UConn Cookie Information

Periodic Ozone Level Spikes Can Lead to Crop Injuries

By: Shuresh Ghimire, Vegetable IPM Specialist, UConn Extension

Ozone is formed when the combustion of fossil fuels react with oxygen in the presence of sunlight. It is the most common air pollutant in the Eastern United States, and moves from areas of high concentration (cities, heavy traffic areas) to nearby fields simply by wind. Common symptoms of ozone injury on crops are very small, irregularly shaped spots that are dark brown to black or light tan to white on the upper leaf surface. Injury is usually more pronounced at the leaf tip and along the margins. It is most likely to occur when the weather is hot, humid, and air masses are stagnant.

As of May 2026, there have been a few recent ozone level surges reaching toxic levels for crops in Connecticut, with the severity changing slightly depending on the precise location in the state. Ozone injury in susceptible vegetable varieties develops when ozone levels are over 80 ppb for four or five consecutive hours, or 70 ppb for a day or two when vegetable foliage is at a susceptible stage of growth. Typically, the most susceptible vegetable crops include cucumber, potatoes, watermelon, cantaloupe, snap beans, pumpkins, and squash.

The best recommendation for managing susceptible crops in when ozone levels are high is to avoid additional stresses on plants, to whatever extent possible. Avoid applying unwarranted pesticides or nutrients during this period. You can also take note of which varieties show fewer symptoms and plan to select varieties that are less susceptible in the future.

For more information on the relationship between the Air Quality Index (AQI) and Ozone levels, visit the Air Quality Guide for Ozone and Particle Pollution. For example, ozone concentrations would be 71-85 ppb when AQI is 101-150. To monitor local trends, vist airnow.gov.

Recent Updates on Pest Management in Sweet Corn

By: Srikanth Kodati¹ and Shuresh Ghimire²

¹Pesticide Safety and IPM Specialist, UConn Extension
²Vegetable IPM Specialist, UConn Extension

In the Northeast, sweet corn is held to high visual quality standards, and even minor insect feeding or foliar disease can reduce marketability. Effective pest management depends on choosing effective active ingredients, applying them at the right growth stage, and timing sprays using monitoring data. This article reviews recent research and offers practical guidance on corn earworm (CEW), an ear-feeding insect, and major foliar diseases, including northern corn leaf blight, common rust, gray leaf spot, and emerging tar spot; tar spot is not yet found in CT, but confirmed in central NY (as far east as Otsego County) in 2025.

Management of corn earworm

Target stage: what you are trying to hit

• Primary target: newly hatched larvae (neonates / early instars) feeding on fresh silks and exposed tip before entering the ear.
• Eggs: most foliar insecticides are not ovicides; timing aims to kill larvae immediately after hatch.
• Late instars inside the ear: control is limited—prevention depends on tight intervals and coverage on fresh silks.
• Trap guidance: Heliothis net traps baited with Hercon Heliothis zeapheromone lures are commercially available and widely used in the region.

Mode of action (MOA) groups and the CEW stage they best target

Table 1. Common insecticide resistance action committee (IRAC) groups used in CEW programs and best-fit target stage.

*IGR= insect growth regulator

Management of foliar diseases

Primary foliar disease targets are northern corn leaf blight (NCLB), common rust, and gray leaf spot (GLS), with tar spot emerging in some areas.

• NCLB management goal: Protect ear leaves and delay defoliation during reproductive growth. If defoliation is delayed until about six weeks after silking, yield loss is less likely, though husk lesions can still reduce fresh-market quality.
• Typical timing: Fungicides are commonly applied at V7–V8 and tassel when disease risk is rising to protect ear leaves.
• Fungicide selection: Use Corn Disease Working Group efficacy ratings, based on multi-location field trials on sweet corn.

Table 2. Fungicide efficacy ratings for key Northeast corn foliar diseases, based on multi-year, multi-location field trials.

Abbreviations: E=Excellent; VG=Very good; G=Good; NL=Not labeled for that disease.

 Northeast field-ready integrated recommendations

1. Use pheromone traps near silking fields and adjust spray intervals based on moth catches.[1]
2. Use directed sprays to the ear zone and maintain 3–6 day intervals during silking, depending on CEW pressure.[1][2]
3. Alternate insecticide (IRAC groups) across silk sprays, especially during high pest pressure, and avoid back-to-back use of the same group.[3][4]
4. Where available, choose resistant or tolerant hybrids and use rotation and residue management to reduce pathogen inoculum; apply fungicides when risk is high and before severe defoliation.[5]
5. Use multi-mode fungicides strategically and rotate FRAC groups when repeated applications are needed; focus on protecting ear leaves from tassel and silk through early grain fill, as needed for your market window.[5][6]

Pesticide resistance management

Corn earworm (CEW): Many CEW populations in Connecticut, as they fly up from South, may be resistance to pyrethroid insecticides, especially during heavy CEW pressure and late-season flights. So do not rely on pyrethroids alone.[7][8]

Table 3. Quick resistance management reminders for key pesticides

Additional resources

[1] Rutgers Plant & Pest Advisory. Corn earworm monitoring (pheromone trap guidance). https://plant-pest-advisory.rutgers.edu/corn-earworm-monitoring/

[2] Owens, D., & Malone, M. 2024. Insecticide efficacy against corn earworm in sweet corn, 2022. Arthropod Management Tests (tsae049). https://academic.oup.com/amt/article/49/1/tsae049/7658966

[3] University of Delaware Extension. Protecting sweet corn from corn earworm / sweet corn ear insect protection (timing notes). https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/factsheets/Protecting-Sweet-Corn-From-Corn-Earworm.pdf

[4] Penn State Extension. Alternative chemistries for managing corn earworm in sweet corn (Gemstar LC + Entrust note). https://extension.psu.edu/alternative-chemistries-for-managing-corn-earworm-in-sweet-corn

[5] Cornell Vegetables. Northern corn leaf blight of sweet corn (management notes/timing). https://www.vegetables.cornell.edu/pest-management/disease-factsheets/northern-corn-leaf-blight-of-sweet-corn/

[6] Corn Disease Working Group. 2023. Fungicide efficacy for control of corn diseases (CPN-2011-W table).  https://cropprotectionnetwork.s3.amazonaws.com/cpn2011_fungicideefficacycontrolcorndiseases_2023-1684787227.pdf

[7] Arthropod Management Tests. Insecticide Efficacy Against Corn Earworm in Sweet Corn, 2021b (notes pyrethroid resistance documented since 2008). https://academic.oup.com/amt/article/47/1/tsac004/6514151

[8] Penn State Extension. Alternative Chemistries for Managing Corn Earworm in Sweet Corn (recommends limiting pyrethroids and rotating MOA). https://extension.psu.edu/alternative-chemistries-for-managing-corn-earworm-in-sweet-corn

[9] FRAC. Summary of FRAC recommendations for cereals and corn (resistance management for QoI and other fungicides). https://www.frac.info/media/mfvlrma1/summary-of-frac-recommendations-for-cereals-and-corn.pdf

Disclaimer

UConn Extension does not endorse any product, manufacturer, or brand name referenced in this factsheet. Product examples are provided for educational purposes only. Always read and follow the pesticide label—the label is the law—including rates, application instructions, personal protective equipment (PPE), restricted-entry intervals (REIs), and pre-harvest intervals (PHIs). Before use, confirm that the product is currently registered for the intended crop/site and use pattern in your state and comply with all federal and state requirements.

Chemical Thinning of Apples in New England Orchards: A Guide for Commercial Producers in Connecticut

By: Evan Lentz, Fruit IPM Specialist, UConn Extension

Introduction

Chemical thinning is a cornerstone of modern orchard management in the northeastern United States. In apples and peaches, the practice is essential for regulating crop load, improving fruit size and quality, and ensuring consistent annual production. Under New England conditions—characterized by variable spring weather and diverse cultivar blocks—effective thinning requires a combination of sound physiology, careful timing, and adaptation to environmental conditions.

Unlike hand thinning, chemical thinning allows growers to manage large acreages efficiently. However, responses can be inconsistent due to weather, tree vigor, and cultivar sensitivity, making a systems-based approach critical.

Why Thin Fruit?

The primary objectives of chemical thinning are:

• Improve fruit size and marketability by reducing competition among fruitlets
• Enhance return bloom and mitigate biennial bearing
• Improve fruit color and quality
• Prevent limb breakage and tree stress from excessive crop loads

Failure to thin adequately can result in small fruit and poor return bloom, often causing significant economic losses. In fact, under-thinning typically causes greater economic loss than moderate over-thinning.

Physiology of Chemical Thinning

Most chemical thinners work by inducing abscission of developing fruitlets, either by:

• Disrupting hormonal balance (auxins, cytokinins, ethylene)
• Causing mild phytotoxic stress (e.g., bloom thinners)
• Altering carbohydrate balance within the tree

Thinning is closely tied to tree carbohydrate status. Maximum thinning occurs when applications coincide with periods of low carbohydrate availability, typically associated with warm temperatures and cloudy conditions following application.

Major Chemical Thinners Used in Apples

1. Auxin-Type Thinners

• • Naphthaleneacetic acid (NAA)
  • Naphthaleneacetamide (NAD)

Timing: Bloom through ~10–12 mm fruit size
Rates: Commonly 2–6 oz per 100 gal dilute (Tree Row Volume (TRV) basis)

Key considerations:

• • Effective under cooler conditions relative to other thinners
  • Risk of pygmy fruit formation, especially when applied late or at high rates
  • Avoid late applications on sensitive cultivars (e.g., ‘Delicious’ strains)

2. Cytokinin-Type Thinners

• • 6-Benzyladenine (6-BA) (e.g., MaxCel, Exilis)

Timing: Petal fall through ~12 mm
Rates: ~48–200 oz per 100 gal depending on formulation

Key considerations:

• • Promotes cell division, increasing fruit size beyond thinning effects
  • Performs best under warm temperatures (~70–80°F)
  • Often combined with carbaryl to enhance thinning response

3. Carbaryl (Carbamate Insecticide)

Timing: Petal fall to ~15 mm
Rates: ~0.5–1.5 pt per 100 gal

Key considerations:

• • Widely used as a “base thinner” in tank mixes
  • Enhances activity of NAA or 6-BA
  • Provides relatively consistent thinning across conditions

4. Ethylene-Releasing Compounds

• • Ethephon (Ethrel)

Timing: Typically, 10–20 days after full bloom (~15–20 mm fruit)

Rates: ~1–1.5 pt per 100 gal

Key considerations:

• • Promotes abscission via ethylene production
  • Can reduce fruit size if applied too early or at high rates
  • Often used to enhance return bloom

5. Newer or Supplemental Thinners

• • Metamitron (Brevis®) – photosynthesis inhibitor
  • Abscisic acid (ABA; Protone®)
  • ACC (Accede®)

Timing: Primarily 8–20 mm fruit window
Rates: Vary by product (e.g., metamitron 16–40 oz/100 gal)

Key considerations:

• • Often used for precision thinning or in challenging years
  • Mode of action often tied to carbohydrate stress

Tank Mixing Strategies

• NAA + carbaryl → reliable, widely used
• 6-BA + carbaryl → strong thinning + fruit size enhancement
• Oil additives → increase absorption and thinning efficacy
• Combination sprays are common because they increase consistency across varying weather conditions.

Rates and Calibration

• Rates are typically expressed per 100 gallons dilute tree-row volume (TRV)
• Adequate spray coverage is critical; ≥100 gal/acre recommended
• Always follow label instructions and adjust for tree size and density

Cultivar Differences

Cultivars vary widely in response to chemical thinning. Some are easy to thin; other require repeated multiple applications and higher rates. Thankfully, the response of most of our well-known varieties is understood fairly well.

• Hard-to-thin: Gala, Fuji, Golden Delicious
• Easy-to-thin: McIntosh, Cortland

Example program (UMass Extension):

• Gala: ATS at bloom → NAA + carbaryl at petal fall → 6-BA + carbaryl at 10–12 mm

Multiple applications are often required for difficult cultivars. If you have questions about a variety not explicitly denoted as hard-to-thin or easy-to-thin, please consult your local Extension professionals.

Timing Windows for Thinning Apples

1. Bloom Thinning

Materials: Ammonium thiosulfate (ATS), lime sulfur (limited registration in New England)

Objective: Reduce initial fruit set

Risk: Weather-dependent and variable

2. Petal Fall (5–6 mm fruit)

Common materials: NAA, carbaryl, 6-BA

Often the first major thinning window

3. 8–12 mm Fruit Size (Key Timing)

Most critical window for chemical thinning

Preferred timing in many New England programs

4. 15–20 mm Fruit Size (Rescue Thinning)

Materials: ethephon, carbaryl, ABA

Effectiveness declines rapidly after ~18–20 mm

Environmental Factors Affecting Thinning

There are a number of environmental factors that affect the performance of chemical thinners. Understanding these effects prior to choosing materials and rates or making applications will allow for more thoughtful and precise management decisions.

Temperature

• Optimal: 70–75°F
• High temps (>85°F): risk of over-thinning
• Cool temps: reduced activity, especially for 6-BA

Light (Cloud Cover)

• Cloudy weather → increased thinning due to reduced carbohydrate supply

Tree Condition

• Young trees: more sensitive (reduce rates)
• Stressed trees (frost, drought): unpredictable responses

Carbohydrate Balance

• Central driver of thinning response
• Models (e.g., Cornell carbohydrate model) are increasingly used to drive decision making.

Additional Resources:

Penn State Extension: Apple Crop Load Management

Washington State University: Apple Chemical Thinning

Penn State Extension: Apple Carbohydrate Thinning Model

They come out at night…a difference between Asiatic garden and Japanese beetles

By: Ana Legrand, Assistant Extension Professor, Department of Plant Science & Landscape Architecture, University of Connecticut

A grower asked the other day about finding white grubs in their vegetable planting at the beginning of the season. Overwintered white grubs can be found in areas that get planted in fields that had sod or are near grassy areas. The term ‘white grubs’ refers to the larval or immature stages of a complex of scarab beetle species that includes the Japanese beetle, Asiatic garden beetle (AGB), European chafer, oriental beetle and others. These species are a problem as grubs feed on plant roots especially in turfgrass and small fruit crops. However, Japanese and Asiatic garden beetles are among those that pose significant problems as adults too. These generalist beetles can feed on hundreds of plant species including ornamentals, fruit and vegetable crops.

Updates from the George Leigh Minor Plant and Soil Health Center

New Modules Added to the Farm Risk Management Course Offerings

UConn’s Farm Risk Management Online Course modules are developed in conjunction with UConn Extension, UConn’s Center for Excellence in Teaching & Learning, and UConn’s Academic Program Development & Support unit, and are funded by a grant from the United States Department of Agriculture (USDA).

Take anywhere from one to all of the online modules. Courses are free, self-paced and offered 100% online and asynchronous. Learn more or register online.

Upcoming Events and Opportunities