A. Taberner

Effect of ploughing and harrowing on a herbicide resistant corn poppy (Papaver rhoeas) population

ABSTRACT A field trial on winter barley, containing a large infestation of a herbicide resistant Papaver rhoeas population, was established in North-eastern Spain during the cropping seasons 1998–99, 1999–00 and 2000–01. After decades of minimum tillage, ploughing was conducted in Winter 1998, Winter 2000 or in both 1998 and 2000 in part of the field as a preventive weed control strategy. Plant density assessments and quantification of the seed bank at the end of 3 years were taken. Less P. rhoeas emerged in the ploughed plots and the effect was still visible 2 years after ploughing. In the twice ploughed plots, emergence was higher than in the once ploughed plots but lower than in the non-ploughed treatment. Harrowing conducted post-emergence as an annual control method in part of the plots caused a remarkable reduction of the weed population in all three years. The effect caused by the harrowing was more important than the ploughing treatments. However, the combination of single ploughing and harrowing induced the lowest weed plant emergence. The depth distribution of P. rhoeas seed was similar for all treatments but there was a higher total seed bank in the twice ploughed plots. Occasional ploughing was found to be an effective method for placing P. rhoeas seeds in non-optimal germination situations. When the initial weed seed bank is very high as in this field trial, the reduction achieved by ploughing is not sufficient and an additional weed control method should be conducted.

Chemical control of herbicide-resistant Lolium rigidum Gaud. in north-eastern Spain

BACKGROUND Lolium rigidum Gaud. is one of the most common weed species in winter cereals in north-eastern Spain, with populations that have evolved resistance to herbicides becoming more widespread since the mid-1990s. Nine trials on commercial fields with herbicide-resistant L. rigidum were conducted during the cropping seasons 2001-2002 to 2003-2004, testing the efficacy of 20 herbicides and mixtures pre- and post-emergence and as sequential applications. Weed populations chosen had different resistance patterns to chlortoluron, chlorsulfuron, diclofop-methyl and tralkoxydim, representative of the resistance problems faced by farmers. RESULTS In pre-emergence, prosulfocarb mixed with trifluralin, chlortoluron or triasulfuron was effective on six populations. In post-emergence, iodosulfuron alone or mixed with mesosulfuron gave the best results but did not control three resistant populations. At Ferran 1, none of the herbicide combinations reached 90% efficacy. CONCLUSIONS The diverse efficacy patterns of the different populations demonstrate the need for detailed knowledge of the populations before using herbicides. Moreover, the unexpected insufficient efficacy of the new herbicide iodosulfuron prior to its field use shows the need to combine herbicides with other non-chemical weed control methods to control resistant L. rigidum in north-eastern Spain.

A germination study of herbicide-resistant field poppies in Spain

Field poppy, Papaver rhoeas L., is a very common weed in winter cereals in North-Eastern Spain. Its control is becoming difficult due to expanding herbicide resistance. To control field poppies there are alternative strategies such as non-chemical control that take into account the weed emergence period. However, there is a lack of knowledge of P. rhoeas emergence patterns in semi-arid conditions. Thus, here we conducted pot experiments on the emergence of P. rhoeas. We aimed to describe the emergence period and to quantify the emergence of a susceptible and of a herbicide-resistant P. rhoeas population at two locations in Catalonia, Spain, from 1998 to 2001 and until 2004 at one of them. Therefore, pots containing seeds of both populations were established at the two locations and emergence was recorded monthly. We studied the origin of the population, the sowing location, the effect of cultivation and the sowing year. First, we found that the main emergence peaks in our experiments occurred in autumn, accounting for between 65.7 and 98.5% of the annual emergence from October to December, and only little emergence was recorded in spring. This emergence pattern is different from those found in the literature corresponding to Northern European countries, where in some cases main flushes occur only in autumn, in spring and winter or only in spring. The emergence was mainly affected by cultivation, but the effect of light stimulus was observed several months later. As a consequence, cultivation should be done in early autumn, promoting emergence during the whole autumn and winter so that emerged seedlings can be controlled before sowing a spring crop. Second, most experiments showed that the emergence was significantly higher in the first autumn than in the following seasons, e.g. 4.1% emergence in the first year and only 2.1, 2.3, 0.5 and 0.6% new emergence at one of the locations for the second, third, fourth and fifth years. Thus, after having a severe P. rhoeas infestation causing a big seed rain, emergence should be stimulated by autumn cultivation in the following season and seedlings controlled by trying to deplete the soil seed bank as much as possible. Despite the fact that emergence will be staggered throughout several years and that there was a significant relationship between rainfall and emergence, so that dry years will cause a smaller emergence rate of the weed, these findings define a cultural management strategy to reduce P. rhoeas infestations and to contribute to integrated weed management strategies combining it with other tools.