Degradation and adsorption of 14C-MCPA in soil—influence of concentration, temperature and moisture content on degradation

MCPA was weakly absorbed in soils with 2.4, 3.0 and 2.9% humus. K_d-values were 0.7, 0.9 and 1.0, respectively. In soil, not previously treated with MCPA, the degradation of 0.05 mg kg^?114C-MCPA followed first-order reaction kinetics whereas degradation of 5 mg kg^?1 was only first-order for 2 weeks; exponentially increasing degradation rates followed indicating enrichment of the soil with MCPA decomposers. Degradation was monitored by evolution of ¹⁴CO₂. The influence of temperature on degradation of MCPA (4 mg kg^?1) could initially be described by Q₁₀ values or by the Arrhenius equation. After 1 day of incubation in two field soils Q₁₀ values were 3.3 and 2.9, respectively, between 0°C and 29°C; the activation energies were 87 and 76 kj mol^?1. Exponentially increasing degradation rates followed with doubling times of about 4.0, 1.8, 1.2 and 0.6 days at 6,10, 15 and 21°C, respectively. After 51 days of incubation, at temperatures between 6°C and 29°C, about 60%¹⁴C was evolved in CO₂ and only traces of MCPA were left in the soil. At 0°C and at 40°C only 1% and 10%¹⁴C, respectively, were evolved as CO₂ after 51 days. ¹⁴C-MCPA (4 mg kg^?1) was incubated at moisture contents from that in air-dried soil to 2.3 times field capacity. Optimum for degradation was from 0.6 to 1.2. field capacity. Degradation was very slow where water contents were below the level of wilting point and was nil in air-dried soil. In wet soil degradation was delayed, but even in water-logged soil (2.3 times field capacity) MCPA was decomposed after 4 to 5 weeks at 10°C.     

An analytical procedure for bromoxynil and its octanoate in soils; persistence studies with bromoxynil octanoate in combination with other herbicides in soil

A method is described for the analysis of the herbicide bromoxynil and its octanoate in soils. Following extraction with aqueous acidic acetonitrile, the octanoate was separated from the phenolic bromoxynil by solvent partitioning. The ester and the phenol were assayed by gas-liquid chromatography without further modification or preparation of a derivative. Recoveries in excess of 93% were obtained from soils treated with the phenol and the ester at levels of 0.5 or 0.1 μg g^?1. The persistence of bromoxynil octanoate applied at a rate of 3 μg g^?1 was studied in the laboratory on a heavy clay and a sandy loam at 85% of field capacity moisture and 20°1°C, both alone and in the presence of 2,4-D (2 μg g^?1); MCPA (2 μg g^?1); MCPA+asulam (both at 2 μg g^?1); and MCPA+difenzoquat (both at 2 μg g^?1). In each soil there was a rapid conversion of bromoxynil octanoate to the free phenol, which then underwent a rapid degradation, so that after 7 days, over 90% of the original treatment had disappeared. There appeared to be no effect on bromoxynil breakdown by any of the herbicides added in combination. Small field plots were treated, in early May 1977 and 1978 at two locations in Saskatchewan, with a combination of commercial formulations containing asulam, bromoxynil octanoate, and MCPA at rates of 1 kg ha^?1 each. After 10 weeks the plots were sampled and analysis showed that in all cases, no asulam, bromoxynil, or bromoxynil octanoate could be extracted from the top 10 cm of soil.     

Soil persistence studies with bromoxynil, propanil and [14C]dicamba in herbicidal mixtures

The persistence of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), [¹⁴C]dicamba (3,6-dichloro-2-methoxybenzoic-7-¹⁴C acid) and propanil [N-(3,4-dichlorophenyl)propionamide] at rates equivalent to 1 kg ha^?1, were studied under laboratory conditions in a clay loam, a heavy clay and a sandy loam at 85% of field capacity and at 20±1°C, both singly and in the presence of herbicides normally applied with these chemicals as tank-mix or split-mix components. The degradation of bromoxynil was rapid with over 90% breakdown occurring within a week in the heavy clay and sandy-loam soils, while in the clay-loam approximately 80% of the bromoxynil had broken down after 7 days. In all three soils degradation was unaffected by the presence of asulam, diclofop-methyl, flamprop-methyl, MCPA, metribuzin or propanil. Propanil underwent rapid degradation in all soil treatments, with over 95% of the applied propanil being dissipated within 7 days. There were no noticeable effects on propanil degradation resulting from applications of asulam, barban, bromoxynil, dicamba, MCPA, MCPB, metribuzin or 2,4-D. The breakdown of [¹⁴C]dicamba in a particular soil was unaffected by being applied alone or in the presence of diclofop-methyl, flampropmethyl, MCPA, metribuzin, propanil or 2,4-D. The times for 50% of the applied dicamba to be degraded were approximately 16 days in both the clay loam and sandy loam, and about 50 days in the heavy clay.     

Chemical control of nodding thistle (Carduus nutans L.) in New Zealand pastures

Broadcast sprays of several herbicides were applied at different times of the year at several sites in Hawkes Bay, Canterbury and Otago. For good thistle control, date of application was more important than types of herbicide. In Hawkes Bay, applications made in April, May and June tended to be the most effective. Under slightly cooler Canterbury conditions, April, September and October were the best application dates. In the Otago trials, spring emergence of thistle seedlings meant that the most consistent results came from September or October applications. At all sites, applications made in July or August were relatively ineffective, probably because of low winter temperatures and slow thistle growth rates. MCPA (potassium salt) at 1·0 kg ha^?1 was the standard herbicide used in all experiments. MCPA at 0·5 kg ha^?1, MCPB (sodium salt) at 0·5 and 1·0 kg ha^?1 and 2,4-D at 0·5 kg ha^?1 did not kill as many thistles as MCPA at 1·0 kg ha^?1. MCPA at 1·5 kg ha^?1 and MCPB (butyl) ester + clopyralid at 0·5 + 0·015 or 1·0+0·03 kg ha^?1 gave consistently better control than MCPA at 1·0 kg ha^?1 2,4-D at 1·0 or 1·5 kg ha^?1, MCPB at 1·5 or 2·0 kg ha^?1, and MCPA + MCPB at 0·33 + 1·0 or 0·67 + 0·5 kg ha^?1 gave results very similar to MCPA at 1 kg ha^?1. Thistle control varied between sites and years. Some of the variation may have been due to different proportions of first and second year thistles present at spraying, and to variation in genetically determined herbicide susceptibility. Chemical control of thistles was short term only, because of dormant seeds in the soil.     

Herbicide residues in waste waters from ricefields

The herbicides bentazone, 2,4-D, MCPA, propanil, molinate, and tiocarbazil, and the insecticide phenthoate, were applied to ricefields in Sardinia at rates equivalent to maximum aqueous concentrations of 0.4-2.8 mg kg^?1, assuming the water to be 20 cm deep. Their concentrations in water were measured by high-performance liquid chromatography. Residues in 162 water samples, collected from 16 ricefields 1, 4, 7, 10, 12, 18, 21 and 120 days after the last spraying, were all below the limit of determination (0.03 mg kg^?1). Residues in 40 water samples taken from five drainage canals were also less than 0.03 mg kg^?1.     

Soil persistence studies with [14C]MCPA in combination with other herbicides and pesticides

The persistence of [¹⁴C]MCPA at a rate equivalent to 1 kg ha^?1 was studied under laboratory conditions in a clay loam, heavy clay and sandy loam at 85% of field capacity moisture and 20±1°C both alone and in the presence of tri-allate, trifluralin, tri-allate and trifluralin, malathion, Vitaflow DB, malathion and Vitaflow DB, bromoxynil, bromoxynil and asulam, bromoxynil and difenzoquat, dicamba, dicamba and mecoprop, linuron, MCPB, metribuzin, propanil, TCA, benzoylprop-ethyl, diclofop-methyl, and flamprop-methyl. Except in the soils treated with asulam, the half-lives of [¹⁴C]MCPA in all three soil types were similar, being approximately 13±1 days, thus indicating that none of the other chemicals studied adversely affected the soil degradation of MCPA. In the asulam treated soils, the half-lives of the MCPA were about 3 days longer than in non-asulam treated soils; the effect was most marked in the clay loam.     

Response of teff (Eragrostis tef(Zucc.) Trotter) to 2, 4-D and MCPA at various growth stages

Teff (Eragrostis tef (Zucc.) Trotter) cv.DZ-01- 354 was sprayed at one-, three-, four-, five- and six-leaf stages with 2.4-D (amine salt) and MCPA (potassium salt) each at 0.75 and 1.5 kg a.e. ha^?1. Teff was also grown in different temperature regimes to see the relation between apical and vegetative development. Photomicrographs were made to determine the stage of development of the growing point and dry matter measurements were made to assess the effects of the herbieide. Teff sprayed at the one leaf stage was killed by both herbieides. At the three- and four-leaf stages 2, 4-D at both rates and MCPA at 1.5 kg a.i. ha^?1 caused severe leaf deformities and reduced dry weights. Less severe effects were noted at the five-leaf stage indicating that teff was then more tolerant to these herbicides. This coincided with a fully elongated shoot apex. However, when sprayed at the six-leaf stage there was evidence of herbicide-induced panicle deformities. Teff was more susceptible to 2, 4-D than to MCPA and both affected the roots more than the shoots. A close correlation was found between leaf number and the development of shoot apex under all the different temperature and day length conditions.     

Untersuchungen über Sonchus arvensis L. III, Metabolismus von MCPA

Research on Sonchus arvensis L. III. Metabolism of MCPA Roots of Sonchus arvenis L. were injected with ¹⁴C-MCPA at the time of planting of the root sections and when the plants had leaves 3 cm, 5–7 cm and 12–15 cm long. After extraction with 70% ethanol and separation by thin layer chromatography, three components, termed 1, 2 and 3, were detected by scanning. Component 2 gave a chromatograph identical to MCPA and was probably the non-metabolized residue of the injected material. Component 3 appeared faster than component 1 but, when heated with 1 N HCl or 1 N NaOH, both of them yielded component 2 (MCPA). In this latter reaction the conversion of component 3 was again the fastest. The older the plants the more rapid was the metabolism of MCPA, the highest metabolic rate occurring in the main roots. In secondary roots and leaves this process occurred more slowly. Dormant roots were capable of metabolizing MCPA quite as well as non-dormant roots. Raising the temperature from 7^° to 23°C accelerated the metabolic process. The liberation of ¹⁴C0₂ proceeded very slowly. During a period of 4 days only 1.3% of the total radio-activity was released as ¹⁴CO₂. In biotests, with Raphanus sativus L. as test species, component 3 appeared to be as phytotoxic as component 2 (MCPA), whereas the more stable component 1 exhibited very low phytotoxicity.     

Breakdown rates of dimethoate in fruit and vegetable dips

In order to determine the effect of pH and temperature on post-harvest dip solutions of dimethoate (500 mg litre^?1), the half-lives and pseudo first-order rate constants were calculated from measurements at pH 4, 6, 8, 10, 11.5, and at two temperatures 25 and 52°C. The half-lives ranged from 206 days to 39.3 min at 25°C, and from 5.6 days to 205s at 52°C; the rate constants ranged from 3.9 × 10^?8 s^?1 to 2.9 × 10^?4 s^?1 at 25°C, and from 1.4 × 10^?6 s^?1 to 3.4 × 10^?3 s^?1 at 52°C. The results show that the water used in dips should have a pH≤7. The addition of benomyl to the dip solutions at two concentrations (0.5 and 1.0 g litre^?1) had no effect on the half-lives and rate constants. The use of hard and salted waters in dips also showed no major effect. A formula was developed that gives the half-life of the dimethoate as a function of the pH and temperature.     

Hydrolysis of the pyrethroid insecticide fenpropathrin in aqueous media

The hydrolysis of [¹⁴C] fenpropathrin ( I ) [(RS)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate] was studied in buffer solutions at pH 1.9–10.4, and in natural river and sea water at 25, 40, 55 and 65°C under laboratory conditions. The hydrolysis of I proceeded predominantly through neutral (pH independent) and base-catalysed processes in the regions below pH 3.9 and above pH 7.0, respectively, whereas both reactions occurred between pH 3.9 and 7.0. The rates of hydrolysis of I in buffer solutions were similar to those in one sample of river and one sample of sea water. If this obtains generally, it may be expected that the half-life of I in natural waters, normally within the range pH 5–9, will range from 1.54 to 1080 days at 40°C, 11.3 to 8520 days at 25°C and, by extrapolation of the data obtained in buffer solutions, 106 to 83 000 days at 10°C. The rate constants for hydrolysis of I in aqueous media can be expressed by: Where log k_N = 9.60–(5.56 × 10³ T^?1) and log k_B = 7.32–(2.56 × 10³ T^?1). The calculated rate constants were in good accord with the observed values in buffer solutions. Cleavage of the ester linkage was more rapid than hydration of the cyano group at any pH and temperature tested.     

Sensitivity of Botrytis cinerea to chitosan and acibenzolar‐S‐methyl

BACKGROUND: The antifungal properties of chitosan and acibenzolar‐S‐methyl were evaluated to assess their potential for protecting grapes against Botrytis cinerea Pers.: Fr. isolated from Vitis vinifera L. The objectives were to determine the effects of these compounds on the in vitro development of B. cinerea and to assess their effectiveness at controlling grey mould on grapes stored at different temperatures. RESULTS: Both agents significantly inhibited the radial growth of this fungus species. The EC₅₀ was 1.77 mg mL^?1 for chitosan and 3.44 mg mL^?1 for acibenzolar‐S‐methyl. In addition, single grapes treated with aqueous solutions of chitosan (1.0 and 2.5 mg mL^?1) and acibenzolar‐S‐methyl (1.0 and 3.0 mg mL^?1) were inoculated with B. cinerea and incubated at both 4 and 24 °C. After 4 days at 24 °C, all the concentrations of chitosan and acibenzolar‐S‐methyl significantly reduced B. cinerea growth. However, at 4 °C, significant differences were only observed between chitosan at 2.5 mg mL^?1 and acibenzolar‐S‐methyl at both 1.0 and 3.0 mg mL^?1 and the corresponding controls. After 3 days at 24 °C, the greatest reduction in lesion size was obtained in grapes pretreated with acibenzolar‐S‐methyl at 3.0 mg mL^?1. Only the highest doses of these products significantly reduced the lesion diameters when grapes were stored for 3 days at 4 °C. CONCLUSIONS: Chitosan and acibenzolar‐S‐methyl could directly inhibit the growth of Botrytis cinerea in vitro and confer resistance on grapes against grey mould. Pretreatment with these compounds could be an alternative to traditional fungicides in post‐harvest disease control in grapes. Copyright © 2010 Society of Chemical Industry     

Hydrolysis of 1, 3-dichloropropene in dilute aqueous solution

Hydrolysis of [¹⁴C]-radiolabeled 1, 3-dichloropropene (1, 3-D) was studied at pH 5, 7 and 9 at 10, 20 and 30°C in sterile buffered water. The rate of hydrolysis was independent of pH at each temperature, with measured half-lives of 3-1 (±0.l), 11.3 (±0.5) and 51 (±2.3) days at 30, 20 and 10°C, respectively. The activation energy for the hydrolysis reaction was determined to be 23.9 kcal mol^?1 deg^?1. One hydrolysis product was formed during the course of the study and was identified by co-chrornatography with analytical standards, using h.p.l.c., to be 3-chloroallyl alcohol. The alcohol appeared to be stable to further hydrolytic conversion and was formed in the same cis: trans ratio as in the initial 1, 3-D starting material, indicating essentially identical rates of hydrolysis for the cis and trans isomers of 1, 3-D.     

Antagonistic effects of 2, 4-D), MCPA and MCPB on uptake and translocation of haloxyfop-ethoxyethyl in oat (Avena sativa L.)

The antagonism of haloxyfop-ethoxyethyl (HE) by selected phenoxy herbicides was evaluated through studies of the foliar absorption and translocation of ¹⁴C]HE in oat (Avena sativa L.). Uptake of [¹⁴C]HE, from simultaneous application in mixture with a phenoxy herbicide, was inhibited by the latter in the order MCPB MCPA2,4-D. In mixtures, the foliar absorption of [¹⁴C]HE was reduced more by salts of the phenoxy herbicides than by the corresponding butyl esters. 2,4-D-butyl enhanced uptake of [¹⁴C]HE. The application rate of phenoxy herbicides (from 0.5 to 1.5 kg a.e. ha^?1) did not affect the uptake of [¹⁴]HE, but did influence translocation. Movement of [¹⁴C]herbicide out of the treated leaf was less than 5% of the total ¹⁴C applied; translocation was significantly reduced by all phenoxy herbicides and was antagonized most by 2,4-D-salt and least by MCPB-butyl. Phenoxy salts invariably reduced [¹⁴C]HE translocation more than the corresponding butyl esters. Prior application of phenoxy salts reduced uptake of [¹⁴C]HE, but this antagonism was reduced as the time interval between spray applications increased. Translocation of ¹⁴C out of the treated leaf was antagonized most by prior application of 2,4-D, and by phenoxy salt formulations. When applied up to 2 days after HE, phenoxy salts reduced uptake, but translocation of ¹⁴C was generally unaffected. Les effets antagonistes du 2,4-D, du MCPA et du MCPB sur la pénétration et la migration de l'haloxyfop-éthoxyéthyl dans l'avoine (Avena sativa L.) L'effet antagoniste de plusieurs herbicides de type phénoxy à l'égard de l'haloxyfopéthoxyéthyl (HE) a étéétudié dans des études de pénétration foliaire et de migration du [¹⁴C]HE chez l'avoine (Avena sativa L.) Lorsqu'il est appliqué en mélange avec un herbicide phénoxy, la pénétration du [¹⁴C]HE est inhibée dans l'ordre suivant: MCPB MCPA 2,4-D. La pénétration foliaire du [¹⁴C]HE était davantage réduite par les sels d'herbicides phénoxys que par les esters butyles correspondants. Le 2,4-D butyle augmentait la pénétration du [¹⁴C]HE. La dose d'herbicides phénoxys (de 0,5 à 1,5 kg m.a. ha^?1) n'affectait pas la pénétration de [¹⁴C]HE mais modifiait sa migration. La migration d'herbicide ¹⁴C hors de la feuille traitée était inférieure à 5 % de la radioactivité appliquée. Elle était significativement réduite par tous les herbicides phénoxys, le plus par le sel de 2,4-D et le moins par le MCPB-butyle. Les phénoxys sous forme de sels diminuaient toujours la migration du [¹⁴C]HE davantage que les esters butyles correspondants. Si l'application de phénoxys sous forme de sel précédait celle de [¹⁴C]HE, sa pénétration était réduite mais cet antagonisme était réduit lorsque l'intervalle de temps entre les deux applications était augmenté. La migration de ¹⁴C hors de la feuille traitée était le plus diminuée par le 2,4-D et par les phénoxys sous forme de sels. Quand ils étaient appliqués jusqu'à deux jours après [¹⁴C]HE, les phénoxys sous forme de sel réduisaient sa pénétration, mais la migration de ¹⁴C n'était généralement pas affectée. Antagonistische Wirkung von 2,4-D, MCPA und MCPB auf die Aufnahme und Translokation von Haloxyfop-ethoxyethyl in Hafer (Avena sativa L.) Die antagonistische Beeinflussung von Haloxyfop-ethoxyethyl (HE) durch ausgewählte Phenoxy-Herbizide wurde anhand der Blattaufnahme und Translokation von [¹⁴C]HE in Hafer (Avena sativa L.) untersucht. Die Aufnahme von [¹⁴C]HE bei gleichzeitiger Anwendung in Mischung mit einem Phenoxy-Herbizid wurde durch die letztgenannten Stoffe in der Reihenfolge MCPB MCPA 2,4-D gehemmt, wobei die Salz-Verbindungen stärker wirkten als die entsprechenden Butylester. 2,4-D-butyl förderte die Aufnahme von [¹⁴C]HE. Die Aufwandmenge der Phenoxy-Herbizide (0,5 bis 1,5 kg AS ha^?1) blieb ohne Einflus auf die Aufnahme von [¹⁴C]HE, beeinflußte aber die Translokation. Aus den behandelten Blättern wurde weniger als 5 % der gesamten [¹⁴C]Menge transloziert; die Translokation wurde durch alle PhenoxyHerbizide signifikant reduziert, am meisten durch 2,4-D-Salz, am wenigsten durch MCPB-butyl. Die Salz-Verbindungen verminderten die [¹⁴C]HE-Translokation mehr als die entsprechenden Butylester. Eine vorausgehende Behandlung mit den Salz-Verbindungen senkte die Aufnahme von [¹⁴C]HE, aber mit zunehmender Zeit zwischen den Anwendungen nahm dieser Antagonis mus ab. Hierbei war der Einfluß von 2,4-D und von den Salz-Verbindungen am stärksten. Wurden diese Stoffe bis zu 2 Tagen nach HE ausgebracht, beeinträchtigten sie die Aufnahme, jedoch im allgemeinen nicht die Translokation von ¹⁴C.     

Dissipation of 4-chloro-2-methylphenoxyacetic acid (MCPA) in a rice field

The dissipation of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in a California rice field was investigated. Samples of water, rice plants and mud were collected at intervals for 20 days and analysed for MCPA by established methods for plants and mud, and by a novel method utilising XAD-2 macro-reticular resin for water. Water residues declined to less than 0.01 parts/10⁶ of MCPA within 14 days after application; plant residues declined from 20 parts/10⁶ to 1 part/10⁶ within 20 days; mud residues remained constant at about 0.1 parts/10⁶. Photolysis of dilute aqueous MCPA solutions with either sunlight or an indoor photoreactor yielded 4-chloro-2-methylphenol as the major product; o-cresol and 4-chloro-2-formylphenol also were identified. While photosensitisation was observed with water taken from the rice field, microbial degradation proceeded at an even faster rate. All environmental compartments except air contained measurable amounts (>0.01 parts/10⁶) at some time, but water contained the bulk of the applied MCPA whose eventual disappearance was shown to be due to biological and chemical degradation and not dilution.     

FACTORS INFLUENCING THE HERBICIDAL EFFICIENCY OF MCPA AND MCPB IN THREE SPECIES OF MICRO-ALGAE

Summary. The herbicidal activity of MCPA and MCPB was compared using three species of unicellular algae grown in liquid mineral salt medium. MCPB inhibited growth, respiration and phosphate uptake to a greater degree than MCPA and appears to be inherently toxic at concentrations of at least 2·5 × 10^?4 M. The enhanced activity of MCPB coincided with more efficient absorption. Uptake of both compounds appears to be optimal at pH conditions favouring movement as the undissociated molecule. Facteurs infiuencant l'efficacite herbicide du MCPA et du MCPB sur trois espèces d'algues micro-scopiques Résumé. L'activité herbicide du MCPA et du MCPB a été comparée en utilisant trois espéces d'algues unicellulaircs cultivées en milieu liquide renfermant des sets minéraux. Le MCPB inhibe la croissance, la respiration et l'absorption du phosphate à un degré plus éevé que le MCPA et il semble être essentiellement toxique à des concentrations d'au moins 2,5 × 10^?4 M. L'activité plus grande du MCPB coïncide avec une absorption plus complète. L'absorption des deux composés semble étre optimale aux conditions dec pH favorisant leur migration sans dissociation de la molécule. Faktoren, welche die hrbizide Wirkung von MCPA und MCPB gegen drei Mikro-Algen-Arlen beeinfiussen Zusammenfassung. Die herbizide Wirksamkeit von MCPA und MCPB wurde bei drci Arten einzelliger Algen, die in flüssigem Mineralsalzmedium angezogen wurden, vcrglichen. MCPB hemmt Wachstum, Respiration und Phosphataufnahme starker als MCPA und ist offcnsichdich in Konzentrationen von mindestens 2,5 × 10^?4 M absolute toxisch. Die bessere Wirkung von MCPB geht mit einer besseren Absorption parallel. Die Aufnahme beider Substanzen ist offensichtlich unter solchen pH-Bedingungen optimal, die den Transport in Form von undissozierten Molekülen begünstigen.     

Effect of high temperatures on survival and longevity of the predator Cryptolaemus montrouzieri Mulsant

The effect of high temperature on survival and longevity of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) female adults was studied in the laboratory by daily exposure of the beetles to 35°C (mean r.h. 52%) combined with 1-, 2- and 3-h intervals of thermal treatment at 38, 40, 42 and 44°C (r.h. 46–48%). Fifty percent of females survived until the 12th–13th day of the thermal treatment at 38°C (depending on the exposure time), the 2nd–10th day at 40°C for 1–2 h exposure and the 4th–5th day at 42°C for 1 h exposure. Survival was 25–38% on the 1st–2nd day of the thermal treatment at 40, 42 and 44°C for 3, 2 and 1 h of exposure, respectively. Three hours of exposure of female C. montrouzieri at 42°C and 2 h exposure at 44°C were lethal for the beetles. Mean longevity of the predator was 33.13?±?1.22 days at 35°C and was significantly shorter as the temperature of the thermal treatments increased from 38^o to 44°C. These results suggest that daily temperature regimes of 35°C combined with 38–40°C for 1–3 h are marginal for the survival and longevity of the C. montrouzieri, whereas temperatures above 42°C are lethal even at short exposure. These results can partly justify the inability of C. montrouzieri to be permanently established in Pakistan environments and could contribute to a pre-evaluation assay of its potential adaptability in such environmental systems.     

Differential response to combined prochloraz and thyme oil drench treatment in avocados against the control of anthracnose and stem-end rot

The ability to meet consumers demand for high-quality standard fruit entails the distribution of unblemished safe fruit free of chemical residues on its edible portion. Therefore, this study was focused on investigating the influence of the combined effect of aqueous plant volatiles with half strength prochloraz solution to control anthracnose and stem-end rot in the green-skinned avocado cultivar (Fuerte). This method was applied due to its practicability on bulk fruits in packhouses and the fruits were subjected to stand-alone and combined treatments to assess the development of the disease after cold storage and observe the elicitation of the residual effect of the treatments on the defence related enzymes in ‘Fuerte’. The incidence of stem-end rot was 10% by the combination of prochloraz® (500 μg mL^?1; P50) with 0.1% v/v thyme oil compared to the 58.8% incidence exhibited by the untreated fruit during storage at 6.5 °C for 14 days followed by 3 days at retail shelf conditions (15 °C) (preventative application). Citral (0.1% v/v), P50 (500 μg mL^?1)?+?0.1% v/v citral and yucca extract alone reduced the stem-end rot incidence to about 25% during storage. More so, thyme oil (0.1% v/v) reduced both anthracnose and stem-end rot incidence to 35% after postharvest storage and P50 (500 μg mL^?1)?+?0.1% v/v thyme oil and 0.1% v/v thyme oil effectively induced the activity of phenylalanine ammonia lyase, chitinase and β-1, 3 glucanase in fruit inoculated with Lasiodiplodia theobromae and Colletotrichum gloeosporioides through the improvement of quality and firmness of the fruit after storage.     

Persistence studies with [14C] 2,4-D in soils previously treated with herbicides and pesticides

The persistence of [¹⁴C] 2,4-D at a rate equivalent to 1 kg/ha was compared under laboratory conditions in samples of heavy clay, sandy loam, and clay loam at 85% of field capacity moisture and 20 ± 1°C which had either received no pre-treatment, or had been pre-treated for 7 days at the 2 μg/g level with the herbicides benzoylprop-ethyl, diclofop-methyl, dinitramine, flamprop-methyl, nitrofen, picloram, tri-allate, trifluralin, and a combination of tri-allate and trifluralin. The breakdown of [¹⁴C] 2,4-D was also studied in the same soils that had similarly received pre-treatments of 2 μg/g of the cereal seed dressing Vitaflo-DB, the insecticide, malathion, and a combination of Vitaflo-DB and malathion. In each soil type, the half-life of the 2,4-D was similar regardless of whether the soil had, or had not, received any pre-treatment, indicating that none of the chemicals investigated adversely affected the soil degradation of 2,4-D.     

Initial pesticide residues in relation to vapour pressure

Field tests, in which several insecticides were applied at equal rates by ground sprayer to oats, rye and alfalfa, showed that residues 1 h after application were much lower for highly volatile compounds than for those of lower volatility. Varying the distance from spray release to target canopy from 10 to 40 cm did not significantly affect the deposits. Results indicate that applying insecticides with a vapour pressure greater than about 10^?4 mmHg (20°C) in aqueous media is very inefficient.     

Effect of low temperatures on 2,4-D behaviour in maize plants

The foliar surface of 4-leaf maize plants was found to be poorly wettable and retained 106 μl g^?1 dry matter when sprayed with a U46D (2,4-D formulation) blank. The third leaf retained 141 μl g^?1. A 7-day cold spell (17/9°C) increased retention per unit dry matter by 53% (135% on the third leaf). Cold stress lowered epicuticular wax quantity by 29% on the third leaf. Contact angles of formulated 2,4-D lay between 115 and 125° and were not significantly affected by cold stress. 2,4-D rapidly entered into maize third leaf (66% in 24 h) but migration from it was less than 1.5%. 2,4-D was readily degraded in maize (80% in 72 h). The most abundant metabolite was probably an ester conjugate; little of the hydroxy derivatives were found. Cold stress reduced 2,4-D degradation, and 72 h after treatment the amount of undegraded 2,4-D was 78% higher in cold-stressed maize plants. It was concluded that 2,4-D selectivity in maize results from low spray retention per unit dry matter and active degradation of penetrated herbicide. Cold stress affects both factors.