Crop Protection in Thailand
How to tell a pest from a nutrient problem, how to stop both before they start, what changes between outdoor, greenhouse and indoor growing, when in the Thai year each pressure arrives — and the legal rules on crop protection products in Thailand. Part three of three.
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Pest damage or nutrient deficiency?
New growers get this wrong more than anything else, in both directions: feeding a plant that has mites, and spraying a plant that is short of magnesium. The cost of guessing is not just the wasted input — it is the two weeks you spend waiting for the wrong fix to work while the real problem doubles.
Four questions that settle most cases before you reach for a lens
- Is it clustered or uniform? Nutrition arrives through the irrigation and hits every plant on that line at the same time. Pests and diseases arrive at a point and spread — hotspots at doors, vents, block edges, one bench. This single observation settles more diagnoses than any other.
- Which leaves — and does the pattern follow leaf age strictly? Mobile nutrients (nitrogen, magnesium, potassium, phosphorus) go from the oldest leaves upward in a strict sequence. Immobile ones (calcium, iron, boron, zinc) hit the youngest. A problem that ignores leaf age and appears wherever the canopy is wettest, shadiest or most crowded is not nutritional.
- Has the leaf shape changed, or only its colour? Deficiencies change colour. Pests, viruses and several diseases change shape and colour together — cupping, strapping, hardening, blistering, distortion. Shape change is a strong signal that you are not looking at a feed problem.
- Is there any sign of an organism? Frass specks, cast skins, webbing, honeydew, sooty mould, eggs, fruiting bodies in a lesion, a rubbing-off powder. A nutrient deficiency never produces any of these. If you find one, stop looking at the feed chart.
The specific confusions, and the test that resolves each
| Looks like | Is often actually | The test |
|---|---|---|
| Zinc deficiency — pale mottling on newer leaves | Thrips | 10× lens inside the pale area: black varnish-like frass specks. Tilt the leaf to the light — thrips silvering flashes metallic, chlorosis does not. |
| Magnesium deficiency — interveinal yellowing on older leaves | Spider mites | 10× lens: discrete pinprick stipples, not a continuous wash. Turn the leaf: eggs and webbing. |
| Magnesium or potassium deficiency — blotchy chlorosis on older leaves | Powdery mildew of the Leveillula type | Turn the leaf over. The white sporulation is on the underside. This one costs growers whole seasons. |
| Calcium or boron deficiency — distorted, hardened new growth | Broad mite or a russet mite | 20–30× lens on the underside of the youngest expanded leaf: transparent eggs covered in rows of white bumps. Also — with a mite, growth stalls; with cultural stress, new leaves keep expanding. |
| Nitrogen deficiency — general yellowing and stunting | Root rot, fungus gnat larvae or root aphid | Wash the root ball. Nitrogen-starved roots are white, intact and often longer than normal. Rotted roots are brown and slip apart. Larvae and root aphids you will see. |
| Potassium deficiency — necrotic leaf margins | Coalescing fungal leaf spot | Potassium scorch is a continuous symmetric margin with a yellow transition band. A blight is discontinuous — merged discrete lesions whose round outlines you can still see. |
| Magnesium or iron chlorosis — mosaic and mottling | Virus | Count the plants. Nutrition hits every plant on the tank; virus hits scattered individuals. And virus distorts the leaf shape as well as the colour. |
| Water stress — wilting | Fusarium wilt or root rot | Fusarium is asymmetric and shows a brown vascular stain on a lengthwise stem cut. Root rot shows brown sloughing roots. Water stress recovers fully and repeatedly once watered. |
If after all of that it really is nutritional — uniform across the block, strictly following leaf age, colour only, no organism anywhere — go to the Nutrient Deficiency Guide, which covers each element's symptoms, the pH and EC conditions that lock nutrients out, and how to correct them. Terms used here that you have not met before are defined in the Grower's Glossary.
Prevention is the whole job
Every treatment section in this guide is what you do when prevention has already failed. In a Thai climate, where a thrips generation is ten days and a broad mite generation is five, the crop that survives is the one that never let the population establish. Six things carry almost all of the weight.
1 · Quarantine everything that arrives
Isolate incoming plant material and inspect it for 4–5 days before it goes anywhere near production VERIFIED. Broad mite, root aphid, mealybug and virus all arrive this way — not through the vents. Inspect for the organism, because broad mite symptoms persist for weeks after the mites are gone, so a damaged-looking plant may be clean and a clean-looking plant may be carrying eggs VERIFIED. Fungus gnats arrive inside bagged growing medium and rooted plugs, which is a documented pathway VERIFIED and the reason a brand-new sealed house has gnats in week one.
2 · Control humidity and air movement — especially in the rains
The verified targets: full air exchange in 5 to 10 minutes; horizontal airflow fans to prevent still boundary layers and condensation; start dehumidifying at about 85% RH and never let it exceed 90%; target VPD 8–10 mbar VERIFIED. Water early in the morning so the canopy dries as temperature rises VERIFIED.
The Thai addition INFERRED: from May to October, Surin runs 11–15.5 rain days a month with mean RH reaching 83.7% in September VERIFIED. You will not hold 85% RH in a naturally ventilated house in a Thai August. What you can control is leaf wetness duration and the rate of temperature change. Both are cheaper than dehumidification and both matter more.
3 · Break the splash path before the rains, not after
Anthracnose, Cercospora, Alternaria, bacterial leaf spot and bacterial soft rot are all splash-dispersed VERIFIED. One intervention addresses all five: a roof with open sides. Add mulch on the soil surface, strip the lowest 30 cm of leaves so the splash zone is bare stem, and switch overhead misting to drip or sub-canopy irrigation. Do this in April, before the first rains — not in July when you already have lesions INFERRED.
Accept the two costs honestly: a roof removes the rainfall that was suppressing powdery mildew VERIFIED, and target spot spreads perfectly well inside a Thai glasshouse on misting water regardless of the weather outside VERIFIED.
4 · Sanitation, which is unglamorous and decisive
- Remove and bag senescent lower leaves — they are the spider mite reservoir, the whitefly pupation site and the tissue Botrytis prefers VERIFIED.
- Never store plant debris inside the structure VERIFIED.
- Remove finished plants promptly and do not overlap crop cycles — that overlap is what perpetuates root aphid INFERRED and gives every other population a bridge.
- Disinfect tools between plants, and never prune, train, harvest or scout a wet crop — for bacterial disease this single habit is worth more than anything you can spray INFERRED.
- Clear volunteer cucurbit and solanaceous plants around the structure; the thrips species here are polyphagous across more than 150 plants VERIFIED. We could not find a Thailand-specific host list for any of these pests UNVERIFIED, so target the obvious relatives of your crop rather than trusting a list you cannot source.
- Control algae on floors, benches and drip lines and the shore flies go with it VERIFIED.
- Control ants — they farm aphids and mealybugs for honeydew and actively disrupt natural enemies VERIFIED.
5 · Monitor on a schedule you actually keep
Blue cards for thrips, yellow for everything else, flat on the medium for fungus gnats, replaced weekly in the same positions. Twenty plants per 93 m², ten minutes per area, edge and middle and interior, bottom to top, leaves turned over. Weekly minimum, twice weekly better VERIFIED. Keep a written record with dates — the trend is what tells you something is starting; a single count tells you almost nothing. Full method in part one.
6 · Choose the structure and the covering material deliberately
If you are building or re-covering, two verified Thai results should drive the decision:
- UV-blocking film and nets cut virus incidence from 96–100% to 6–10% in a Bangkok trial, with no measured temperature or humidity penalty VERIFIED.
- If you screen, you must force-ventilate. Fine mesh cuts the ventilation rate VERIFIED, and a CFD-optimised north-east Thai design with a 15° inlet angle and three bottom-mounted exhaust fans held the interior 7.88 °C below ambient VERIFIED.
Outdoor, greenhouse and indoor
The same organism behaves differently in the three systems, and the management that helps in one can hurt in another. This is the part most foreign guides skip, because they assume one system.
Open field
What you get free: rain physically washes powdery mildew conidia off the crop VERIFIED, and heavy rain almost certainly knocks down thrips and whitefly populations — although we should be honest that we could not find a quantified rainfall-mortality figure for any of the Thai vector species, and the EPPO datasheet for Thrips palmi contains no information on rainfall effects at all UNVERIFIED. Keep scouting in the rains; do not assume the vectors have gone.
What you pay: full splash dispersal, unbroken leaf wetness, waterlogging and the oomycetes that follow it. The rainy season is the worst season outdoors, comprehensively INFERRED.
Hot season outdoors: root-zone overheating is the main risk, plus soft rot wherever irrigation supplies water and handling supplies wounds, plus the thrips and mite peak. Powdery mildew and Botrytis are suppressed by the heat for free.
Plastic greenhouse or rain shelter
Rainy season — this is when it earns its cost. Breaking splash dispersal removes the dominant driver of five pathogen groups in one move INFERRED. Keep the sides open; ventilation is the binding constraint.
Hot season — this is when it becomes a heat and thrips trap. A naturally ventilated plastic house in Isaan in April faces 36 °C ambient with extremes recorded to 43.6 °C VERIFIED. The fine mesh you need to exclude thrips reduces ventilation VERIFIED, so the house heats further. The result is a structure that is simultaneously too hot for the crop, ideal for P. aphanidermatum in the root zone, ideal for Ceratothripoides claratris at its 30 °C optimum, and — if any thrips got in before the mesh or through a door — a predator-free incubator INFERRED. Force-ventilate, shade with care (remembering that shade favours powdery mildew), and watch the substrate temperature rather than the air temperature.
Cool season — condensation peaks. A closed house at night against an 11.6 °C outside day/night differential VERIFIED drips on the inner skin and on the plants. This is the Botrytis window. Manage it with thermal screens and gradual pre-dawn temperature ramps, dehumidifying at about 85% RH VERIFIED.
Sealed, climate-controlled indoor
The strongest argument for indoor production in Thailand is that it decouples you from splash dispersal, leaf wetness and monsoon vectors entirely INFERRED. The residual risks are all self-inflicted: oomycetes in recirculated irrigation water VERIFIED, target spot dispersed by your own misting VERIFIED, and condensation.
The trap nobody warns new indoor growers about. A room held at 20–26 °C sits inside the powdery mildew optimum of 20–25 °C and inside the Botrytis optimum of 16–24 °C VERIFIED. You have manufactured, at some expense, the two diseases that the Thai hot season would have suppressed for you for free INFERRED. Indoor production in Thailand does not remove disease pressure — it swaps a monsoon problem for a temperate one.
The cross-cutting indoor rule: a sealed room's danger is not the monsoon, it is the rate of temperature change at lights-off. Build against the verified targets — dehumidify at about 85% RH, never exceed 90%, VPD 8–10 mbar, humidify above 12.5 mbar, full air exchange in 5–10 minutes, horizontal airflow fans running VERIFIED — and remember that at about 12 mbar VPD the stomata are already around 50% closed and you are limiting photosynthesis VERIFIED. In the cool season, outside air is dry and cool and is the cheapest dehumidification of the year, if the room can use it.
Thailand's pest and disease pressure calendar
This is the part that no foreign document contains, because it requires reading measured biological thresholds against Thai climate normals. The seasons used are hot (March–May), rainy (May–October) and cool (November–February).
The climate that drives it
Monthly normals for Surin, 1991–2020, the closest full-normals station to Buriram VERIFIED:
| Month | Mean high °C | Mean low °C | Mean °C | Rain mm | Rain days | Mean RH % |
|---|---|---|---|---|---|---|
| Jan | 31.3 | 18.5 | 24.5 | 6.6 | 0.7 | 64.9 |
| Feb | 33.4 | 20.4 | 26.5 | 9.9 | 1.3 | 62.3 |
| Mar | 35.4 | 23.3 | 28.9 | 47.2 | 3.0 | 62.5 |
| Apr | 36.1 | 24.9 | 29.9 | 85.9 | 6.3 | 66.4 |
| May | 34.9 | 25.2 | 29.2 | 186.4 | 11.3 | 74.8 |
| Jun | 33.8 | 25.0 | 28.6 | 194.1 | 12.7 | 77.7 |
| Jul | 32.8 | 24.6 | 28.0 | 219.9 | 14.6 | 79.5 |
| Aug | 32.4 | 24.5 | 27.7 | 270.7 | 15.5 | 81.7 |
| Sep | 31.8 | 24.3 | 27.4 | 266.5 | 14.8 | 83.7 |
| Oct | 31.3 | 23.2 | 26.8 | 113.5 | 8.1 | 79.5 |
| Nov | 31.3 | 21.0 | 25.8 | 29.7 | 2.6 | 71.8 |
| Dec | 30.3 | 18.7 | 24.2 | 3.0 | 0.4 | 66.7 |
| Year | 32.9 | 22.8 | 27.3 | 1,433 | 91.3 | 72.6 |
Cross-checks VERIFIED: Nakhon Ratchasima (Korat) annual mean 27.7 °C, 1,123 mm over 79.8 rain days, April mean high 36.6 °C, September RH 81.2%. Buriram itself, 1989–2018: mean highs 30.2–36.5 °C, means 23.8–29.5 °C, mean lows 18.1–24.7 °C, RH 66–84%, annual 1,212 mm over 116 rain days. Bangkok for comparison: September 335.9 mm over 18.0 rain days at 79.3% RH; December mean low 23.2 °C.
Three things this table tells a grower that no foreign document will INFERRED, read straight off the verified numbers:
- Isaan is colder at night in the cool season than Bangkok, and hotter by day in the hot season. Surin's December mean low is 18.7 °C against Bangkok's 23.2 °C — a 4.5 °C difference — and Surin's December day/night differential is 11.6 °C against Bangkok's 9.1 °C. Big differentials make dew. That one number is the entire cool-season disease story.
- Isaan's rainy season is wetter at the peak than Bangkok's (Surin August 270.7 mm over 15.5 rain days at 81.7% RH) and its humidity ceiling is higher (September 83.7% against 79.3%). Anyone who thinks of Isaan as "the dry region" will under-build drainage.
- The driest month in Isaan is February, not the hottest month. RH bottoms out at 62.3% in February; April is already at 66.4% and rising. The "hot and dry" mental model is wrong by a month — February is dry, April is hot and humidifying.
The calendar
| Problem | Hot Mar–May |
Rainy May–Oct |
Cool Nov–Feb |
The governing number |
|---|---|---|---|---|
| Pythium aphanidermatum root rot | HIGH | Moderate, where drainage fails | Low | Optimum 35–40 °C; above 28 °C in the root zone is risk V |
| Pythium ultimum / Globisporangium | Low | Moderate | Moderate | Optimum 25–30 °C V |
| Fusarium wilt | HIGH, then self-limits above 34 °C | Moderate | Low, unless nematodes present | Optimum 28 °C; retarded above 34 °C V |
| Powdery mildew | Low outdoors — high if shaded or cooled | Low outdoors — high under a roof | HIGHEST | Optimum 20–25 °C, RH ≥40%, rain kills conidia V |
| Grey mould (Botrytis) | Very low | Low to moderate | HIGHEST — the only lowland window | 16–24 °C, RH ≥85%, 8–12 h moisture film V |
| Anthracnose (Colletotrichum) | Rising from May | HIGHEST | Low | Optimum 25–28 °C, splash-dispersed V |
| Target spot (Corynespora) | Moderate | HIGH, including indoors on misting | Low | Thai record Jun–Aug, in a glasshouse V |
| Cercospora / Alternaria leaf spot | Low | HIGH | Low | Needs >11 h leaf wetness; RH 90–95% V |
| Bacterial leaf spot (Xanthomonas) | Rising | HIGHEST | Low | Optimum 28.9 °C; only 5 h wetness needed at 25–35 °C V |
| Bacterial soft rot | HIGH where irrigation supplies water | HIGHEST | Low — below minimum temperature | Optimum 31–34 °C; minimum 20–23 °C V |
| Thrips and tospovirus | HIGHEST | Lower U | Moderate | C. claratris optimum 30 °C; 10-day virus latent period V |
| Whitefly and begomovirus | HIGH | Lower U | Moderate | 57% of 585 Thai samples begomovirus-positive V |
| Spider mites | HIGHEST | Low | Moderate | A documented dry-season threat V |
| Broad mite | Moderate | HIGHEST | Moderate | Thrives 21–27 °C and 80–90% RH; 5-day generation V |
| Aphids | Low — 35 °C kills the immatures | Moderate | HIGHEST | Optimum 22.5–30 °C; lethal at 35 °C V |
| Caterpillars (S. litura) | HIGHEST | HIGH | Moderate | Optimum 30–35 °C, peaking at 35 °C V |
| Southern blight (Sclerotium rolfsii) | Spikes at the first irrigation or rain after a dry spell | Moderate | Low | Rainfall following drought favours it V |
The two transitions are sharper than the seasons
First rains, late April into late May
Surin goes from 6.3 rain days and 85.9 mm in April to 11.3 rain days and 186.4 mm in May, with mean RH stepping from 66.4% to 74.8% VERIFIED — a doubling of rain days and an eight-point humidity step inside four weeks.
Why that is disproportionately dangerous INFERRED: dry-season debris and soil surface have been accumulating inoculum with nothing to move it, and the first rain releases and disperses months of stored inoculum in a single event. Temperature is still at its annual maximum (May mean 29.2 °C) while the water has arrived — hot-season temperatures with rainy-season water is briefly more favourable than either season's core for Xanthomonas (optimum 28.9 °C), anthracnose (25–28 °C) and soft rot (31–34 °C). The crop is at its most heat-stressed. And the thrips population built through the hot season is still there when the first infections establish.
Direct support for the mechanism: for Sclerotium rolfsii, "some rainfall (or irrigation) following a period of drought favors growth of the fungus in the soil" VERIFIED. A Thailand-specific study testing a first-rain disease surge across pathogens was not found UNVERIFIED; the generalisation rests on verified splash dispersal plus a verified climate step-change.
What to do about it: every splash-breaking measure — roof, mulch, lower-leaf stripping, switch off overhead misting — belongs in April, not July.
End of the rains, late October into November
Surin goes from 113.5 mm over 8.1 rain days at 79.5% RH in October to 29.7 mm over 2.6 rain days at 71.8% RH in November, with the mean low falling from 23.2 to 21.0 °C and the day/night differential widening from 8.1 to 10.3 °C VERIFIED.
Four things change at once INFERRED:
- Rain stops but dew starts. Surface wetness does not disappear — its source switches from rainfall to radiative condensation. A grower who relaxes because "the rains are over" loses the leaf-wetness battle to dew instead.
- The pathogen roster flips. Splash-dispersed bacteria and leaf spots crash; powdery mildew and Botrytis take over. Any protocol built for the rains is now aimed at the wrong targets.
- A large standing crop of senescing tissue exists at the end of the wet season — exactly the substrate Botrytis prefers VERIFIED.
- Night minima cross biological thresholds rather than merely shifting. 23.2 °C in October, 21.0 °C in November, 18.7 °C in December crosses the Dickeya solani minimum (23 °C), the Dickeya dadantii minimum (21 °C) and the Pectobacterium minimum (20 °C) in three consecutive months VERIFIED. Crossing thresholds produces step changes in disease, not gradual ones.
No literature explicitly testing either transition as a discrete risk event in Thailand was found UNVERIFIED; both are reasoned from verified thresholds and verified climate normals.
Using crop protection products legally in Thailand
This is the heaviest constraint in this guide, and it is a legal one, not an agronomic one. In Thailand, crop protection products are regulated as hazardous substances under the Hazardous Substances Act (พระราชบัญญัติวัตถุอันตราย), and the responsible authority for agricultural products is the Department of Agriculture (กรมวิชาการเกษตร, DOA). Using an unregistered product, or using a registered product outside its label, is a legal exposure before it is anything else. For a farm working to GACP, pesticide residue is also an existential commercial risk — a residue failure can invalidate a harvest. We do not interpret GACP requirements here; that is a compliance question for your certifying body and your own advisers.
Four rules, every time
- Buy by the registration number, not by the trade name. Ask to see the hazardous-substance registration (ทะเบียนวัตถุอันตราย) on the label. If the seller cannot show you one, the product does not go on your farm.
- Read the label and follow it exactly — the approved crops, the rate, the method, and the pre-harvest interval. Using a product on a crop it is not labelled for is off-label use, and it is not something a technical adviser can authorise for you.
- Never mix active ingredients on your own initiative. Tank-mix compatibility is a formulation question with real phytotoxicity and residue consequences. If the label does not say it, do not do it.
- Rotate by mode-of-action group, never by product name. Two different brands frequently contain the same active or the same IRAC or FRAC group, so a grower who "rotates products" may be applying the same selection pressure every time. Ask for the IRAC group (insecticides and miticides) or FRAC code (fungicides) and rotate those.
What is banned — verified, with the instrument
Type 4 hazardous substances (วัตถุอันตรายชนิดที่ 4) may not be produced, imported, exported or possessed. The classification is made by ประกาศกระทรวงอุตสาหกรรม เรื่อง บัญชีรายชื่อวัตถุอันตราย — a Ministry of Industry announcement, not a Ministry of Agriculture one, with DOA named as the responsible agency for the agricultural annex VERIFIED.
Announcement No. 6, B.E. 2563, published in the Royal Gazette on 19 May 2020 and effective 1 June 2020 VERIFIED, moved to Type 4:
- Chlorpyrifos (คลอร์ไพริฟอส) and chlorpyrifos-methyl
- Paraquat (พาราควอต), paraquat dichloride and paraquat methosulfate
Earlier Type 4 announcements banned, among 96 substances in total, DDT, endrin, dieldrin, aldrin, heptachlor, parathion-ethyl, monocrotophos, methamidophos, parathion-methyl and endosulfan (excluding the CS formulation) VERIFIED.
Announcement No. 8, B.E. 2568, effective 8 July 2025 VERIFIED, added pentachlorobenzene and hexachlorobutadiene — neither of which is a horticultural product — and, more usefully for a grower, removed several plant extracts from hazardous-substance control entirely: turmeric (ขมิ้น), galangal (ข่า), lemongrass (ตะไคร้หอม) and citronella oil. Those are no longer hazardous substances at all, so no registration is required to sell or use them.
Two corrections to things growers commonly say. First, glyphosate is restricted, not banned. It sits at Type 3 and is governed by a Ministry of Agriculture announcement of 23 April 2019, effective about 20 October 2019, which requires trained and certified users and sellers, approved spray equipment and PPE, record-keeping, and sale only to certified persons VERIFIED. Second, methomyl, carbofuran, dicrotophos and EPN were not classified as Type 4. Carbofuran and dicrotophos appear in the consolidated list as Type 3 substances VERIFIED. What happened around 2013 is that DOA suspended or refused their registration, which removes products from the market without a Type 4 listing — but we could not retrieve the DOA instrument itself UNVERIFIED. The defensible wording is "no longer registered", not "banned".
Actives we could verify as listed under DOA responsibility
The table below lists only active ingredients we could confirm appear in Thailand's Hazardous Substances List (บัญชีรายชื่อวัตถุอันตราย, บัญชี 1) under DOA responsibility at Type 2 or Type 3 — meaning products containing them are lawfully registrable with DOA and a registered product should exist. Type 2 requires notification plus registration; Type 3 requires registration plus a licence VERIFIED.
| Active ingredient | Type | Group | Used against |
|---|---|---|---|
| Bacillus thuringiensis | 2 | IRAC 11A | Caterpillars — effective on small larvae, poor on large ones |
| Beauveria bassiana | 2 | IRAC UNF | Thrips, whitefly, aphids. Not spider mites — minimal susceptibility was measured V |
| Trichoderma harzianum | 2 | FRAC BM 02 | Soilborne disease, root rot, anthracnose. Preventative, not curative |
| Bacillus subtilis | 2 | FRAC BM 02 | Anthracnose (86–100% leaf severity reduction in an Isaan net-house trial V), root rot, foliar disease |
| Sulfur (กำมะถัน) | 3 | FRAC M 02 | Powdery mildew. Multi-site, low resistance risk. Phytotoxic at high temperature |
| Copper hydroxide | 3 | FRAC M 01 | Bacterial leaf spot, some fungal disease. Protectant only |
| Copper oxychloride | 3 | FRAC M 01 | As above |
| Chlorothalonil | 3 | FRAC M 05 | Fungal leaf spots. Multi-site protectant, applied before a wet period |
| Propamocarb (and hydrochloride) | 3 | FRAC 28 | Oomycetes — Pythium, Phytophthora. Does not touch true fungi |
| Difenoconazole | 3 | FRAC 3 | Powdery mildew, leaf spots. Single-site — must be rotated |
| Tebuconazole | 3 | FRAC 3 | As above. Same group as difenoconazole — rotating between these two is not a rotation |
| Thiamethoxam | 3 | IRAC 4A | Sucking insects. Harmful to released natural enemies; resistance documented in the same whitefly cryptic species in India V |
All Type and list entries VERIFIED against the consolidated Hazardous Substances List; IRAC and FRAC codes VERIFIED against IRAC MoA Classification v11.5 (February 2026) and the FRAC Code List 2025.
What we could NOT verify, stated plainly. The DOA registered-product database and the annual สรุปข้อมูลวัตถุอันตราย summary files were unreachable from our connection despite repeated attempts, so for a long list of actives we can confirm neither registration nor its absence. That list includes every miticide we looked at — abamectin, hexythiazox, etoxazole, spiromesifen, spirotetramat, fenpyroximate, pyridaben and bifenazate — plus spinosad, azadirachtin and neem, mineral and petroleum spray oils, potassium salts of fatty acids, potassium bicarbonate, imidacloprid, acetamiprid, emamectin benzoate, chlorantraniliprole, indoxacarb, lufenuron, metalaxyl, fosetyl-aluminium, azoxystrobin, myclobutanil, propiconazole, iprodione, fludioxonil, boscalid, pyraclostrobin and mancozeb UNVERIFIED. Absence from our table means we could not check it, not that it is unregistered. Several of these are in routine legal use in Thailand. Check the registration number on the actual label with your supplier and, if you need certainty, with DOA directly.
Reading a Thai label
Thai pesticide labels carry a toxicity colour band occupying at least 15% of the label area, under ประกาศกระทรวงเกษตรและสหกรณ์ เรื่อง ฉลากและระดับความเป็นพิษของวัตถุอันตราย พ.ศ. ๒๕๓๘, published in the Royal Gazette on 16 November 1995 VERIFIED:
| Toxicity class | Band colour | Required wording | Symbol |
|---|---|---|---|
| 1a | Red (แถบสีแดง) | พิษร้ายแรงมาก — extremely toxic | Skull and crossbones |
| 1b | Red | พิษร้ายแรง — highly toxic | Skull and crossbones |
| II | Yellow (แถบสีเหลือง) | อันตราย — harmful | Cross symbol |
| III | Blue (แถบสีน้ำเงิน) | ระวัง — caution | Warning text |
A green band for the least hazardous class is commonly described in practice but appears in neither source we could retrieve, so we do not list it UNVERIFIED.
Look on the label for the hazardous substance registration number (ทะเบียนวัตถุอันตรายเลขที่) and the pre-harvest interval (ระยะเวลาที่ต้องหยุดใช้ก่อนเก็บเกี่ยว). In the interests of being straight with you: we could not retrieve the specific legal instrument that mandates those two items on a commercial label — the 1995 label announcement and the 2009 "other required label text" announcement were both unreachable UNVERIFIED. Every Thai pesticide label we are aware of carries them, and you should absolutely look for them, but we are not going to cite a law we did not read.
The residue reminder, and it applies to every treatment section in this guide: use only a product registered in Thailand for the crop you are treating, read the label, follow the rate and method exactly, and observe the pre-harvest interval. For a farm working to GACP, pesticide residue is a pass-or-fail matter for the harvest, not a detail — build your programme so that the last chemical application is comfortably outside the PHI, and keep written application records.
Where AZ Growshop fits
AZ Growshop supplies horticultural inputs to farms in Thailand: plant nutrition and fertilizers, substrates and growing media, rooting and propagation products, and plant protection inputs. In the sequence described in this guide, those sit in the prevention and cultural steps — the substrate that drains properly, the propagation hygiene that stops damping-off, the balanced nutrition that avoids the soft over-fed growth Botrytis prefers — and, where a registered product is appropriate, the supply of it with its documentation. Our technical team can help you read a label and identify the IRAC or FRAC group before you buy. Request a wholesale quotation or contact the technical team.
Sources and how to read them
Everything marked VERIFIED across all three parts of this guide comes from one of the sources below. Everything marked INFERRED is our own reasoning from those sources — usually taking a measured biological threshold and reading it against Thai climate normals — and has not itself been measured in Thailand. Everything marked UNVERIFIED is something we looked for and could not confirm.
We have been deliberate about flagging the gaps rather than smoothing over them, because the gaps are real and a grower making decisions deserves to know which numbers are measurements and which are arguments. The largest single gap is that Thai Department of Agriculture technical material was largely unreachable from our connection, which is why the registration table above is shorter than it should be, and why several sections rely on regional rather than Thai data.
Thai and Southeast Asian primary sources
Nationwide Thai pest mite survey, 61 districts in 33 provinces 2021–2023, Thai Agricultural Research Journal · Thrips species on organic roses, Pak Chong, JASM · Entomopathogenic fungi from Chiang Mai sweet-pepper screen-houses, CMU Journal of Agriculture · Sticky trap colour against Thrips palmi in Thai orchid gardens, Life Sciences and Environment Journal · Natural enemies of Thrips palmi in Thailand, Biological Control · Predatory mite release rates, Thai Department of Agricultural Extension via the Entomology and Zoology Association of Thailand · Bemisia tabaci cryptic species in Thailand and Vietnam, Journal of Asia-Pacific Entomology · Cypermethrin resistance in Thai Spodoptera litura, Agriculture and Natural Resources · First detection of fall armyworm in Thailand, IPPC official pest report · Fall armyworm in mainland Southeast Asia, Frontiers in Insect Science · Pythium diversity in eastern Thailand, Agriculture and Natural Resources · Bacillus subtilis against chilli anthracnose, Suranaree University of Technology, Agriculture and Natural Resources · Marine Trichoderma against anthracnose and black spot, Kasetsart University, European Journal of Plant Pathology · Thai indigenous Trichoderma against Phytophthora palmivora, Journal of Plant Diseases and Protection · Colletotrichum on Capsicum across Asia, IMA Fungus · Corynespora cassiicola on hydroponic lettuce in Songkhla, Australasian Plant Disease Notes · Powdery mildew in Southeast Asia, Technology in Agronomy · Tospoviruses in Thailand, Archives of Virology · Tomato necrotic ringspot virus, first isolated in Thailand, Archives of Virology · Begomoviruses in Thailand, 585 samples from 17 provinces, Crop Protection · Ceratothripoides claratris as a CaCV vector in Thailand, Phytopathology · UV-blocking films and nets, Asian Institute of Technology Bangkok, Environmental Entomology · Greenhouse ventilation design for north-east Thailand, Ain Shams Engineering Journal · Tropical vegetable IPM, World Vegetable Center
Thai regulation
ประกาศกระทรวงอุตสาหกรรม เรื่อง บัญชีรายชื่อวัตถุอันตราย (ฉบับที่ ๖) พ.ศ. ๒๕๖๓ — Department of Industrial Works · Consolidated Hazardous Substances List B.E. 2556 — DIW · Announcement No. 8, B.E. 2568 — Royal Gazette · Restricted-use measures for glyphosate, chlorpyrifos and paraquat, B.E. 2562 — Royal Gazette · Pesticide registration procedure, B.E. 2551 — Department of Agriculture · DOA hazardous substances section — doa.go.th · DOA registered-substance summaries — doa.go.th · Label and toxicity classification, B.E. 2538, via the Office of the Consumer Protection Board · IRAC Mode of Action Classification v11.5 · FRAC Code List 2025
International pest and disease references
EPPO Global Database datasheets for Thrips palmi, Frankliniella occidentalis, Ceratothripoides claratris, Spodoptera litura and Helicoverpa armigera · Thrips palmi temperature-dependent development, Taiwan, Journal of Insect Science · Thrips palmi economic thresholds on greenhouse eggplant, Applied Entomology and Zoology · UF/IFAS melon thrips · Scirtothrips dorsalis overview · Thrips parvispinus review · Arthropod Pesticide Resistance Database · NC State, twospotted spider mite · Cornell fact sheets for Amblyseius swirskii and Neoseiulus californicus · A. swirskii review, Journal of Integrated Pest Management · UConn, managing broad mites · Koppert, broad mite · Broad mite biology at 26 °C, Journal of Entomology and Zoology Studies · Bemisia tabaci thermal biology, Pakistan Journal of Biological Sciences · Trialeurodes vaporariorum phenology model, ScienceDirect · Asia-I and Asia-II whitefly resistance, Scientific Reports · Aphis gossypii temperature response, Journal of Pest Science · Aphidius temperature response, Environmental Entomology · Beauveria bassiana humidity thresholds, Environmental Entomology · USDA CPHST, Spodoptera litura · S. litura temperature and humidity meta-analysis, Insects · Kansas State, fungus gnat management · Rice root aphid in protected cultivation, Journal of Integrated Pest Management · UMass Extension scouting, fungus gnats and shore flies, aphids and Botrytis blight · Rutgers, pest counts and action thresholds · Oklahoma State, greenhouse scouting · UConn, insect screening · NGMA insect screen guide · Insect-proof net field trial, Insects · AHDB, thrips damage symptoms · British Columbia, Pythium diseases of greenhouse vegetables · British Columbia, understanding humidity control · Dissolved oxygen in soilless systems, Frontiers in Plant Science · Pythium species temperature optima · NCSU, Fusarium oxysporum and NC State, Fusarium wilt of tomato · Root-knot nematode allowing Fusarium wilt below its minimum temperature, PubMed · Ohio State, powdery mildew epidemiology · PNW Handbook, powdery mildew · UC IPM, Leveillula taurica on pepper · Silicon suppression of powdery mildew inhibited at high temperature, Plant Disease · Tropical Colletotrichum infection model, European Journal of Plant Pathology · UNL, Cercospora leaf spot · UMN, early blight · Bacterial leaf spot of chilli, Plants · Xanthomonas leaf-wetness infection model, PLOS ONE · Pectobacterium and Dickeya cardinal temperatures, European Journal of Plant Pathology · Propagative transmission of WSMoV by Thrips palmi, PLOS ONE · Slow sand filtration against Phytophthora, Water Research · Southern blight in the Pacific, CTAHR/ADAP
Climate data
Monthly climate normals 1991–2020 for Surin, Nakhon Ratchasima and Bangkok are those published by the Thai Meteorological Department, the Royal Irrigation Department and the World Meteorological Organization; we accessed them through their compiled tables rather than from the agencies' own pages, which were not reachable. The Thai Meteorological Department publishes national 30-year normals directly, though we found no monthly relative-humidity normals table there.
Images
Photographs in this guide are from CANNA Research, reproduced with permission and hosted on our own servers. All show ordinary horticultural crops. Where we could not obtain a correctly identified image under a clear licence for a particular organism, we have described it in words rather than use a photograph we could not verify — this applies to broad mite, mealybug, caterpillars, root aphid, and all of the root, vascular, bacterial and virus diseases. If you hold rights in an image in this guide and want the credit amended or the image removed, email info@azgrowshop.asia and we will act the same day.
A closing note on how to use a guide like this. Nothing here replaces looking at your own crop with a lens and writing down what you see, on a date, every week. The published thresholds are from other crops in other countries; the climate normals are thirty-year averages and your farm is not an average. What this guide gives you is the right list of suspects for Thailand, the right questions to ask in the right order, and an honest account of which numbers are measurements and which are arguments. The record you keep yourself is what turns it into a decision.
Questions about a specific problem on your farm: contact the AZ Growshop technical team.