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The extended use of glyphosate resulted to its reduced efficacy against increasingly problematic weeds, such as Conyza spp. The objectives of this study were to determine the occurrence of glyphosate resistance in horseweed (C. canadensis) and fleabane (C. albida) populations in Greece, to evaluate the effect of weed growth stage on glyphosate efficacy under controlled environmental conditions and to study seed germination patterns of glyphosate-resistant (GR) and glyphosate-susceptible (GS) populations. Plants from 28 and 14 populations of horseweed and fleabane, respectively, sampled from five prefectures in Greece were sprayed with glyphosate at recommended rates. 68% of the tested populations of horseweed were potentially resistant or intermediate, while the relative percentage for fleabane was significantly lower (50%), probably because of the later introduction of this species. After initial screening, six populations from each species were selected and dose-response experiments were conducted. Glyphosate rates required to control some populations were 7 to 14 times greater than that for control of the reference susceptible populations. Sensitivity of GR horseweed and fleabane populations to glyphosate was strongly dependent on growth stage, with plants at the seedling stage being most sensitive to the herbicide. Moreover, when seeds of GR and GS populations from both species were subjected to different alternating temperature, germination occurring and seedling vigour did not differ between them with maximum germination at 10/20 and 15/25 °C. Consequently, various integrated management strategies should be urgently implemented in order to manage or slow the spread of glyphosate resistance in these species. [ABSTRACT FROM AUTHOR]

The effect of row spacings and irrigation levels on the earliness of seed production of cotton was investigated under the Mediterranean environment of central Greece. This particular cotton growing area is exposed to risk of autumn rainfall that might cause low seed quality in fields allocated primarily for seed production. Two varieties of cotton, Celia and Hersi, were planted in two row spacings (93 and 75 cm) and two irrigation levels (normal and low levels 6160 and 3080 mm ha'). No significant difference in the yield was found among the two varieties, nor between the two row spacings. The low irrigation level had significantly negative effects on the number of squares, boIls, total dry weight and seed cotton production when compared with irrigation level. However, the low irrigation level resulted in a harvest earlier by ten days, which contributed to avoiding autumn rainfall. Seed quality (measured by germination and Warm-Cold Vigour Index Test) was better in seeds from the low irrigation level than in those from the normal irrigation level. Although yield of both varieties was higher under normal irrigation, seed quality was lower compared to low irrigation level. This was evidenced by the higher Free Fatty Acid (FFA) in "normally" irrigated plants. The results of this study showed that low irrigation level offers substantial benefits for early harvesting and production of high seed quality. Moreover, the FFA could be successfully employed as a quick criterion for seed quality ranking. [ABSTRACT FROM AUTHOR]