Christoph Gutjahr

Decision Rules for Site-Specific Weed Management

For precision weed management decision rules are needed that take into account spatial and temporal variability of weed populations and weed-crop interactions. The following chapter describes different decision rules for online and offline site-specific weed management. Those decision rules use crop-weed competition models, dose-response functions, weed population models and cost functions to calculate the best intensity of weed control for each field section. It is shown that herbicide input and weed control costs can be significantly reduced when farmers use those models in combination with modern sensor and application technologies.

Integrating Economics in the Critical Period for Weed Control Concept in Corn

Abstract The effect of weed interference on corn yield and the critical period for weed control (CPWC) were determined in Germany and Benin. Treatments with weed control starting at different crop growth stages and continuously kept weed-free until harvest represented the “weed-infested interval.” Treatments that were kept weed-free from sowing until different crop growth stages represented the “weed-free interval.” Michaelis–Menten, Gompertz, logistic and log–logistic models were employed to model the weed interference on yield. Cross-validation revealed that the log–logistic model fitted the weed-infested interval data equally well as the logistic and slightly better than the Gompertz model fitted the weed-free interval. For Benin, economic calculations considered yield revenue and cost increase due to mechanical weeding operations. Weeding once at the ten-leaf stage of corn resulted already profitable in three out of four cases. One additional weeding operation may optimize and assure profit. Economic calculations for Germany determined a CPWC starting earlier than the four-leaf stage, challenging the decade-long propagated CPWC for corn. Differences between Germany and Benin are probably due to the higher yields and high costs in Germany. This study provides a straightforward method to implement economic data in the determination of the CPWC for chemical and nonchemical weed control strategies. Nomenclature: corn, Zea mays L.

Untersuchungen zur Resistenz von Acker-Fuchsschwanz in Baden-Württemberg und zur Wirkung von Herbiziden in Winterweizen im Hinblick auf die Vermeidung von Resistenz

In Verdachtsproben aus unterschiedlichen Gebieten in Baden-Wurttemberg konnte in den Jahren 2008 bis 2010 bei Acker-Fuchsschwanz Resistenz gegen Herbizide aus der HRAC-Gruppe A nachgewiesen werden. 2008 traten auch Biotypen mit Resistenz gegen Flupyrsulfuron (HRAC-Gruppe B) auf. 2010 wurde bei weiteren Herbiziden aus dieser Gruppe eine deutliche Wirkungsminderung festgestellt. Dieses Ergebnis spiegelte sich auch in den Ergebnissen der Feldversuche wider. Bei den Fruhjahrsbehandlungen war nur mit der Variante Atlantis OD + Artus + Primus eine sehr gute Wirkung zu erzielen. Bei den anderen Varianten blieben auf einzelnen Standorten mit hohem Acker-Fuchsschwanzbesatz zu viele Ahren/m² stehen. Auf diesen Standorten sollte die Acker-Fuchsschwanzbekampfung bevorzugt im Herbst durchgefuhrt werden. Mehrere Herbizidkombinationen mit Bodenherbiziden aus den HRAC-Gruppen K1/3 und F1 erzielten auch in fruh gesatem Winterweizen sowohl gute Bekampfungserfolge, als auch Mehrertrage, und waren wirtschaftlich. Stichworter: Ertrage, Fruhjahrs- und Herbstanwendungen, Herbizidkombinationen, Resistenztest, Unkrautbekampfung, Wirtschaftlichkeit Investigations into resistance in black-grass ( Alopecurus myosuroides ) in Baden-Wurttemberg and into herbicidal efficiency to reduce the risk of resistance developing Suspicious samples of black-grass seeds from fields in Baden-Wurttemberg were tested in the greenhouse in 2008 to 2010 for their degree of resistance. The resistance to ACCase-inhibiting herbicides was widespread. In the year 2008, black-grass plants from a few samples survived treatments with the ALS inhibitor flupyrsulfuron. In 2010, a few other ALS-inhibiting herbicides showed a reduced performance. Resistance to ALS and ACCase inhibitors occurred in the field trails too. Spring only applications of Atlantis OD + Artus + Primus provided very good levels of control. The other herbicides did not provide an acceptable level of control on some fields. There was still a high number of seed heads remaining in the field. On these fields, preemergence herbicides (HRAC groups K1/3 und F1) have a valuable role in resistance management strategy. The treatments in autumn with pre-emergence herbicides in mixture or sequence provided good control and economic surplus. Keywords: Application in spring and autumn, combinations of herbicides, economics, resistance test, weed control, yield