Cranberry Station Newsletter 2026 Vol. 27:4

Cranberry Irrigation Management During Fruit Set

By Leela Uppala, Peter Jeranyama and Giverson Mupambi

Finding the right balance between too wet and too dry. Most cranberry beds across Massachusetts are now transitioning from late bloom into fruit set, one of the most important periods for irrigation management. During this stage, vines are supporting newly developing fruit while coping with increasing temperatures and evaporative demand.

While hot weather can raise concerns about crop stress, adding more water is not always beneficial. The objective is to maintain adequate soil moisture while avoiding prolonged saturated conditions. Both insufficient and excessive irrigation can reduce vine performance and may negatively affect fruit development, fruit quality, and yield.

How cranberry vines stay cool. Cranberry vines naturally cool themselves through transpiration. Water is moved from the soil through the roots and shoots and out through pores (stomata) in the leaves. When this process occurs, moisture is depleted from the soil. As water evaporates from the leaves, it lowers plant temperature and helps protect vines from heat stress. This natural cooling system works well when adequate moisture is available in the root zone. 

It is possible that the transpiration process is sometimes inadequate to cool cranberry plants. In conditions with high humidity and high air temperatures (85°F air temperature can translate to approximately 105°F on the bog) a brief 10–20-minute application of water can provide in-day cooling. The applied water physically evaporates (a separate process from the evaporation of transpiration through plant leaves). 

Why soil moisture matters. When soil becomes too dry, transpiration slows, photosynthesis declines, and fruit development may suffer. Conversely, soil that remains continuously saturated reduces oxygen available to the roots, limiting water and nutrient uptake while increasing the risk of root diseases such as Phytophthora root rot. Excessive irrigation can also prolong canopy wetness, creating favorable conditions for fruit rot.

PRACTICAL IRRIGATION RECOMMENDATIONS

Avoid irrigating simply because temperatures are high or several days have passed since the last irrigation.

Before Irrigating:

• Check soil moisture using tensiometers or other soil moisture sensors whenever possible. Current UMass Cranberry Station irrigation guidance recommends initiating irrigation at 6.5 kPa, although studies conducted in Canada recommend initiating irrigation closer to 7-7.5 kPa.
• Consider the contribution of the water table and ditch water. 

If the Root Zone Is Becoming Dry:

• Consider pre-dawn irrigation so adequate moisture is available before temperatures increase. Starting the day with adequate soil moisture supports transpiration.
• Where appropriate, maintain adequate ditch water levels. 

During Extreme Heat: 

• Vines growing in adequately moist soil do not require routine daytime cooling irrigation.
• If sunny, humid conditions exist, and on-bog temperatures are excessive, consider using a short irrigation cycle (10–20 minutes). This becomes more relevant when fruit are developing color and absorb solar radiation which raises the risk of scald. 
• Allow the canopy to dry between irrigation events. 
• Discontinue cooling irrigation once temperatures moderate. 

The objective of cooling irrigation is to lower canopy temperature through evaporative cooling not to replenish soil moisture in the root zone.

Table 1. Practical Irrigation Decision Guide During Fruit Set

Please Note:

• Soil water tension is technically expressed as a negative metric potential. Consistent with UMass Cranberry Station Extension publications and the way tensiometers are commonly read in practice (Use of soil tensiometer), values in this article are presented as positive numbers.
• Research conducted in Massachusetts and Canada has shown that cranberry growth and yield are influenced by soil-water tension; however, the precise irrigation trigger varies among studies, production systems, cultivars, and management objectives.
• The thresholds presented in Table 1 are intended as practical irrigation scheduling guidelines based on current UMass Cranberry Station recommendations and should not be interpreted as fixed optimum soil moisture targets for every bog. Always consider recent rainfall, weather forecasts, soil type, water table depth, and individual bog conditions when making irrigation decisions.
• The UMass Cranberry Station is committed to conducting future research to refine irrigation recommendations under Massachusetts growing conditions, including newer hybrid cultivars and changing environmental conditions.

News from the Cranberry Physiology/Fruit Quality Lab

By Giverson Mupambi

DATA COLLECTION: EVAPORATIVE COOLING

As our summers grow hotter, managing heat stress and preventing fruit scald is becoming one of our biggest challenges. There have been inquiries about turning on sprinklers for evaporative cooling during extreme heat waves, but there is a lack of research-based data about how much water is needed and how to avoid issues like fruit rot. To find the sweet spot, we are seeking to connect with growers who are currently using evaporative cooling. We would love to collect data on canopy temperatures and fruit quality to evaluate its efficacy. The data and insights collected will be shared with the grower community. If you are interested in having us collect data, reach out to Giverson Mupambi at gmupambi[at]umass[dot]edu (gmupambi[at]umass[dot]edu)  or 508-970-7638.

News from the Cranberry Weed/IPM Lab

By Katie Ghantous and Marty Sylvia

PROLINE AND CRANBERRY PHYTOTOXICITY 

Phytotoxicity is an adverse effect or damage to plants caused by exposure to chemicals (pesticides, fertilizers, etc.). It is most commonly associated with herbicides – chemicals that are intended to cause plant stress.

This year, we have had two growers report that they observed phytotoxicity on cranberry vines after they applied the fungicide Proline (active ingredient prothioconazole, a demethylation inhibitor (DMI) in the triozole class). Proline has been in use for many years in cranberry; this is the first time we have encountered a possible crop safety issue! The affected varieties were Haines and Mullica. These two “super-hybrids” are also known to be more sensitive to herbicides than older varieties.

The injury manifested as minor-to-moderate bleaching of upright tips, similar to the tip-flashing we sometimes see after mesotrione (Callisto) herbicide applications. After looking into available research, we discovered that triazole injury is an occasional and known issue in soybeans. And just like what was recently observed in cranberry, in soybeans the affected leaves are in the upper canopy where active growth is occurring. 

While it is difficult to attribute the injury to Proline definitively because there were only two reported cases, this type of injury is documented in other crops and turf.  The mechanism is not well understood, but triazoles are xylem-mobile (meaning they move in plant vascular tissue with water). It is thought that drought conditions and heat stress are associated with the appearance of symptoms in soybeans. It is likely that the heat and ongoing drought stress is a factor in the appearance of symptoms in cranberry. Both growers report that the vines appear to be recovering from the injury. In soybean, there is no crop losses associated with the phytotoxicity from prothioconazole. Since the cranberry plants are growing out of the symptoms, it is unlikely that there will be associated crop loss in cranberry either.

We believe that this is uncommon, driven by environmental stress (heat/drought) and likely not a serious issue. If you have observed any unusual bleaching after a Proline application, please let us know!

NOTES ON “ROUND UP”

Despite the fact many people use the terms “glyphosate” and “Round Up” interchangeably, there are many products with the tradename “Round Up” that are not actually glyphosate. In the homeowner market, Round Up can contain a variety of things (like triclopyr and imazapic) that are not registered for use on cranberry and have zero glyphosate. And likewise, there are MANY different glyphosate products that are registered for use on cranberry. 

Make sure you are paying close attention to active ingredient (a.i.) and not just product names. Make sure that any glyphosate product you are using on bog is actually registered for cranberry use and check the label for % a.i. and other important info that can impact the way you mix and use it. 

DODDER

As with many other weeds, it is much more effective to treat dodder BEFORE it flowers. Unfortunately, the best and most effective options for dodder management are preemergence herbicides. It is a bit of a mystery why postemergence applications of Callisto by chemigation for dodder work very well for some growers and don’t work at all for others. We are not sure if it is a timing issue, surfactants, variation in the dodder itself (different species are present), or other unknown factors that lead to such mixed results from bog to bog and grower to grower. 

QuinStar works best for dodder when an early season application (soon after dodder germinates and begins seeking host plants) is followed by an application in July after cranberry bloom. A single post-bloom application did not seem to be effective for dodder control in the year of treatment BUT some growers feel they get control the year after they apply QuinStar. Many handlers are restricting QuinStar, so this is not an option for many growers. 

If your dodder is in isolated patches, you can do a spot treatment spray with concentrated Callisto. This has been demonstrated to be effective. We have the SLN label on our web site under Services/Pesticide Labels. Remember that spraying before dodder flowers is much more effective than spraying after flowers or seed are present. I have seen dodder treated while in bloom become completely bleached by mesotrione but still go on to produce viable seed. 

Dodder seed can remain viable for 20 or more years in the soil seed bank. If you have a heavy dodder infestation, it will produce many thousands (or millions) of seeds. It is also a bit of a mystery why some growers have tiny patches of dodder that never spread or seem to escalate, while others see such heavy and widespread issues!

News from the Cranberry Pathology Lab

 By Leela Uppala

SEASONAL FRUIT ROT MANAGEMENT

When to Consider an Additional Fruit Rot Spray? An additional application may be worth considering when:

• A late-maturing cultivar is still in the bloom to early fruit set phase.
• The previous application may have been compromised by poor coverage or rainfall shortly after spraying.
• The cultivar is susceptible or the bog has a history of high fruit rot pressure.
• The product label permits another application based on the required spray interval and maximum number of seasonal applications.

When an Additional Spray May Not Be Necessary:

• Fruit rot pressure has been low in your bog.
• The cultivar is relatively tolerant.
• Previous applications were properly timed and achieved good coverage.
• The crop has moved beyond bloom and early fruit set-the critical periods for fruit rot infection.

Should You Consider Copper Fungicides for Cranberry Fruit Rot? Copper fungicides are multi-site protectants that help prevent new infections when applied before favorable infection periods. They are not curative or systemic and can be incorporated into a resistance-management program.

Key Considerations:

• Follow product-specific rates, application intervals, seasonal limits, PHIs, REIs, and adjuvant directions. 
• Apply under conditions that allow sprays to dry before rainfall or irrigation. 
• Avoid incompatible tank mixes and conditions that increase the risk of phytotoxicity.
• Avoid excessive use, as repeated copper applications can contribute to soil accumulation. 

SEASONAL REMINDERS FOR MANAGING CRANBERRY PHYTOPHTHORA ROOT ROT

• Accurate diagnosis is essential because vine decline, stunting, and root injury can also result from poor drainage, drought, nutrient deficiencies, or other stresses. Fungicides should supplement not replace good drainage and water management.
• Following laboratory confirmation of Phytophthora, two fungicide groups are commonly used to manage cranberry Phytophthora root rot: phenylamides (FRAC 4) and phosphonates (FRAC 33).

Phenylamide Fungicides (FRAC 4):

• Examples include mefenoxam- and metalaxyl-containing products registered for cranberry. 
• They have direct activity against susceptible Phytophthora populations. 
• Resistance risk is high. 
• Apply as a soil treatment during periods of active root growth (generally June–August), following the product label. 
• Follow label directions for application method, rates, timing, PHIs, and seasonal limits.

Phosphonate Fungicides (FRAC 33):

• Examples include fosetyl-Al and phosphite-containing products registered for cranberry. 
• They provide direct activity against Phytophthora while also stimulating plant defense responses. 
• Apply as a foliar treatment during periods of active root growth (generally June–August), following the product label. 
• Some products have label restrictions regarding foliar applications near copper sprays. For example, the Rampart 6.8 label recommends not making foliar applications within 20 days of a foliar copper application to reduce the risk of phytotoxicity. Because restrictions vary among products, always consult the individual product label. 

Integrated Recommendations:

• Confirm Phytophthora before treatment. 
• Improve drainage and avoid prolonged soil saturation. 
• Rotate fungicides with different FRAC groups. 
• Remember that fungicides protect healthy roots but cannot restore roots that have already died from Phytophthora.

HELPFUL YOUTUBE VIDEOS

Cranberry Fruit Rot: Time for one more Spray?

When to skip that extra fruit rot Spray?

Coppers for Fruit Rot Application

Questions? Please contact Leela Uppala (suppala[at]umass[dot]edu (suppala[at]umass[dot]edu) or 508-970-7644).

Station News

BOGSIDE WORKSHOPS

Save the dates! The Cranberry Station has 2 additional Bogside Workshops scheduled. Join us bogside (weather permitting) at the Cranberry Station, 1 State Bog Road, East Wareham. Please see details below. 

Thursday, July 30, 2026 (1 credit) Free

8:00-9:00 AM

Topic of the day: “All about Adjuvants”

Thursday, August 14, 2026 (1 credit) Free

8:00-9:00 AM

Topic of the day: “Spotting phytophthora”

For more information contact Krystal DeMoranville krystald[at]umass[dot]edu (krystald[at]umass[dot]edu) or 508-542-2605.

T-SHIRT DESIGN CONTEST EXTENDED TO AUGUST 1, 2026