The effects of glyphosate and triclopyr on common bryophytes and lichens in northwestern Ontario

1999 ◽  
Vol 29 (7) ◽  
pp. 1101-1111 ◽  
Author(s):  
Steven G Newmaster ◽  
F Wayne Bell ◽  
Dale H Vitt
Keyword(s):  
Species Richness ◽  
Community Dynamics ◽  
Herbicide Application ◽  
Northwestern Ontario ◽  
Application Rates ◽  
Open Forest ◽  
Randomized Design ◽  
Completely Randomized Design ◽  
The Relationship

The effects of two silvicultural herbicides (Vision®, Release®) on bryophytes and lichens were studied in a harvested boreal mixedwood ecosystem. A completely randomized design with 115 plots of 1 m2 allowed direct comparison between herbicides and their effects on community dynamics. Regression models were used to analyze the relationship between herbicide application rates (0.71-6.72 kg active ingredient/ha) and changes in bryophyte and lichen abundance and species richness for 2 years following herbicide application. Results showed that bryophyte and lichen abundance and species richness decreased after herbicide treatments. In general, herbicide applications reduced the diversity of forest mesophytes and weedy colonizers to an ecosystem with only a few species of colonizers. A combination of clustering techniques and ANOVA were used to divide bryophytes and lichens into three ecologically defined response groups: herbicide-tolerant colonizers, semi tolerant long-term stayers from dry open forest, and sensitive forest mesophytes.

scholarly journals Response of Rubber Tree Saplings to Dolomite and Kieserite Application and K:Mg Ratio

2021 ◽  
Vol 29 (4) ◽  
Author(s):  
Chakkrit Poonpakdee ◽  
Khwunta Khawmee ◽  
Jumpen Onthong
Keyword(s):  
Nutrient Uptake ◽  
N Uptake ◽  
Rubber Tree ◽  
Control Treatment ◽  
Leaf Chlorophyll ◽  
Application Rates ◽  
Randomized Design ◽  
Completely Randomized Design ◽  
K Concentration ◽  
The Relationship

This study aimed to examine the effect of the application of dolomite and kieserite on the growth and nutrient uptake of rubber tree saplings and the relationship between K:Mg ratios in soils and nutrient uptake. The experiment followed a completely randomized design with five replicates. Budded stumps of RRIM 600 rubber were planted in soil with low extractable Mg (< 0.30 cmolc kg-1). Kieserite application at a rate of 0.5 cmolc Mg kg-1 significantly promoted the greatest sapling height, stem diameter, Mg and S concentrations, and leaf chlorophyll levels. High kieserite application rates (1.0 cmolc Mg kg-1) were more likely to decrease K and N uptake significantly. Applying dolomite (0.5 cmolc Mg kg-1) also significantly increased rubber growth compared with the control treatment but the significant increases were lower than those for kieserite application. Applying K at 72, 108, and 180 mg kg-1 significantly increased leaf K concentration, but significantly decreased Mg concentrations. Therefore, rubber plantations should apply Mg at a rate of 0.5 cmolc Mg kg-1 in the form of kieserite, and a ratio of K:Mg 2:1 is suitable for promoting rubber tree growth.

Effect of Temperature on Clopyralid Safety in Strawberry

2018 ◽  
Vol 32 (3) ◽  
pp. 347-351 ◽  
Author(s):  
Shaun M. Sharpe ◽  
Nathan S. Boyd ◽  
Peter J. Dittmar ◽  
Greg E. MacDonald ◽  
Rebecca L. Darnell
Keyword(s):  
Weed Management ◽  
Growth Chamber ◽  
Effect Of Temperature ◽  
Herbicide Application ◽  
Horticultural Crop ◽  
Randomized Design ◽  
Completely Randomized Design ◽  
Pre Treatment ◽  
Hand Weeding ◽  
Growing Conditions

AbstractStrawberry is an important horticultural crop in Florida. The long growing season and escapes from fumigation and PRE herbicides necessitate POST weed management to maximize harvest potential and efficiency. Alternatives to hand-weeding are desirable, but clopyralid is the only broadleaf herbicide registered for use. Weed control may be improved by early-season clopyralid applications, but at risk of high temperature and increased strawberry injury. The effect of temperature on clopyralid safety on strawberry is unknown. We undertook a growth chamber experiment using a completely randomized design to determine crop safety under various temperature conditions across acclimation, herbicide application, and post-application periods. There was no effect of clopyralid on the number of strawberry leaves across all temperatures. Damage to the strawberry manifested as leaf malformations. Acclimation temperatures affected clopyralid-associated injury (p=0.0309), with increased leaf malformations at higher temperatures (27 C) compared to lower (18 C) temperatures. Pre-treatment temperatures did not affect clopyralid injury. Post-application temperature also affected clopyralid injury (p=0.0161), with increased leaf malformations at higher temperatures compared to lower ones. Clopyralid application did not reduce flowering or biomass production in the growth chamber. If leaf malformations are to be avoided, consideration to growing conditions prior to application is advisable, especially if applying clopyralid early in the season.

scholarly journals Influence of the sowing depth and amount of sugarcane straw on the emergence of Chloris polydactyla and Eleusine indica and their control by herbicides applied pre-emergence

2017 ◽  
Vol 38 (3) ◽  
pp. 1187
Author(s):  
Marcelo Rafael Malardo ◽  
Patrícia Andrea Monquero ◽  
Paulo Henrique Vieira dos Santos ◽  
Nagilla Moraes Ribeiro ◽  
Paulo Vinicius da Silva ◽  
...  
Keyword(s):  
Rainfall Regime ◽  
Herbicide Application ◽  
Dry Period ◽  
Sowing Depth ◽  
Eleusine Indica ◽  
Sugarcane Straw ◽  
Randomized Design ◽  
Emergence Percentage ◽  
Completely Randomized Design ◽  
Rainfall Regimes

The objective of this study was to evaluate the effect of the sowing depth and amount of sugarcane straw on the soil on the emergence of Chloris polydactyla (‘capim-branco’) and Eleusine indica (Indian goosegrass) and to determine the efficacy of herbicides applied pre-emergence in the control of these species under different straw amount and rainfall regime conditions. The experiments were conducted in a completely randomized design with four replications. In the first experiment, the effects of six sowing depths (0.5, 1, 2, 4, 8, and 10 cm) and six sugarcane straw amounts (0, 1, 2, 4, 8 and 10 t ha -1) were assessed on the emergence of Indian goosegrass and ‘capim-branco’ in a 6 x 6 factorial arrangement. In the second experiment, the efficacy in the control of these species was evaluated for one control without herbicide and five treatments (indaziflam, metribuzin, tebuthiuron, indaziflam + metribuzin, and indaziflam + tebuthiuron) applied pre-emergence over four straw amounts (0, 1, 2, and 4 t ha-1) in a 6 x 4 factorial arrangement. This experiment was evaluated under two rainfall regimes in separate experiments (simulation of 20 mm of rainfall 1 or 10 days after herbicide application). The ‘capim-branco’ showed a marked reduction in emergence beginning at 2 t ha-1 of straw and a 2 cm sowing depth. For the Indian goosegrass, the decline in emergence mainly occurred beginning at 4 t ha-1 of straw and a 4 cm sowing depth. Only some of the Indian goosegrass plants emerged at the greater sowing depths (8 and 10 cm) and straw amounts (8 and 10 t ha-1), whereas no emergence of the ‘capim-branco’ was observed under these conditions. The treatments with sowing at a 1 cm depth and with 0, 1, 2, and 4 t ha-1 of straw provided the highest emergence percentage for the species. Application of the herbicide indaziflam alone was the only ineffective treatment for the control of the weeds regardless of the amount of straw and the water regime used. We concluded that the increase in the sowing depth and the amount of straw significantly reduced the emergence of the species and that the presence of straw and the dry period interfered with the herbicide efficacy.

scholarly journals PENGATURAN PEMBUNGAAN TANAMAN JAMBU BIJI (Psidium guajava L.) ‘KRISTAL’ MELALUI APLIKASI WAKTU STRANGULASI YANG BERBEDA

2020 ◽  
Vol 22 (3) ◽  
pp. 243
Author(s):  
RA Diana Widyastuti ◽  
Slamet Susanto ◽  
Maya Melati ◽  
Ani Kurniawati
Keyword(s):  
Psidium Guajava ◽  
Single Factor ◽  
Flowering Induction ◽  
Flowering Response ◽  
Randomized Design ◽  
Completely Randomized Design ◽  
Leaf N Content ◽  
The Relationship ◽  
Experimental Garden ◽  
Leaf N

<p align="center"><strong>ABSTRACT</strong></p><p align="center"><strong><em> </em></strong></p><p><strong><em>Arrangement of Guava Flowering </em></strong><strong><em>(Psidium</em></strong><strong><em> g</em></strong><strong><em>uajava</em></strong><strong><em> </em></strong><strong><em>L.</em></strong><strong><em>)</em></strong><strong><em> ‘Krystal’ through the Application of Different Strangulation Times. </em></strong>The seasonal production of guava (<em>Psidium guajava</em>) requires flowering manipulation technique such strangulation in order to be available throughout the years. This study aimed to explain the relationship between strangulation time, the period of flowering and harvesting of guava cv 'Krystal'. The experiment was conducted from February to December 2017, in Cikabayan experimental garden of IPB University, Bogor, Indonesia. The experiment used a completely randomized design with single factor, i.e strangulation times that consisted of control (no strangulation), strangulation in March, in April and in May. The results showed that strangulation treatment was able to accelerate the emergence of flowers and increase the number of generative shoots, the number of flowers per tree and the number of fruits harvested. The increase of flowering response on strangulated trees was supported by a higher leaf C/N compared to control, which is related to the low leaf N content in strangulation treatments. The strangulation treatment could accelerate the time of flower emergence six days earlier than control.<em>  </em><strong><em></em></strong></p><p><strong>Key</strong><strong>word<em>s</em></strong>: <em>guava, </em><em>C/N, flowering induction, ringing, seasonal production</em><strong><em></em></strong></p><p align="center"><strong> </strong></p><p align="center"><strong>ABSTRAK</strong></p><p align="center"><strong> </strong></p><p>Produksi buah jambu biji (<em>Psidium guajava</em>) yang bersifat musiman memerlukan teknik pengaturan pembungaan agar dapat tersedia sepanjang tahun. Penelitian ini bertujuan untuk menjelaskan keterkaitan antara waktu strangulasi dengan pola pembungaan dan panen buah jambu biji ‘Kristal’. Percobaan dilaksanakan mulai Februari sampai Desember 2017, di Kebun Percobaan Cikabayan IPB Bogor. Rancangan yang digunakan adalah Rancangan Acak Lengkap (RAL) dengan faktor tunggal yaitu waktu strangulasi yang terdiri dari 4 (empat) taraf, yakni tanpa strangulasi, strangulasi bulan Maret, strangulasi bulan April dan strangulasi bulan Mei. Hasil penelitian menunjukkan bahwa perlakuan strangulasi mampu mempercepat munculnya bunga dan meningkatkan jumlah tunas generatif, jumlah bunga per pohon, jumlah bakal buah per pohon dan jumlah buah yang dipanen. Peningkatan respon pembungaan akibat strangulasi didukung oleh C/N daun yang lebih tinggi dibandingkan tanpa stangulasi, yang berhubungan dengan rendahnya kandungan nitrogen daun pada perlakuan strangulasi. Perlakuan strangulasi mampu mempercepat waktu muncul bunga 6 hari lebih cepat dibandingkan tanpa strangulasi.</p><p><strong>Kata </strong><strong>k</strong><strong>unci: </strong>jambu biji, C/N, induksi pembungaan, pencekikan batang, produksi musiman</p>

scholarly journals Antioxidant activity and physiological performance of popcorn seed after saline stress and analysis of seedling images

2020 ◽  
Vol 44 ◽  
Author(s):  
Hugo Cesar Rodrigues Moreira Catão ◽  
Franciele Caixeta ◽  
Amanda Moreira Lopes ◽  
Flavia Andrea Nery-Silva ◽  
Adílio de Sá Júnior
Keyword(s):  
Antioxidant Activity ◽  
Salt Stress ◽  
Dry Mass ◽  
Saline Stress ◽  
Physiological Performance ◽  
Randomized Design ◽  
Physiological Quality ◽  
Completely Randomized Design ◽  
The Relationship

ABSTRACT Salinity influences all germination stages and may adversely affect seedling establishment in the field. The objective of this research was to determine the relationship between the antioxidant activity and the physiological performance of seeds and to verify the efficacy of the imaging analysis of popcorn seedlings after seed exposure to saline stress. A completely randomized design was used that consisted of four replicates in a factorial scheme. This scheme comprised three popcorn hybrids (P618, AP6002, and AP8203) and five saline potential levels (0.0; -0.1; -0.3; -0.6, and -0.9 MPa) that were obtained from KCl solutions of different concentrations. First count germination, germination and seedling vigor classification (strong normal seedlings), and dry mass of seedlings were evaluated to determine the physiological quality of the seed. The images of seedlings were used to evaluate the coleoptile and root lengths, indices of vigor, uniformity, and growth using the Groundeye® software. The activities of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) were also determined. Saline stress compromises the physiological quality and antioxidant activity of seeds and the performance of popcorn seedlings. Computerized image analysis using Groundeye® was efficient in evaluating the popcorn seedlings after being subjected to salt stress. Hybrids AP6002 and AP8203 were more tolerant to salt stress than hybrid P618.

scholarly journals Herbicide selectivity in alfalfa crops

2013 ◽  
Vol 31 (4) ◽  
pp. 903-918 ◽  
Author(s):  
N. Hijano ◽  
P.A. Monquero ◽  
W.S. Munhoz ◽  
M.R. Gusmão
Keyword(s):  
Plant Height ◽  
Soil Texture ◽  
Untreated Control ◽  
Clay Soil ◽  
Recommended Dose ◽  
Herbicide Application ◽  
The Third ◽  
Randomized Design ◽  
Chlorimuron Ethyl ◽  
Completely Randomized Design

This study aimed to determine the selectivity of herbicides applied in pre- and post-emergence for alfalfa crops. Three separate experiments were carried out under greenhouse conditions. The first experiment was arranged in a completely randomized design with three replications in a 4 x 11 + 1 factorial scheme , with eleven herbicides (bentazon, chlorimuron-ethyl, fomesafen, fluazifop-p-butyl, saflufenacil, imazethapyr, clethodim, nicosulfuron, imazaquin, haloxyfop-methyl and MSMA), four doses of each herbicide (0.5 D, 0.75 D, 1.0 D and 1.25 D, where D = recommended dose), plus an untreated control. The products were applied to alfalfa plants at the stage of 4 to 5 leaf pairs. In the second experiment, the effect of pre-emergent herbicides on early alfalfa development was observed through a completely randomized design with five replications in a 3 x 4 x 2 factorial scheme, with three herbicides (hexazinone, atrazine + simazine, S-metolachlor), four doses (0.5 D, 0.75 D, 1.0 D and 1.25 D), and two types of soil texture (loamy and clay soil), plus an untreated control. The third experiment evaluated the action of atrazine, 2,550 g ha-1; clomazone - 600 g ha-1; diclosulam - 25 g ha-1; diuron+hexazinone - 936 + 264 g ha-1 and diuron+hexazinone +sulfometuron - 1,386 + 391 + 33.35 g ha-1 on alfalfa sown at different times after herbicide application. The effects of the treatments on alfalfa were evaluated according to visual phytotoxicity symptoms, plant height, and biomass of roots and shoots. Among the herbicides applied at post-emergence, imazethapyr, clethodim, haloxyfop-p-methyl and MSMA were selective for alfalfa, while among those applied at pre-emergence, none were selective, regardless of soil texture. The results of the third experiment showed that the herbicides diclosulam, hexazinone + diuron and atrazine caused less toxicity in alfalfa plants.

scholarly journals Pertambahan Biomassa dan Produksi Minyak Atsiri Tanaman Selasih (Ocimum basilicum L.) pada Usia Panen yang Berbeda

2021 ◽  
Vol 6 (2) ◽  
pp. 124-130
Author(s):  
Rasyid Abdulaziz ◽  
Sri Widodo Agung Suedy ◽  
Munifatul Izzati
Keyword(s):  
Essential Oil ◽  
Oil Production ◽  
Ocimum Basilicum ◽  
Growth Data ◽  
Randomized Design ◽  
Number Of Leaves ◽  
Completely Randomized Design ◽  
The Relationship ◽  
Range Test ◽  
Essential Oil Production

Selasih (Ocimum basilicum L.) memiliki kandungan minyak atsiri yang dapat digunakan dalam industri kosmetik, parfum, dan medis. Penelitian ini bertujuan mengetahui hubungan usia panen dengan biomassa dan produksi minyak atsiri pada organ daun serta batang selasih. Penelitian menggunakan Rancangan Acak Lengkap (RAL) pola faktorial, dengan faktor pertama usia panen (1; 1,5; dan 2 bulan), dan faktor kedua organ tanaman (daun dan batang). Media tanam menggunakan tanah dan kompos (1:1) yang dimasukkan dalam polibag ukuran 30cm x 30cm, dan diberi naungan paranet 25%. Parameter yang diamati: data pertumbuhan (tinggi tanaman, jumlah daun dan cabang primer), biomassa, dan produksi minyak atsiri. Analisis data menggunakan Anaylysis of Variance (ANOVA) dan Duncan's Multiple Range Test(DMRT) pada taraf kepercayaan 95 %. Penelitian menunjukkan hasil bahwa tanaman yang dipanen pada umur lebih tua menunjukkan pertumbuhan, biomassa dan produksi minyak atsiri yang lebih tinggi. Pada usia 1,5 bulan, biomassa meningkat 114,485% dibanding usia 1 bulan, sedangkan pada usia 2 bulan, peningkatan biomasa 91,410%  dibanding usia1,5 bulan. Produksi minyak atsiri tertinggi dihasilkan oleh organ daun pada usia panen 2 bulan sebesar 0,273g, dan 0,023g pada organ batang. Kesimpulan penelitian ini menunjukkan bahwa usia panen berbeda berpengaruh nyata terhadap biomassa dan produksi minyak atsiri tanaman selasih. Basil (Ocimum basilicum L.) contains essential oils that can be used in the cosmetic, perfume, medical industries. This study aims to determine the relationship between harvest age and biomass and essential oil production in basil leaves and stems. The study used a completely randomized design (CRD) with a factorial pattern, with the first factor being harvest age (1; 1.5; and 2 months), and the second factor being plant organs (leaves and stems). The planting medium used soil and compost (1:1) which was put in 30cm x 30cm polybags and was given a 25% para net shade. Parameters observed: growth data (plant height, number of leaves, and primary branches), biomass, and essential oil production. Data analysis used Analysis of Variance (ANOVA) and Duncan's Multiple Range Test (DMRT) at a 95% confidence level. Research shows that plants harvested at an older age show higher growth, biomass, and essential oil production. At the age of 1.5 months, biomass increased by 114.485% compared to the age of 1 month, while at the age of 2 months, the increase in biomass was 91.410% compared to the age of 1.5 months. The highest essential oil production was produced by leaf organs at 2 months of harvesting at 0.273g, and 0.023g in stem organs. The conclusion of this study showed that different harvest ages had a significant effect on the biomass and essential oil production of basil plants.

scholarly journals Performance of Quail with Different Hatch Body Weight by Fasting Treatment Post-hatch

2018 ◽  
Vol 3 (2) ◽  
pp. 35-39
Author(s):  
Bahri Syamsuryadi ◽  
K. Khaeruddin
Keyword(s):  
Body Weight ◽  
Feed Consumption ◽  
Feed Conversion ◽  
Initial Body Weight ◽  
Randomized Design ◽  
Weight One ◽  
Completely Randomized Design ◽  
Relationship Of ◽  
The Relationship

The purpose of this study was to determine the relationship of broiler quail’s initial body weight which is fastened at post-hatch to growth and attainment the last body weight. One hundred thirty-five quails aged 12 post-hatch had kept in a cage plot which had prepared based on a completely randomized design with 3x3 factorial pattern and three replications which each replication consisted of 5 quails. The first factor is body weight post-hatch (B) consist of B1 = 5.1 – 6.0 g (light), B2 = 6.1 – 7.0 g (medium) and B3 = 7.1 – 8.0 g (heavy), the second factor is the duration of fasting post-hatch (P) consist of P1 = 24 hours, P2 = 36 hours and P3 = 48 hours. The observed parameters to fasting were feed consumption, body weight, and feed conversion. The result of this study is the quail with light early body weight (5.1-6 g) post hatch showed that the lightest last body weight is related to the value of feed conversion. Accession good performance of quail can be reached by access feed approximately 24 hours.

The time spent in fresh cow pen influences total lactational performance

2020 ◽  
Vol 158 (3) ◽  
pp. 247-253
Author(s):  
F. Hoseyni ◽  
D. Zahmatkesh ◽  
E. Mahjoubi ◽  
M. Hossein Yazdi ◽  
R. A. Patton
Keyword(s):  
Milk Yield ◽  
Esterified Fatty Acids ◽  
Randomized Design ◽  
Grouping Strategy ◽  
Long Term Effect ◽  
Lactational Performance ◽  
Grouping Strategies ◽  
Completely Randomized Design ◽  
First Time

AbstractThis research paper addresses the effect of different grouping strategies of fresh cows on total lactational and reproductive performance. Hundred-sixty multiparous Holstein cows were enrolled in a completely randomized design and assigned to one of following treatments: 21 days in fresh pen with 12.5 kg/day concentrate (C21, n = 60), 10 days in fresh pen with 12.5 kg/day concentrate (C10, n = 50) and 10 days in fresh pen with 10 kg/day concentrate (L10, n = 50). Although there were no differences among treatments within the first 10 days in milk (DIM), C10 and L10 cows tended to produce more milk than C21 from 10 to 21 DIM. In addition, greater milk yield was obtained in C10 and L10 cows during 22–28 DIM and 29–70 DIM. Higher production in early lactation resulted in a tendency for greater milk production for C10 and L10 cows throughout a 305 days lactation. There was no difference in productivity between C10 and L10 groups at any time point. No blood metabolites (Ca, P, non-esterified fatty acids and β-hydroxy butyrate) were affected by treatments. Pregnancy at first, second and third service was 38, 39 and 40%, respectively, which were not influenced by the days in fresh pen or concentrate allowance. Collectively, our results for the first time suggest that fresh cow grouping strategy has a long-term effect on productivity but that adding 2.5 kg/day concentrate has no effect on milk yield in fresh pen.

scholarly journals EFEITO DA CHUVA SOBRE A AÇÃO DO HERBICIDA IMAZAPYR NO CONTROLE DE PLANTAS DANINHAS AQUÁTICAS.

Irriga ◽  
2010 ◽  
Vol 15 (2) ◽  
pp. 151-158 ◽  
Author(s):  
Caio Ferraz de Campos ◽  
Guilherme Sasso Ferreira de Souza ◽  
Maria Renata Rocha Pereira ◽  
Dagoberto Martins
Keyword(s):  
Chemical Control ◽  
Water Hyacinth ◽  
Eichhornia Crassipes ◽  
Pistia Stratiotes ◽  
Aquatic Weed ◽  
Herbicide Application ◽  
Time Intervals ◽  
Randomized Design ◽  
Completely Randomized Design ◽  
And Control

O objetivo deste estudo foi avaliar a influência de diferentes períodos de chuva ocorridos após a aplicação do herbicida imazapyr, em sua eficiência de controle sobre plantas de Pistia stratiotes e Eichhornia crassipes. Foram estudadas chuvas de 10 mm, aplicadas durante 5', em diferentes períodos de tempo (0h, 2h, 4h, 6h, 8h, 12h, 24h e não simulação de chuva) após a aplicação de imazapyr, na formulação Arsenal NA, a 250 g i.a. ha-1(1,0 L p.c. ha-1). O delineamento experimental utilizado foi o inteiramente casualizado, com quatro repetições. As plantas foram avaliadas visualmente aos 7, 14, 21, 28 e 35 dias após a aplicação (DAA), sendo os resultados obtidos submetidos à análise de variância pelo teste F e as médias dos tratamentos comparadas pelo teste de Tukey (p<0,05). A ocorrência chuvas em até 6 horas após a aplicação do herbicida imazapyr, em plantas de P. stratiotes, afetou negativamente sua eficiência de controle e, chuvas após intervalos acima de 8 horas não influenciaram no controle. A ocorrência de chuva em todos os intervalos de tempo, não interferiu no controle de plantas de E. crassipes.   UNITERMOS: aguapé, alface-d'água, controle químico, fitointoxicação     CAMPOS, C.F.; SOUZA, G.S.F.; PEREIRA, M.R.R.; MARTINS, D. EFFECT OF RAINFALL ON  IMAZAPYR  ACTION IN AQUATIC WEED CONTROL     2 ABSTRACT   The aim of this study was to evaluate the influence of different periods of rainfall that occurred after the application of the imazapyr herbicide on the control efficiency of Pistia stratiotes and Eichhornia crassipes. We studied 10 mm rainfall, applied for 5' at different time periods (0h, 2h, 4h, 6h, 8h, 12h, 24h, not simulated rainfall) after the application of imazapyr formulation Arsenal NA, 250 g ai ha-1 (1.0 L cp ha -1). The experiment had completely randomized design with four replications. Plants were evaluated at 7, 14, 21, 28 and 35 days after application (DAA), and the results submitted to analysis of variance by F test and treatment means compared by Tukey's test (p <0. 05). The occurrence of rainfall up to 6 hours after herbicide application, plants of P. stratiotes, negatively affected its efficiency and control; rainfall intervals over 8 hours had no effect in control. The occurrence of rainfall at all time intervals  did not affect the control of E. crassipes plants.  KEYWORDS: water hyacinth, waterlettuce, chemical control, phytotoxicity  

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