Weekly defoliation controls, but does not kill broad‐leaved dock (Rumex obtusifolius)

Broad‐leaved dock (Rumex obtusifolius L.) is a troublesome weed that predominantly grows in pastures and grassland. We hypothesised that frequent defoliation of Rumex will, over time, result in a reduction in root weight and leaf area, to the point where the impact on grass production is negligible. In order to investigate this hypothesis, we conducted three experiments. The objective of the first experiment was to perform a preliminary test of the hypothesis, using potted plants growing in the controlled conditions of a glasshouse. This experiment showed a rapid decline in leaf growth in plants that were defoliated weekly. The objective of the second experiment was to test the hypothesis in realistic outdoor conditions while still being able to collect detailed plant growth information. This experiment confirmed the findings of the glasshouse experiment and provided evidence that leaf growth ceased as a result of a dwindling supply of carbohydrate reserves in the root. Defoliated plants did not exhibit increased mortality. Finally, the objective of the third experiment was to test the hypothesis in a commercial pasture where normal field operations, specifically grass harvesting (three times) and slurry injection (twice), were performed. The results of this experiment were consistent with the results of the other two experiments. We conclude that weekly defoliation, maintained for three or more months, is an effective method to control (reduce the impact on grass production), but not kill, R. obtusifolius in pasture

Increased virulence of Globodera pallida during repeated rearing on different resistant potato cultivars explained by a simple model

Selection for virulence of Globodera pallida on potato cultivars was studied for four generations under controlled conditions. The reproduction rate (Pf/Pi) of a mixed Pa2/3 population increased by a factor of 61 during rearing on the partially resistant potato cv. Darwina compared to rearing on the susceptible cv. Irene. This was a result of selection for virulence on cv. Darwina, and achieving the Hardy–Weinberg equilibrium on cv. Irene. Increased virulence also significantly raised the reproduction rate on several other Solanum genotypes. These changes could be explained reasonably well by the monogenic inheritance of a virulence factor breaking the Grp1 locus. The virulence changes were probably mainly evoked by this gene only, inherited from S. vernei 1-3 or S. vernei 24/20. The Grp1 locus has probably provided the differential S. vernei hybrid (VTn)2 62-33-3 with its resistance to the Pa2 group and not to the Pa3 group. Alternation of cultivars did not halt selection if the cultivars highly differentiated between the Pa2 and Pa3 populations. Only when alternation was with cultivars that harboured a different resistance gene against Pa3 was selection for virulence delayed. Differences in virulence levels (i.e. reproduction rates) within the nematode population determined the rate of selection, not the resistance level itself. Selection of a Pa3 population for three generations on cv. Karakter not only increased the reproduction rate on cv. Karakter itself by a factor 4.2, but also raised the reproduction on other potato genotypes. A simple monogenic model could explain these changes in virulence

Het testen van opgeschaalde Seinhorst-opspoelkannen

Om een voldoende grote statistische betrouwbaarheid voor de bepaling van populatiedichtheden van Globodera spp. in wetenschappelijke experimenten of bij het testen van aardappelcultivars ten behoeve van hun partiele resistentie-eigenschappen te verkrijgen, is het nodig om zowel de begin- als de einddichtheid van het aaltje nauwkeurig te bepalen. Twee methoden voor de bepaling van de relative vatbaarheid van aardappelrassen voor aardappelcysteaaltjes worden vergeleke

A scaled-up Seinhorst elutriater for extraction of cyst nematodes from soil

In order to process large soil samples containing potato cyst nematodes, the Seinhorst (1964) cyst elutriator was scaled up to process both sandy and marine-clay soils in batches of up to 2.5 kg. Several modifications were implemented. To maintain the required upward current of 3.01 min¿1, an inflow of 8.01 min¿1 was necessary in the enlarged, 7.5 cm diam. sedimentation tube. Also water inflow is now regulated using a flow meter with pressuriser. Several experiments were undertaken, using artificial sandy soil and marine-clay soil, both naturally infested with potato cyst nematodes. In the final experiment, using the 8.01 min¿1 inflow for 4 min, there was a loss of 0.65% and 0.74% of cysts, and eggs and juveniles, respectively. This indicates that the yield (99%) of the scaled-up elutriator matches that of the original Seinhorst elutriator and, therefore, is suitable for statutory and scientific researc

Data from: Weekly defoliation controls but does not kill broad-leaved dock (Rumex obtusifolius L.)

Data from three experiments in which the leaves of the grassland weed Rumex obtusifolius L. (broad-leaved dock) were repeatedly removed, and in which regrowth was monitored