Selective herbicides for establishing weed-free grass: The effect of mixtures and sequences of herbicides, including ethofumesate and methabenzthiazuron

Two field experiments compared various sequences of ethofumesate, methabenzthiazuron and mecoprop, and mixtures of metamitron, ethofumesate and methabenzthiazuron for their control of Poa annua L. and Stelluria media (L). Vill. during the establishment of autumn-sown perennial ryegrass (Lolium perenne L.). In experiment 1 pre-emergence treatments required a second, post-emergence spraying to give complete control of P. annua. Grass seedlings reappeared in early spring following ethofumesate treatment, but populations built up earlier where methabenzthiazuron had been used. The most successful treatment was ethofumesate at 1.4 kg a.i. ha^?1 followed by 0.7 kg a.i, ha^?1 in spring. Methabenzthiazuron at 0.8 kg a.i. ha^?1 followed by ethofumesate at 0.7 kg a.i. ha^?1 in December was also effective. Methabenzthiazuron at 1.6 kg a.i. ha^?1 damaged ryegrass but was effective as a secondary treatment at lower doses in spring. Most treatments controlled S. media satisfactorily, but this sometimes increased the yield of P. annua. Metamitron greatly reduced tiller numbers of P. annua in experiment 2, especially when sprayed with methabenzthiazuron. Only treatments which included ethofumesate controlled S. media adequately but there was no advantage in combining this herbicide with any other for controlling P. annua.     

A study of competition between seedlings of gorse (Ulex europaeus L.) and perennial ryegrass (Lolium perenne L.) by means of a replacement series experiment

Competiton between seedlings of gorse (Ulex europaeus L.) and perennial ryegrass (Lolium perenne L cv. Grasslands Nui) was studied in a replacement series experiment under glasshouse conditions. Without cutting, the shoot growth of gorse in monoculture exceeded that of ryegrass over 22 weeks but was reduced more by competition from ryegrass than the grass growth was reduced by competition from gorse. The root system of gorse was small compared with that of ryegrass and was further reduced by competition. Cutting three times at 2 or 4 cm reduced the total growth of both species and gorse was affected more than ryegrass. With grass, however, the ‘growth between succeeding cuts declined faster than that of gorse and in the final harvest period, gorse in monoculture oulyielded ryegrass. The relative crowding coefficients of gorse were low compared with those of ryegrass and their products consistently exceeded 1.0. The results are discussed in relation to lirmiting seedling establishment of gorse in the field.     

Response of spring cereal crops to soil residues of ethofumesate*

For evaluation of soil residues of ethofumseate [(±)2-ethoxy-2,3-dihydro-3,3-dimethylbenzofuran-5-yl-methylsulphonate], spring barley (Hordeum vulgare L.) and spring wheat (Triticum aestivum L.) were sown in soil planted 11 months previously with sugar-beet (Beta vulgaris L.) and previously treated with band or broad-cast applications of the herbicide at rates of 1.68-4.48 kg/ha. The height of barley and wheat was suppressed only where ethofumesate was applied broadcast and the soil was not ploughed after sugar-beet harvest. Three months after sowing, the 4.48 kg/ha rate suppressed the height of barley 18% and wheat 34%. In another experiment, barley grew normally on soil treated the previous year with pre-planting and post-emergence applications of ethofumesate where ploughing followed sugar-beet harvest. For all treatments, yields of straw and grain were not significantly lower than those of the untreated check plots. The dissipation of ethofumesate 24 weeks after application to sugar-beet was 89–100% when applied on a band compared to 85-95% when applied broadcast.     

Sugarbeet tolerance of post-emergence applications of desmedipham and ethofumesate*

Tolerance of sugarbeet (Beta vulgaris L.‘Mono-Hy Al') to post-emergence treatments of ethofumesate [(±)2-ethoxy-2,3-dihydro-3,3-dimethylbenzofuran-5-yl-melhansulfonate] and desmedipham [(3-ethoxy-carbonylamino)phenyl-N-phen-ylcarbamate] was studied in the glasshouse and in the field at several growth stages. The response of sugarbeet to these herbicides was dependent on the growth stage of the plants and the amount of desmedipham in the mixture. Foliar growth was suppressed most when the herbicides were applied at the cotyledon stage; however, recovery from herbicide injury was rapid. Tolerance of sugarbeet increased considerably from the cotyledon stage to the six-leaf stage. At equivalent herbicide rates, sugarbeet were more tolerant to ethofumesate than desmedipham and their response to mixtures of the herbicides was governed mainly by the rate of desmedipham. Root yields were reduced significantly by the herbicides only when sugarbeet were treated in the cotyledon stage with mixtures that contained 1.12 kg/ha of desmedipham.     

Growth of seedling Achillea millefolium L. (yarrow) in association with pea (Pisum sativum L.)

When Achillea millefolium L. (yarrow) seedlings were grown in the field in association with a pea (Pisum sativum L.) crop vegetative growth of yarrow was significantly reduced by 6 weeks after emergence. Flowering was totally suppressed while the pure stand of yarrow developed flower clusters at 13 weeks after seedling emergence. Rhizome development occurred at 8 weeks after seedling emergence in the pure stand, but not until 15 weeks when grown with pea. The early suppression of seedling yarrow in a glasshouse experiment was associated with root interference, although by 5 weeks shoot interference by pea plants was important in reducing yarrow growth. The greatest suppression of yarrow occurred when both roots and shoots of the two species were allowed to interfere. Yarrow had low aggressivity against pea when grown in various combinations in a replacement series experiment in the glasshouse.     

Reactions of Cowpea to Meloidogyne incognita in Eastern Nigeria

Abstract

One hundred and three cultivars of cowpea (Vigna unguiculata) were rated in replicated trials in the field and glasshouse for their reactions to the root-knot nematode, Meloidogyne incognita. Forty-one cultivars consistently showed some resistance to the nematode in both field and glasshouse trials; 25 were consistently susceptible and the remaining 37 were inconsistent.     

Development of a rapid,accurate glasshouse bioassay for assessing fusarium wilt disease responses in cultivated Gossypium species

A rapid glasshouse‐based bioassay method to screen large numbers of cotton plants for responses to Fusarium oxysporum f. sp. vasinfectum (Fov) was developed. Different Fov inoculum concentrations and methods of inoculation were assessed using resistant and susceptible cotton cultivars. Cotton seeds were planted directly into Fov‐inoculated soil. Studies of seed germination, seedling establishment, seedling mortality and fusarium wilt symptoms (i.e. stunting, foliar symptoms and vascular browning) were performed to optimize the bioassay parameters. Growing seedlings in Fov‐inoculated soils at 5 × 10⁴ or 1 × 10⁵ CFU g^?1 soil, in individual seedling tubes with 12 h at 28–30°C and 12 h at 15–18°C, gave consistent results when assessing Fov disease responses 6 weeks after inoculation. When fusarium wilt resistance ranks (FWRRs) and vascular browning index (VBI) means of 18 Australian and other cotton cultivars from the Fov glasshouse bioassay were compared against their fusarium field performance ranks (F‐ranks), assessed on adult plants for cotton cultivar release, Pearson’s correlation was highly significant for both comparisons. The level of congruence between field and glasshouse data indicated that this protocol should be an effective tool for large‐scale screening for Fov‐resistance responses in diverse germplasm and breeding populations and for advancing genetic research to develop molecular markers for Fov resistance in cotton.     

Aspects of the selective phytotoxicity of methazole. I. Measurements of species response, spray retention and leaf surface characteristics

The responses of onion (Allium cepa). Veronica persica, Matricaria matricarioides and Stellaria media to post-emergence applications of methazole were measured in field and glasshouse experiments. Stellaria media was the most susceptible species and V. persica the least. Plants of all species became more tolerant the larger they were at the time of treatment, and this was most pronounced in onion. Onion generally retained less spray per unit of dry weight than the other three species and retention was less on old compared with young plants, whereas with the weed species, this did not change appreciably with age. There was a progressive increase in the amount of structured crystalline wax on successive onion leaves which resulted in larger contact angles between droplets and the leaf surfaces and lower spray retention per unit of dry weight. There was less wax development on the leaf surfaces, increased spray retention, and increased susceptibility to methazole in onion treated pre-emergence with ethofumesate thus confirming that these factors are interrelated. While the increased tolerance of onion to methazole with age could be explained in part by decreased retention of herbicide, this was not so for the weed species, and other factors must determine their change in tolerance with age.     

<Emphasis Type="Italic">Lupinus luteus</Emphasis>, a new host of <Emphasis Type="Italic">Phytophthora cinnamomi</Emphasis> in Spanish oak-rangeland ecosystems

Phytophthora cinnamomi is an aggressive pathogen on Lupinus luteus (yellow lupin), causing root rot, wilting and death of this crop, common in oak-rangeland ecosystems ('dehesas') in south-western Spain. The oomycete, the main cause of Quercus decline in the region, was isolated from roots of wilted lupins in the field. Artificial inoculations on four cultivars of L. luteus reproduced the symptoms of the disease, both in pre- and post-emergence stages, recovering the pathogen from necrotic roots. These results suggest the potential of yellow lupin as inoculum reservoir for the infection of Quercus roots. This is the first report of P. cinnamomi as root pathogen of L. luteus.     

The interaction between planting depth of four winter wheat cultivars, Alopecurus myosuroides Huds. and Bromus sterilis L. and their susceptibility to post-emergence applications of isoproturon and chlorotoluron

Seeds of four winter wheat cultivars, Slejpner, Galahad, Avalon and Penman, were sown at depths ranging from 6–75 mm in soil in pots, and isoproturon or chlorotoluron was then applied to the soil surface. For chlorotoluron-treated plants (both pre- and post-emergence) the dose required to produce a 50% effect (ED₅₀) was unaffected by depth of planting. In contrast, for isoproturon applied pre-emergence, the ED₅₀ for both Avalon and Slejpner was strongly affected by sowing depth. Although chlorotoluron was much more active in a second experiment when applied post-emergence to Slejpner wheat, the ED₅₀ for both herbicides increased with greater depth of sowing. Protection of wheat from isoproturon damage by deeper planting was enhanced if the adsorption capacity of the soil was raised from K_d 0.5 to 2.0 by incorporation of activated charcoal in the soil. Isoproturon entry into plants (as measured by the effect on rate of photosynthesis) was slower in those that had been sown deeper and were growing in more adsorptive soils, but there was no obvious relationship between these observations and isoproturon distribution in the soil profile. In nutrient culture the four wheat cultivars responded similarly to a range of doses of isoproturon. The chlorotoluron-sensitive cultivars, Slejpner and Galahad, were damaged by much lower doses of chlorotoluron than were Avalon and Penman. Bromus sterilis L. responded similarly to wheat with regard to its interaction with isoproturon and planting depth. Alopecurus myosuroides Huds., however, was less damaged by isoproturon when the zone above the seed was protected from the herbicide by growing the shoot through a plastic straw.     

The biology of African feather grass (Pennisetum macrourum Trin.) in Tasmania, I. Seedling establishment

Seedling establishment of Pennisetum macrourum was studied in a series of glasshouse and field experiments. Maximum germination of 88% occurred at a constant temperature of 30C. In the glasshouse, highest seedling establishment was obtained from seeds buried 1 cm deep; it was less than 25% from seeds sown on the soil surface. Dormancy was induced in seeds buried 8 cm deep but only 6.4% remained viable after 6 months. Few viable seeds of P. macrourum were found in the soil and only one seedling was observed to establish in the field over a 20 month period. Up to 98% of seedlings transplanted into the field established successfully. The results suggest that reproduction by seed would not be a major problem in the control of P. macrourum.     

Combining competition from Lolium perenne and an insect–fungus combination to control Rumex obtusifolius seedlings

Although adult Rumex obtusifolius are problematic weeds, their seedlings are poor competitors against Lolium perenne, particularly in established swards. We investigated the possibility of using this weakness to augment control of R. obtusifolius seedlings with combinations of Gastrophysa viridula (Coleoptera: Chrysomelidae) and the rust fungus Uromyces rumicis. Rumex obtusifolius seedlings were grown in competition with L. perenne sown at different rates and times after R. obtusifolius: they competed successfully with L. perenne when sown 21 days before the grass. Sowing both species at the same time resulted in a dominant grass sward, with R. obtusifolius becoming dominant when sown 42 days prior to L. perenne. Grass sowing rate had no effect on R. obtusifolius growth or biomass. A second experiment investigated how competition from L. perenne sown 21 days after R. obtusifolius combined with damage from G. viridula and/or U. rumicis (applied at either the 3–4‐ or 10–13‐leaf stage, or at both stages) affected the growth and final biomass of R. obtusifolius. Beetle grazing at the latter leaf stage was the only treatment that reduced R. obtusifolius biomass, although rust infection at the earlier application led to an increase in shoot and root weight. The results are discussed in terms of the potential for use of these agents in the field.     

Differences between spring wheat cultivars in tolerance to <Emphasis Type="Italic">Fusarium</Emphasis> seedling blight under organic field conditions

Use of Fusarium-infected seed for cereal crops results in a reduced plant density due to seedling blight. This is especially a problem in organic agriculture, for which currently no practical seed disinfection methods are available. In the present paper we investigated whether spring wheat cultivars differ in tolerance to seedling blight in vivo, whether the possible differences could be linked to cultivar differences in initial growth rates, and whether differences in weed infestation were related to differences in emergence. Seed six spring wheat cultivars (Melon, Lavett, SW Kungsjett, Epos, Pasteur, Thasos), containing three Fusarium infection levels were obtained and sown in two field experiments in 2006 and 2007 and in an outdoor pot experiment in 2007. Results indicated that the six spring wheat cultivars differed in their tolerance to seedling blight, and consequently in the percentage of emergence of their seeds. The relative levels of tolerance to seedling blight of the six cultivars were robust in the three experiments performed. No clear relationship between initial growth rates and tolerance was found. In our experiments, no early and homogenous weed pressure was present, but in the 2007 field experiment a relationship between initial seedling emergence and weed infestation after anthesis was determined. Based on the presented results we suggest that additional to resistance to Fusarium head blight (FHB), differences in tolerance to seedling blight should also be considered during selection of wheat cultivars for organic agriculture.     

The fungicide tridemorph as a selective herbicide for the control of Holcus lanatus in ryegrass and of Bonus sterilis in barly

The potential of the fungicide tridemorph selectively to control established plants of Holcus lanatus L. in ryegrass (Lolium perenne L) and Bromus sterilis L. in barley (Hordeum vulgare L.) was examined in glasshouse trails. A dose of 4.2 kg ha^?1 tridemorph gave selectively between H. lanatus and ryegrass similar to, but more costly than, that which would be provided by 1.2 kg ha^?1 asulam. B sterilis was more sensitive to tridemorph than was barley. Two additives, glycerol and the oil-surfactant mixture ‘PF’ enhanced this selectivity when tridemorph was applied at 2.1 kg ha^?1.     

Asulam mixtures for weed control in flax

Five field experiments were conducted from 1972 to 1975 to evaluate weed control in flax (Linum usitatissimum L.) using post-emergence treatments of asulam [methyl (4-aminobenzenesulphonyl) carbamatel alone and in combination with other herbicides. The ¹⁴C-asulam absorption by leaf segments and roots of glasshouse grown wild oats (Avena fatua L.) was also investigated. Asulam at 1.12 kg/ha gave good wild oat control and acceptable control of green foxtail (Setaria viridis (L.) Beauv.). However, wild oat control was poorer when asulam was combined with other herbicides: on a 3-year average, as compared with asulam alone at equal rates, the asulam+MCPA mixture resulted in a greater antagonism and a significant 6% reduction in flax seed yield, whereas the asulam+bromoxynil/MCPA mixture gave the least antagonistic effect, improved broadleaf weed control and increased yield by 13%. In mixtures, the potassium salt of MCPA was more compatible with asulam for weed control than the amine form. Both leaf segments and roots of wild oats absorbed and distributed less ¹⁴C-asulam from solutions containing MCPA than from those containing bromoxynil or bromoxynil/MCPA.     

Resistance of lettuce and related species to anthracnose (Microdochium panattonianum) in Australia

All 35 commercial lettuce cultivars available in Australia, two cultivars of chicory, one cultivar of endive and single accessions of Lactuca saligna, L. serriola and Sonchus oleraceus were tested for susceptibility to Microdochium panattonianum under glasshouse and field conditions. Under controlled environmental conditions log lesion density on cv. Cos Verdi was linearly related to log inoculum concentration. Inocula from L. saliva and L. serriola were cross-infective but did not infect the single accessions of L. saligna and S. oleraceus tested. All lettuce cultivars were susceptible. Some cultivars showed a relatively greater increase in susceptibility than others at an increased inoculum concentration. Latent periods for different cultivars ranged from 3 to 7 days under glasshouse conditions and from 8 to more than 17 days in a field trial. There was poor correlation between glasshouse and field trials for the disease rating of cultivars. Chicory, endive and the L. saligna accession were immune (symptomless) and the L. serriola accession was highly resistant. The results indicate that L. saligna, L. serriola. endive and chicory are possible sources of genes for resistance to M. panattonianum.     

Weed control in glyphosate-tolerant sugarbeet (Beta vulgaris L.)

The effect of glyphosate on weeds was evaluated in greenhouse bioassays with five weed species and compared with a commercial mixture of phenmedipham and ethofumesate. Glyphosate was more active than a mixture of phenmedipham and ethofumesate on the weeds. Solanum nigrum was the most sensitive species to both herbicide treatments. The relative potency of glyphosate between the weeds showed consistency at 50% and 90% control levels for four out of five weed species, which could be ranked independently of control level because of similar response curves. In a field trial on sugarbeet genetically engineered to acquire glyphosate tolerance, a total of 720 g a.i. ha^?1 of glyphosate applied in one, two or three applications gave similar or superior control of weeds to a total of 3.17 kg a.i. ha^?1 mixture of metamitron, phenmedipham and ethofumesate applied in three repeated applications.     

Inhibition of seed germination and early stem elongation of Cuscuta australis by ethofumesate

Hmergence of dodder (Cuseuta australis R. Br.) was unexpecledly prevented in plois of a sugarbeet field where ethofumesate had been applied at 1.6 Kg/ha. Appropriate laboratory tesls have shown that ethofumesate is a potent inhibitor of dodder seed germination (I D₅₀= 10 μg/ml) and of early stem elongalion (ID₅₀= 73μg/ ml). Wheat. a standard susceptible species to field applications of ethofumesate, is equally susceptible to inhibition of stem elongation (ID₅₀=68 μg/ml), but it is far less susceptible to inhibition of germination (I D₅₀=188 μg/ml). Compared to propyzamide. ethofiimesate is a stronger inhibitor of germination. Metolachlor and Hercules 22234 [eihyl N-chloroacetyl-N-(2,6-diethylphenyl) aminoacetate] are also active in inhibiting dodder germination and stem elongation, but at higher concentrations than ethofumesate. Current methods of controlling dodder in sugarheets may be improved with inclusion of pre-emergence use of ethofumesate.     

Allelopathic potential of Acacia melanoxylon on the germination and root growth of native species

Water extracts that were obtained from the flowers and phyllodes of Acacia melanoxylon were used to determine their allelopathic potential in relation to the germination and seedling growth of the native species, cocksfoot (Dactylis glomerata), perennial ryegrass (Lolium perenne), and common sorrel (Rumex acetosa), as well as a general biotest specie, lettuce (Lactuca sativa), in laboratory bioassays. The flowers and phyllodes of A. melanoxylon were soaked separately in distilled water in a ratio of 1:1 (w/v) for 24 h in order to prepare the aqueous extracts. Distilled water was used as the control. The seeds of the target species were germinated in Petri dishes and counted daily for up to 7 days. The A. melanoxylon flower extract (100%, 75%, and 50%) decreased the seed germination of D. glomerata, R. acetosa, L. perenne, and L. sativa. The flower extract caused the most reduction in the germination index and germination speed in D. glomerata, L. perenne, and L. sativa. The mean LC₅₀ value of the A. melanoxylon flower and phyllode extracts in relation to the germination inhibition of L. perenne was 43% and 41%, respectively, 40% and 38%, respectively, in R. acetosa, and 53% and 41%, respectively, in L. sativa. All four concentrations of the flower extract proved to be more phytotoxic than the phyllode extract, reducing the root length of all four species, while the phyllode extract decreased the root length of L. perenne and R. acetosa at the 100% concentration. The L. perenne and D. glomerata grass seeds were more sensitive regarding germination, as compared to L. sativa and R. acetosa. The flower aqueous extract of A. melanoxylon was more phytotoxic, as compared to the phyllode aqueous extract, even at the lowest concentration (25%).     

Establishment of Senecio jacobaea L. from seed in grassland and in boxed swards

The effects of a high or a low level of nitrogen fertilizer and the presence or absence of a grass-suppressing herbicide (propyzamide) upon the establishment of Senecio jacobaea L. (common ragwort) in three sizes of bare soil patch in a perennial ryegrass sward (Lolium perenne L.) were investigated both in boxed swards and in the field.