Corn poppy (Papaver rhoeas) cross-resistance to ALS-inhibiting herbicides

BACKGROUND: Papaver rhoeas (L.) has evolved resistance to tribenuron in winter wheat fields in northern Greece owing to multiple Pro₁₉₇ substitutions. Therefore, the cross‐resistance pattern to other sulfonylurea and non‐sulfonylurea ALS‐inhibiting herbicides of the tribenuron resistant (R) and susceptible (S) corn poppy populations was studied by using whole‐plant trials and in vitro ALS catalytic activity assays. RESULTS: The whole‐plant trials revealed that tribenuron R populations were also cross‐resistant to sulfonylureas mesosulfuron + iodosulfuron, chlorsulfuron and triasulfuron. The whole‐plant resistance factors (RFs) calculated for pyrithiobac, imazamox and florasulam ranged from 12.4 to > 88, from 1.5 to 28.3 and from 5.6 to 25.4, respectively, and were lower than the respective tribenuron RF values (137 to > 2400). The ALS activity assay showed higher resistance of the ALS enzyme to sulfonylurea herbicides (tribenuron > chlorsulfuron) and lower resistance to non‐sulfonylurea ALS‐inhibiting herbicides (pyrithiobac > florasulam ≈ imazamox). CONCLUSION: These findings indicate that Pro₁₉₇ substitution by Ala, Ser, Arg or Thr in corn poppy results in a less sensitive ALS enzyme to sulfonylurea herbicides than to other ALS‐inhibiting herbicides. The continued use of sulfonylurea herbicides led to cross‐resistance to all ALS‐inhibiting herbicides, making their use impossible in corn poppy resistance management programmes. Copyright © 2011 Society of Chemical Industry     

Wild Mustard (Sinapis arvensis L.) Competition with Three Winter Cereals as Affected by Nitrogen Supply

Two field experiments were carried out in northern Greece during the 1993–94 and 1994–95 growing seasons to investigate the effect of nitrogen (N) supply on interspecific competition between wild mustard (Sinapis arvensis L.) and wheat (Triticum aestivum L.), barley (Hordeum vulgare =distichum L.) and triticale (Triticosecale). The presence of 140 S. arvensis plants m⁻² until early March (averaged over N levels) did not have any adverse effect on the dry weight of all crops. However, its further presence significantly reduced the dry weight of wheat and triticale, but not that of barley. N fertilization (150 kg N ha⁻¹ regardless of application time) slightly increased the dry weight of wheat and triticale grown without weed competition compared with that of control (0 kg N). On the contrary, the presence of wild mustard, until harvest, reduced dry weight of wheat and triticale by 31 and 26 %, respectively, while the corresponding reduction for barley was only 1.5 %. Furthermore, N fertilization (150 kg N ha⁻¹) increased dry weight of wild mustard grown with wheat and triticale by 10 and 16 %, respectively, compared with that of control (0 kg N). Grain yield of wheat and triticale was reduced to 26 and 27 % by the competition of wild mustard, respectively, while the corresponding reduction for barley was only 3.5 %. Moreover, the wild mustard presence reduced total N content of wheat and triticale by 20 and 19 %, respectively, but this was not the case for barley.     

Interference between Avena sterilis, Phalaris minor and five barley cultivars

Field experiments were carried out in Northern Greece from 1994 to 1997 to study interference between Avena sterilis L. or Phalaris minor Retz. and five autumn-sown barley cultivars. Weed:crop interference began in early April. Avena sterilis at 120 plants m⁻² showed greater interference against barley than P. minor at 400 plants m⁻². The greatest grain yield and ear number reduction due to interference by either weed was recorded for cvs Klipper and Plaisant, and the least for cv. Athinaida; with cvs Carina and Thermi intermediate. Yield reduction due to A. sterilis for cvs Athinaida, Carina, Thermi, Klipper and Plaisant was 8, 16, 27, 61 and 67%, respectively, while corresponding losses to P. minor were 1, 8, 14, 45 and 55%. These results clearly indicate that growth and consequently yield components of cv. Athinaida were unaffected by the presence of either weed species, while those of cv. Carina were affected by A. sterilis , but not by P. minor . However, dry weight and panicle number of both weed species were severely reduced by interference with cvs Carina, Athinaida and Thermi compared with cvs Klipper and Plaisant. The order of interference of the five barley cultivars tested against A. sterilis and P. minor was Athinaida > Carina > Thermi > Klipper ≥ Plaisant.     

Effects of aromatic plants incorporated as green manure on weed and maize development

A 2-year field experiment was conducted in northern Greece to study the mulch effects of seven annual [anise (Pimpinella anisum L.), sweet fennel (Foeniculum vulgare P. Mill.), sweet basil (Ocimum basilicum L.), dill (Anethum graveolens L.), coriander (Coriandrum sativum L.), parsley (Petroselinum crispum (P. Mill.) Nyman ex A.W. Hill) and lacy phacelia (Phacelia tanacetifolia Benth.)] and three perennial [mint (Mentha X verticillata L.), oregano (Origanum vulgare L.) and common balm (Melissa officinalis L.)] aromatic plants, used as incorporated green manure, on the emergence and growth of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], common purslane (Portulaca oleracea L.), puncturevine (Tribulus terrestris L.), common lambsquarters (Chenopodium album L.) and maize (Zea mays L.). In addition, the phytotoxic potential of the abovementioned aromatic plants extracts was determined in the laboratory using a perlite-based bioassay with maize and barnyardgrass. The bioassays indicated that germination, root elongation and fresh weight of barnyardgrass were reduced by the most aromatic plant extracts. However, maize growth parameters were only affected by the extracts of anise, sweet fennel, coriander, common balm and oregano. In the field, emergence of barnyardgrass, common purslane, puncturevine or common lambsquarters was reduced by 11–50%, 12–59%, 26–79% or 58–83% in green manure-treatment plots, respectively, as compared with green manure-free plots (control). On the contrary, maize emergence was not affected by any green manure. At harvest, maize grain yield in green manure-herbicide untreated plots was 10–43% greater than that in the corresponding green manure-free plots. In particular, maize grain yield in anise, dill, oregano or lacy phacelia green manure-herbicide untreated plots was 27–43% greater than that in the green manure-free-herbicide untreated and slightly lower than that obtained in the corresponding herbicide treated plots. These results indicated that green manure of aromatic plants, such as anise, dill, oregano or lacy phacelia could be used for the suppression of barnyardgrass and some broadleaf weeds in maize and consequently to minimize herbicide usage.     

Competitive interactions of fifty barley cultivars with Avena sterilis and Asperugo procumbens

A 2-year study was conducted in northern Greece to assess the ability of 29 six-row and 21 two-row barley (Hordeum vulgare L.) cultivars to compete with winter wild oat [Avena sterilis spp. ludoviciana (Durieu) Gill & Magne] and German-madwort (Asperugo procumbens L.). The fresh weight of both weeds grown in competition with six of the most competitive six-row barley cultivars (Bulk Resist. Desc-Sutter, Lignee 640, Paico's, Mantnan's-EH 165, Pistacho and Malebo) was reduced by 61–75% compared with one of the least competitive six-row cultivars [Gloria's-Copal's (30B-4Y-20M)]. The corresponding fresh weight reduction of both weeds grown in competition with three of the most competitive two-row barley cultivars (Goldmarker, Shanon and Helena) ranged from 59 to 76% compared with one of the least competitive two-row cultivars (Guanajuato). The ability to withstand competition (AWC) from winter wild oat and German-madwort of the six-row and two-row cultivars ranged from 33.7 to 78.3% and 26.7 to 69.2%, respectively. Representative yield losses ranged from 24 to 68% and 30 to 75%, respectively. The corresponding ability to compete (AC) indices ranged from 22.5 to 64.8% and 21.1 to 59.1%. The results of this study indicated that the barley cultivars Ligne 640 and Pistacho (2B-1Y-1B) had high AWC from winter wild oat and German-madwort and provided high grain yield in both weedy and weed-free conditions. Consequently, they could successfully be used in Mediterranean organic (no herbicide use) and conventional agricultural systems with reduced herbicide use. Barley cultivars with high AC and ability to produce high grain yield under weedy conditions [with Bulk Resist. Desc-Sutter, Arupo's and Gloria's-Copal's (30B-4Y-23M) among the most efficient] could also successfully be used in organic fields infected by the two weeds.     

Activity, adsorption and mobility of three acetanilide and two new amide herbicides

Activity, adsorption, and mobility of emulsifiable concentrate (EC) and microencapsulated (ME) formulations of alachlor and acetochlor as well as of metolachlor, S-metolachlor, dimethenamid and flufenacet were studied. Petri-dish bioassay, based on root response of oats ( Avena sativa L.), was used for their activity in sand and in a silty clay loam soil, and for determination of herbicide concentrations in soil solution (not adsorbed) and in column leachates of the adsorption and mobility studies respectively. Flufenacet and both acetochlor formulations showed the highest activity in both soils and ME-alachlor and metolachlor the lowest; the activity of dimethenamid, EC-alachlor and S-metolachlor was intermediate. Activity of both formulations of alachlor and acetochlor decreased with increasing organic matter content, but alachlor activity was reduced more than that of acetochlor. Lower amounts of dimethenamid and S-metolachlor were adsorbed by soil compared with the other herbicides and, consequently, greater amounts of these two herbicides were leached through that soil. None of the herbicides tested was detected below 30 cm. Less alachlor and acetochlor were biologically available in soil solution after their application as ME-formulations and, therefore, lower amounts of both ME-alachlor and ME-acetochlor were leached through the soil compared with those applied as EC-formulations.     

Critical periods of weed competition in cotton in Greece

Four experiments were conducted in central Greece during 1997 and 1998 to determine the late-season presence of weeds in cotton (Gossypium hirsutum L.) and the critical times for removing weeds. Experiments were conducted in natural, heavily infested cropland. The presence of weeds for more than 3 weeks after crop emergence caused significant reductions in crop growth and lint yields. However, weeds that emerged 11 weeks or more after crop emergence did not adversely impact yields. Total weed biomass increased with increasing time prior to weed removal. A weed-free period of 11 weeks after crop emergence was needed to prevent significant reductions in cotton height, biomass, number of squares, and yield. These results indicated that postemergence herbicides or other control measures should be initiated within 2 weeks after crop emergence to avoid significant yield reduction. For greater efficiency, soil-applied herbicides in cotton should provide effective weed control for at least 11 weeks. Curvilinear regression equations were derived to describe the relationship between critical periods of weed presence and cotton growth and fruit development.     

Activity,adsorption, mobility and field persistence of sulfosulfuron in soil

Petri dish bioassays, based on root response of corn grown in soil or in perlite, were used to study the activity, adsorption, mobility and field persistence of sulfosulfuron in a silty clay loam and a sandy loam soil. Both bioassays indicated that activity of sulfosulfuron increased with increasing herbicide concentration, and to a slightly greater degree in sandy loam soil than in silty clay loam soil. More sulfosulfuron was adsorbed on the sandy loam (not biologically available) than on the silty clay loam soil. Consequently, slightly greater amounts of sulfosulfuron were leached through the silty clay loam than through the sandy loam soil. Biologically available sulfosulfuron was not detected at depths below 40 cm after application in sandy loam, but this was not the case for the silty clay loam soil. In 2002, all sulfosulfuron rates showed field persistence of less than 5 months. On the other hand, in 2003, biologically available sulfosulfuron was detected in the 0–10-cm soil depth 150 days after application. http://www.phytoparasitica.org posting May 6, 2004.