Littleseed Canarygrass (<i>Phalaris minor</i>) and Short-spiked Canarygrass (<i>Phalaris brachystachys</i>) Interference in Wheat and Barley

Field experiments were established in Greece from 1990 to 1993 to study the effect of littleseed and short-spiked canarygrass density on wheat and barley yield, as well as the influence of littleseed canarygrass removal time on wheat yield. Competitive ability of both canarygrass species in wheat was similar, though littleseed canarygrass showed faster growth rate and formed more panicles than short-spiked canarygrass. Grain yield of wheat was not significantly affected by the presence of 76 plants m−2 of either canarygrass species, but it was reduced by 36 to 39% by the presence of 304 canarygrass plants m−2. None of the canarygrass species at any density had any effect on grain yield of wheat when cold and dry conditions prevailed during the early stages of growth. Grain yield of barley was not affected by any density of either canarygrass species. Growth and consequently panicle number of both canarygrass species were severely reduced by the interference of barley. The littleseed canarygrass removal time study indicated that emergence of this weed was completed by the middle of February. Grain yield of wheat grown with 150 littleseed canarygrass plants m−2 was not affected even when these plants were removed early in April. However, the presence of these canarygrass plants until harvest reduced grain yield of wheat by 23 to 28%.</jats:p

First Report of Branched Broomrape (<i>Orobanche ramosa</i>) on Oilseed Rape (<i>Brassica napus</i>), Wild Mustard (<i>Sinapis arvensis</i>), and Wild Vetch (<i>Vicia</i> spp.) in Northern Greece

Branched broomrape (Orobanche ramosa L.) is a chlorophyll-lacking, root parasitic plant that infects many crops and wild species (2). Plants are densely hairy with minute, glandular hairs, particularly on flowers and upper stems. Stems are erect, often branched just above the ground, and brown to straw yellow. Leaves are sparse, triangular, dark brown or purple, and arranged alternately mainly near the base of the stem. Flowers are numerous, arranged along an upright spike with a lance-shaped bract beneath the flower (about a third of the length of the flower). Petals are pale blue to purple and united into a slender tube approximately 15 mm long with two lips, the upper divided into two lobes and the lower into three lobes. The flowers have two short and two long stamens. During 2010 and 2011, a severe broomrape infection was found in an oilseed rape (Brassica napus L., cvs. Nelson and W31) crop on light-textured soil in northern Greece (Paralimnio-Serres, 41°01′N, 23°32′E, 40 m above sea level), where oriental tobacco (Nicotiana tabacum L.), a susceptible host of branched broomrape, was grown 20 years ago. The field had been cultivated with oilseed rape for three consecutive seasons in rotation with sunflower (Helianthus annuus L.). The infestation of the oilseed rape crop was confirmed in April by digging in the soil (25 to 30 cm deep) to verify attachment of the broomrape to roots of the crop plants. Density of the broomrape ranged from 20 to 120 stems per m2 and broomrape stems were 15 to 30 cm tall. Yield losses were estimated at 30 to 60%. In 2011, branched broomrape was found parasitizing wild mustard (Sinapis arvensis L.) growing as a weed in the oilseed rape field. Attachment of the broomrape was verified on a lateral root of the wild mustard plant near the soil surface, 0.95 m from the main root of the weed. Additionally, branched broomrape was found in April 2010 and 2011 parasitizing wild vetch (Vicia spp.) growing in field margins at the Cotton and Industrial Plants Institute-National Agricultural Research Foundation (Sindos, 40°41′N, 22°48′E, 17 m above sea level). The parasitized vetch plants were growing on light-textured soil. Attachment of the broomrape to roots of the host plants was verified at a 5-cm soil depth. Stems of the parasite were short (7 to 10 cm). The monthly mean air temperature for February (7.3°C), March (9.6°C), and April (14.1°C) and mean soil temperature at a 10-cm depth for February (7.0°C), March (9.5°C), and April (13.4°C), before verification of the broomrape infestation at Sindos, were much lower than the temperature range reported (18 to 23°C) for branched broomrape infestations (1). To our knowledge, this is the first report of O. ramosa on oilseed rape, wild mustard, and wild vetch in northern Greece. Since branched broomrape could be a significant parasite for oilseed rape, which was introduced to Greece as a commercial crop 5 years ago, measures should be taken to avoid significant yield losses from this parasitic plant. References: (1) I. Faithfull and D. McLaren. Landcare Note LC0272. Department of Sustainability and Environment, State of Victoria, Melbourne, Australia, 2004. (2) C. Parker. Pest Manag. Sci. 65:453, 2009. </jats:p

Multiple resistance of silky windgrass to acetolactate synthase-and acetyl-CoA synthase-inhibiting herbicides

Field and pot experiments were conducted in Greece to study the occurrence of resistance in silky windgrass to acetolactate synthase (ALS)-and acetyl-CoA synthase (ACCase)-inhibiting herbicides. Twenty-four populations of silky windgrass were examined in whole-plant response experiments. High levels of field-evolved resistance to chlorsulfuron (0% to 28% control in terms of fresh weight reduction) with the recommended field rates were confirmed in most silky windgrass populations. However, other ALS inhibitors, such as pyroxsulam and a premix of mesosulfuron-methyl and iodosulfuron, provided adequate control (76% to 100% in terms of fresh weight reduction) of most populations, except eight silky windgrass populations that were found to be cross-resistant to all ALS-inhibiting herbicides tested (i.e., chlorsulfuron, commercial mixture of mesosulfuron-methyl plus iodosulfuron, and pyroxsulam). Conversely, most silky windgrass populations were controlled effectively (90% to 100% in terms of fresh weight reduction) with the recommended field rates of ACCase inhibitors cycloxydim, clethodim, and pinoxaden, but five populations were also found to be resistant to clodinafop-propargyl (10% to 68% control in terms of fresh weight reduction). The ALS gene sequencing of the eight silky windgrass populations, with cross-resistance to ALS inhibitors, revealed a point mutation at the Pro-197 position, causing amino acid substitution by Ser or Thr in the ALS enzyme. Overall, chlorsulfuron and clodinafop-propargyl were selecting agents of field-evolved multiple resistance to ALS-and ACCase-inhibiting herbicides in five silky windgrass populations. As the available postemergence-applied chemistries/modes of action registered for grass weed control in cereals are rather limited, adopting integrated management practices and implementing proactive and reactive measures to delay the evolution of resistant populations is essential.

Arable weeds identified as new sources of beet mosaic potyvirus in Greece

Field and laboratory studies were carried out between 1992 and 1994 to assess the potential for arable weeds to act as reservoirs of beet mosaic potyvirus (BtMV) in fields where sugar beet is cultivated for seed. 933 weed samples were collected and tested by biological methods, while a representative number of weeds were tested by serological methods. The results showed that 97 samples, representing 14 weed species from eight families, were infected with BtMV. The following weeds were found to be naturally infected with BtMV for the first time: Bilderdykia convolvulus, Nonea pulla, Cerastium glomeratum, Galium aparine, Conyza (Erigeron) spp., Fumaria officinalis, Heliotropium europaeum and Rumex spp. The most common weeds found to be infected with BtMV in high percentage were members of the Papaveraceae

Influence of Different Organic Amendments on the Leaching and Dissipation of Terbuthylazine in a Column and a Field Study

Terbuthylazine (TA) is a herbicide that has been introduced for weed control in corn cultivations as a direct replacement for atrazine. Because incorporation of different organic amendments (OAs) is a common practice in this crop, this study investigated the effects of different OAs, including urban sewage sludge, poultry compost, and corn straw on the dissipation and metabolism of TA. A column study and a field dissipation study were used. In the Column study, no residues of TA and desethyl-terbuthylazine (DETA) were detected in the leachate of amended and non-amended columns. The addition of OAs increased the persistence of TA and DETA in the upper soil layers (0-10 cm) but did not affect the mobility of TA and DETA in either experiment. Although the presence of OAs led to a significant increase in DETA production in the upper soil layers, the presence of DETA in lower depths did not significantly differ with the non-amended soil in either experiment. A gradual accumulation of DETA was evident in the soil layers amended with corn straw, whereas a rapid formation of DETA and a gradual decline thereafter was observed in the other treatments. Overall, the addition of OAs did not appear to significantly influence the mobility of TA and DETA, which did not move below the top 30 cm, thus indicating low risk for ground water contamination. In addition, the dissipation rate of TA in the field was faster than that in the column study

Influence of different organic amendments on the degradation, metabolism, and adsorption of terbuthylazine

The behavior of the herbicide terbuthulazine (TA) was studied in a clay loam soil after the addition of the addition of different organic amendments (OAs). Addition of poultry compost (PC) and urban sewage sludge (USS) retarded degradation of TA (half-life 55.5 d) compared with its degradation in nonamended soils (half-life 57.3 d). Sterilization of amended and nonamended soils resukted in a partial inhibition of TA led degradation, indicating that biotic and abiotic processes are invloved in TA degradation, indicating that biotic and abiotic processes are involved in TA degradation in soil. Degradation of TA led to the formation of desethyl-terbuthylazine, which was detected in low amounts (< 80% of the initially applied TA) in all soils. Adsorption of TA was relatively low, with K-d values ranging from 2.31 L kg(-1) in the soil amended with USS. In general, K-d values increased with increasing soil amended with USS. In general, K-d values increased with increasing soil organic carbon content. The dissolved organic matter extracted from tho OAs did not appear to interact with the pesticide or the soil surfaces, suggesting that it would not probably facilitate herbicide transport. Desorption studies indicated a slight hysteresis of TA desorption in the amended soils compared with TA desorption in the nonamended soil, which is entirely reversible. These findings might have practical implications for the environmental fate of TA in agricultural soils, where the studied OAs are commonly used