IRAC Groups for Vineyard Insecticides Explained

By VitiScribe Editorial·November 3, 2025·Updated December 8, 2025

Diamide (Group 28) resistance in grape berry moth has been documented in US vineyards -- that's the most recent and most practically notable insecticide resistance development in US viticulture. VitiScribe tracks IRAC groups in spray records to flag consecutive-mode-of-action insecticide use before resistance compounds into a management crisis.

TL;DR

Diamide (Group 28 -- Altacor, Belt, Coragen) resistance in grape berry moth is confirmed in the Lake Erie region (Pennsylvania, Ohio, New York) and in parts of California and Oregon with high historical Group 28 use -- switching to a different brand with the same active ingredient does not overcome this resistance
Group 5 (spinosyn -- Delegate, Entrust) resistance is also emerging in some high-use GBM populations; both Group 28 and Group 5 should each appear in no more than 2 of the 3 annual GBM generations
Group 4A (neonicotinoid -- imidacloprid, dinotefuran, clothianidin) applied to soil persists in plant tissue through bloom -- avoid soil-applied neonicotinoids when bloom is approaching within the systemic uptake window
Group 3A pyrethroids (lambda-cyhalothrin, bifenthrin) are highly toxic to bees, disrupt biological control of spider mites, and have PHIs of up to 21 days that limit late-season use for all three constraints simultaneously
Group 15 (Intrepid -- methoxyfenozide) has no known cross-resistance with Group 28 diamides, making it the most important rotation partner for GBM in situations where diamide pressure is building
VitiScribe tracks IRAC groups in insecticide records and displays rotation history by block -- the same cross-season visibility provided for FRAC groups in fungicide programs

Understanding IRAC groups is the insect equivalent of understanding FRAC groups for fungicides. The principle is the same: rotating among different modes of action slows resistance development by preventing any single mechanism from being the target of continuous selection pressure.

What an IRAC Group Is

IRAC stands for Insecticide Resistance Action Committee. The committee assigns numerical codes to insecticides based on their mode of action -- the specific mechanism by which they kill or disable insects. Like FRAC groups, insecticides sharing an IRAC group have the same target site in the insect, and resistance to one product in a group often confers cross-resistance to others in the same group.

The practical implication: if grape berry moth populations in your vineyard develop resistance to Altacor (chlorantraniliprole, Group 28), switching to Coragen -- a different brand, same IRAC group, same active ingredient -- won't help. The resistance mechanism targets the same site regardless of the product name.

Key IRAC Groups for Vineyard Insect Management

IRAC Group 1 (Organophosphates and Carbamates):

Products: Imidan (phosmet), Lorsban (chlorpyrifos -- check current CA registration), Diazinon, Carbaryl (Sevin). Older chemistry with longer safety profiles but higher REI (24 hours) and more notable worker protection requirements. Still effective against GBM, leafhoppers, and mealybug. PHI 7-21 days depending on product.

IRAC Group 3A (Pyrethroids):

Products: Warrior II (lambda-cyhalothrin), Brigade (bifenthrin), Asana (esfenvalerate). Contact activity against a broad range of insects. High bee toxicity -- avoid during bloom. 21-day PHI for some products limits late-season use. Disrupts biological control of spider mites when applied during mite management season.

IRAC Group 4A (Neonicotinoids -- Nicotinic Acetylcholine Receptor Agonists):

Products: Admire Pro (imidacloprid), Venom (dinotefuran), Assail (acetamiprid), Belay (clothianidin). Highly systemic insecticides effective against sucking insects (mealybug, leafhoppers) and some caterpillar pests. Bee toxicity concerns for soil-applied neonicotinoids persist in plant tissue through bloom. PHI 7-21 days depending on product.

IRAC Group 5 (Spinosyns):

Products: Delegate WG (spinetoram), Entrust SC (spinosad -- OMRI-listed). Act on nicotinic acetylcholine receptors at different binding sites than neonicotinoids (Group 4A). Excellent GBM and leafhopper efficacy. 7-day PHI and 4-hour REI make these operationally convenient. Entrust is OMRI-listed for organic programs. Group 5 resistance developing in some high-use GBM populations -- important to rotate off spinosyns periodically.

IRAC Group 6 (Avermectins):

Products: Agri-Mek SC (abamectin). Used primarily for spider mite management, but classified as an insecticide/miticide. Disrupts GABA-gated chloride channels. 28-day PHI in grapes substantially limits late-season mite management use.

IRAC Group 15 (Diacylhydrazines -- Insect Growth Regulators):

Products: Intrepid 2F (methoxyfenozide). Disrupts the molting process in caterpillars by acting as an ecdysone agonist. Most effective against young larvae. 4-hour REI and 7-day PHI. Low toxicity to beneficial insects compared to most other options. No known cross-resistance with Group 28 diamides -- important rotation partner for GBM in diamide-pressure situations.

IRAC Group 23 (Spirotetramat):

Products: Movento 240SC (spirotetramat). Inhibits lipid biosynthesis. Bidirectional systemic movement in plant tissue -- reaches sucking insects feeding on both shoots and roots. Highly effective against mealybug crawlers and aphids. 24-hour REI, 7-day PHI. Must be applied with a penetrant adjuvant.

IRAC Group 28 (Diamides -- Ryanodine Receptor Modulators):

Products: Altacor WG (chlorantraniliprole), Belt SC (flubendiamide), Coragen (chlorantraniliprole). Disrupt calcium release from muscle cells, causing irreversible paralysis. Excellent GBM and caterpillar efficacy with low mammalian toxicity. 4-hour REI, 5-7 day PHI.

Critical resistance point: Diamide resistance in grape berry moth has been confirmed in the Lake Erie region (Pennsylvania, Ohio, New York) and in parts of California and Oregon with high historical Group 28 use. If you've been applying Altacor or Belt for all 2-3 GBM generations each season for multiple years, resistance selection pressure is building. Rotate off Group 28 for at least one generation per season and supplement with Group 5 (Delegate) or Group 15 (Intrepid).

IRAC Group 7C (Pyriproxyfen -- Juvenile Hormone Mimics):

Products: Esteem WP (pyriproxyfen). Disrupts normal insect development. Most effective against eggs and young nymphs. Used for mealybug management. 12-hour REI, 7-day PHI.

Building Your IRAC Rotation for GBM Management

A practical IRAC rotation for three-generation grape berry moth management:

First generation (egg hatch at ~100-150 DD50):

Group 28 (Altacor) OR Group 5 (Delegate) -- alternate each season to avoid consecutive-year Group 28 selection

Second generation (egg hatch at ~750-850 DD50):

Rotate to a different group than first generation -- if Group 28 was used at Gen 1, use Group 5 or Group 15 at Gen 2

Third generation (egg hatch at ~1,150-1,300 DD50, PHI critical):

Select based on PHI constraints and harvest timing
Group 28 (5-day PHI) allows late use in most varieties
Group 5 (7-day PHI) workable for most harvest timing
Group 15 (7-day PHI)

By rotating groups across generations within a season, you avoid consecutive generations selecting for the same resistance mechanism. By alternating which groups you use at each generation across years, you further slow resistance development.

VitiScribe tracks IRAC groups in your insecticide records and displays rotation history by block. See how VitiScribe connects scouting records to spray decisions for GBM management.

See the FRAC groups vineyard fungicides guide for how the same rotation principles apply to fungicide programs across powdery mildew, botrytis, and downy mildew targets.

IRAC Groups for Mealybug Management

Mealybug management benefits from group rotation because of the multiple generations per season and the ability to target different life stages with different products.

First generation crawlers (systemic approach):

Group 23 (Movento/spirotetramat) -- apply 2-3 weeks before peak crawler emergence for systemic uptake that reaches feeding crawlers

First generation crawlers (contact approach):

Group 5 (Delegate) -- contact activity during active crawler movement

Group 4A (Admire Pro) -- systemic, but 21-day PHI limits timing flexibility later in season

Second generation:

Rotate to a different group from first generation application

Do not use neonicotinoids (Group 4A) during bloom periods due to bee toxicity risk from systemic residues in pollen and nectar.

Frequently Asked Questions

What is an IRAC group for vineyard insecticides?

An IRAC group is a numerical classification from the Insecticide Resistance Action Committee that identifies insecticides sharing the same mode of action -- the same mechanism for killing or disabling pest insects. Insecticides in the same IRAC group share cross-resistance: if insects develop resistance to one product, they're often resistant to all others in the same group. Rotating among different IRAC groups prevents any single mode of action from being the target of continuous selection pressure, slowing resistance development. Examples: Group 28 (diamides -- Altacor, Belt), Group 5 (spinosyns -- Delegate, Entrust), Group 23 (spirotetramat -- Movento).

Which IRAC groups are at highest risk for resistance in US vineyards?

Diamide (Group 28) resistance in grape berry moth is confirmed in Lake Erie vineyards (Pennsylvania, Ohio, New York) and has been documented in some California and Oregon populations with high Group 28 use history. This is the most notable current resistance concern for vineyard insect management. Spinosyn (Group 5) resistance in some GBM populations is also emerging in high-use situations. Organophosphate (Group 1) resistance in leafhoppers is present in some California populations from decades of OP use.

How do I build an IRAC rotation for vineyard insecticide programs?

Map out your target pest's generation cycle (GBM has 3 generations; mealybug has 2-3). Assign different IRAC groups to each generation rather than using the same product or group for all applications. For GBM: use Group 28 for no more than 2 of the 3 annual generations, supplementing with Group 5 (Delegate) or Group 15 (Intrepid) for at least one generation. For mealybug: combine Group 23 (Movento) for systemic early-crawler coverage with Group 5 for contact crawler knockdown, rather than relying on either alone. Across seasons, alternate which group is used at each generation to avoid multi-year consecutive selection pressure.

How do I document suspected diamide resistance to present to an extension plant pathologist or PCA?

Suspected resistance documentation should include: the application date, product, rate, and timing relative to GBM degree day accumulation; the pre-application scouting counts showing population size; the post-application scouting counts from 7-14 days after treatment; weather conditions at the time of application; and a multi-year history of Group 28 applications to the affected block. The combination of correctly timed and dosed applications with reduced efficacy compared to historical results, in a block with high Group 28 use history, is the pattern that extension diagnosticians use to evaluate suspected resistance. VitiScribe's IRAC rotation report and block scouting history provide the longitudinal data for this analysis in a single exportable view.

Should IRAC rotation records be shared with winery buyers alongside FRAC rotation records?

IRAC rotation records are increasingly relevant to winery buyers and sustainable certification programs that review multi-year input histories. A rotation record showing intentional group alternation across GBM generations -- not just within a single season but across multiple seasons -- demonstrates resistance-conscious insecticide stewardship in the same way that FRAC rotation records demonstrate fungicide stewardship. For winery buyers with sustainability programs, the insecticide rotation history tells a story about long-term pest management philosophy. VitiScribe generates IRAC rotation reports in the same exportable format as FRAC rotation reports, making it straightforward to include both in a grower sustainability package.