Pendimethalin

Pesticides

Pesticide -> EPA IRIS

Herbicides

Active substance -> EU Pesticides database: Approved

Pesticides -> Herbicides, Nitroaromatic

Herbicides

log Kow = 5.20

4.78

Soluble in most organic solvents

All at 20 °C: acetone, 800 g/L; xylene, >800 g/L; hexane, 48.98 g/L, dichloromethane, >800 g/L; Readily soluble in benzene, toluene, and chloroform; slighlty soluble in petroleum ether and petrol

Acetone, 161; DMSO, 21.4; n-heptane, 11.2; methanol, 5.5; methylene chloride, 232; toluene, 128.4; xylene soluble (all in g/100 mL, 25 °C)

In water, 0.33 mg/L at 20 °C

Warning

H361d: Suspected of damaging the unborn child [Warning Reproductive toxicity]

P203, P273, P280, P318, P391, P405, and P501 (click each P-code to see the statement)

Warning

H302 (12.8%): Harmful if swallowed [Warning Acute toxicity, oral]

P203, P261, P264, P270, P272, P273, P280, P301+P317, P302+P352, P318, P321, P330, P333+P317, P362+P364, P391, P405, and P501 (click each P-code to see the statement)

Hazard Traits - Bioaccumulation; Environmental Persistence; Other Toxicological Hazard Traits

Commission Regulation No 844/2012

Pendimethalin is listed in the dataset of EPA Human Health Benchmarks for Pesticides under the Safe Drinking Water Act (40 eCFR 141)

03/31/EC, Reg. (EU) 2016/950, Reg. (EU) 2017/1114, Reg. (EU) 2017/841, Reg. (EU) 2019/724, Reg. (EU) 2020/2007, Reg. (EU) 2024/2221, Reg. (EU) No 540/2011, Reg. (EU) No 823/2012

Pendimethalin: Does not have an individual approval but may be used under an appropriate group standard

The New Jersey Worker and Community Right to Know Act requires public and private employers to provide information about hazardous substances at their workplaces. (N.J.S.A. 34:5A-1 et. seq.)

Solvent system in emulsifiable concentration may be irritating to skin and eyes. [HSDB] May cause skin sensitization; [eChemPortal: ESIS] May cause irritation; [MSDSonline] Mixing and loading workers should wear chemical resistant gloves; [Reference #1]

USEPA/Office of Pesticide Programs; Reregistration Eligibility Decision Document - Pendimethalin, EPA 738-R-97-007 (June 1997). The RED summarizes the risk assessment conclusions and outlines any risk reduction measures necessary for the pesticide to continue to be registered in the U.S.[Available from, as of July 12, 2010: http://www.epa.gov/pesticides/reregistration/status.htm]

Tolerances are established for residues of the herbicide pendimethalin, including its metabolites and degradates, in or on the commodities. Compliance with the tolerance levels specified in the following table below is to be determined by measuring only pendimethalin, [ N - (1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and its metabolite, 4-[(1-ethylpropyl)amino]-2-methyl-3,5-dinitrobenzyl alcohol, calculated as the stoichiometric equivalent of pendimethalin, in or on the following commodities: [Table#6218]

Time-limited tolerances specified in the following table are established for combined residues of the herbicide pendimethalin, [ N -(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and its metabolite 4-[(1-ethylpropyl)amino]-2-methyl-3,5-dinitrobenzyl alcohol, in or on the specified agricultural commodities, resulting from use of the pesticide pursuant to FIFRA section 18 emergency exemptions. The tolerances expire and are revoked on the date specified in the table. [Table#6219]

Based on the reviews of the generic data for the active ingredients pendimethalin, the Agency has sufficient information on the health effects of pendimethalin and on its potential for causing adverse effects in fish and wildlife and the environment. The Agency/ has determined that pendimethalin products, labeled and used as specified in this Reregistration Eligibility Decision, will not pose unreasonable risks or adverse effects to humans or the environment. Therefore, the Agency concludes that products containing pendimethalin for all uses are eligible for reregistration.

As the federal pesticide law FIFRA directs, EPA is conducting a comprehensive review of older pesticides to consider their health and environmental effects and make decisions about their continued use. Under this pesticide reregistration program, EPA examines newer health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether the use of the pesticide does not pose unreasonable risk in accordance to newer saftey standards, such as those described in the Food Quality Protection Act of 1996. Pendimethalin is found on List A, which contains most pesticides that are used on foods and, hence, have a high potential for human exposure. List A consists of the 194 chemical cases (or 350 individual active ingredients) for which EPA issued registration standards prior to FIFRA '88. Case No: 0187; Pesticide type: herbicide; Registration Standard Date: 03/01/85; Case Status: RED Approved 04/97; OPP has made a decision that some/all uses of the pesticide are eligible for reregistration, as reflected in a Reregistration Eligibility Decision (RED) document.; Active ingredient (AI): Pendimethalin; Data Call-in (DCI) Date(s): 09/04/90, 03/03/95, 10/13/95; AI Status: OPP has completed a Reregistration Eligibility Decision (RED) document for the case/AI.

Acute Tox. 4 (12.8%)

Skin sensitisation - category 1

Hazardous to the aquatic environment (Acute) - Category 1

Carcinogenicity - Category 2

Repr. 2

Store above 40 °F. Extended storage at temperatures less than 40 °F can result in the formation of crystals on the bottom of the container. If crystallization does occur, store the container on its side at room temperature (70 °F) and rock occasionally until crystals redissolve. Do not store near food or feed products.

SRP: The most favorable course of action is to use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity or environmental contamination. Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in soil or water; effects on animal and plant life; and conformance with environmental and public health regulations.

Do not discharge effluent containing this product into lakes, streams, ponds, estuaries, oceans, or public waters unless in accordance with the requirements of a National Pollutant Discharge Eliminations System (NPDES) permit and the permitting authority has been notified in writing prior to discharge. Do not dis charge effluent containing this product to sewer systems without previously notifying the local sewage treatment plant authority. For guidance, contact your State Water Board or Regional Office of the Environmental Protection Agency.

Follow manufacturer's instructions for cleaning/ maintaining PPE. If no such instructions for washables exist, use detergent and hot water. Keep and wash PPE. separately from other laundry. Discard clothing or other absorbent materials that have been drenched or heavily contaminated with this product's concentrate. Do not reuse them

User Safety Recommendations: Users should wash hands before eating, drinking, chewing gum, using tobacco, or using the toilet. Users should remove clothing/ PPE immediately if pesticide gets inside. Then wash thoroughly and put on clean clothing. Users should remove PPE immediately after handling this product. Wash the outside of gloves before removing. As soon as possible, wash thoroughly and change into clean clothing.

Do not apply this product in a way that will contact workers or other persons, either directly or through drift. Only protected handlers may be in the area during application.

Avoiding spray drift at the application site is the responsibility of the applicator and the grower. The interactions of many equipment and weather-related factors determine the potential for spray drift. The applicator and the grower are responsible for considering all these factors when making decisions.

For more Preventive Measures (Complete) data for Pendimethalin (9 total), please visit the HSDB record page.

Tolerances are established for residues of the herbicide pendimethalin, including its metabolites and degradates, in or on the commodities. Compliance with the tolerance levels specified in the following table below is to be determined by measuring only pendimethalin, [ N - (1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and its metabolite, 4-[(1-ethylpropyl)amino]-2-methyl-3,5-dinitrobenzyl alcohol, calculated as the stoichiometric equivalent of pendimethalin, in or on the following commodities: [Table#6216]

Time-limited tolerances specified in the following table are established for combined residues of the herbicide pendimethalin, [ N -(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and its metabolite 4-[(1-ethylpropyl)amino]-2-methyl-3,5-dinitrobenzyl alcohol, in or on the specified agricultural commodities, resulting from use of the pesticide pursuant to FIFRA section 18 emergency exemptions. The tolerances expire and are revoked on the date specified in the table. [Table#6217]

Excerpt from ERG Guide 171 [Substances (Low to Moderate Hazard)]:

Engineering Controls for Aerial Application: Pilots must use an enclosed cockpit that meets the requirements listed in the Worker Protection Standard for agricultural pesticides [40 CFR 170.240(d)(6)].

Engineering Controls for Flagging for Aerial Applications: Human flagging is prohibited. Flagging to support aerial application is limited to the use of Global Positioning System (GPS) or mechanical flaggers.

Mixers, loaders, applicators, and other handlers must wear: -long-sleeve shirt, -long pants, -shoes and socks, and -chemical-resistant gloves for mixers and loaders.

Restricted-entry Interval for WPS products: Do not enter or allow worker entry into treated areas during the restricted entry interval (REI) of 12 hours.

For more Personal Protective Equipment (PPE) (Complete) data for Pendimethalin (6 total), please visit the HSDB record page.

In case of oral exposure, administer charcoal as a slurry. Consider gastric lavage after ingestion of a potentially life-threatening amount of poison if it can be performed soon after ingestion (generally within 1 hour). Protect airway by placement in Trendelenburg and left lateral decubitus position or by endotracheal intubation. Control any seizures first. In case of inhalation, move patient to fresh air, monitor for respiratory distress. If the exposure occurred via eye contact, irrigate exposed eyes with copious amounts of room temperature water for at least 15 minutes. Remove contaminated clothing and wash exposed area thoroughly with soap and water if the exposure occurred via dermal contact. (T36)

LD50 Anas platyrhynchos (mallard duck) oral 1421 mg/kg bw (Technical, 8 days)

LD50 Apis mellifera (Honey bee) oral > 49.7 ug/bee

LC50; Species: Anas platyrhynchos (Mallard Duck); Concentration: > 4640 ppm for 8 days

LC50; Species: Colinus virginianus (Bobwhite quail); concentration: 4187 ppm for 8 days Technical /Conditions of bioassay not given/

For more Ecotoxicity Values (Complete) data for Pendimethalin (12 total), please visit the HSDB record page.

TERRESTRIAL FATE: Based on a classification scheme(1), measured Koc values ranging from 6,500 to 43,863(2,3) indicates that pendimethalin is expected to be immobile in soil(SRC). Volatilization of pendimethalin from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 8.56X10-7 atm-cu m/mole(4). However, adsorption to soil is expected to attenuate volatilization(SRC). Pendimethalin is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 9.4X10-6 mm Hg at 25 °C(5). Pendimethalin has been shown to degrade much faster in laboratory studies using non-sterile inocula versus sterile media(2,6). Biodegradation rates may be attenuated by the strong adsorption to soil with difficult desorption from the soil resulting in no bioavailablity(7). Field dissipation half-lives have been reported to range from 90-120 days, 360-480 days and 82-242 days with a median half-life of 174 days(3). A typical field half-life of 44 days has been reported, but noted to vary with soil temperature and moisture(5); incorporation in soil generally slows pendimethalin dissipation(5). A soil half-life of 3-4 months has also been reported(8). These studies indicate that biodegradation is not an important environmental fate process in soil under some conditions(SRC).

TERRESTRIAL FATE: The persistence of pendimethalin in different soil types as affected by rate of application and moisture regime was studied under greenhouse conditions with the use of bioassay and GLC. Pendimethalin was rapidly lost from the soil 20 to 50 days after application and slowly thereafter. Higher residual phytotoxicity was obtained in clay loam soil than in clay and fine sandy loam soils at 50 and 110 days. Herbicide residues were very minimal after 3 mo in all 3 soils. At rates higher than the recommended rate of application there was greater and more prolonged residual phytotoxicity. Higher residues in all sampling periods were likewise detected. Loss of pendimethalin under low soil water levels was very slow. Marked residual phytotoxicities were still apparent at 110 days with 4 day interval watering. Leaching is not a principal means of pendimethalin loss. The herbicide remained in the upper 5 cm soil layer even if water was applied at 100% field capacity daily.

TERRESTRIAL FATE: Preemergence application of neburon-pendimethalin mixture (83591-04-2) (6 kg/ha of 60% neburon plus 6 L/ha solution which contained 330 g pendimethalin/L) controlled Viola arvensis and Stellaria media completely, and Galium aparine incompletely, and increased barley grain yield by 7.04%. Neburon remained mainly in the top 10 cm of soil, where its residues decreased from an initial 2.17 to 0.56 ppm of soil solids, at harvest. The decrease in neburon was accompanied by an increase in neburon metabolites which may be hydrolyzed to 3,4-dichloroaniline, which reached 1 ppm at harvest time. Pendimethalin also was fixed in the top 10 cm of soil, where its residues decreased from 1.09 to 0.33 ppm at harvest time.

TERRESTRIAL FATE: When released in soil, pendimethalin will bind strongly to soil with the amount accumulating in tightly bound soil fractions increasing over 4 months(5). Pendimethalin exhibits low volatility in soil(6). Although some volatilization and photolysis losses may occur initially at the soil surface, these appear to be minor. Increased dissipation of pendimethalin in flooded soil is not due to increased volatilization. Persistence in soil is influenced by soil temperature, cultivation practices, soil type and moisture conditions(4). Anaerobic degradation of pendimethalin as in other dinitroaniline herbicides normally proceeds faster than aerobic degradation. The primary reaction observed is the reduction of a nitro group, followed in some cases by dealkylation (1,2). In contrast, dealkylation is normally the primary reaction under aerobic conditions(1,2). In a case of a related herbicide trifluralin, the redox potential had to be below a threshold value to initiate rapid degradation under flooded conditions(3) indicating that degradation in soil may be chemical, rather than microbiologically in nature(SRC).

For more Environmental Fate (Complete) data for Pendimethalin (11 total), please visit the HSDB record page.

/AQUATIC SPECIES/ The Collembola species Proisotoma minuta was exposed to herbicides in an artificial sea salt solution for seven days. The salt solution did not prohibit the insects' reproduction system. The seven day LD50 /value for pendimethalin was 10.4 mg/L/...

/AQUATIC SPECIES/ ... To determine the toxicity of technical-grade current-use pesticides to glochidia and juvenile life stages of freshwater mussels. ... Acute toxicity tests with glochidia (five species) and juveniles (two species) exposed to a suite of current-use pesticides including ... pendimethalin /were conducted/. ... The relative risk associated with acute exposure of early life stages of mussels to ... Pendimethalin ...

/AQUATIC SPECIES/ Highly toxic to coldwater fish, highly to moderately toxic to warmwater fish, and highly to moderately toxic to freshwater inverterbrates.

/OTHER TERRESTRIAL SPECIES/ Tiphia vernalis Rohwer is a hymenopteran ectoparasitoid of Japanese beetle, Popillia japonica Newman, larvae. The adult wasps feed on nectar or honeydew between mid-April and late June. Adults may contact pesticides when landing on foliage or when females hunt for grubs in the soil. The lethal effect of nursery, turf, and landscape pesticides was determined by exposing wasps to treated foliage in the laboratory. Pesticides tested at labeled rates /included/ ... pendimethalin ... . During 2001 and 2002, male and female T. vernalis were exposed to pesticides by using turf cores. ... Mortality of males in response to herbicides and fungicides was more variable than for females; in 2002 trials, male mortality was higher after exposure to ... pendimethalin ... than the control...

For more Ecotoxicity Excerpts (Complete) data for Pendimethalin (7 total), please visit the HSDB record page.

After application of pendimethalin 60DG on irrigated and nonirrigated turfgrass field plots, the dislodgeable (detergent- stripped) pendimethalin residues on grass clippings were (concn irrigated (nonirrigated) plot in ug/sq cm at time after application): 0.20 (0.40) at 2 hr; 0.07 (0.24) at 2 days; and 0.01 (0.03) at 7 days(1). In terms of percentages of nominal application rates, the dislodgeable residues for irrigated (nonirrigated) plots declined from 4.53% (9.21%), 2 hours after application, to 0.35% (0.75%) after 7 days(1). Pendimethalin completely volatilizes from leaf surfaces within 24 hr(2).

Tolerances are established for residues of the herbicide pendimethalin, including its metabolites and degradates, in or on the commodities. Compliance with the tolerance levels specified in the following table below is to be determined by measuring only pendimethalin, [ N - (1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and its metabolite, 4-[(1-ethylpropyl)amino]-2-methyl-3,5-dinitrobenzyl alcohol, calculated as the stoichiometric equivalent of pendimethalin, in or on the following commodities: [Table#6218]

Time-limited tolerances specified in the following table are established for combined residues of the herbicide pendimethalin, [ N -(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and its metabolite 4-[(1-ethylpropyl)amino]-2-methyl-3,5-dinitrobenzyl alcohol, in or on the specified agricultural commodities, resulting from use of the pesticide pursuant to FIFRA section 18 emergency exemptions. The tolerances expire and are revoked on the date specified in the table. [Table#6219]

Based on the reviews of the generic data for the active ingredients pendimethalin, the Agency has sufficient information on the health effects of pendimethalin and on its potential for causing adverse effects in fish and wildlife and the environment. The Agency/ has determined that pendimethalin products, labeled and used as specified in this Reregistration Eligibility Decision, will not pose unreasonable risks or adverse effects to humans or the environment. Therefore, the Agency concludes that products containing pendimethalin for all uses are eligible for reregistration.

As the federal pesticide law FIFRA directs, EPA is conducting a comprehensive review of older pesticides to consider their health and environmental effects and make decisions about their continued use. Under this pesticide reregistration program, EPA examines newer health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether the use of the pesticide does not pose unreasonable risk in accordance to newer saftey standards, such as those described in the Food Quality Protection Act of 1996. Pendimethalin is found on List A, which contains most pesticides that are used on foods and, hence, have a high potential for human exposure. List A consists of the 194 chemical cases (or 350 individual active ingredients) for which EPA issued registration standards prior to FIFRA '88. Case No: 0187; Pesticide type: herbicide; Registration Standard Date: 03/01/85; Case Status: RED Approved 04/97; OPP has made a decision that some/all uses of the pesticide are eligible for reregistration, as reflected in a Reregistration Eligibility Decision (RED) document.; Active ingredient (AI): Pendimethalin; Data Call-in (DCI) Date(s): 09/04/90, 03/03/95, 10/13/95; AI Status: OPP has completed a Reregistration Eligibility Decision (RED) document for the case/AI.

(AZ) ARIZONA 280 ug/l

(FL) FLORIDA 280 ug/l

The metabolism of the dinitroaniline herbicide pendimethalin was investigated in rats with emphasis on the identification of metabolites in tissues and urine. Royal Hart Wistar rats were administered a single oral dose of radiolabeled methyl labeled or ethyl labeled pendimethalin. Radioactivity was excreted rapidly both in urine and feces at dosage levels of 7.3 and 37 mg/kg of radiolabeled pendimethalin. After 96 hr, the residues were less than 0.3 ppm in all tissues except fat, which had a residue of 0.9 ppm. The major metabolic routes of pendimethalin involved hydroxylation of the 4-methyl and the N-1-ethyl group, oxidation of these alkyl groups to carboxylic acids, nitro reduction, cyclization, and conjugation based on the identification of the 12 metabolites in urine and tissues. Products of cyclization reactions giving rise to methylbenzimidazole carboxylic acids were unique to liver and kidney. All major metabolites retained both radioactive labels of pendimethalin, indicating that N-dealkylation of the isopentyl group was not significant. This investigation extends the knowledge on the fate of dinitroanilines in the rat and demonstrates that pendimethalin is metabolized by several major pathways.

Pendimethalin which does become absorbed into the bloodstream from the gastrointestinal tract is rapidly metabolized in the kidneys and liver and is then excreted in the urine. The major metabolic routes of pendimethalin involved hydroxylation of the 4-methyl and the N-1-ethyl group, oxidation of these alkyl groups to carboxylic acids, nitro reduction, cyclization, and conjugation based on the identification of the 12 metabolites in urine and tissues. Products of cyclization reactions giving rise to methylbenzimidazole carboxylic acids were unique to liver and kidney (A624, L1133).

Pendimethalin is eliminated from body with 70% being excreted in feces, primarily parent compound, and 20% in urine within 24 hr /in rats/.

By 24 hr after the administration of 37 mg/kg of radio-labeled pendimethalin to rats, 90.3% of the dose was recovered in the feces and urine. After 96 hr, 95.8% of the dose was recovered in the urine (20.9%) and feces (74.9%). When a lower dose was administered (7.3 mg/kg), 99.8% was recovered in the urine (21.8%) and feces (78.0%) after 12 hr. After 96 hr, residues were less than 0.3 ppm in all body tissues except fat, which had 0.9 ppm. This study indicates that ingested pendimethalin is largely unabsorbed by the bloodstream and excreted through the feces. Pendimethalin which does become absorbed into the bloodstream from the gastrointestinal tract is rapidly metabolized in the kidneys and liver and is then excreted in the urine.

Used as selective pre- and post-emergence herbicide for field corn, potatoes, rice, sorghum, cotton, soybeans, tobacco, peanuts, and sunflowers; [HSDB] Workers may be exposed in food, feed, ornamental, turf, and right-of-way treatments; [Reference #1]

Farming (Pesticides) [Category: Industry]

For pendimethalin (USEPA/OPP Pesticide Code: 108501) ACTIVE products with label matches. /SRP: Registered for use in the U.S. but approved pesticide uses may change periodically and so federal, state and local authorities must be consulted for currently approved uses./

Selective herbicide; Control of most annual grasses and many annual broad-leaved weeds, at 0.6-2.4 kg/ha, in cereals, onions, leeks, garlic, fennel, maize, sorghum, rice, soya beans, peanuts, brassicas, carrots, celery, black salsify, peas, field beans, lupins, evening primrose, tulips, potatoes, cotton, hops, pome fruit, stone fruit, berry fruit (including strawberries), citrus fruit, lettuce, aubergines, capsicums, established turf, and in transplanted tomatoes, sunflowers, and tobacco. Applied pre-plant incorporated, pre-emergence, pre-transplanting, or early post-emergence. Also used for control of suckers in tobacco.

Pendimethalin is a selective herbicide registered for control of broadleaf weeds and grassy weed species on a variety of agricultural crops, turf, and ornamentals. Pendimethalin disrupts the process of mitosis in the growth of shoots and roots. It acts as a microtubule disruptor by inhibiting cell division and cell elongation in plants, and is generally applied early in the growing season. Absorption of the herbicide takes place at the roots and the shoots.

Pendimethalin is a selective herbicide used to control most annual grasses and certain broadleaf weeds in field corn, potatoes, rice, cotton, soybeans, tobacco, peanuts and sunflowers. It is used both preemergence, that is before weed seeds have sprouted, and early postemergence (A183).

A mixture of 4-chloro-3,5-dinitro-o-xylene (0.61 mol), 3-pentaneamine (1.82 mols), and xylene (1,400 mL) is brought to reflux. After refluxing overnight, the reaction mixture is cooled and filtered. The precipitate is washed with petroleum ether. The filtrate and washings are combined, washed with 500 ml of 10% hydrochloric acid, and finally with 2 liters of water. The organic layer is separated and dried. Removal of the drying agent and the solvent leaves an orange oil which crystallizes with the addition of methanol. A yellow orange solid with melting point of 56-57 °C is collected in about 85% yield.

... Obtained from 3,4-xylidine by alkylation and dinitration.

Emulsifiable concentrate

Formulation types: Emulsifiable concentrate, Granule, Suspension concentrate, Water dispersible granules

Formulation types: Manufacturing product 90.0%; Liquid 60.0%; Solid 86.8%; End Use Product: Emulsifiable concentrate 21.9 to 42.3%; Liquid 34.4%; Granular 0.7 to 2.0%; Soluble concentrate/liquid 22.0%; Water dispersible granules up to 60%; Wettable powder 50.0%

Anderson's Fertilizer Plus Preemergent Weed Control (Anderson's Lawn Fertilizer Division) pendimethalin 0.875

For more Formulations/Preparations (Complete) data for Pendimethalin (63 total), please visit the HSDB record page.

Herbicides

Environmental transformation -> Pesticides (parent, predecessor)

Damping-off caused by Rhizoctonia solani in cotton was increased in the field by the recommended rates of 11 soil herbicides. This increase was significant at p = 0.05, with all the herbicides, except for nitralin, trifluralin and linuron. Dinitroaniline herbicides (penoxalin, nitralin and dinitramine), at 50 ug/g sterilized sand, significantly increased cotton resistance to the pathogen. The relative disease indexes were 39.5, 29.7, and 40.5, respectively, while urea and triazine herbicides at the same rate, significantly decreased resistance; for example, relative disease index for fluometuron, linuron, tomilon, atrazine, and cyanazine were 204.9, 521.6, 289.2, 462.7, and 357.8, respectively. At 1 ug, trifluralin, atrazine, and bromofenoxim increased the cotton resistance; relative disease indexs were 8.1, 40.5, and 36.8, respectively. Thus, the effect of the herbicides on resistance depended on concn. The increase of the disease incidence by the herbicides under the field conditions might be due to a side effect of the cmpd on the soil microorganisms and soil microflora which could encourage potential pathogen. In addition, the possible microbial degradation products of the herbicides might affect the host susceptibility, hence the seedlings become less resistant to the pathogen. Other possibility would be that the degradation products of the herbicides might influence the pathogen virulence.