fungicide resistance management — Page 2

April 4, 2026 Kaitlin Quinn, Katrina DeWitt and Janine Spies

Fruit IPM Updates Week of 3/30/2026

Tree Fruit Phenology Update

Tree fruit phenology is progressing across New Jersey, with development in southern counties remaining slightly advanced and northern regions beginning to catch up. Overall, the 2026 season is showing a more compressed phenology window than typical. Warm temperatures this week significantly advanced phenology.

In apples, most varieties have reached tight cluster across the state, with early varieties in southern counties at pink bud. In pears, most varieties are at early white bud to popcorn, with Asian pears more advanced and approaching bloom. Peach varieties have reached pink bud across New Jersey, with nectarines near or in bloom in South Jersey.

Apples

Apple Phenology Update

Apple phenology continues to progress across New Jersey. Observations indicate that northern counties are primarily at tight cluster, while southern counties are at pink bud in early varieties.

This stage marks a critical transition in disease management, particularly for apple scab, powdery mildew, and cedar apple rust, as well as key insect management timings.

Phenology Dates by County (earliest varieties)

County	Green Tip	Tight Cluster	Pink Bud
Cumberland	3/22	3/28	4/3
Gloucester	3/22	3/28	4/3
Burlington	3/22	3/28	4/2
Mercer	3/22	3/28	4/2
Middlesex	3/22	4/1	TBD
Monmouth	3/22	TBD	TBD
Hunterdon	3/22	TBD	TBD
Morris	3/26	TBD	TBD
Warren	3/30	TBD	TBD
Sussex	3/31	TBD	TBD
Bergen	3/22	4/1	TBD

Figure 1: Pink Lady apple variety in pink bud. Gloucester County, NJ. Photo by Katrina DeWitt

Apple Scab

Models

Apple scab models are available through NEWA and RIMpro. These models currently indicate that ascospore maturity is increasing and will continue to rise rapidly over the next several days. Apply fungicides before infection events.

Current Update using the Upper Deerfield Station

~13% maturity on April 1
~15% on April 2
Forecasted to reach 25–40% by April 4–8

Management Considerations

Now that we have reached the tight cluster stage, it is important to select fungicides that target both apple scab and powdery mildew. Manzate is ineffective against powdery mildew. Keep in mind that powdery mildew prefers warm, dry conditions and does not require rainfall to infect. For farms in southern counties that have reached pink stage, it is important to begin targeting cedar apple rust. Manzate is effective against cedar apple rust.

Manzate + single-site fungicide
DMI (FRAC 3) for high pressure
Vangard (FRAC 9; not effective on cedar apple rust)
FRAC 7 (save Aprovia for summer; not effective on cedar apple rust)
Axios (great for scab and powdery mildew; novel FRAC 52)
FRAC 11 (save for summer)
Topsin (limited uses; consider saving for summer; FRAC 1; not effective on cedar apple rust)

Monitor:

NEWA models
Weather/wetting events
Phenology

Early control is critical to avoiding season-long pressure.

Insect Update

Ambrosia Beetle:

Ambrosia beetles have been detected in Burlington, Salem, Gloucester, and Middlesex counties
Activity has not yet been observed further north at this time
Observed activity is low and is not a concern

Continue monitoring traps, particularly in stressed or newly planted blocks, as activity may increase with warming temperatures.

Mating Disruption Timing:

Codling moth (CM) mating disruption should be applied around pink
Growers should begin preparing materials and planning applications now

Summary

Apple phenology is progressing across New Jersey, with northern counties at tight cluster and southern counties at pink bud in early varieties
This stage marks a critical period for apple scab and powdery mildew management, as well as key insect timings
Apple scab ascospore maturity is increasing (~13–15%) and is forecasted to reach 25–40% over the next several days, increasing infection risk
Fungicide applications should be applied prior to infection events, with materials selected to target both scab and powdery mildew
In southern counties at pink, begin targeting cedar apple rust

Pears

Pear Phenology Update

Pear phenology has advanced rapidly across southern New Jersey over the past week. Observations made on April 2 indicate that most European pear varieties are now at early white bud, following cluster separation but prior to petal show, with some blocks progressing into popcorn stage.

Asian pear varieties are more advanced, with many blocks at popcorn stage and approaching bloom.

Figure 2. White bud/popcorn. Asian pear variety phenology. Salem County, NJ. Photo by Katrina DeWitt.

Pear Psylla

Pear psylla activity has been variable across southern New Jersey. Observations from April 2 indicate differences by county:

Salem County: adults and eggs observed
Gloucester County: none observed
Burlington County: no activity observed to date
Mercer County: no activity observed to date

Overall pressure remains relatively low in many orchards. This is likely due, in part, to recent oil applications, particularly where oil was combined with materials such as Esteem, which can suppress egg laying and early population development.

At this stage (white bud to popcorn):

Continue monitoring for adults, eggs, and the onset of nymph hatch
Use beating trays to assess adult activity
Examine developing shoots and leaves for egg presence

Management considerations:

In blocks without prior applications, or where psylla is present, consider a pre-bloom insecticide application
Consider applying particle films such as dormant oil or Surround to deter egg laying
With pre-bloom insecticide applications, softer materials should be used to avoid harming pollinator or beneficial insect populations
In blocks where adults are present at low pressure, insecticide options include Esteem (up to 2 applications 14 days apart), Centaur, or Aza-Direct
In blocks where adults are present at high pressure (more than 4 adults per beating tray), insecticide options include Apta, Assail, or AgriMek
Insecticides should be applied prior to bloom, as use during bloom is restricted due to pollinator protection

As bloom approaches (particularly in Asian pears):

Avoid applications that may impact pollinators
Management focus will shift to early nymph control post-bloom

Pear Diseases

Fire Blight and Early Season Management

As pears approach bloom, fire blight risk will increase significantly, especially given the recent wet conditions and continued rainfall through the weekend. These conditions are favorable for bacterial spread and infection.

As bloom approaches:

Begin planning for antibiotic applications, particularly if warm and wet conditions persist
Kasumin may be used at bloom and petal fall
Streptomycin and oxytetracycline remain key options, particularly post-bloom
Rotate chemistries to support resistance management

Pear Scab

RIMpro modeling for pear scab in Upper Deerfield has indicated low infection risk to date, but conditions are rapidly becoming more favorable for infection.

The primary infection model shows maturing ascospores present and available, with multiple wetting events occurring from late March through early April. These rain events are driving spore release and infection potential, with additional infection periods forecasted in the coming days.

From white bud to popcorn:

Protective fungicide programs should now be in place and maintained, particularly ahead of rain events
Applications of mancozeb or ziram tank-mixed with Procure, Cevya, or Vangard are effective options for scab control
Applications should be made prior to rainfall events, as infections occur during wetting periods
If 2 inches or more of rainfall occur following an application, a follow-up spray should be considered to maintain protection

As we move toward bloom:

Continue programs targeting pear scab, rust diseases, and Fabraea leaf spot
Particular attention should be paid to Asian pear varieties, which are further advanced and at greater risk

Summary

Observations from April 2 indicate most European pears are at early white bud, with some at popcorn stage
Asian pears are at popcorn and approaching bloom
Pear psylla activity remains variable across counties, with adults and eggs observed in Salem County
Reduced pressure in some blocks is likely due to oil applications, with or without Esteem
Where oil was not applied, or psylla is present, pre-bloom insecticide applications should be considered
Insecticide applications must be completed prior to bloom to protect pollinators
Recent and continued rainfall is increasing disease pressure, particularly for pear scab and fire blight
Fungicide programs should be actively maintained, with reapplication needed after significant rainfall (2 inches or more)
Fire blight risk will increase rapidly as bloom approaches, so antibiotic programs should be prepared

Continued scouting is critical over the next 7–10 days as phenology and pest pressure accelerate.

Peaches

Peach Phenology

Peach varieties across New Jersey were observed at the pink bud stage this week. Nectarines are more advanced, with the majority observed near or in bloom in South Jersey. Development is progressing steadily and will continue as temperatures warm.

Brown Rot

Blossom infections from the brown rot fungus can occur whenever pistils are exposed, and favorable environmental conditions are present.

Infections can occur during any wetting period when temperatures are between 41 and 86°F. Optimum conditions occur with wetting and temperatures in the mid-70s. During extended wetting periods (several days or more), blossoms can be infected regardless of temperature. Infections under suboptimal conditions are generally less severe.

Blossoms and fruitlets remain susceptible until the pistil desiccates, which occurs sometime between petal fall and shuck split.

Management Considerations

Fungicides used for control at the blossom blight stage should not overlap with fungicides used in the pre-harvest stage of brown rot
Try to save fungicide options with low pre-harvest intervals for later in the season
Bravo Weather Stik + single-site fungicide
Vangard (applied at pink stage)
Rovral (applied at full bloom)
Flint Extra (applied at petal fall)

Initiate coverage for blossom blight starting at pink for short-petaled varieties and at 5–10% bloom for showy flowers. Refer to the NJ Commercial Tree Fruit Production Guide for recommended materials and rates.

Insect Update

Mating Disruption Timing:

Oriental fruit moth mating disruption should be applied at pink
Growers should begin preparing materials and planning applications now

Scale:

Oil applications may be safely applied up to pink on peach
Oil can be applied alone or in combination with insecticides, including Centaur, Sivanto Prime, and Esteem

Green Peach Aphid:

Scouting should begin at pink stage
Thresholds for treatment are 1 colony/tree in nectarines or 2–3 colonies/tree in peaches

Summary

Observations indicate peaches are at pink bud across New Jersey, with nectarines more advanced and approaching or in bloom in South Jersey
Development is progressing steadily and will accelerate with warming temperatures
Brown rot infection risk is present whenever blossoms are exposed under wet conditions, particularly between 41–86°F
Blossoms remain susceptible through petal fall to shuck split
Fungicide programs should be initiated at pink to early bloom, depending on flower type, while avoiding overlap with pre-harvest materials
Oriental fruit moth mating disruption should be applied at pink; growers should prepare materials now
Oil applications for scale can be made up to pink and may be tank-mixed with labeled insecticides
Green peach aphid scouting should begin at pink, with treatment thresholds of 1 colony/tree in nectarines and 2–3 colonies/tree in peaches

Continued scouting and timely applications will be critical over the next 7–10 days as phenology advances.

Filed Under: Commercial Ag Updates, Disease Forecasting, Fruit, Tree Fruit Tagged With: apple, Apple Disease, Apple Insect, fungicide resistance management, Insect management, IPM, Peach Disease, Peach Insect, Pear, pear disease, pear insect, pear psylla, pest scouting guide, tree fruit

August 1, 2025 Andy Wyenandt

The A-B-C’s of cucurbit powdery mildew control

Cucurbit powdery mildew (CPM), caused by Podosphaera xanthii, is one the most important diseases of cucurbit crops throughout the world. The pathogen is an obligate parasite, just like cucurbit downy mildew, meaning it needs a living host in order to survive. In northern regions that have a killing frost in the fall the pathogen will die out when the crop freezes. Not being able to overwinter, the pathogen must be re-introduced each spring or summer in the mid-Atlantic region. The pathogen accomplishes this by re-infecting cucurbit crops in the spring as they are planted up the east coast starting in Florida, then the Carolina’s, Virginia, and so forth. By late May, as soon as cucurbit crops begin to germinate in the mid-Atlantic region, the potential threat for potential powdery mildew infections begin.

The first step in mitigating CPM begins with planting powdery mildew tolerant (PMT) or resistant (PMR) cultivars if they meet your needs. It is important to remember that these cultivars are not “immune” to CPM; they will become infected at some point in the growing season depending on disease pressure. Hopefully, this will occur later in the season when compared to CPM susceptible cultivars. Organic growers hoping to mitigate losses to powdery mildew should always chose CPM tolerant or resistant cucurbit cultivars first. There are a number of OMRI-approved fungicides labeled to help suppress CPM development, these should always be used in concert with CPM tolerant or resistant cultivars and a preventative fungicide program. Cultural practices such as increasing in-row plant spacing to improve air flow and cultivation to keep weeds to a minimum will also be advantageous. Avoiding the use of overhead irrigation will help reduce disease pressure from another important pathogen, cucurbit downy mildew. Thus, growing cucurbits on a mulch with drip irrigation has its advantages, but also increases costs.

In the past, a typical conventional fungicide program consisted of rotating two different FRAC group fungicides every other week, such that the pattern looked like:

A – B – A – B – A – B

Often a protectant fungicide such as chlorothalonil or mancozeb is added to the tank mix on a weekly basis to 1) help control other important fungal diseases, such as anthracnose or gummy stem blight and 2) to help reduce selection pressure on the high-risk fungicide that was being applied. This type of preventative program was used for many years, because, in most cases there were just a few effective fungicides available for CPM control depending on the crop. An example of this would be:

A = (azoxystrobin [FRAC group 11] + chlorothalonil (MO5) rotated weekly with B = (myclobutanil [FRAC group 3] + chlorothalonil (MO5)

This type of control strategy worked extremely well as long as the pathogen didn’t develop resistance to either the FRAC group 11 (azoxystrobin) or FRAC group 3 (myclobutanil) fungicide. To better understand modes of action and how fungicide resistance develops in FRAC group 11 and FRAC group 3 fungicides please click here. Unfortunately, because of fungicide resistance development this type of program is no longer effective and is no longer recommended for CPM control.

Over the past 10 years, there have been a number of new fungicides released with new modes of action (i.e., new FRAC groups) for CPM control in cucurbit crops. Unfortunately, all have a moderate to high-risk for resistance development because of their specific modes of action. The good news are these new fungicide chemistries have less effects on humans, non-target organisms, and the environment.

These fungicides include:

FRAC group 13 (quinoxyfen)
FRAC group 39 (fenazaquin)
FRAC group 50 (metrafenone)
FRAC group U06 (cyflufenamid)
FRAC group U013 (flutianil)

Not all of the fungicides listed above are labeled for all cucurbit crops. Growers will need to refer to local recommendations and the label for crop specifics. Remember, the label is the law.

These fungicides offer new strategies when it comes to controlling and mitigating losses to CPM. Instead of rotating two fungicides with a moderate to high-risk for resistance development every other week ( A – B – A – B), growers now have option to reduce the total number of times any single fungicide might be applied during the production season; further reducing the risk for resistance development to any one mode of action. For example, in pumpkin, a new CPM preventative fungicide program may look like this:

A – B – C – D – E – A – B – C – D – E

Where A=(FRAC group 3);B=(FRAC group 13); C=(FRAC group 50); D=(FRAC group U013); E=(FRAC group 11)

A protectant fungicide such as chlorothalonil or mancozeb should be added to the tank mix with each high-risk fungicide to reduce selection pressure and to help control other important diseases such as anthracnose and plectosporium blight.

In this type of CPM preventative program any one high-risk fungicide would only be applied twice per growing season and 5 weeks apart greatly reducing the risk for fungicide resistance development. Importantly, for cucurbit growers, the easiest method to mitigate the potential for fungicide resistance development are to reduce the total number of applications of any one high-risk fungicide during the production season.

When to start spraying for CPM

Initiating a preventative spray programs begins with paying attention to Extension reports, scouting, and when the crop was seeded. If the crop is seeded the early-spring (i.e., early to late May) there is a very good chance CPM is not present in the mid-Atlantic region. If CPM is not present, there is no need to initiate a spray program using high-risk fungicides. In this instance, general protectant fungicides such as chlorothalonil will help mitigate other foliar diseases. As cucurbit crops are seeded into early to mid-June (and afterward) the risk for CPM development will rise in the mid-Atlantic region. This is when scouting and paying close attention to Extension reports becomes important. The first application should be done when CPM has been detected in the immediate region or when it is detected by scouting (e.g., with one lesion found on the underside of 45 mature leaves per acre). This will help reduce the use of unwarranted high-risk fungicide applications early in the production season. Importantly, the use of PMR or PMT cucurbit varieties will also help delay the onset of CPM development as well. Once CPM preventative fungicide programs are initiated, applications need to occur at every 7 to 10 days (at the latest) for as long as you expect to harvest (e.g., summer squash) or hold the crop (e.g., pumpkin and winter squash). During harvest, growers need to pay careful attention to pre-harvest intervals because they may vary significantly between different FRAC groups or fungicides within the same FRAC group (a good example are fungicides in FRAC group 3). Once harvest is complete, those blocks or fields need to be destroyed immediately to help reduce the spread of CPM to other blocks or fields that are scheduled to be harvested later in the production season. This is especially important for other diseases such as cucurbit downy mildew.

In some instances, rotating between many different FRAC group fungicides are not an option because the chemistries aren’t available for use. An example would be leaf spot control in spinach, where FRAC groups (7, 11, 7 + 11, 7 + 12, and 9 + 12) are available. In this example, options for control might look like this:

A – B – C – D

Where A=(FRAC group 7); B=(FRAC group 9 + 12); C=(FRAC group 11); D=(FRAC group 7 + 12)

Here, we have maximized the use of as many different FRAC groups as possible and spread their use as far apart as we can during the production season. Its important to remember that fungicides with more than one active ingredient (e.g., 7 + 11) should also be rotated as far apart as possible with fungicides that contain the single active ingredient (e.g., FRAC group 7 or FRAC group 11).

Monitoring fungicide efficacy

With the use of high-risk fungicides, all growers need to monitor fungicide efficacy accordingly. Once the lack of efficacy is detected there is a chance that fungicide resistance might be present. Importantly, the lack of efficacy should not be misconstrued with poor applications or waiting too long between fungicide applications. Reports of poor efficacy from Extension personnel from one region may not reflect fungicide efficacy in another region. Therefore, fungicide efficacy needs to be done at the farm level and the only way to accomplish this is to scout your fields and know what is and isn’t working for you.

The principles mentioned above also extend to other important diseases in vegetable production where there are multiple FRAC groups with high-risk fungicides available to control specific diseases. As a general rule, growers need to rotate as many different modes-of-action (i.e., fungicides from different FRAC groups) as possible during the production season to help mitigate fungicide resistance development in conjunction with best management practices.

For more information on fungicide use, FRAC groups, and specific control recommendations please see the 2024/2025 Mid-Atlantic Commercial Vegetable Production Recommendation Guide.

Filed Under: Vegetable Crops Tagged With: cucurbit powdery mildew, fungicide resistance management

July 31, 2025 Andy Wyenandt

Quick reviews of fungicide chemistries, FRAC groups, and fungicide resistance management

Did you know that first EBDC fungicide was registered for use in vegetable crops in 1964 followed by chlorothalonil in 1966. Historically speaking, the first New Jersey Vegetable Production Recommendations Guide was produced in 1969 and was only 33 pages long (it’s 502 pages now). Things have changed significantly over the past 55 years when it comes to pest management! For a quick review on fungicides, FRAC groups, and managing fungicide resistance development please click on the links below.

Using tank mixes and fungicide rotations and information on FRAC group 4, FRAC group 7, and FRAC group 3 and FRAC group 11 fungicides.

As a reminder, the new 2024-2025 Mid-Atlantic Commercial Vegetable Production Recommendations Guide can be purchased at most county offices and is also available for FREE on-line here!

Filed Under: Vegetable Crops Tagged With: fungicide resistance management

July 11, 2025 Andy Wyenandt

Preparing for cucurbit downy mildew in 2025

In 2004, cucurbit downy mildew re-emerged in the US with a vengeance causing significant losses in cucurbit production. In most years prior to this, concern for CDM control was minimal, since the pathogen arrived late in the growing season (in more northern regions), or the pathogen caused little damage, or never appeared. After 2004, with significant losses at stake, and with very few fungicides labeled for its proper control, CDM became a serious threat to cucurbit production. Importantly, at the time, cucumber varieties with very good levels of CDM resistance were no longer resistant, suggesting a major shift in the pathogen population. Research done over the past 19 years has led to a better understanding of the pathogen. Recent research has determined that the CDM falls into two separate clades: Clade I and Clade II. [Read more…]

Filed Under: Vegetable Crops Tagged With: cucurbit downy mildew, fungicide resistance management

July 8, 2025 Andy Wyenandt