Plant Growth Regulator Mepiquat Chloride Research Articles

Cotton (Gossypium hirsutum) Response to Plant Protection Products using Different Spray Nozzles

Application of dicamba to dicamba-tolerant cotton (Gossypium hirsutism L.) cultivars (Xtend Cotton, Bayer Crop Science, Research Triangle Park, NC) requires use of nozzles that deliver large spray droplets to avoid off-site movement through particle drift onto susceptible crops and other plants including endangered species. Twenty trials over a three-year period were conducted to determine if nozzles required to deliver dicamba plus glyphosate would be equally effective in delivering other pesticides including the herbicide glufosinate, the plant growth regulator mepiquat chloride, the insecticide bifenthrin plus dichrotophos and co-application of ethephon plus thidiazuron plus tribufos for removal of cotton foliage to improve harvest efficiency. Agrichemicals were applied using: a) Air Induction (AI) nozzles for agrichemicals except dicamba plus glyphosate b) Turbo Teejet Induction (TTI) nozzles for all agrichemicals c) TTI nozzles for glufosinate and dicamba plus glyphosate and AI nozzles for other agrichemicals. Applications were made in 145 L/ha at 152 kPa at a ground speed of 5 km/h. Cotton height at the end of the season, node above first fruiting branch, nodes above cracked boll, node of uppermost boll, total nodes, lint yield, and cotton fiber quality were similar regardless of nozzles used to deliver agrichemcials. Control of a complex of broadleaf signal grass (Urochloa platyphylla L.), goosegrass [Eleusine indica (L.) Gaert.], and large crabgrass (Digitaria sanguinalis L.) and Palmer amaranth (Amaranthus palmeri Watts.) was slightly lower when glufosinate was applied with TTI nozzles rather than AI nozzles. However, control of these weeds was similar regardless of nozzle selection when dicamba plus glyphosate was applied after glufosinate. These results suggest that growers can use nozzles that limit off-site movement through particle drift of agrichemicals throughout the cropping cycle with no major adverse effect on weed control and cotton growth and yield.

High dosage of mepiquat chloride delays defoliation of harvest aids in cotton

The plant growth regulator mepiquat chloride (MC) has been widely used to regulate cotton growth and development worldwide. However, little is known about whether MC application during cotton growing season affects defoliation efficiency of the harvest aids (TE), a novel product with the mixture of 10% thidiazuron and 40% ethephon. Here, a 3-year (2018–2020) field experiment was carried out in Hejian, Hebei province, China, involving six treatments as three different MC rates (MC free, farmers’ practice-conventional amount, high MC amount) and two defoliant rates (0 ml ha−1 [CK] and 2250 ml ha−1 [TE]). High MC rate delayed cotton leaf abscission and decreased the defoliation percentage at 7 days after TE treatment, but hardly affected harvest aids efficacy at harvest time. The delay of leaf abscission was due to an increase in auxin and cytokinin concentration of cotton leaves in MC treatment. The MC treatment accelerated the natural maturation of cotton, achieving a higher boll-opening percentage before defoliant spraying, and increased cotton lint yield. Over the 3-year period, compared to CK, the defoliant application TE increased the defoliation percentage by 43.4%, the boll-opening percentage by 10.4%, and the cotton lint yield by 9.1% due to an increase in opened boll number per unit land area. We concluded that the optimal MC dose (about 200 g ha−1) would decrease the risk of reducing defoliation and achieve higher cotton lint yield.

Risk assessment of predatory lady beetle Propylea japonica's multi-generational exposure to three non-insecticidal agrochemicals

The effects of non-insecticidal agrochemicals on pest natural predators remain largely unexplored except bees and silkworm. The herbicide quizalofop-p-ethyl (QpE), fungicide thiophanate-methyl (TM), and plant growth regulator mepiquat chloride (MC) have been extensively applied as non-insecticidal agrochemicals. Here, we systematically evaluated multiple effects of these 3 non-insecticidal agrochemicals on three generations of Propylea japonica, an important agroforestry predatory beetle, including the effects on its development, reproduction, enterobacteria, and transcriptomic response. The results showed that QpE exhibited a hormetic effect on P. japonica, thus significantly increasing the survival rate of generation 2 (F2) females, generation 3 (F3) females, and F3 males and body weight of F3 males. However, three successive generations exposed to TM and MC had no significant effect on longevity, body weight, survival rate, pre-oviposition period, and fecundity of P. japonica. Additionally, we investigated the effects of MC, TM, and QpE exposure on gene expression and gut bacterial community of F3 P. japonica. Under MC, TM, and QpE exposure, the overwhelming genes of P. japonica (99.90 %, 99.45 %, and 99.7 %) remained unaffected, respectively. Under TM and MC exposure, differentially expressed genes (DEGs) were not significantly enriched in any KEGG pathway, indicating TM and MC did not significantly affect functions of P. japonica, but under QpE exposure, the expression levels of drug metabolism-related genes were down-regulated. Although QpE treatment did not affect gut dominant bacterial community composition, it significantly increased relative abundances of detoxification metabolism-related bacteria such as Wolbachia, Pseudomonas and Burkholderia in P. japonica. However, TM and MC had no significant effect on the gut bacterial community composition and relative abundance in P. japonica. This study revealed for the first time the mechanism by which P. japonica might compensate for gene downregulation-induced detoxification metabolism decline through altering symbiotic bacteria under QpE exposure. Our findings provide reference for the rational application of non-insecticidal agrochemicals.

DPC can inhibit cotton apical dominance and increase seed yield by affecting apical part structure and hormone content

The plant growth regulator mepiquat chloride (1,1-dimethylpiperidinium chloride, DPC) has been successfully used worldwide in cotton production. Fortified DPC (DPC+) can slightly damage young tissues of the epidermis, which has shown potential in cotton chemical topping in China. The underlying mechanism remains unclear. We investigated whether apical meristem and leaf morpho-physiological traits contribute to delayed growth of the main stem and increased seed yield in DPC or DPC+ as a chemical inhibitor. Two different DPC-sensitive varieties (Xinluzao 60, L60; Jinken 1402, JK1402) were field-grown using three different topping treatments manual topping (MT), no topping (NT) and chemical topping (DPC+ and DPC) in irrigated arid lands of Xinjiang for two years. The plant height decreased by 1.4–13.6% for the DPC+ and DPC treatments compared with the NT treatment and increased by 3.8 –9.2% compared with the MT treatment. The thickness of the leaves, palisade tissue (Pt) and spongy tissue (St) increased by 5.1–21.5% under DPC treatment compared with other treatments. The 3-indoleacetic acid (IAA) content of the leaves significantly increased by 25.0–93.8% at 10 days under the DPC treatment compared with that under the MT and NT treatments. The zeatin riboside (ZR) content of the leaves and apical buds increased up to 7.5 times at 40 days under the DPC+ and DPC treatments compared with that under the NT treatment. The accumulation of reproductive organ biomass and proportion of reproductive organ dry matter to total dry matter under the DPC+ and DPC treatments increased by 2.0–39.7% compared with that under the MT and NT treatments. The seed cotton yield between the DPC+ and DPC treatments showed no significant difference. However, the seed cotton yield of JK1402 under the DPC+ and DPC treatments significantly increased by 9.5–11.7% compared with that under the MT and NT treatments. The main stem length was significantly correlated with the stem length of the upper part and gibberellin (GA) content in the apical buds. The leaf Pt and ZR contents were significantly correlated with the boll weight and seed cotton yield. Collectively, the data suggest that improved morpho-physiological traits of the apical part, such as an increase in the IAA and GA contents in the apical buds, leaf Pt and ZR contents, and boll weight, inhibited growth of the main stem and increased seed cotton yield for DPC, which is cheaper than DPC+ as a chemical inhibitor under chemical regulation during the whole growth period.

Effects of plant density and mepiquat chloride application on cotton boll setting in wheat–cotton double cropping system

Sowing cotton directly after harvesting wheat in the Yangtze River Valley of China requires early mature of cotton without yield reduction. Boll-setting period synchronisation and more yield bolls distributed at the upper and middle canopy layers are also required for harvesting. The objective of this study is to quantify the individual and interaction effects of plant density and plant growth regulator mepiquat chloride (MC) on temporal and spatial distributions of yield bolls, as well as yield and yield components. During the 2013–2016 cotton growing seasons, the experiments were conducted on a short-season cotton cultivar CRRI50 at Yangzhou University, China. Various combinations of plant density (12.0, 13.5 and 15.0 plants m−2) and MC dose (180, 270 and 360 g ha−1) were applied on cotton plants. The combination of 13.5 plants m−2 and 270 g ha−1 MC resulted in the greatest boll number per unit area, the highest daily boll setting number and more than 90% of bolls positioned within 45–80 cm above the ground. In conclusion, appropriate MC dose in combination of high plant density could synchronize boll-setting period and retain more bolls at the upper and middle canopy layers without yield reduction in the system of direct-seeded cotton after wheat harvest, and thus overcome the labor-intensive problem in current transplanting cropping system.

Physiology and Yield of Confection Sunflower under Different Application Schemes of Mepiquat Chloride

The use of plant growth regulator mepiquat chloride (MPC) has been a widespread practice for the control of vegetative growth in cotton production for several decades. As a growth retardant, MPC could potentially provide a means of controlling plant height in field sunflower (Helianthus annuus L.), but this possibility has not been studied. Field experiments over two years were conducted in northern Greece to study the influence of MPC at rates of 37.5 plus 37.5 g ha−1 (named double application) and 37.5 plus 37.5 plus 37.5 g ha−1 (named triple application) on sunflower growth and yield. MPC provided a height reduction of 9.5% (25 cm) with the double application and a height reduction of 14.4% (49.2 cm) with the triple application at maturity. The number of nodes was also reduced, indicating shorter plants, whereas stem width did not show a consistent response. Moreover, MPC resulted in increased crop growth rate with the triple application scheme. MPC reduced nitrogen utilization efficiency in both growing seasons. However, a reduction in achene yield per plant by 19.9% was observed with the triple application scheme. The achene yield reduction resulted by the reduction in the 100-achene weight (22.3%), given that the number of filled achenes was similar to control. None of the application schemes reduced seed nitrogen and oil content. The results from testing application schemes could be a basis for further research on the use of MPC in this crop, e.g., different timing of applications could be tested for benefits to height reduction.

Mepiquat Chloride Effects on Castor Growth and Yield: Spraying Time, Rate, and Management

The use of plant growth regulators on castor (Ricinus communis L.) plants may be an alternative to reduce excessive vegetative growth, which would ease harvest and even increase seed and oil yield. This study aimed to evaluate the effects of both spraying time and rate of the plant growth regulator mepiquat chloride (MC) on growth parameters, yield components, seed yield, and seed oil content of castor cultivar IAC 2028 cultivated under high plant population density conditions in a spring–summer growing season in Botucatu, southeastern Brazil. One greenhouse experiment and two field experiments were performed. Mepiquat chloride application reduced leaf growth, height, and dry matter (DM) and increased the shoot/root ratio of castor plants. When sprayed during the vegetative phase (expanded leaf at nodes 6–8 of the primary stem), MC reduced the height and DM of castor plants; however, application during the first raceme flowering or at two sequential times (expanded leaf at the eighth node of the primary stem and third expanded leaf on a secondary stem) was more effective at reducing plant height and increasing seed yield. Spray rates between 100 and 200 g a.i. ha−1 of MC resulted in lower plant height and a greater number of filled fruits per raceme (24.0–38.8%), seed weight (2.6% in one experiment), and seed yield (17.4–33.1%). The increased number of filled fruits per raceme in response to MC application influenced seed yield. Mepiquat chloride spraying did not affect castor seed oil content.

Hormesis Effect of Dichlorophenoxy Acetic Acid Sub-Doses and Mepiquat Chloride on Cotton Plant

ABSTRACT: The aim of this study was to evaluate the hormesis effect of sub-doses of dichlorophenoxy acetic acid herbicide and the plant growth regulator mepiquat chloride on the vegetative and productive characteristics of two cotton cultivars (FMT 701 and Fibermax 966). The experiment was conducted from November 2013 to May 2014. The experimental design was a randomized block in a factorial scheme 6 x 2 x 2, with four replications, totaling 96 installments with 24 treatments: the witness and five sub-doses of the herbicide 2,4-D: 0.68, 1.36, 2.04, 2.72 and 3.40 g equivalent acid (e.a) per ha, with and without application of mepiquat chloride at a dose of 200 mL ha-1 in the cotton cultivars FMT 701 and Fibermax 966. The sub-doses applied were 2,4-D at 45 days after the emergence of the plant (DAE), and the growth regulator was applied at 70 DAE. It was found that the use of the growth regulator (mepiquat chloride) at a dose of 200 mL ha-1 was effective in controlling plant development relative to its variable height. The application of sub-doses of 2,4-D up to 1.75 g e.a ha-1 provides increased seed cotton productivity FMT 701 and Fibermax 966). The cultivar FMT 701 got greater plant height, stem diameter, number of reproductive branches, bolls per plant and seed cotton productivity compared to the cultivar Fibermax 966.

Interactions of Single Mepiquat Chloride Application at Different Growth Stages with Climate, Cultivar, and Plant Population for Cotton Yield

Cotton (Gossypium hirsutum L.) yield responses to the plant growth regulator mepiquat chloride (1,1‐dimethyl piperidinium chloride, MC) are associated with climate, cultivar, and plant population. However, the interactions of these factors with MC for yield are inconsistent or unexpected. We hypothesize that climate (mainly precipitation), cultivar, and plant density only interact with MC applied at specific growth stages to affect yield. Experiments were thus conducted in two contrasting years (2013–2014). Mepiquat chloride was applied at the seedling, squaring, early bloom, full bloom, and post‐topping of the main stem (close to the time of cutout) stages. Plant populations were 6.5 and 11.4 plants m−2, and the two cultivars SCRC36 and Han7860 were used. The results showed that the yield averaged over all treatments significantly increased by 5.6, 5.0, and 6.1% because of MC application at the seedling, early bloom, and full bloom stages, respectively. Additionally, the interaction of the year (climate) × MC for yield occurred when MC was applied at the early bloom and full bloom stages. Cultivars differed in yield responses to MC applied at the full bloom and post‐topping stages. Plant density influenced yield response to early MC application at the seedling stage. These results supported our hypothesis, which is helpful in guiding the rational combination of multiple MC applications according to varying conditions in view of yield formation.

Effects of plant growth regulator mepiquat chloride on content of active compounds in Scutellaria baicalensis

To study the effect of plant growth regulator mepiquat chloride (DPC) on the growing development of plant and the content of active compounds in Scutellaria baicalensis. After spraying DPC during the seedling period, the length of taproot, fresh weight of root, diameter of taproot and the length of stem were measured. The contents of baicalin, baicalein and wogonin were determined by HPLC, respectively. Total flavonoids and scavenging DPPH were determined with ultraviolet spectrophotometry. After spraying DPC, fresh weight of S. baicalensis root was significant increased, and root diameter was also increased. The contents of baicalin and total flavonoids were significantly increased and baicalein and wogonin were decreased remarkably. Compared with controls, scavenging activity of ethanol extracts on DPPH free radical was no significant changed after spraying DPC. Plant growth regulator DPC could regulate the growth on the ground and underground effectively, and could enhance the content of flavonoids compounds of S. baicalensis.

Respostas de cultivares de algodão ao cloreto de mepiquat aplicado via embebição de sementes

As recomendações de reguladores de crescimento cloreto de mepiquat (CM) geralmente não consideram as diferenças entre cultivares de algodoeiro utilizadas para o cultivo. O trabalho teve como objetivo avaliar o crescimento e o desenvolvimento de cultivares de algodão ante a embebição das sementes com regulador de crescimento cloreto de mepiquat, visando à sua caracterização quanto à resposta ao tratamento. Foram utilizadas as cultivares IPR-120, IAC-24, CD-405, Delta Opal e Fibermax 966, cujas sementes foram embebidas em solução contendo 2,0 g de cloreto de mepiquat para cada 100 mL de água deionizada por 12 horas e cultivadas em vaso, em casa de vegetação. Foram avaliadas: a altura de plantas, a altura da inserção do nó cotiledonar, o diâmetro caulinar, a área foliar e a massa da matéria seca da parte aérea. As cultivares tiveram resultados diferenciados ao tratamento de sementes via embebição com regulador de crescimento, sendo as cultivares Fibermax 966, Delta Opal e CD 405 as mais sensíveis. O tratamento foi eficiente na redução do porte, da inserção do nó cotiledonar, da área foliar e da massa da matéria seca da parte aérea do algodoeiro, além de alterar a partição dos assimilados, comparadas com plantas originadas de sementes sem tratamento.

Determination of Mepiquat Chloride Residues in Cotton and Soil by Liquid Chromatography/Mass Spectrometry

A liquid chromatographic/mass spectrometric (LC/MS) method is reported for the determination of the onium-type plant growth regulator mepiquat chloride in cotton and soil. The pesticide was extracted from the sample with ethanol and water containing 2% NH4Cl. The extract was cleaned up on a solid-phase extraction C18 column, and the pesticide was determined by LC/MS. The average recoveries were 85.9-93.8, 81.3-91.7, and 78.1-94.7%, with corresponding relative standard deviations of 3.4-9.6, 3.7-12.3, and 4.0-9.8%, from soil, cotton leaves, and cotton seeds, respectively. A coefficient of determination of R2 = 0.9964 was obtained for the analyte calibration graph, from 0.05 to 100 microg/mL. Decision limits, CCalpha, and detection capability, CCbeta, were calculated. Electrospray ionization LC/MS in the positive-ion mode (ESI+) was used to detect mepiquat chloride in extracts of soil, cotton leaves, and cotton seeds. The ion at m/z 114 in the mass spectrum was monitored.

Second-generation Glyphosate-Resistant Cotton Tolerance to Combinations of Glyphosate with Insecticides and Mepiquat Chloride

Field trials were conducted in 2005 and 2006 to evaluate application of glyphosate alone or plus the plant growth regulator mepiquat chloride with 20 different insecticides to second-generation glyphosate-resistant cotton at the pinhead square or first bloom growth stages. At 7 DAT, averaged across cotton growth stages and herbicide treatments, combination with insecticides profenofos and methomyl resulted in 5 and 9% plant injury, respectively, and were the only insecticide combinations that resulted in injury greater than glyphosate or glyphosate plus mepiquat chloride applied alone. By 14 DAT, cotton injury was less than 2% for all treatments. Averaged across cotton growth stages and insecticides, addition of mepiquat chloride to glyphosate resulted in a 4 and 6 cm height reduction at 7 and 28 DAT, respectively. Seed cotton yield and percent first harvest were similar for all treatments, indicating that cotton injury and height reductions observed after application did not result in yield reductions or maturity delays. Glyphosate combined with insecticides and mepiquat chloride, in accordance with herbicide labeling for second-generation glyphosate-resistant cotton, offers producers the ability to integrate pest and crop management strategies and reduce application costs with minimal effect on the crop.Nomenclature: Acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emamectin benzoate, gamma-cyhalothrin, glyphosate, imidacloprid, indoxacarb, lambda-cyhalothrin, mepiquat chloride, methomyl, novaluron, oxamyl, profenofos, spinosad, thiamethoxam, thiodicarb, zeta-cypermethrin, cotton, Gossypium hirsutum L

Early Flower Bud Loss and Mepiquat Chloride Effects on Cotton Yield Distribution

Abscission or abortion of the initial cotton (Gossypium hirsutum L.) flower buds or bolls increases the importance of retaining fruit on adjacent or subsequent fruiting positions. Use of the plant growth regulator mepiquat chloride (MC) (N, N dimethylpiperidinium chloride) improves boll retention on lower reproductive branches (sympodia), reduces vegetative growth, and in some cases reduces upper sympodial productivity. Our objective was to determine the effect of doses and application timings of MC and different levels of early flower bud removal on within‐plant yield distribution. Zero or an average of two or four flower buds located at first positions on lower sympodia were removed from each plant prior to MC applications at two field locations in 1992. This bud loss resulted in higher retention at second positions on lower sympodia and on slightly higher sympodia. Two biweekly doses of 24.5 g ha−1 of MC applied at early bloom also enhanced compensation and yield on lower sympodial second positions. Primarily at one location, four weekly MC doses of 12.25 g ha−1 each beginning when buds were 1 cm long resulted in increased monopodial branch yield when there was moderate early bud loss. Depending on field location, one or the other of the MC treatments reduced the number of fruiting positions and yield on higher sympodia when fruit retention on lower sympodia was high. Loss of early buds, which resulted in small increases in vegetative growth, ameliorated this effect. The biological responses produced by early bud loss and MC treatments interacted positively. After early bud loss, plants treated with MC generally improved compensation on lower sympodia without negative effects on upper sympodia.

Effects of the Plant Growth Regulator Mepiquat Chloride on Silverleaf Whitefly (Homoptera: Aleyrodidae) Infestations on Cotton2

Cotton, Gossypium hirsutum L., plants were treated with the plant growth regulator mepiquat chloride (Pix™) in greenhouse and field plot tests to determine its effect on infestations of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring. In the greenhouse, Pix-treated plants were significantly shorter and had thicker leaves than untreated plants by the end of the second week following application. Most of the Pix treatments caused significant reductions in adults, eggs and nymphs on leaves by fourth and final week of the test. In a separate test, leaf water potentials were equal for Pix-treated and well-watered plants which were significantly lower than for water-stressed and control plants. Pix-treated plants in two field plot tests showed the same changes in plant morphology observed in Pix-treated plants in the greenhouse. However, leaf water potentials were the same as in untreated plants and no reductions in whitefly infestations were found during the 6 to 7 wk test periods. Pix-treated plants in a third field plot test showed no changes in plant morphology or in whitefly infestations. The reduced whitefly infestations of Pix-treated plants in the greenhouse, but not in field plots, may have been due to reduced leaf water potentials in Pix-treated greenhouse plants but not in field plants.

Modeling mepiquat chloride-temperature interactions in cotton: the model

The plant growth regulator mepiquat chloride (1,1-dimethylpiperidinium chloride) is used to reduce vegetative growth in cotton. It is commonly used to control the side effects of optimization of inputs such as water and nitrogen. It has been shown that mepiquat chloride (MC) suppresses excessive plant growth by decreasing plant height, number of nodes, fruiting and vegetative branch lengths, and leaf area. A model was developed using data collected under controlled environmental conditions for a range of temperatures. Equations were developed to calculate the concentration of MC in the plant tissue on a daily basis after accounting for the dry-weight increments in plant tissue and abscission of plant parts. A set of stress factors was calculated to account for the reduction in growth of various cotton plant parts as a function of air temperature and tissue concentration of MC. The MC model was incorporated in a cotton simulation model, GOSSYM. The model simulations compared well with observed yields under a range of conditions.

Mepiquat Chloride and Irrigation versus Cotton Growth and Development

AbstractCotton (Gossypium hirsutum L.) produces excessive vegetative growth when grown under optimum water and nutrient conditions. The plant growth regulator Mepiquat Chloride (MC); 1,l‐dimethyl piperidinium chloride reduces vegetative growth and can promote early maturity. Its effect on yield has been inconsistent, with some researchers showing an increase while others have indicated a decrease. This variation in yield has often been attributed to environmental factors and variations in water and fertilizer inputs. This study examined the effect of MC on cotton growth, under varying irrigation treatments, to determine if soil moisture interacts with MC. The experiment was conducted in 1987 with two cotton cultivars, Stoneville 825 (‘ST825’) and Deltapine 20 (‘DP20’), grown in pots, with five irrigation treatments [1.2,1.0,0.8,0.6, and 0.4 times previous day's pan evaporation (PE)] each with and without MC applied. Mepiquat Chloride reduced plant height, number of main stem nodes, and internodal length. The effect on boll numbers was mixed between cultivars. In some instances under the same irrigation treatment (1.2 PE), the number of bolls was higher in ST825 with MC applied than with control while in DP20 the control treatment had the higher number of bolls. Mepiquat chloride's effectiveness on vegetative growth tended to decrease as the number of days after application increased. Differences in response within irrigation treatments was attributable to MC. Differences in response between irrigation treatments with MC applied was attributable to irrigation and cultivar differences and not to interaction between soil moisture and MC.

Determination of mepiquatchloride in animal and plant matrices by ion chromatography with conductivity detection

A new residue method, based on ion chromatography, for the determination of trace amounts of the ionic plant growth regulator mepiquatchloride is described. The method is adapted to plant and animal matrices and does not require any derivatization steps. This new technique provides higher recoveries of the analyte, better reproducibility and increased speed than the previous method. The limit of determination is 0.05 mg/kg.

Effect of the Plant Growth Regulator Mepiquat Chloride on Host Plant Resistance in Cotton to Bollworm (Lepidoptera: Noctuidae)

The effects of a plant growth regulator, mepiquat chloride (PIX), on bollworm, Heliothis zea (Boddie) growth, survival, and damage to cotton fruit, Gossypium hirsutum L., were studied at Corpus Christi, Tex., in whole-plant field cages in 1982 and 1983. At 48 h after PIX relative condensed tannin concentration and astringency increased significantly in the treated plants, but terpenoid concentration remained unchanged. Neonate larvae placed on treated and untreated plants at this time and allowed to feed for 7 days did not differ significantly in the resistance parameters measured, except for higher larval mortality on treated plants in 1982. At 14 days after PIX application, tannin concentration had increased further and terpenoid concentration increased significantly in the treated plants. H. zea larvae developing on these plants weighed less, had lower survival rates, and damaged less fruit than larvae on untreated plants. Application of PIX to cotton induced plant resistance to H. zea.