vineyard is back under contract.

Summary

There are many different ways to approach vineyard idling, just as there are many ways to approach active vineyard management. The information provided here, and in Idling Vineyards in the Pacific Northwest, are designed to provide the tools necessary for your to make your own farm-tailored decision during periods of low grape sales.

After an Extreme Drought, Vineyard Recovery is a Long Haul

Authors: Charles Obiero and Markus Keller, Washington State University

Winegrape growers in the Pacific Northwest are increasingly affected by more frequent droughts. These weather extremes threaten not only the current season’s crop but also the long-term health, productivity, and winter survival of the grapevine [1,2]. To cope with this condition, many growers have adopted one common practice: removing fruit during severe drought to reduce stress on the vine and improve long-term survivability. However, this practice has largely been guided by experience rather than by robust scientific evidence. The approach also introduces an important tradeoff. Removing fruit reduces immediate crop value and requires additional labor, creating high economic costs. Thus, there is a clear need for science-based information to help growers make informed, cost-effective, and water-efficient decisions that will enable vineyards to remain productive and sustainable amid increasing weather extremes.

In 2025, at a WSU research vineyard in Prosser, we assessed shoot growth, yield, and fruit composition in Cabernet Sauvignon and Riesling vines that had previously experienced three consecutive years (2022–2024) of drought stress. Stress was imposed annually in those years from either fruit set or veraison (no irrigation until post-harvest), combined with 0%, 50%, or 100% fruit removal. All vines received full irrigation through bloom to support early-season vine vigor and fruit set, and again after harvest to protect roots from winter injury. These treatments were compared with a standard industry practice that did not include fruit removal.

Relative to the regulated deficit irrigation (RDI) control, post-fruit-set shoot length in the recovery year declined by one-third in Cabernet Sauvignon and one-quarter in Riesling following drought initiated at fruit set in each of the preceding three years (Figures 1 and 2). Fruit removal improved shoot growth only in Riesling, where vines with complete fruit removal matched the RDI control (Figure 1).

A comparison of shoot length between different irrigation treatments when fruit was or wasn't removed. Shoots were longer in RDI treatments relative to drought treatments for both Cabernet Sauvignon and Riesling. Removing fruit also resulted in longer shoots. — **Figure 1.** Post–fruit‑set shoot length of Cabernet Sauvignon and Riesling vines during the 2025 recovery year. Vines had previously undergone a three‑year consecutive drought and fruit removal, imposed annually at fruit set, and compared with RDI control vines. Error bars are SE.

Looking down two vineyard rows, where the row on the left has shorter shoots because it did not receive a water recovery treatment. The row on the right did receive a recovery treatment and has longer shoots. An inset image has two shoots next to each other, one that is shorter, one that is longer. — **Figure 2.** Cabernet Sauvignon vines during the recovery period showing canopy differences among vines that had previously experienced a three‑year consecutive drought imposed annually at fruit set (blue end post), compared with the RDI control (red)

In Cabernet Sauvignon, up to 10% cordon dieback occurred in vines stressed from fruit set, and fruit removal did not mitigate this structural damage (Figure 3).

A vine where half of the canopy is missing due to cordon dieback, likely a result of severe water stress. — **Figure 3.** Cordon dieback (red arrow) in Cabernet Sauvignon during the recovery period following a three-year drought imposed annually from fruit set through harvest. The photo was taken in the early season of 2025; drought was imposed in 2022‒2024.

Berry weight was largely the same across treatments, but yield losses remained severe: yields were halved in vines previously stressed from fruit set and reduced by one-fifth in those stressed from veraison (Table 1). Complete fruit removal restored the yield in both varieties, but this yield was still 23–39% numerically lower than the RDI control (Table 1). Fruit composition (TSS, TA, and pH) remained largely unchanged. Surprisingly, however, Cabernet Sauvignon vines that had previously experienced a three‑year consecutive drought imposed at fruit set produced fruit with 27% higher YAN (158 mg/L) compared with the RDI control. Riesling showed no change in YAN. After the recovery year, vines previously exposed to drought from fruit set still had 58% lower pruning weight than the RDI control in both varieties (Table 1). Fruit removal improved pruning weight only in Riesling, where previously stressed vines with complete fruit removal matched the RDI control. In contrast, vines stressed from veraison had pruning weights similar to the RDI control in both varieties.

Irrigation	Fruit removed	Cabernet Sauvignon Yield (tons / acre)	Cabernet Sauvignon Pruning Weight (lb / plant)	Riesling Yield (tons / acre)	Riesling Pruning Weight (lb / plant)
RDI control	0%	4.8 a	1.88 ab	7.1 a	1.48 a
Drought Fruit Set	0%	2.8 bc	0.93 cd	3.0 d	0.56 b
Drought Fruit Set	50%	1.5 c	0.53 d	3.6 cd	0.66 b
Drought Fruit Set	100%	2.9 abc	0.97 cd	5.5 abc	0.93 ab
Drought Veraison	0%	3.1 abc	1.30 bcd	4.3 bcd	0.77 b
Drought Veraison	50%	3.9 ab	1.44 abc	5.9 ab	0.89 ab
Drought Veraison	100%	4.9 a	2.18 a	6.5 ab	1.37 a

Table 1. Yield and winter pruning weight of Cabernet Sauvignon and Riesling vines after one year of recovery. Vines had previously experienced a three‑year consecutive drought imposed annually at fruit set or at veraison, through harvest, with or without fruit removal, and are compared with RDI control vines without fruit removal. Drought and fruit‑removal treatments were applied simultaneously. Means with different letters within a column differ significantly at Tukey’s 5% probability.

These results show that both drought itself and fruit dropping during drought years have major economic implications for Washington’s wine industry. With about 50,000 irrigated acres statewide and a cost of $350 per acre to reduce crop load, say from 6 to 3 tons per acre in Riesling vines, not dropping fruit saves growers approximately $17.5 million in a single season. In addition to avoiding this direct cost, retaining the 3 tons per acre that would otherwise be dropped and selling it at about $1,000 per ton generates substantial income, whereas fruit removed during drought years cannot be sold at all. Following a severe drought, vines perform poorly during the subsequent recovery year regardless of fruit removal. Although complete fruit removal can restore yield after drought, it does not prevent the long‑term physiological and structural damage caused by drought, and crop thinning only marginally alleviates these impacts. This suggests that, in many drought scenarios, the economic cost of fruit removal is not offset by meaningful gains in vine recovery. Strategic water management, especially protecting vines through veraison and ensuring post‑harvest irrigation, is a far more impactful lever than crop thinning alone. When water supply is restricted, withholding irrigation after veraison is much less destructive to grapevines than withholding it during the entire berry development period.

Key Takeways

Fruit removal is not an effective drought‑mitigation strategy. Even though complete fruit removal can restore yield, it does not prevent the long‑term structural and physiological damage caused by drought.
Drought starting at fruit set is much more damaging than drought starting at veraison. Protecting vines early in the season should be a top priority when water is limited.
Recovery from severe drought is slow and incomplete. Expect reduced shoot growth and yield losses even after irrigation is restored.
Fruit composition is quite stable under drought. Quality is not the main concern; vine health and future productivity are.
Economic costs of fruit removal outweigh benefits. Avoiding crop thinning during drought can save Washington growers more than $17 million per year without compromising vine recovery.
Water timing matters more than crop load. Maintain some level of irrigation through veraison and after harvest; use deficit irrigation strategically rather than relying on fruit removal.

Funding and Acknowledgements

This work is supported by the USDA Northwest Center for Small Fruits Research, the Washington State Grape and Wine Research Program, and the Chateau Ste. Michelle Distinguished Professorship. We thank Alan Kawakami and Zilia Khaliullina for their technical support

References

Keller M. 2023. Climate change impacts on vineyards in warm and dry areas: challenges and opportunities. American Journal of Enology and Viticulture 74:0740033.
Hochberg U, Perry A, Rachmilevitch S, Ben-Gal A, Sperling O. 2023. Instantaneous and lasting effects of drought on grapevine water use. Agricultural and Forest Meteorology 338:109521.

From Probes to Pixels: Evaluating Tools for Measuring Grape Heat Stress

Authors: Nipun Thennakoon, Dattatray Bhalekar, Joshua Oliver, Lav Khot, Washington State University

Introduction

Heat stress is a significant challenge in grape production, with some regions experiencing up to 40% crop damage. In extreme heat events, direct solar exposure can elevate the temperature on the sun-exposed side of a berry by as much as 22°F (12°C) above the ambient air temperature (Smart and Sinclair, 1976; Spayd et al., 2002). Once temperatures rise above 113°F (45°C), berries are highly prone to shriveling due to sunburn injury (Keller, 2023).Such damage leads to substantial reductions in both grape yield and wine quality (Gambetta et al., 2021). Berry surface temperature (BST) serves as a reliable indicator of sunburn and heat stress susceptibility.

Accurately measuring BST is essential for timely management decisions. Traditional contact-type sensors, like bead thermocouples or temperature probes, require physical contact with the berry. This is an invasive approach and can damage the berries by puncturing the skin, leading to juice leakage and increased disease incidence in the cluster and adjacent vines. As it is a laborious point-sampling approach, scaling across a commercial vineyard would be an additional challenge (Li et al., 2014). Non-contact sensors, such as infrared thermometers (IRTs) and thermal infrared cameras, offer a faster, non-destructive alternative. While these tools can be influenced by environmental factors like humidity and air temperature, they allow rapid monitoring. A major advantage of thermal imaging over single-point sensors is the ability to capture spatial temperature patterns across clusters, allowing growers to identify specific risk areas.

Overall, for better heat stress management decisions, selecting the right BST measurement tool is critical. We evaluated thermocouples, infrared thermometers, and thermal infrared cameras for their effectiveness and accuracy in berry temperature quantification. Those results are described below.

Experimental Design

The study was conducted at the WSU Roza experimental vineyard (Prosser, WA) for two Vitis vinifera cultivars, ‘Chardonnay’ and ‘Cabernet Sauvignon’. Measurements were taken during peak heat hours (2:00 p.m. and 4:00 p.m., Pacific Time) over two distinct high-heat days when ambient air temperatures exceeded 95°F (35°C). There were four vineyard locations within each variety, four vines within each vineyard location, and on each vinemm an eastern and western-facing cluster was monitored.

Both surface and internal temperature measurements were taken from each of the selected grape clusters using four different sensors (Figure 1). Internal berry temperatures were recorded using a K-Type temperature probe (Thermapen One Blue, ThermoWorks, American Fork, UT, USA; Figure 1b) inserted approximately 0.25 inches under the berry skin.

A four-panel collage illustrates different methods for measuring the temperature of grape clusters in a sunny vineyard. The first three panels show hands using contact probes and a non-contact infrared gun, while the last panel shows a thermal image on a smartphone. — **Figure 1.** Quantifying berry temperature using (a) Fluke 568-2 bead thermocouple, (b) Thermapen One Blue temperature probe, (c) Fluke 568-2 infrared thermometer, and (d) FLIR One Edge Pro thermal IR camera connected to AWN CropAI mobile app.

For berry surface measurements, a combination of contact and non-contact sensing tools were used. To ensure scientific accuracy, all instruments were calibrated across an operating range of 77°F (25°C) to 140°F (60°C). A dual-purpose handheld unit (Fluke 568-2, Fluke Corporation, Everett, WA, USA) provided both the infrared and bead thermocouple readings. The bead thermocouple was the reference measurement for BST as it provides a direct measurement of the berry surface without being influenced by environmental factors. Additionally, a wireless thermal IR camera (FLIR One Edge Pro; Teledyne FLIR LLC, Wilsonville, OR, USA) was used in conjunction with the AWN CropAI mobile application (AgWeatherNet, Washington State University, WA, USA). The app segments the berry clusters from the canopy background and estimates the BST using the hottest 20% of pixels in the image. For all “spot” sensors, measurements were taken on the same randomly selected berry within the cluster to ensure a direct comparison.

Results

As expected, the trial results demonstrated that solar exposure is the primary driver of changes in BST. Across all surface-sensing instruments, clusters on the sun-exposed west side of the canopy consistently measured 12°F (6.7°C) to 14°F (7.8°C) hotter than those on the east side. Both the thermocouple and the AWN CropAI app recorded peak temperatures exceeding the 113°F (45°C) threshold, at which point sunburn damage and shriveling become imminent. In contrast, the maximum temperatures recorded by the handheld infrared thermometer remained approximately 3°F (1.7°C) below this critical threshold (Figure 2).

This box plot compares berry surface temperatures across three sensing methods: Infrared Thermometer, Thermocouple, and AWN CropAI, on both the East and West sides of a vineyard. — **Figure 2.** Comparison of berry surface temperature readings across sensing methods.

There was a strong linear relationship between BST measurements using the thermal IR camera (connected to AWN CropAI app) and the reference thermocouple. Overall, AWN CropAI consistently provided a more conservative estimate by reporting slightly higher temperatures than the thermocouple. The results also showed that under extreme temperatures (>100°F [37.8°C]), the temperatures across the cluster become more variable, and the thermal IR camera is able to capture cluster-specific “hot spots.” This will assist grape growers in identifying specific “sunburn zones” during heat events.

A strong linear relationship between BST surface temperature measurements using the handheld infrared thermometer and the reference thermocouple was also seen. However, it consistently recorded temperatures below what was measured by the reference thermocouple. This consistent underestimation likely stems from the infrared thermometer’s fixed field of view. Unlike the AI-driven segmentation used by the AWN CropAI app, the infrared thermometer averages all thermal energy within its circular measurement area. By including relatively cooler background elements, such as shaded stems, leaves, or the gaps between berries, the device essentially “dilutes” the true heat of the berry surface. For a grower, this is a critical distinction: relying on an infrared thermometer might suggest a “safe” temperature of 110°F (43.3°C), while the most exposed berries may have already crossed the 113°F (45°C) critical threshold.

A comparison of internal and surface temperature (Figure 3) shows that on the shaded east side of the canopy, the berry surface temperature remained 2.0°F (1.1°C) warmer than the internal temperature in both cultivars. However, this relationship becomes volatile on the sun-exposed west side. Cabernet Sauvignon showed extreme surface spikes, with surface temperatures measuring as much as 10 to 12°F (5.6 to 6.7°C) hotter than the internal berry temperature. Interestingly, both cultivars (Chardonnay and Cabernet Sauvignon) also exhibited instances where the internal berry temperature was higher than the berry surface temperature.

This box plot compares the difference between surface and internal berry temperatures for Chardonnay and Cabernet Sauvignon cultivars on the East and West sides of a vineyard. The data shows that the temperature difference varies more significantly on the West side for both cultivars compared to the more stable East side. — **Figure 3**. Comparison of internal berry temperature (Thermapen) with berry surface temperature (Thermocouple) for two cultivars and either side of the canopy.