K. Hamouzová

Mechanisms of resistance to acetolactate synthase-inhibiting herbicides in populations of Apera spica-venti from the Czech Republic

BACKGROUND This study investigates the mechanisms of resistance to acetolactate synthase-inhibiting herbicides in populations of Apera spica-venti (L.) P.B. from the Czech Republic. RESULTS The proportion of resistance due to mutant acetolactate synthase (ALS) alleles was estimated by genotyping individuals from each of three populations for the eight ALS mutations known to confer resistance. Four resistance-conferring ALS mutations were identified: Pro-197-Ala, Pro-197-Thr, Trp-574-Leu and previously unreported Trp-574-Met substitution. Two populations (R1, R3) have amino acid substitution at positions Pro-197 and Trp-574. Individuals from the R3 population had two different resistance alleles. In the R2 population, only the resistant Trp-574-Met substitution was detected. Ten other single point mutations were identified, but these were not related to resistance. The cytochrome malathion decreased chlorsulfuron resistance in the resistant populations that were examined. Although malathion increased mortality, the GR50 values were too high to conclude that non-target-based mechanism was the main one for the resistance in Apera spica-venti populations tested in this study. CONCLUSIONS Individuals of Apera spica-venti populations tested in this study possess the target-site ALS resistance mutation and an additional so far unknown resistance mechanism(s).

Efficacy and Selectivity of Pre-emergent Sunflower Herbicides under Different Soil Moisture Conditions

Chenopodium album, Echinochloa crus-galli, Amaranthus retroflexus, Mercurialis annua, and Solanum physalifolium ) was only slightly affected by the soil moisture and these herbicides can be used in arid and semiarid regions. The efficacy of linuron, prosulfocarb, and pethoxamid was strongly affected by soil moisture and was insufficient under dry conditions. The majority of herbicides showed good selectivity for sunflower. Crop injury rate of 5–15% was recorded after application of flurochloridone and ace tochlor. For flurochloridone, the phytotoxicity increased due to irrigation after herbicide application. The highest sunflower injury rate (27–35%) was recorded after application of oxyfluorfen.

The effect of eight common herbicides on the predatory activity of the agrobiont spider Pardosa agrestis

The impact of eight herbicides in different residual stages on the predatory activity of a potential biological control agent, the wolf spider Pardosa agrestis, was studied in the laboratory. We found that fresh wet residues of all tested herbicides negatively affected the total and cumulative predatory activity of this species. Moreover, treatment with 48-h-old residues of the glufosinate ammonium herbicide Basta induced a significant increase in predatory activity in P. agrestis, presumably as a consequence of hormesis. These results imply that the natural pest control provided by the agrobiont spider P.agrestis can be weakened by the application of the studied herbicides. On the basis of our results, we suggest that sublethal effects on beneficial organisms should be considered in the planning of weed management of agroecosystems and should not be omitted from the herbicide registration process.

Disruption of the chemical communication of the European agrobiont ground-dwelling spider Pardosa agrestis by pesticides

Lycosid spiders are among the most abundant and diverse insectivores occurring in all agroecosystems. Certain pest management practices, such as the application of pesticides, can disrupt their role in insect pest control. Therefore, understanding the effects of pesticides, including sublethal effects, is essential for the assessment of chemical effects on beneficial arthropods. We investigated the sexual chemical communication of the beneficial agrobiont spider Pardosa agrestis and its disruption by two widely used pesticides, the glyphosate‐based herbicide Roundup and the pyrethroïd‐based insecticide Nurelle D. A two‐choice olfactometer and Y‐maze were used to study the effectiveness of female airborne and dragline pheromone cues and the disruptive effect of the pesticides. Males of P. agrestis did not locate females via airborne cues, but were very receptive to female dragline silk and male dragline silk. When both female dragline silk and male dragline silk were provided at the same time, the males preferred female silk. Pesticide treatments significantly affected the male ability to follow female cues deposited on dragline silk. The 3‐h residues of both Roundup and Nurelle D significantly disrupted the male ability to follow female cues deposited on dragline silk. Treatment by 48‐h residues significantly disrupted the male ability only in the case of Nurelle D. Our results demonstrate that pesticides reduce the ability of male spiders to search for a mate due to the disruption of the males ability to detect the silk cues of the female.

Effect of a non-woven fabric covering on the residual activity of pendimethalin in lettuce and soil.

BACKGROUND Lettuce (Lactuca sativa L.) is a crop that is very sensitive to herbicide contamination owing to its short growing season. The use of long-residual herbicides and non-woven fabric coverings could therefore influence pendimethalin concentrations in soil and lettuce. RESULTS The pendimethalin half-life in soil ranged between 18 and 85 days and was mainly affected by season (i.e. weather), and especially by soil moisture. Pendimethalin degradation in soil was slowest under dry conditions. A longer pendimethalin half-life was observed under the non-woven fabric treatment, but the effect of varying application rate was not significant. Pendimethalin residue concentrations in lettuce heads were significantly influenced by pendimethalin application rate and by non-woven fabric cover, especially at the lettuces early growth stages. The highest pendimethalin concentration at final harvest was determined in lettuce grown on uncovered plots treated with pendimethalin at an application rate of 1200 g ha-1 (7-38 µg kg-1 ). Depending on growing season duration and weather conditions, pendimethalin concentrations in lettuce grown under non-woven fabric ranged from 0 to 21 µg kg-1 . CONCLUSION Use of transparent non-woven fabric cover with lettuce can help to reduce application rates of soil herbicides and diminish the risk of herbicide contamination in the harvested vegetables.

Environmental and agronomic monitoring of adverse effects due to cultivation of genetically modified herbicide tolerant crops

Herbicide tolerance allows a specific crop variety to survive a herbicide treatment without injury despite the fact that the herbicide cannot be used selectively in a common variety of the same crop. Widely adopted and used worldwide are genetically modified herbicide tolerant (GMHT) crops with tolerance to the non-selective herbicide active ingredients glyphosate and glufosinate. Development of GMHT crops has substantially changed weed control systems and sometimes crop rotations and soil tillage systems. Attention must be given to the environmental and agro-environmental aspects and sustainability of agro-ecosystems based on HT crops because some adverse effects with this technology can appear, especially if used without knowledge of the risks involved and their prevention. This paper identifies main areas that should be monitored and discusses such potential adverse effects as hybridization with related taxa, occurrence of feral crops, and evolved herbicide resistance within weed communities. If there is no principal difference between conventional and GM crop cultivation, we propose monitoring approaches shall be based mainly on existing methods and monitoring networks. Scientific approaches as basis, decentralization with site-specific focus, as well as reasonable extent of data collection and their effective utilization should be the main features of the monitoring.

One generalist or several specialist species? Wide host range and diverse manipulations of the hosts’ web-building behaviour in the true spider parasitoid Zatypota kauros (Hymenoptera: Ichneumonidae)

Parasitoid wasps of the Polysphincta genus‐group are highly specialised on their spider hosts, and most of them are known to manipulate their hosts into building a special web in which the parasitoid pupates. Trophic niche and the plasticity of host use were investigated in the koinobiont parasitoid Zatypota kauros Gauld from Queensland, Australia. We found that Z. kauros attacks spider hosts from different families, each differing widely in their web‐building behaviours, which makes it unique in the breadth of its host range. Molecular analyses revealed that the taxon Z. kauros contains three divergent mitochondrial lineages. Lineage A was associated exclusively with spiders of the genus Anelosimus (Theridiidae), which builds tangle webs; lineage B was associated with the genus Cyrtophora (Araneidae), which weaves tent webs; and lineage C was associated with a broad range of hosts, including spiders of both the families Araneidae and Theridiidae. Unique host manipulations could be observed in the web‐building behaviours of the different host groups. Nevertheless, nuclear data from two ribosomal genes and three introns did not add any support to the existence of different evolutionary lineages, nor did they coincide with the different host groups. The partial correspondence of mitochondrial lineage and host use, together with an apparent mito‐nuclear conflict might indicate maternal effects or very recent and/or incomplete speciation in this taxon. Given their wide host range and intriguing interactions with their hosts, the Z. kauros complex represents a promising system for studying parasitoid specialisation and its potential impact on speciation.

Cytoplasmic male sterility as a biological confinement tool for maize coexistence: Optimization of pollinator spatial arrangement

Cytoplasmic male sterility (CMS) allows efficient biological confinement of transgenes if pollen-mediated gene flow has to be reduced or eliminated. For introduction of CMS maize in agricultural practice, sufficient yields comparable with conventional systems should be achieved. The plus-cultivar-system in maize offers a possibility for biological confinement together with high and stable yields whereas pollinator amount and distribution within the CMS crop is crucial. The aim of this EU-funded study was to identify the best proportion (10, 15, and 20%) and spatial arrangement (inserted rows, mixed seeds) of the pollinator within the CMS maize cultivar under field conditions in the Czech Republic, in Germany and in Spain. In Germany and in the Czech Republic, a pollinator proportion of 10% produced significantly lower yield than the treatments with a pollinator proportion of 15% and 20%. Differences in yield between row and mix arrangements were not detected. No differences between the tested arrangements occurred in Spain. With respect to practical conditions, a pollinator proportion of 15% can be recommended for achieving a satisfactory yield. CMS maize cultivar released no or merely a small amount of pollen and self-pollinated plants developed no or only a small number of kernels indicating that currently recommended isolation distances between genetically modified (GM) and non-GM fields can be substantially shortened if the CMS confinement tool is used

Effects Of Spring Herbicide Treatments On Winter Wheat Growth And Grain Yield

Abstract Herbicides provide a low-cost solution for protecting crops from significant yield losses. If weed infestations are below damage thresholds, however, then herbicide application is unnecessary and can even lead to yield loss. A small-plot field trial was conducted to examine the effect of herbicides on winter wheat yields. Weeds were removed manually from the trial area before herbicide application. Twenty-four treatments were tested in four replications. Treatment 1 consisted of an untreated weed-free control, whereas the other treatments comprised applications of the following herbicides and their combinations: metsulfuron-methyl + tribenuron-methyl (4.95 + 9.99 g ha−1), pinoxaden (30 g ha−1), fluroxypyr (175 g ha−1), and clopyralid (120 g ha−1). Water (250 l ha−1) or a urea-ammonium nitrate fertilizer solution (UAN, 120.5 l ha−1) was used as the herbicide carrier. Crop injury 30 days after treatment and yield loss were recorded. Results showed minor crop injury by herbicides and their combinations when applied without UAN and moderate injury caused by UAN in combination with herbicides. Yield losses reached 5.3% and 4.3% in those treatments where all of the tested herbicides were applied with and without UAN, respectively. The effect of all treatments on crop yield was, however, statistically insignificant (P = 0.934).

Evapotranspiration and Transpiration Measurements in Crops and Weed Species by the Bowen Ratio and Sapflow Methods Under the Rainless Region Conditions

The aim of this chapter is to provide a systematic description of the measurements of total evapotranspiration and transpiration of selected agricultural crops and weeds, results of investigation, and perspectives of these methods for agricultural usage. This study provides a contribution towards increased knowledge on the consumptive water use of arable crops and weeds within the temperate climatic zone under specified weather conditions and actual crop structure given by biometric observation. The water consumption of plants represents a significant part of the landscape water balance (Merta et al. 2001). An important factor influencing the water balance of the plant stands on agricultural soil and thereby in the countryside is the species composition of phytocoenosis. Within the framework of phytocoenosis, the cultivated plants and weeds take share in influencing the water balance (Pivec & Brant 2009). Competition between plants to capture the resources essential to plant growth (i.e. light, water and nutrients) is one of the key processes determining the performance of natural, semi-natural and agricultural ecosystems (Kropff & van Laar, 1993). The issue of evapotranspiration and transpiration demands of field crops is a subject of intensive study especially in arid and semi-arid areas. In terms of eliminating the negative impact of agriculture on the environment and in terms of increasing the efficiency of the production systems, its monitoring is important for the temperate climate as well.