Every distributor has heard it: “the same product that worked last season barely touched the pest this year.” Most of the time the product has not changed — the pest population has. This guide explains, from a manufacturer’s standpoint, why resistance builds, how the IRAC and FRAC numbering systems translate into concrete rotation rules, and how mixtures and biological products slot into a program. The mixture examples used throughout are real registered products from the BNSD Agro (Shandong Bainong Sida Biotechnology Co., Ltd.) portfolio.
Why Resistance Happens: Selection Pressure in One Paragraph
A fungicide or insecticide never kills every individual in a pest population. The susceptible majority dies; the small fraction carrying natural tolerance survives, breeds, and passes that tolerance on. Spray the same mode of action (MOA) again and again and each application selects a little harder for the tolerant fraction, until the population is dominated by resistant individuals. Three well-established points follow from this:
- Resistance is a population problem, not a product defect. A batch test will show the product exactly on specification; the failure is in the selection the program imposed.
- Cross-resistance is real. A pest resistant to one active is often resistant to other actives in the same group, because the mechanism targets the shared mode of action.
- The unit of rotation is the mode of action, not the brand. Swapping trade names while staying inside one chemical group changes nothing.
IRAC and FRAC: Turn the Label Numbers into Rules
The two industry bodies — IRAC for insecticides and acaricides, FRAC for fungicides — classify every active ingredient by mode of action and assign it a group number, printed on the product label. This is what makes rotation practical: a farmer does not need to know chemistry, only numbers.
The resulting rules are the backbone of resistance management worldwide:
- Do not follow a group with the same group against the same pest in the same generation or crop stage. If tebuconazole (FRAC 3) was just used, the next fungicide for the same target should come from a different FRAC group.
- Limit the number of applications from any one group per season or crop cycle. The tighter the crop cycle and the faster the pest’s generations, the stricter the cap should be.
- Rotate between unrelated groups, not just different actives. Pyraclostrobin and tebuconazole are different molecules but also different FRAC groups (11 and 3) — that is a genuine rotation; two DMI fungicides are not.
Where Mixtures Fit — and What They Cannot Do
A mixture combines two effective modes of action in one application, so a resistant individual must carry tolerance to both actives simultaneously to survive — an event far rarer than tolerance to either alone. This is why pre-mixed products are a legitimate resistance-management strategy, provided both components remain effective against the target.
Pre-mixes also remove a practical failure point: the ratio of the two actives is fixed and quality-controlled at the factory, instead of depending on the operator measuring two separate products into every tank. The registered two-active products in the BNSD Agro range (company information) illustrate the range of pairings:
| Product | Mode-of-action pairing | Registered uses (Chinese label) |
|---|---|---|
| 30% pyraclostrobin + tebuconazole suspension concentrate (SC) | FRAC 11 + FRAC 3 | Wheat powdery mildew and rust 20–40 mL/667 m²; pepper anthracnose 60–70 mL/667 m² |
| 11.6% emamectin + chlorantraniliprole SC | IRAC 6 + IRAC 28 | Diamondback moth 5–10 mL/667 m² |
| 12% chlorfenapyr + lufenuron SC | IRAC 13 + IRAC 15 | Beet armyworm 25–42 g/667 m² |
| 10.5% abamectin + pyridaben emulsifiable concentrate (EC) | IRAC 6 + IRAC 21 | Apple red spider mite 2500–3500× |
| 45% bifenazate + etoxazole SC | Two unrelated acaricide MOAs (all mite stages, ovicidal) | Citrus red mite 6000–8000× |
| 45% kasugamycin + oxine-copper SC | Antibiotic + copper-based partner | Peach bacterial shot hole 2000–3000× |
Two cautions keep mixtures honest. First, a mixture is not a licence to spray more often — the same per-season caps still apply. Second, if one component of a pairing has already been overused on its own in the region, the mixture inherits that weakness; both partners must still be effective locally.
Biologicals as Rotation Partners
Biopesticides give the program rotation steps that no chemical group can, because their modes of action sit outside the chemical numbering entirely:
- Bt (Bacillus thuringiensis) 16000 IU wettable powder (WP) — rice leaffolder at 100–150 g/667 m², and tobacco budworm on its label. A microbial insecticide whose midgut-specific action is unlike any chemical group.
- Beauveria bassiana 200 bn spores/g oil dispersion (OD) — diamondback moth at 15–20 mL/667 m². An entomopathogenic fungus that infects through the cuticle.
- Amino-oligosaccharin 5% aqueous solution (AS) — tomato viral disease at 64–107 g/667 m². An immunity elicitor: it acts on the plant’s own defences rather than the pathogen directly.
Because resistance to these products develops slowly and rarely, inserting them between chemical applications reduces the total selection pressure on any chemical group. They are strongest against young larvae and under favourable conditions, so the usual positioning is early in each pest generation, with a conventional product held for knockdown when populations breach thresholds. The full insecticide range, including biologicals, is in the insecticides and acaricides catalogue; fungicide groups for rotation planning are in the fungicides catalogue. For the complete mixture catalogue, samples or destination-label documents, contact BNSD Agro.
FAQ
What is the single most important resistance-management rule?
Rotate modes of action. Concretely: know the IRAC or FRAC group number of every product in the program, never follow one group with itself against the same pest generation, and cap the number of applications from each group per season. Brand-swapping inside the same group achieves nothing.
How many applications from one group are allowed per season?
There is no universal number — it depends on the pest’s generation time, the crop cycle and local resistance history, which is why the destination-market label and local advisory services set the specific cap. The principle is fixed: the more generations the pest completes per season, the fewer applications from any single group the program can afford.
Do mixtures prevent resistance on their own?
No. A mixture is one tool that lowers selection pressure by requiring resistance to two modes of action at once. It works only while both components remain effective, and it must still sit inside a rotation plan with per-season caps. Products such as 30% pyraclostrobin + tebuconazole SC or 11.6% emamectin + chlorantraniliprole SC are best understood as rotation building-blocks, not stand-alone solutions.
Where do biological products fit in a rotation?
Between chemical applications, early in each pest generation. Bt 16000 IU WP (rice leaffolder 100–150 g/667 m²) and Beauveria bassiana 200 bn spores/g OD (diamondback moth 15–20 mL/667 m²) act by modes of action outside the chemical groups, so they impose no meaningful cross-selection pressure. Expect slower action than a conventional insecticide and position them accordingly.
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