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Effects of tillage systems on the seed bank persistence and seedling emergence of ten arable weeds
Summary
To test the effects of different tillage implements on soil seed bank decline and on seedling emergence, 5000 seeds m-2 of the arable weed species Avena fatua, Echinochloa crus-galli, Stellaria media, Spergula arvensis, Sinapis arvensis, Capsella bursa-pastoris, Raphanus raphanistrum, Thlaspi arvense, Solanum nigrum and Tripleurospermum perforatum were broadcast in experimental plots. The implements were the curry comb, the cultivator and the plough. After 25 months, the percentage of weed seeds recovered ranged from 0-12 %, depending on the species. The highest number of re-detected seeds was for Thlaspi arvense in soils under plough tillage. In contrast, no seeds were recovered from Spergula arvensis and Avena fatua. As there were no significant differences among the three treatments concerning the decline of the soil seed bank, seedling emergence in the curry comb and the cultivator plots significantly exceeded the values of the plots under plough tillage.
The impact of post harvest weed seed predation compared to stubble cultivation on weed seed decline
Summary
The complete article is written in German
Experiments were conducted in 2002 and 2003 to study the impact of weed seed losses due to predation without stubble cultivation and fatal germination after stubble cultivation between harvest of winter wheat and seeding of winter barley. In both years, defined numbers of seeds from different weed species and small annual grains where placed in plots on a winter wheat stubble and predation by birds, rodents and small organisms in the soil was determined. Additionally, the same amount of seeds were filled in flax bags and buried into the stubble after cultivation. Six weeks later, the number of viable and dormant seeds was counted. Weed seed decline caused by predators varied between 30 and 60 %. Small annual grains were almost completely fed by predators. In 2003 weed seed decline caused by predators was higher than by fatal germination after stubble cultivation. The results can be used to predict dynamics of weed populations under different tillage practices.
Effect of soil tillage intensity on seedbank dynamics of oilseed rape compared with plastic pellets as reference material
Summary
Tillage operations with different intensities following the input of oilseed rape seeds and an inert reference material (plastic pellets) resulted in seed banks which varied in size and vertical distribution. The size of the rapeseed bank has mainly to be attributed to seed losses in or on the soil, since seed bank and seed losses correlated with 0.84. Highest seed losses and consequently smallest soil seed banks were determined in treatments without stubble tillage and primary tillage by using a plough or a rigid tine cultivator in late autumn. A comparison with the reference material showed seed losses mainly in the soil horizon 0-10 cm (maximum seed: reference ratio 0.17) for treatments without stubble tillage, with non-inversion tillage operations or with zero tillage. A treatment with immediate, shallow incorporation of seeds and ploughing in late autumn resulted in seed losses mainly in soil horizons 10-20 cm and 20-30 cm (maximum seed: reference ratio 0.19). Several mortality factors e.g. predators or fatal germination seem to differently affect seeds depending on cultivation sequence and soil depth.
The study allows to divide the occurrence and vertical distribution of seeds in a soil seed bank into effects of mechanical shifting and into effects of seed mortality. The data will be integrated in models for seed bank dynamics of oilseed rape and weeds.
Predicting the potential geographical distribution of parasitic weeds, a contribution to risk management: case study of Orobanche crenata
Summary
The complete article is written in German
The potential distribution of the parasitic weed Orobanche crenata was studied in a combined literature, laboratory and simulation study. Populations of the root parasite only exist in regions with mediterranean climate, although individuals are able to reach maturity under conditions of temperate climate, too, and although O. crenata seeds can survive temperatures of -20 °C. The dormancy behaviour of its seeds is likely to impede the northward spread of this species, since in a continuously moist environment, hardly any dormancy release takes place. Results of sensitivity analyses using simulation models suggest that a change to warmer and/or drier climate would substantially increase the risk of O. crenata establishment at higher latitudes. The collected information can, particularly when combined with data on host crop production, contribute to parasitic weed risk management.
Distribution, importance and control of Bromus species in the Middle West of Germany
Summary
The complete article is written in German
Bromus species are important weeds in arable crops. Due to the increase of reduce tillage systems and larger areas of winter oilseed rape and winter wheat there is still a small increase of Bromus sp. However, even if the plough is used year by year occurrence of Bromus may not be avoided. Bromus sterilis is the most important species, but combination the other Bromus sp. can often be observed. The distribution in the field shows that Bromus is mainly a problem of the field margins. However, even all other possible distribution forms can also be observed. The coverage of the whole field is rare. In these cases often other reasons like contaminated crop seeds are involved. There are no regional borders for the occurrence of Bromus. Main arable regions showed a higher and regions with higher altitude above sea level showed a lower infestation with these weeds.
If a field is stronger infested farmers started with control activities. Management of field margins, intensification of stubble tillage (incl. use of glyphosate) and the additional use of selective gramicides are of importance. The use of special ALS-inhibitors for control of Bromus often is not as good as expected. More experience and recommendation are needed to improve the efficacy of these herbicides.
Weed and weed seed-bank response to tillage systems, straw and catch crops in continuous barley
Summary
Weed and weed seed-bank response to different tillage systems, straw and catch crops was investigated over the years 2000-2003 in a field trial with continuously grown barley. We found no effect of straw on weed density on the first two years of the experiment. Lower number of weeds in plots with straw was found on later years. Shallow loosening in spring, shallow catch crop incorporation in spring and no-tillage significantly increased weed infestation, compared to conventional deep plowing. No-tillage favored spread of Sonchus arvensis L. and Tripleurospermum perforatum L., but decreased the number of Chenopodium album L. Tillage systems had no effect on weed seed-bank. Straw incorporation decreased weed seed-bank, especially of Chenopodium album and, therefore, future weed infestation.
Pre-dispersal predation and seed damage of Centaurea scabiosa L. (Asteraceae)
Summary
Centaurea scabiosa L. (Asteraceae) is host plant of several Tephritidae (Diptera) species. They use flower heads for development and are the main predators of the seed. We studied the mechanism of fruit fly damage in number, weight and germination of the seeds.
Dominant species in C. scabiosa flower heads was Terellia colon (Terelliinae), which destroyed 11 % of seeds. Undamaged seeds from central flower heads were significantly lighter than in lateral flower heads.
Germination of the seeds was not significantly correlated with proportion of damaged seeds. However damage to flower head, significantly reduced weight of the remaining healthy seeds.
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