Effect of cold-water irrigation on bacterial wilt pathogen of tomato

Bacterial wilt caused by Ralstonia solanacearum is one of the most devastating bacterial diseases of plants worldwide. Management of bacterial wilt in tomato and other crops has been difficult, and so novel but easily implemented control methods are being sought. To evaluate the effect of cold-water irrigation on bacterial wilt of tomato, four treatments were used in which CF (chemically fertilized) soil and CF + FYM (chemical fertilizer + farmyard manure [FYM]) soil were inoculated with a bacterial suspension (R. solanacearum strain YU1Rif43) at 10⁶ colony forming units (CFU) g^?1 soil. Tomato seedlings were grown in Agri-pots in a plant growth chamber. The soil was irrigated with water that was kept at the same temperature in each treatment: 4, 10, 20, or 30°C. Incidence and severity of wilt, counting of the colonies of the culturable population of pathogen, and dry-mass and height of the plants were examined. After 45 days and in both kinds of soil, most of the plants had wilted in soil irrigated at 30°C. Wilt incidence was substantially reduced when transplanted seedlings were irrigated at lower temperatures (4–20°C). Survival of R. solanacearum was also reduced after being irrigated with water at lower temperatures, indicating that the reduced incidence of wilt was linked to reduced survival of the pathogen. Dry-mass and plant height were slightly higher under control conditions than in soils irrigated at lower temperatures. This study suggests that cold-water irrigation could significantly reduce bacterial wilt of tomato and have an adverse effect on survival of the wilt pathogen.     

Recovery of Ralstonia solanacearum from canal water in traditional potato-growing areas of Egypt but not from designated Pest-Free Areas (PFAs)

Surveys over three seasons of irrigation, drainage and artesian well water throughout the major potato-growing areas of Egypt indicated that Ralstonia solanacearum bv. 2 race 3 (phylotype II sequevar 1), cause of potato brown rot, was limited to the canals of the traditional potato-growing areas in the Nile Delta region, with positive findings more commonly associated with the network of smaller irrigation canals flowing through potato-growing areas. Pathogen populations in the canals of the Delta (~100–200 cfu l^?1) were generally variable throughout the year with presence linked to potato cultivation in the immediate area. The pathogen was not detected in irrigation or drainage water associated with potato cultivation in the newly reclaimed desert areas (designated as Pest-Free Areas, PFAs) or in the main branches of the Nile upstream from these areas. In vitro studies showed that temperature and microbial activity were the main factors affecting survival of the pathogen in canal water. In experiments at temperatures of 4, 15, 28 and 35°C, survival was longest at 15°C and shortest at 35°C. Survival at 4 and 28°C tended to be intermediate between these extremes as was survival when the bacterium was grown at fluctuating temperatures. Aeration, solarisation and pH variation between 4 and 9 appeared to have little effect on survival. Survival in autoclaved or filter-sterilised canal water was longer than in untreated water irrespective of other factors with survival times exceeding 300 days at 15°C in some experiments. Evidence is presented indicating that survival in water-saturated sediment may be longer than in the overlying water suggesting that sediment may provide a protective niche for the pathogen in some circumstances. The maximum survival time in non-sterile Egyptian canal water at high inoculum pressure was estimated to be up to 300 days at optimum temperature for survival (15–30°C) suggesting the potential for long-distance spread in Egyptian surface waters from sources of contamination.     

Überleben von Ralstonia solanacearum Biovar 2 (Rasse 3), dem Erreger der Schleimkrankheit der Kartoffel, in Boden und auf verschiedenen Materialien (Mikrokosmos)

Microcosm studies were carried out to test the survival of Ralstonia solanacearum biovar 2 (race 3) in soil at the permanent wilting point (wp) water content and at field capacity (fc) water content and on various material. Soils were placed at permanent ?5°C, 4°C, 15°C and 20°C and weekly fluctuating ?10/0/+10°C and the material at 5, 15 °C, 20°C with relative humidity (rh) uncontrolled or at constant 10% or 90%. In soil, survival was clearly dependent on temperature independent of water content. At 20°C Ralstonia solanacearum could be reisolated up to 364 days, at 15°C up to 290 days, at 4°C up to 209 days and at fluctuating temperatures (?10/0/+10°C) only up to 18 days. The lower the temperature, the more the population declined. At 15°C and 20°C appr. 10⁷ cfu/g soil were detected after 100 days, whereas at ?5°C only 10² cfu/g soil were detected after only 18 days. The pathogen was longer detectable in sandy-clay loam than in lighter sandy soil. It could be longer reisolated at wilting point and the populations did not decline as rapidly as at field capacity. Ralstonia solanacearum could best survive on material surfaces like rubber, plastic and varnished metal with maximum survival of 40 days at 5°C and 10% rh. In general there is a low risk of Ralstonia solanacearum overwintering under European climatic conditions when the fields are cleared of plant debris and the soil is frozen. Contamined material surfaces pose the risk of pathogen transmission to healthy tubers.     

Eradication of Plasmodiophora brassicae during composting of wastes

Survival of infectious inoculum of the clubroot pathogen Plasmodiophora brassicae was assessed following bench-scale flask composting experiments and large-scale composting procedures. Clubroot-affected material was provided by artificial inoculation of Chinese cabbage or naturally infected Brussels sprout and cabbage roots. Both sets of diseased material were used in flask experiments, and the latter in large-scale windrow and aerated tunnel experiments. Municipal green wastes, onion waste and spent mushroom compost were evaluated in flask experiments with varying temperature, aeration and moisture conditions. Green wastes were used in larger-scale composts. Within the limits of a Chinese cabbage seedling bioassay, both temperature and moisture content were critical for eradication of P. brassicae spores extracted from composted clubroot-affected residues. Incubation in compost at 50°C for 7 days or 1 day at 60°C with high moisture levels (= −5 kPa matric potential or 60% w/w moisture content) eradicated inoculum from artificially inoculated Chinese cabbage roots. In large-scale windrows and aerated tunnels, the pathogen was eradicated from naturally infected brassica wastes after 6–7 days at 54–73°C.     

Compost enhances plant resistance against the bacterial wilt pathogen Ralstonia solanacearum via up-regulation of ascorbate-glutathione redox cycle

The interactions between the pathogen Ralstonia solanacearum and potato Solanum tuberosum plants were studied to investigate the reactive oxygen species metabolic system and ascorbate (ASC)-glutathione (GSH) redox cycle in response to compost application. Single potato eyepieces were germinated and grown in pots containing sandy soil with or without compost at a rate of 7.5 g kg^?1 soil. Non-compost- and compost-treated plants (CTP) were inoculated with R. solanacearum 25 days after planting and then analyzed after 10 days, unless otherwise stated. The present results revealed that pathogen infection caused a remarkable decrease in plant growth related parameters and productivity and an increase in disease incidence. However, under these conditions compost had substantially improved plant growth and decreased disease incidence and bacterial population. R. solanacearum resulted in significant enhancement in the activities of NADPH oxidase, lipoxygenase, the production rate of superoxide and hydroxyl radicals, levels of hydrogen peroxide, membrane lipid peroxidation, and protein oxidation indicating the induction of oxidative stress in potato roots. However, the pathogen-mediated enhancement in indices of oxidative stress was considerably decreased by compost application, which enhanced the activities of ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) in infected potato plants, implying a better ROS-scavenging activity. Data also indicated that there were general increases in ASC and GSH content in infected compost treated plants, but non-compost treated ones significantly had lower levels of such redox metabolites. In addition, significantly higher ratios of ASC/DHA (dehydroascorbate) and GSH/GSSG (glutathione disulphide) were generally found in CTP than in non-compost treated-ones. The obtained results suggest that compost provides effective protection against the Ralstonia bacterial pathogen via up-regulation of the capacity of the ASC-GSH cycle and modulation of the cellular redox status, thereby eliminating ROS damage and sustaining membrane stability.     

Potato brown rot incidence and severity under different management and amendment regimes in different soil types

Ralstonia solanacearum race 3 biovar 2, the causative agent of potato brown rot (bacterial wilt), is an economically important disease in tropical, subtropical and temperate regions of the world. In view of previous reports on suppression of the disease by organic amendments, and the expansion of organic agriculture, it was timely to compare the effects of organic and conventional management and various amendments on brown rot development in different soils (type: sand or clay; origin: Egypt or the Netherlands). Brown rot infection was only slightly reduced in organically compared to conventionally managed sandy soils from Egypt, but organic management significantly increased disease incidence and pathogen survival in Dutch sandy and clay soils, which correlated with high DOC contents in the organic Dutch soils. There was no correlation between disease incidence or severity and bacterial diversity in the potato rhizosphere in differently managed soils (as determined by 16S DGGE). NPK fertilization reduced bacterial wilt in conventional Egyptian soils but not in Dutch soils. Cow manure amendment significantly reduced disease incidence in organic Dutch sandy soils, but did not affect the bacterial population. However, cow manure did reduce densities of R. solanacearum in Egyptian sandy soils, most probably by microbial competition as a clear shift in populations was detected with DGGE in these and Dutch sandy soils after manure amendment. Amendment with compost did not have a suppressive effect in any soil type. The absence of a disease suppressive effect of mineral and organic fertilization in Dutch clay soils may be related to the already high availability of inorganic and organic nutrients in these soils. This study shows that the mechanism of disease suppression of soil-borne plant pathogens may vary strongly according to the soil type, especially if quite different types of soil are used.     

Suppression of Fusarium wilt of spinach with compost amendments

The effect of different organic composts on the suppression of wilt disease of spinach caused by Fusarium oxysporum f. sp. spinaciae was evaluated in a continuous cropping system in both containers and in microplot field trials. Test soils infested with the pathogen were amended with wheatbran, wheatbran and sawdust, coffee grounds, chicken manure, or mixture of different composts with and without 5% (w/w) crab shell powder either once (5%, w/w) or continuously (2.5%) into the test soils infested with the pathogen. In the container trials, the soil amended with composts became suppressive to disease development on the second and third cropping. The suppressive effect was notable in the soil amended with the mixture of compost with and without crab shell powder. The coffee compost lowered soil pH but became suppressive to the disease after modifying the soil pH. In the field trial using the mixture of the different composts containing 5% crab shell powder, a combination of 5% before the first cropping and 2.5% every second cropping gave stable disease control and promoted plant growth. After compost amendment, populations of fungi, bacteria and actinomycetes as measured by dilution plate counting and the total microbial activity as evaluated by fluorescein diacetate hydrolysis increased and population of the pathogen gradually decreased. These phenomena were especially notable in soils amended with the mixture of different composts. These results indicate that diversity in the organic materials promotes higher microbial activity and population in the soil thereby enhancing disease suppressiveness.     

Inactivation of Macrophomina phaseolina Propagules during Composting and Effect of Composts on Dry Root Rot Severity and on Seed Yield of Clusterbean

Survival of a heat-tolerant pathogen Macrophomina phaseolina, causing dry root rot of clusterbean, was studied by incorporation and retrieval of infected residue samples at various stages of the composting process of pearl millet (Pennisetum glaucum) and clusterbean (Cyamopsis tetragonoloba) residues. During the heating phase, temperatures varied from 48–51°C at 30cm and 60–62°C at 60cm depth in compost pits. Reduction in survival of M. phaseolina propagules (13–23%) was significantly higher in the residues enriched with 4% urea-N and kept at 60cm compared to 2% urea-N and at 30cm. However, a heat phase (48–62°C) was not enough to completely eradicate M. phaseolina propagules from infected residues. Further reductions (54–61%) in survived propagules were achieved by sub-lethal temperatures (48–53°C) when moistened compost materials were exposed to heat during summer days. Beneficial effects of composts were ascertained on dry root rot intensity, seed yield of clusterbean and densities of M. phaseolina, Nitrosomonas and antagonists in soil. In a two-year field study, all the composts significantly reduced plant mortality due to dry root rot and increased the yield of clusterbean. The highest disease suppression and yield promotion were recorded in soil amended with pearl millet compost and cauliflower leaf residue compost, respectively. Soil amendment with compost also lead to a significant reduced density of M. phaseolina and an increased density of antagonistic actinomycetes, lytic bacteria and Nitrosomonas. Among composts, greater potential of cauliflower compost in enhancing population of antagonists in soil was discernible.     

Persistence of 2,4,5-T in a heavy clay soil

The persistence of the herbicide 2,4,5-T was studied at different controlled temperatures and moisture levels in Regina heavy clay. Degradation approximated to first-order kinetics and the half-life varied from about 4 days at 35°C and 34% soil moisture to about 60 days at 10°C and 20% soil moisture. The laboratory data were used in conjunction with the appropriate measurements of surface soil temperature and moisture content in the field to simulate the degradation pattern for the herbicide in five separate micro-plot experiments. Satisfactory agreement with the observed patterns of loss was obtained in two of the experiments but in the other three, the model over-estimated rates of loss. It is suggested that the reason for this was the difficulty of obtaining a correct measure of soil moisture content to use in the simulation program.     

The degradation of methazole in soil. I. Effects of soil type,soil temperature and soil moisture content

[¹⁴C]-Labelled methazole was incubated in six soils at 25°C and with soil moisture at field capacity. Under these conditions, methazole was unstable, the concentration declined following first-order kinetics with half-life values in the soils ranging from 2.3 to 5.0 days. The main degradation product was 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) which was more stable than the parent compound. After about 160 days, DCPMU accounted for 30 to 45% of the initial methazole concentration. Degradation of methazole and DCPMU was affected by soil temperature and moisture content. With methazole, half-lives in one soil at field capacity moisture content and temperatures of 25, 15 and 5°C were 3.5, 8.7 and 31.1 days respectively. The half-life at 25°C was increased to 5.0 days at 50% of field capacity and 9.6 days at 25% of field capacity. A proportion of the initial radioactivity added to the soil could not be extracted and this proportion increased with time. After 160 days this unextractable radioactivity accounted for up to 70% of the amount applied.     

Overwintering of alternaria macrospora in Cotton Debris

An epidemic ofAlternaria macrospore in cotton started 1 month earlier, and developed faster in plots contaminated withA. macrospora-infected cotton debris than in debris-free plots. Overwintering of the pathogen in debris was associated with survival of the debris itself. With the exception of debris in dry soil, overwintering was better in debris located on the soil surface than in that buried beneath the surface. Under all conditions it was better in dry than in wet soil and in sterilized than in unsterilized soil. Survival was associated with micTobial activity in the soil, was highest in pure sand and decreased progressively in sandy loam, heavy soil and peat. The survival in debris was highest in soil kept at 10°C and decreased progressively at 20, 30 and 40°C. Increasing the soil moisture content reduced survival. Overwintering was better in a cotton field that was not cropped during the winter than in a field sown with wheat between the cotton seasons. The rate of transfer of disease to seedlings from debris buried in soil was low except when debris was in contact with the seed. The main means of disease transfer was by airborne spores produced on debris located on the soil surface. These spores had low infectivity and caused few lesions, but the second generation of spores formed on these lesions was highly infectious.     

Simulation of herbicide persistence in soil .III. Propyzamide in different soil types

The effects of soil temperature and soil moisture content on the rate of degradation of propyzamide in five soils were examined under controlled laboratory conditions. Half-lives in soils incubated at field capacity varied from 23 to 42 days at 25°C and from 63 to 112 days at 15°C. The variation in half-life at 25°C and 50% of field capacity was from 56 to 94 days. When the laboratory data were used in conjunction with the relevant meteorological records and soil properties in a computer simulation program, predicted degradation curves for propyzamide in four of the soils in micro-plots were in close agreement with those observed. Use of the program to predict residues of propyzamide in the fifth soil at crop maturity in a series of field experiments concerned with continuity of lettuce production gave values fairly close to those observed when appropriate corrections were made for initial recoveries.     

Risk of dissemination of Clavibacter michiganensis ssp. sepedonicus with potato waste

To estimate the risk of dissemination of Clavibacter michiganensis ssp. sepedonicus through potato residues from processing industries, the various processes and the usage of residues from plants from different processing branches were analysed with regard to the effect they can have on the pathogen. The residues were classified into different risk categories, from category 0 (no risk of dissemination) to category 4 (high risk of dissemination). Residues not heated during processing and used in agriculture, e.g., as fertilizer, were pooled in the highest risk category 4. Residues that were sanitised before use in agriculture, e.g., by composting or pasteurisation, were still classified as probably high risk (risk category 3), as no information on these treatments concerning the inactivation of the pathogen was available so far. Therefore the effect of composting and pasteurisation under varying conditions was tested on samples (ready-made compost mould) contaminated with Clavibacter michiganensis ssp. sepedonicus. Viable bacteria could be extracted after all experiments via bioassay on eggplants, and cultivated on semi-selective media from plant sap forming characteristic colonies. The viable pathogen could be extracted after composting for 6 days at maximum temperatures at 70 °C, 13 days at 55 °C and 90 min pasteurisation at 70 °C. It can be concluded that these sanitation treatments are not sufficient to inactivate Clavibacter michiganensis ssp. sepedonicus and the previous classification of treated residues in category 3 (probably high risk) could thus be confirmed.     

Fate of fluroxypyr in soil

Fluroxypyr-MHE (methylheptyl ester) was added to four soils and incubated at 26 ± 1°C and approximately 0.1 MPa moisture. After initial rapid hydrolysis of the ester to fluroxypyr, fluroxypyr degraded with half-lives of 12, 12, 23, and 7 days in Barnes loam, Catlin silt loam, Hanford sandy loam, and Mhoon clay soils, respectively. Two metabolites (4-amino-3,5-dichloro-6-fluoro-pyridin-2-ol and 4-amino-3, 5-dichloro - 6 - fluoro - 2 -methoxypyridine) were identified, with the pyridinol at its maximum concentration after 2 to 4 weeks of incubation, and the methoxypyridine after 8 weeks. Degradation rates of fluroxypyr and its pyridinol were not significantly altered by diurnally varying soil temperature (21°C to 32°C) or moisture, nor by the presence of growing grass. Methoxypyridine dissipation was more rapid under greenhouse conditions, suggesting that laboratory studies underestimated the dissipation rate of this metabolite.     

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.     

Suppression of bacterial wilt of tomato by soil amendment with mushroom compost containing <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> IUMC7

Bacillus amyloliquefaciens IUMC7 and its culture supernatant, which we previously found to suppress Fusarium wilt, were found here to have antimicrobial activity against Ralstonia solanacearum. In in vivo experiments, mushroom compost inoculated with IUMC7 significantly reduced disease severity in tomato plants over that in control soils. The R. solanacearum population decreased in soil inoculated with IUMC7. A TLC–bioautography assay showed that one of the antimicrobial substances produced by IUMC7 is likely an iturin-like lipopeptide. These results suggest that these antimicrobial compounds are responsible for disease suppression and that mushroom compost containing IUMC7 has potential as a biocontrol product.     

Diuron mineralisation in a Mediterranean vineyard soil: impact of moisture content and temperature

BACKGROUND: The diuron‐mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS: The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 °C/19.3% for maximum mineralisation rate and 21.9 °C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 °C versus 28 °C) or incubate (28 °C versus 20 °C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION: Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues. Copyright © 2010 Society of Chemical Industry     

Survival of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> in infected tissues of <Emphasis Type="Italic">Capsicum annuum</Emphasis> and in soils of the state of Pernambuco,Brazil

The survival of Ralstonia solanacearum A1-9^Rif race 1 phylotype I was studied in ten different soil types in the absence of the host plant as well as in infected tissues of the stem and root of bell peppers buried in the soil at 0, 5, and 15 cm. The survival time of R. solanacearum A1-9^Rif in the ten soil types ranged from 42 up to 77 days. Among the chemical and physical characteristics of the soil, clay content, residual moisture, and available water were positively correlated, and pH was negatively correlated, with survival time, population size at 42 days, and area under the population curve. The pathogen survival differed significantly in relation to the plant tissues, but not with respect to the incorporation depth of the infected tissues. The root tissue of bell pepper supported a larger bacterial population at 7 and 21 days (5 × 10⁴ and 3.1 × 10⁴ CFU g⁻¹ tissue, respectively) compared with the stem tissue (0.35 × 10⁴ and 0.48 × 10⁴ CFU g⁻¹ tissue, respectively) and also had a larger area under the population curve. On the other hand, the stem tissues presented a greater decomposition rate and pH compared with the roots. In conclusion, the different types of studied soils as well as the infected bell pepper tissues were considered potential primary sources of R. solanacearum inocula, but only for a short period.     

Conversion rates of aldicarb and its oxidation products in soils. I. Aldicarb sulphone

The rate of loss of aldicarb sulphone was studied in incubation experiments on soils from four plough layers and two deeper layers. In all instances the loss could be described by first-order kinetics in the first period of two to three times half-life. However, in a clay loam soil and a greenhouse soil a faster degradation rate was observed after the first 56 and 112 days of incubation respectively. The half-lives of sulphone in plough layer soils at 15°C ranged from 18 days in a clay loam to 154 days in a peaty sand. Conversion in deeper layers was considerably slower than in the corresponding top layers of the soil profile. In a silty layer at 70 to 90 cm depth the half-life at 15°C was 46 days, whereas in a sand layer at 90–110 cm no clear loss was found during the 294 days of incubation.     

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.