Translocation and Complex Formation of Root-applied 2,4-D and Picloram in Susceptible and Tolerant Species

Translocation and complex formation of ¹⁴C-labelled 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram) in seedlings of sunflower (Helianthus annuus L. var. uniflorus), rape (Brassica napus L. cv. Nilla), wheat (Triticum aestivum L. cv. Starke), and Norway spruce (Picea abies (L.) H. Karst.) were studied. The herbicides were absorbed through the roots from the nutrient solution, Picloram was well translocated to the shoots of the four species; while the acropetal translocation of 2,4-D was small except in rape. In 2,4-D-susceptible sunflower and rape and in picloramsusceptible sunflower and spruce the herbicides were recovered mainly in the uncomplexed form. In 2,4-D tolerant wheat and spruce most of the absorbed 2,4-D was converted into water-soluble or TCA-insoluble complexes. In picloram-tolerant wheat and in relatively picloram-tolerant rape, the absorbed picloram was also converted into complexes recovered predominantly in the water-soluble fraction. Most of the complexes released free herbicides by hydrolyzing in NaOH or HCI. The results further support the hypothesis that complex formation counteracts herbicide toxicity.     

Translocation and Complex Formation of Picloram and 2,4-D in Wheat Seedlings

Uptake, translocation and metabolism of ¹⁴C-labelled 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-dichlorophenoxyacetic acid (2,4-D) in seedlings of wheat (Triticum aestivum L.) were studied. The uptake of the herbicides through the upper surface of the first leaf was slow but was almost complete after nine days. Picloram was absorbed faster than 2,4-D. Picloram was also translocated into the stem and the untreated leaves to a greater extent than 2,4-D. Only small fractions of the activity were recovered from the roots and from the nutrient solution. Picloram and 2,4-D formed water-soluble conjugates in the tissues. These conjugates were very labile and hydrolyzed under release of the unchanged herbicides. The isotope from 2,4-D was also incorporated in an insoluble fraction, containing cell walls and proteins. Also from this fraction biologically active 2,4-D could be released by hydrolysis. The formation of the complexes was partly prevented by cycloheximide. It is suggested that herbicide detoxification through complex formation is of importance for the relatively low sensitivity of wheat to auxin herbicides.     

Colonisation of seedling roots by 2,4-D degrading bacteria: A plant-microbial model

The development of model plant-microbial associations between Gram negative soil microbes capable of degrading phenoxyacetate herbicides, such as 2,4-D and 2,4-D methyl ester, and the crops canola and wheat was described. Both an Acinetobacter baumannii pJP4 transconjugant and Alcaligenes eutrophus JMP 134 colonised non-parasitically on the roots of sterilised seedlings in a hydroponic system. Laser scanning confocal microscopy has shown that colonisation occurred both on the root surface and deeper inside the mucilage layer or inside some surface root cells. When 2,4-D was added to the hydroponic medium supporting the growth of those seedlings colonised by 2,4-D degrading bacteria, the gas chromatographic analysis showed a rapid decrease in the concentration of this herbicide. These bacteria colonising the root system were shown to be responsible for the degradation of 2,4-D. Plants inoculated with the 2,4-D degrading microbes were subsequently found to be less susceptible to damage by the herbicide in such hydroponic systems.     

Response by coccinellids to spatial variation in cereal aphid density

The objectives of this study were to determine if coccinellids adjusted their distribution within spring wheat fields in response to spatial variation cereal aphid density in the fields and to describe the patterns of cereal aphid population growth that resulted. Field experiments were completed in which the physical dimensions of patches infested with cereal aphids, cereal aphid density, and access to patches by coccinellids were varied. Aphid infestations consisted of naturally occurring densities (natural patches) and much greater densities created by supplementing patches with aphids (supplemented patches). Coccinellids were denied access to some supplemented patches (exclusion patches) but allowed unlimited access to others. Densities of adult Hippodamia convergens and Coccinella septempunctata were correlated with aphid density in patches whereas density of Coleomegilla maculata was not. Aggregation by coccinellids was independent of patch area. The realized aphid population growth rate (r) was lower in supplemented than natural patches in all four trials but was significantly lower in only one trial. The lower r in supplemented patches was not exclusively caused by coccinellid predation, and emigration of aphids from patches probably also contributed. r was significantly greater in exclusion patches than supplemented and natural patches, indicating that coccinellids markedly reduced aphid numbers in patches even when aphid density was extremely high. Received: February 17, 1999 / Accepted: February 1, 2000     

Translocation and Complex Formation of Picloram and 2,4-D in Rape and Sunflower

Uptake, translocation and complex formation of ¹⁴C-labelled 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-dichlorophenoxyacetic acid (2,4-D) in seedlings of rape (Brassica napus L. cv. Nilla) and sunflower (Helianthus annuus L. var. uniflorus) were studied. Sunflower is susceptible both to 2,4-D and picloram, while rape is susceptible to 2,4-D but more tolerant to picloram. The uptake of the herbicides through the leaves was almost complete in both species. Translocation of 2,4-D into the roots took place more readily than that of picloram. In sunflower about 50 per cent of the applied 2,4-D was extruded through the roots into the nutrient solution after 9 days. In the picloram-treated sunflower most of the activity was found in the aerial parts, while in picloram-treated rape most of the activity still occurred in the treated leaf after 9 days. No activity at all was found in the roots or in the nutrient solution of the picloram-treated rape seedlings. While the major part of 2,4-D always was found in the state of free herbicide, a large fraction of picloram was rapidly bound into water-soluble complexes. This binding was especially pronounced in rape. Separation by paper chromatography showed that different radioactive compounds were formed. Most of these could be hydrolyzed, thereby releasing free herbicide. The results support the hypotheses that complex formation could counteract herbicide translocation and toxicity of auxin herbicides.     

Adult Coccinellid Activity and Predation on Aphids in Spring Cereals

Improved understanding of coccinellid activity and predation on aphids in the field could clarify their potential in aphid biological control. Our objective was to determine the influence of abiotic and biotic factors on activity and predation by adults of three coccinellid species (Hippodamia convergens Guerin-Meneville, H. tredecimpunctata tibialis (Say), and Coleomegilla maculata DeGeer) in spring cereal fields. The proportion of time coccinellids spent searching was correlated with air temperature, aphid density, and time of day. The relationship between searching and these variables differed among species. Mean walking speed ranged from 66.4 cm/min for C. maculata to 83.2 cm/min for H. tredecimpunctata and increased with temperature for all species. The frequency of short flights (<2 m) by beetles increased with temperature and decreased with increasing aphid density for all species, but the relationship of short flight frequency to these variables differed among species. The frequency of long flights (>2 m) was similar for all species and influenced by temperature and calendar date. The frequencies with which aphids were encountered and eaten were correlated with aphid density and temperature for H. convergens and H. tredecimpunctata. Despite over 250 h spent observing adult coccinellid behavior in the field, predation data were insufficient to develop a useful predation model.     

Deleterious effect of herbicides on waterhyacinth biocontrol agents Neochetina bruchi and Alternaria alternata

The integration of biological and herbicidal methods is advocated to manage waterhyacinth, but this can only be achieved when herbicides are nontoxic to the biocontrol agent. Therefore, laboratory experiments were conducted to determine the toxic effect of herbicides on the insect biocontrol agent, the waterhyacinth weevil, Neochetina bruchi Hustache, and phytopathogen, Alternaria alternata, with two commonly used herbicides, glyphosate and 2,4-dichlorophenoxy acetic acid at three recommended doses. The herbicides were sprayed on the waterhyacinth weevils and added to the nutrient media of A. alternata. 2,4-D caused higher weevil mortality (6.7, 13.3 and 15.6%) as compared to glyphosate (3.3, 5.6 and 11.1%), at three doses over 72 h. There was also a decrease in feeding in the herbicide treated leaves. When the weevils were allowed to move freely between the herbicide treated and untreated plants, higher orientation of the weevils was found on the untreated waterhyacinth than on the treated ones. Neither of the two herbicides actually killed the fungus but both inhibited its growth. Glyphosate though, delayed mycelial growth yet stimulated sporulation while 2,4-D inhibited both growth and sporulation. Glyphosate at low concentration did not affect the virulence of A. alternata, while fungi grown on 2,4-D amended plates lost their virulence.     

Natural Fusarium Grain Infection Level in Wheat, Barley and Oat after Early Application of Fungicides and Herbicides

In Norway, early application of fungicides against cereal leaf diseases (before Zadoks 60) is common practice amongst farmers. Whether this procedure has any effect on Fusarium infection of the mature grain has been little investigated. To evaluate effects on Fusarium grain infection, cereal grains were sampled during 1996, 1997 and 1998 from 12 field trials where early spraying against fungal diseases in spring wheat, spring barley and oats was carried out. Percentage infected grains and frequency of different Fusarium species was analysed in every grain sample. The effect of fungicides, glyphosate and postemergence herbicides on Fusarium grain infection was studied. Significant increase in Fusarium infection was detected in fungicide‐treated plots compared with untreated plots. Fusarium avenaceum and F. tricinctum were the most frequent species detected. The internal ranking of Fusarium species remained the same after spraying. No significant effects were found on the level of Fusarium infection after glyphosate treatment in autumn or herbicide treatment during the growing season.     

Influence of Auxin-Like Herbicides on Tobacco Mosaic Virus Multiplication

Tobacco (Nicotiana tabacum L., cv. Samsun) leaf discs inoculated with tobacco mosaic virus (TMV) were treated with auxin-like herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), 3-amino-1,2,4-triazol (Amitrol) and 6-chloro-2-ethylamino-4-isopropylamino-1,3,5-triazine (Atrazin). All herbicides in the concentration of 10^–7 M enhanced the virus content (MCPA to 227.4 %, Amitrol to 218.1 % and Atrazin to 257.3 % of values found in TMV-infected, herbicide untreated discs). The 2,4-D alone did not affect the activity of the glucose-6-phosphate dehydrogenase and ribonucleases, but the 2,4-D treatment together with TMV infection raised their activities twice as high as in the untreated control discs. Polyacrylamide gel electrophoresis of acidic extracellular proteins washed from leaf discs treated with 2,4-D did not prove the induction of PR-proteins.     

Potassium influx and efflux of 2,4-D- and MCPA-treated rice plants

Summary A study was made of the effects of the herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (4-chloro-2-methyl-phenoxyacetic acid) on ion uptake, leakage and growth of rice seedlings. Using isotopically-labelled solutions containing different concentrations of 2,4-D or MCPA, it was established that 10^–4 M 2,4-D or MCPA effectively inhibited potassium ion uptake, while K-ion leakage from the roots occurred only at 10^–3 M. The growth of the rice seedlings was markedly retarded even at low (10^–6 M) concentrations, and the roots and shoots showed different tolerances to the herbicide. At 10^–8 M herbicide, the effects were not injurious, but rather favourable. Reduction in root length by herbicides was not in accordance with dry-matter production.     

The effect of weeds on the numbers of hoverfly (Diptera: Syrphidae) adults and the distribution and composition of their eggs in winter wheat

The abundance and species composition of syrphid adults in herbicide-treated and untreated headlands was recorded in a replicated within-field experiment conducted over a two-year period. The highest numbers of the most abundant syrphid species, Episyrphus balteatus, were recorded in the untreated headland strips. Analysis of the behaviour of the adult flies showed that they were retained in the untreated strips because they were foraging on the flowering non-crop plants. The distribution of syrphid eggs between herbicide treated and untreated headland replicates was examined. A significant positive relationship between the numbers of eggs per aphid and weed density was detected during June in the second year of the study. This is in part attributed to the tendency of Melanostoma females to oviposit on non-crop plants. The implications of the implementation of a modified herbicide regime in the headlands of cereal fields for the biological control of cereal aphids by syrphid larvae is discussed.     

Evidence for utilization of Diptera in the diet of field-collected coccinellid larvae from an antibody-based detection system

Aphidophagous coccinellid larvae have a wide range of potential prey in alfalfa and during times of low aphid abundance, larvae may supplement their diet with alternative prey. To understand the effects of the seasonal aphid availability on alternative prey use, an order-specific monoclonal antibody, DrosW-VI-B8, was used to examine the frequency of dipteran predation by these important natural enemies. Over 400 larvae were hand-collected from alfalfa and, in parallel, arthropod abundance was recorded. Harmonia axyridis and Coccinella septempunctata larvae were abundant early in the season when aphid populations were at their peak and Coleomegilla maculata larvae were collected later in the season when potato leafhoppers were abundant in the alfalfa. A relatively low proportion of field-collected H. axyridis, C. septempunctata, and C. maculata tested positive for dipteran proteins throughout the season. Similar to prior studies examining stage differences in coccinellid food breadth, older instars tested positive for dipteran proteins (3rd instar, 6% positive; 4th instar, 7% positive) but no early instars screened positive. This study provides a valuable insight into the trophic linkages that exist between coccinellid larvae and Diptera.     

Studies on synthetic hybrids of british species of Senecio: I Senecio viscosus L. × S. vulgaris L.

Summary

Four aquatic hyphomycetes and one terrestrial fungus were examined for their responses to the phenoxy herbicides (±)-MCPP and 2,4-D as both single and binary preparations with respect to hyphal extension, sporulation and respiration. Hyphal extension of all species was unaffected at concentrations less than 100 mg l^?1. At higher concentrations there was a variable inhibitory response to the herbicides but no clear pattern was observed between the five fungi. The binary herbicide mixture had a weak synergistic effect on inhibition of growth rate. For the four aquatic hyphomycetes sporulation was reduced at several herbicide concentrations, but there was no consistent reduction over the experimental period. Flagellospora curvula and Clavariopsis aquatica showed increased sporulation at 100 and 1000 mg l^?1 for only some herbicide combinations. The respiration rates of the fungi varied with species and herbicide concentration and ranged between stimulation at 100 mg l^?1 to inhibition at 4000 mg l^?1. The results indicate that the five fungi are not likely to be severely effected by the phenoxy herbicides at concentrations normally occurring in the field. The possible effects of these herbicides on nutrient cycling are briefly discussed.     

Competitive interactions between an exotic and a native ladybeetle: a field cage study

We conducted field‐cage studies on the direct interactions between a coccinellid species native to North America, Coleomegilla maculata De Geer, and a species introduced from Asia, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). We compared the mortality and weight gain of larvae of both species in field cages that enclosed one or both species with corn plants containing high or low aphid numbers. We did not find a significant effect of the presence of H. axyridis on the survival or weight gain of C. maculata, but H. axyridis larvae weighed more when kept with C. maculata for 5 days than when kept with equal numbers of conspecifics. This suggests that intraspecific competition was stronger for H. axyridis than the interspecific competition with C. maculata. The spatial distribution of C. maculata over the plants differed between single‐species and two‐species treatments in a manner that suggested that this species avoided interactions with H. axyridis.     

Effect of certain herbicide treatments on pasture composition and inoculum of the take-all fungus

The improvement of pastures by the use of a range of herbicides to eliminate grasses, and their effect on populations of the take-all fungus (Gaeumannomyces graminis vartritici=Ggt) were studied in the field (at Esperance Downs, on the south-coast of Western Australia) from 1982 to 1985. Field trials were conducted to evaluate three herbicide treatments (2,4-D amine+propyzamide; 2,4-D amine+paraquat; paraquat/ diquat) and an unsprayed control. A pot trial involving these treatments with two levels of nitrogen was undertaken to confirm treatment effects observed in the field trial. All herbicide treatments resulted in reduced grass composition of pastures, in both the year of spraying and in the second year of pasture, but reduced dry matter production in the year of spraying. In the year of spraying, however, inoculum ofGgt was reduced (P<0.1) only following the 2,4-D amine+propyzamide treatment and was greater (P<0.1) after 2,4-D amine+paraquat treatment than the unsprayed treatment. Despite reduced grass levels in the herbicide-treated plots in the second year of pasture,Ggt inoculum did not differ between treatments, nor did it after a wheat crop which followed a second year pasture. There was high correlation (P<0.001) between disease levels and dry weights of grasses in the pot trial. There was significantly less (P<0.001) grass in pots treated with herbicides compared to the unsprayed control but no difference (P>0.05) was evident between treatments. Inoculum levels were lower (P<0.05) in the treated pots than the unsprayed control with no evidence of differences among treatments (P>0.05). Nitrogen level had no effect on disease (P>0.05). All herbicide treatments tested reduced grass level and total dry matter, both in the field and in pots. Whereas in the pot trial reduced grass levels resulted in reducedGgt inoculum, in the field such a reduction occurred only with the 2,4-D amine+propyzamide treatment and only in the year of spraying. Herbicide treatments had no effect onGgt inoculum in second year of pasture or crop. Unknown soil and environmental factors in the field precluded a simple relationship between grass level in pasture and subsequent level ofGgt inoculum, and where such a relationship did occur (2,4-D amine+propyzamide treatment) it appeared to be shortlived.     

Mode of action of herbicidal derivatives of aminomethylenebisphosphonic acid. I. Physiologic activity and inhibition of anthocyanin biosynthesis

N-Pyridylaminomethylenebisphosphonic acids constitute a class of promising herbicides. Since their mode of action at the cellular level is still poorly understood, we studied the influence of N-pyridylaminomethylenebisphosphonic acids on plant growth, at the whole plant and undifferentiated tissue levels, using seedlings and cell suspension cultures of mono- and dicotyledonous species. These compounds exhibited strong herbicidal properties, being equipotent with the popular herbicide glyphosate. Since they also depressed buckweed anthocyanin biosynthesis, the shikimate pathway could represent a site of action of N-pyridylaminomethylenebisphosphonic acids.Abbreviations EPSP 5-enol-pyruvylshikimate-3-phosphate - 2,4-D 2,4-dichlorophenoxyacetic acid.     

Engineering 2,4-D resistance into cotton

Summary To reduce damage by drift-levels of the herbicide 2,4-dichlorophenoxyacetic acid, we have engineered the 2,4-D resistance trait into cotton (Gossypium hirsutum L.). The 2,4-D monooxygenase gene tfdA from Alcaligenes eutrophus plasmid pJP5 was isolated, modified and expressed in transgenic tobacco and cotton plants. Analyses of the transgenic progeny showed stable transmission of the chimeric tfdA gene and production of active 2,4-D monooxygenase. Cotton plants obtained were tolerant to 3 times the field level of 2,4-D used for wheat, corn, sorghum and pasture crops.     

Influence of wheat and oat cultivars on the development of the cereal aphid parasitoid Aphidius rhopalosiphi and the generalist aphid parasitoid Ephedrus plagiator

The effects of three wheat cultivars and two oat cultivars on the development of the cereal aphid parasitoid Aphidius rhopalosiphi De Steph. and the generalist aphid parasitoid Ephedrus plagiator (Nees) (Hymenoptera: Braconidae) were evaluated in the laboratory. The level of hydroxamic acids, a family of secondary metabolites that can affect the mean relative growth rate of cereal aphids in cereals, were measured in the different cultivars. The parasitoids were reared in Sitobion avenae (F.) (Homoptera: Aphididae), using plants grown under greenhouse conditions. A. rhopalosiphi showed a longer developmental time on wheat relative to oat cultivars. This effect was accounted for by a significant increase in the time from oviposition to pupation (mummy formation), while the duration of the pupal stage remained constant between treatments. No further effects were observed in other variables evaluating A. rhopalosiphi performance, such as adult longevity, adult body weight and secondary sex ratio. The generalist E. plagiator did not show significant differences in any of the variables analysed, both between cultivars and cereal species. Hydroxamic acids levels correlated negatively with mean relative growth rates of S. avenae, but positively with the observed developmental time of A. rhopalosiphi. The results are discussed in terms of tritrophic effects and the development of breeding programmes trying to improve plant resistance to aphids.     

The potential of hydroxamic acids in tetraploid and hexaploid wheat varieties as resistance factors against the bird‐cherry oat aphid,Rhopalosiphum padi

The potential for exploiting natural wheat resistance to control the cereal aphid Rhopalosiphum padi, the most important aphid pest of small grain cereals in the UK, was investigated as an alternative approach to the use of insecticides. The investigation focussed on a group of secondary metabolites, the hydroxamic acids or benzoxazinones, present naturally as glucosides, but which hydrolyse on tissue damage to give biologically active aglycones, e.g. 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one (DIMBOA) which are associated with natural plant defence. These can be important for resistance against insects, fungi, bacteria and nematodes for a range of cultivated monocotyledonous plants and could ultimately be combined with other defence mechanisms to provide a general approach to cereal aphid control. Levels of hydroxamic acids, particularly DIMBOA‐glucoside, were determined in hexaploid (Triticum aestivum) and tetraploid (Triticum durum) wheat varieties and differences were found between species and varieties. The effect of feeding by R. padi on the level of hydroxamic acids in the leaf tissue was also investigated. Thus, after 24 h of aphid feeding, as an apparently localised hydrolytic defence reaction in the leaf, levels of DIMBOA‐glucoside decreased noticeably. When aphids were fed on sucrose solution containing low doses of DIMBOA there was a significant mortality compared to the sucrose control. However, the levels of and variation in hydroxamic acids in the wheat varieties investigated were insufficient for significant differences in aphid behaviour and development.