Cranberry Station Newsletter 2026 Vol. 27:3

Growing Degree Day Models and Spring Frost Management

By Sandeep Bhatti and Peter Jeranyama

GROWING DEGREE DAY MODELS AND SPRING FROST MANAGEMENT

Growing Degree Day (GDD) models help to predict when to start monitoring for frost and the tolerance temperature at which the cranberries should be protected. The GDD numbers are calculated for State Bog, East Wareham, and updated on UMass Cranberry Station’s website (view webpage) biweekly during the spring season. The GDD numbers at your farm location may be a little different depending on where you are in the state. The CCCGA Frost Committee uses the GDD models as a tool but also relies on traditional visual observation (Spring Frost Tolerances of Cranberry Buds). The models are still being evaluated as they work better in some years than others and should not be relied on exclusively for frost management. They should only be used as another guide in understanding how the season is progressing, helping growers make more informed frost decisions. Below are key models being used by cranberry growers:

1. Dee model (developed by Irving DeMoranville) – 44°F base temperature; accumulation starts from Jan 1. When 100 GDD is reached, be extra vigilant for frost and white bud stage is expected.

      2. WI Simple model: 41°F base temperature. When 90-100 GDD is reached, be extra vigilant for frost and dormant phase should have ended.

      3. WI Complex model: Temperatures between 41°F and 86°F; if minimum temperature is less than 41°F, set to 41°F and if maximum temperature is more than 86°F, set to 86°F. When 90-100 GDD is reached, be extra vigilant for frost and dormant phase should have ended.

Note that for both WI models, accumulation starts with observance of 13-hour day (usually on April 7 in Massachusetts)

As of April 15, 2026, the GDD numbers at State Bog (East Wareham, MA) are as follows:

1. Dee model (base 44°F and Jan 1): 83.4
2. WI simple (base 41°F and April 7): 60.5
3. WI complex (base 41°F, max 86°F and April 7): 80.6

COMPARISON OVER THE YEARS

The progression of GDD from the three models is shown in Figures 1 and 2 for each year between 2023–2026. The three models consistently aligned on the timing of 100 GDD and reached this threshold within 3 days of each other (Figure 1). Even though the WI models did not start GDD accumulations till April 7, these models usually exceed the Dee model by mid to late April (Figure 1). The annual variability in GDD for each model can be observed from Figure 2. By March, the Dee model accumulated the largest GDD in 2024, but this progression slowed considerably in April due to colder temperatures when compared to 2023 and 2025. Overall, the strong agreement among the models on threshold timing is reassuring, but the year-to-year variability highlights the importance of monitoring these models in real time to study the season progression and prepare for spring frost management. In general, the three models are usually within 1–3-day error margin of each other and as such are in agreement except in years with exceptionally cold spring nights.

Figure 1. Comparison of the three GDD models for each year from 2023-2026.

Figure 2. Comparison of the GDD accumulations from each model over the four years between 2023-2026.

2026 Preliminary Keeping Quality Forecast (PKQF)

by Peter Jeranyama and Leela Uppala

The preliminary forecast indicates VERY POOR keeping quality for the 2026 Massachusetts cranberry crop.

As of April 1, 2026, 0 out of a possible 10 points have accumulated toward preliminary keeping quality. Based on current conditions, keeping quality is expected to be very poor. Unless the final keeping quality forecast (to be issued after June 1) shows improvement, we do not recommend reducing either the number or rates of fruit rot fungicide applications. Particular attention should be given to beds with a history of fruit rot issues.

With respect to Late Water (LW), this is a year in which its use may be beneficial. However, the decision to implement LW should be based on individual bed conditions. Recent field studies in Massachusetts indicate that late water may be associated with increased fruit rot incidence and reduced yield during the year of application, particularly in more susceptible cultivars. However, these effects were not observed in the following year, and yield recovery may occur depending on cultivar and management. Therefore, late water should be implemented cautiously and integrated with appropriate fungicide and nutrient management (especially Nitrogen) programs, especially during the treatment year. Please refer to the table below and the Late Water section of the Chart Book for detailed guidance on implementation.

For additional information or questions, please contact Leela Uppala suppala[at]umass[dot]edu (suppala[at]umass[dot]edu) or 508-970-7644.

LATE WATER GUIDANCE

Late Water May Be Considered When:

• Applied once every three years for approximately 4 weeks (mid-April to mid-May).
• The bog is healthy and shows no signs of stress.
• Flower buds remain red and tight (dormant stage).
• The bed received adequate winter flooding during cold periods.
• Scale insects and/or fruit rot incidence were high in 2025.
• There is access to adequate, good-quality water supplies.

Late Water is Not Advised When:

• Late water was applied within the past two years.
• The bog produced a heavy crop in 2025.
• Buds have broken dormancy.
• The bed was sanded in the previous year.
• The bog shows signs of stress or winter injury.
• The bog is severely out of grade. 

News from the Cranberry Weed/IPM Lab

by Katie Ghantous

KERB SECTION 18 EMERGENCY EXEMPTION FOR 2026

Massachusetts cranberry growers have been granted a renewed Section 18 (Emergency Exemption) to use Kerb SC for dodder control. This is active April 15 through June 30, 2026. This product can ONLY be used in Massachusetts for dodder control ONLY! If you do use Kerb in 2026, you must fill out an “Applicator Reporting Form” and return it to MDAR. You can find a link to both the label and the reporting form on our website under “Services/Special Labels”. 

Kerb can be applied as: 

• A single application of 2.5 - 5.0 pints (1.0 - 2.0 lb a.i.) per acre 

OR 

• Two applications made at a rate of up to 2.5 (1.0 lb a.i.) per acre. If making two applications, they must be separated by a minimum of 20 days. 

Total product applied must not exceed 5.0 pints (2.0 lb a.i.) per acre per year. Kerb has a 75- day PHI and a 24-hr REI. Check with your handler prior to use for restrictions. Kerb is a state RESTRICTED USE PESTICIDE and is Zone II restricted! Contact Katie Ghantous if you want to use Kerb and you are in a Zone II kghantou[at]umass[dot]edu (kghantou[at]umass[dot]edu) or 508-970-7634. 

SPRING WEED MANAGEMENT

Unfortunately, preemergence herbicides are some of the most expensive pesticides. In a time when many growers are looking to cut costs, preemergence weed management is often on the chopping block. While you might not feel the impacts of skipping weed management for years (like you would if you skipped insect management), weeds are a creeping issue that is exacerbated every year and is harder to get under control the longer you wait. The goal of preemergence herbicides is to keep beds clean, and some such as Devrinol will not be effective for managing existing weed issues. Many of our perennial weeds are difficult to manage once they are established as adult plants on the bed. 

Dodder Management. Dodder has a very long-lived seedbank in the soil. While most of the seeds produced last year will germinate this year, others can remain viable and germinate for 20+ years. If you had a dodder issue last year, you will likely need to manage your beds for dodder this spring.  

• QuinStar: Quinclorac is effective against loosestrife and other broadleaf species, dodder, and some grasses. However, there remain many export (MRL) issues with quinclorac, and most handlers are restricting use for export fruit. Check with your handler before using. QuinStar can be used preemergence, early postemergence, or postemergence. Most growers report having the best results when making one application early season (preemergence or early post emergence after the dodder has germinated but before it is attached) and following that with a second application later in the summer after cranberry bloom has passed.   

• Casoron: Some growers that have reported poor dodder control with 40 lb/A, and saw improved efficacy by increasing the rate to 60 or 80 lb/A. If you have had unsatisfactory control with 40 lb/A in the past, consider increasing the rate.  

• Callisto: There are very variable results using mesotrione to control dodder (both as a preemergence and as a postemergence).  It is unclear why it works really well for some growers and not at all for others! If using it postemergence, it is much more effective to treat dodder before it flowers.  

• Spartan: In greenhouse studies, sulfentrazone significantly reduced dodder seed germination. It is unclear if it performs well for dodder control in the field/real world. 

• Kerb: The Section 18 allows for grower to use Kerb in 2026 for dodder. It is a very effective product, but costly and has handler restrictions.  

Moss Management. If using sulfentrazone (Spartan) for moss management, try to get the herbicide out as early as possible. You want to time this application to maximize crop safety – the moss is already there and green so do not wait. Apply well before cabbage head stage! Mullica Queens seem to show more sensitivity to this herbicide compared to other varieties.  

Herbicides and Frost Nights. There is always the concern of when to apply preemergence herbicides in relation to a predicted string of frost nights. Devrinol needs to stay within the upper root zone to be effective. If you apply prior to a string of frost nights, it is likely that you wash the herbicide past the root zone and will have reduced efficacy. Devrinol has good crop safety, so it is possible to wait a few more weeks to apply.  

Herbicide application during elongation/roughneck. The cranberry appears to be more sensitive to herbicides when they are at the development stage of elongation/roughneck. We have noted that applications of clethodim products (e.g. Select Max, Intensity, etc.) made during this growth stage can cause floral deformities and may reduce yields on sensitive varieties (Howes seem most prone to these issues). In experimental Devrinol plots, we also noted some very minor yield reduction when applications were made during roughneck.

Fertilizer Application Drone Workshop (limited space available)

by Giverson Mupambi

Event date/time: April 29, 2026: 10:00 AM - 12:00 PM (Rain Date: April 30, 2026)

Event Type: In-person

Event location: UMass Cranberry Station, 1 State Bog Road, East Wareham

Are you interested in learning how to use a drone to apply fertilizer on your bog? We are hosting a workshop at the Cranberry Station in partnership with NexGen Drone (A.D. Makepeace Company) on April 29, 2026 (Rain date April 30, 2026) to demonstrate fertilizer application. The workshop will cover FAA regulatory requirements, launch preparations, and conclude with a drone fertilizer application demonstration. 

For safety reasons, a maximum of 15 participants will be allowed for the workshop. The participants will serve as visual observers during the operation. Preference will be given to growers who have a drone and are planning to apply fertilizer this coming season. We are planning to hold another workshop in August if there is enough demand. 

WORKSHOP AGENDA:

10:00 - 10:30 AM   FAA regulatory requirements and preparations to get ready to fly 

10:35 - 11:30 AM. Launch preparations and fertilizer application flight

11:30 AM – 12:00 PM - Q&A

Speaker(s) / Instructor(s)

Jake Arnold and Giverson Mupambi

HOW TO REGISTER: 

• If you are interested in attending, please complete the following Google Form. 

• Priority will be given to growers who own a drone and plan to apply fertilizer this coming season. 

• We will confirm a week before the event if you have made the list of 15. 

 For more information about the workshop, contact Giverson Mupambi at gmupambi[at]umass[dot]edu (gmupambi[at]umass[dot]edu) or 508-970-7638, and Jake Arnold at jarnold[at]Admakepeace[dot]com (jarnold[at]Admakepeace[dot]com)

The Ag Drone Podcast: Navigating Insurance for Aerial Application

The Federal Aviation Administration is offering a webinar to help navigate the complexities of insurance for spray drone operations. Insurance is often the most misunderstood hurdle for professional UAS Part 137 operations, yet getting it right is essential to protecting your equipment, your livelihood, and your reputation. This session offers a deep dive into the practicalities of ag drone coverage, providing a clear breakdown of everything from hull insurance and spare parts to the critical nuances of drift claims and chemical application liability. The webinar will share actionable insights from experts who bridge the gap between traditional manned ag aviation and the rapidly evolving UAS spray sector, ensuring you have the professional protection needed to apply pesticides with confidence. 

Date and Time: Tuesday, April 28, 2026, 20:00 EDT

Registration link: Register here

Station News

ANNUAL WPS TRAINING FOR HANDLERS 

• Wednesday May 6, 2026, or Wednesday May 20,2026

• 8:00-9:00 AM, hybrid option

Anyone working on the cranberry bogs (bogs that have been treated within 30 days) that does not have a MA Pesticide Certification needs to have worker protection training each year.  This will be a handler training and will allow workers to help apply general use pesticide and apply Roundup (glyphosate) or spot treat with Intensity or Stinger.  Krystal DeMoranville will be running hybrid trainings in the AD Makepeace room here at the Station; you can choose to join by Zoom or in-person.  This training can be done with each person on a smartphone or computer, or in a group setting around a screen.  Paperwork will be completed to cover EPA WPS requirements.

Please contact Krystal DeMoranville at 508-970-7631 or krystald[at]umass[dot]edu (krystald[at]umass[dot]edu) to sign up or for more information.

BE INFORMED AND BRING YOUR SAMPLES IN! INSECT & DISEASE CLINICS IN MAY

Insect & Disease Clinic I (2 credits)

• Tuesday, May 12, 2026

• 8:00-10:00 AM, in-person UMass Cranberry Station

• FREE to attend

Insect & Disease Clinic II (2 credits)

• Tuesday, May 26, 2026

• 8:00-10:00 AM, in-person UMass Cranberry Station

• FREE to attend

Each clinic will begin in the AD Makepeace meeting room, followed by a transition to the Labs for hands-on training. Participants will learn to identify and manage emerging insect pests (Cranberry Black Bug, Blunt-nosed Leafhopper, Vaccinium Scale and Collembola) and disease issues, starting with an introductory discussion and then working directly with field samples from the bog. Participants are encouraged to bring in sweep net contents and/or vine samples from areas showing suspicious dieback. During the lab session, you will have the opportunity to inspect your sweep net contents and to run a phytophthora test on your own samples. For more information, please contact Marty Sylvia martys[at]umass[dot]edu (martys[at]umass[dot]edu) or 508-265-6921.

2024-2026 CRANBERRY CHART BOOK NEW DIGITAL VERSION

For decades, the Cranberry Chart Book has been a cornerstone of UMass Extension outreach, providing Massachusetts cranberry growers with trusted, research-based guidance on pest, fungicide, weed, water, and nutrient management. While the print edition remains available, this essential resource is now more accessible than ever through its new digital format. The updated online version continues the Chart Book’s mission of delivering timely, practical information to the cranberry community. We extend our thanks to Evonne Gong, CAFE web designer and online strategist, for her work in bringing the new digital version of the Cranberry Chart Book online. Explore it here.

2026 CHART BOOK UPDATE

The 2026 update to the 2024-2026 Chart Book is now available and you can find it here.  If you would like a copy of the update mailed to you, please contact Robyn Hardy at 508-970-7635 or rmhardy[at]umass[dot]edu (rmhardy[at]umass[dot]edu). 

MDAR 2025 PESTICIDE USE REPORTING DUE JUNE 1, 2026

MDAR requires all pesticide certified applicators to submit annual reports detailing the quantities of all pesticides used.  Failure to submit a use report (find form here) can result in the loss of eligibility for renewal of your license.  Paper forms are no longer used; forms must be completed online. Each form includes a product look-up based on the required EPA Registration Number.  Required fields for product information include drop-down menu to make reporting the product and related data quick and easy.

Submit one report on behalf of multiple Pesticide Applicators or Licensed Dealers that work for the same farm or company.  MDAR automatically receives notification of the submission, and a confirmation email will be sent from PestExamLicense[at]mass[dot]gov (PestExamLicense[at]mass[dot]gov) to the email address provided in the report. If you are having trouble or cannot complete this, Marty can help at 508-265-6921 or martys[at]umass[dot]edu (martys[at]umass[dot]edu).