Browsing by Author "Logan, D"

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    Environmental factors affecting Adelina in the Burdekin region : final report CE004
    (BSES, 2003) Dall, D; Logan, D
    The project aimed to determine why the canegrub pathogen Adelina does not infect a significant proportion of the canegrub population in the Burdekin Delta area. It examined the effect of physical characteristics of soil (pH, sodicity and composition) and three other environmental parameters (temperature, relative humidity and compaction) on retention of oocyst infectivity for larvae over periods corresponding to one and two cycles of grub infestation of crops in the field. In addition, the project raced the establishment and persistence of Adelina infection in two experimentally inoculated field plots in the Burdekin canegrowing area. A ‘sentinel larva’-based bioassay that allows examination of the effect of various environmental factors on the retention of infectivity of Adelina was developed. Results of such a bioaasay showed no differences between the three types of soils tested, despite one soil coming from a region where the pathogen is very common (Bambaroo), and another from a region where it is quite rare (Burdekin Delta). The test did clearly show that drying conditions can be highly detrimental to retention of infectivity of the pathogen. Extrapolation from these results would suggest that field locations where there are prolonged periods of dry soil conditions would be at a relative disadvantage as regards maintenance of high levels of the pathogen in grub populations. Under field conditions in the Burdekin, Adelina did survive at levels sufficient to cause infection in the following generation of canegrubs in some areas and in one of two years; in the other plots and year, there was no subsequent infection. These results thus show that while oocysts of protozoan pathogens such as Adelina have robust external walls, they are, nevertheless, susceptible to the influence of adverse environmental conditions. Under field conditions, where exposure to any potential inoculum is likely to be more transient, the influence of an adverse environmental factor is even more acute. Improved understanding of the physical tolerances of the infective stages of Adelina has assisted in the design of crop-management strategies that maximise the impact of the pathogen on canegrub populations. These strategies have been incorporated into the GrubPlan program that has been successful in reducing the impact of greyback canegrub.
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    Farming systems that optimise the control of greyback canegrubs by BioCane� : SRDC final report BSS226
    (BSES, 2002) Samson, P; Logan, D; Milner, J; Kettle, C
    The carry-over of BioCane from one crop to the next is likely to be affected by soil cultivation during seedbed preparation. Metarhizium spores were concentrated in the rows in ratoon crops, either as spores surviving from the original BioCane application or as new spores produced by cadavers that are likely to be aggregated beneath stools. Soil disturbance was analysed using plastic beads as a marker. There was surprisingly little lateral displacement of the beads after cultivation. However, the rows themselves are likely to be displaced when crops are replanted unless minimum tillage planting into the old rows is practiced. In one field site prepared conventionally, spore concentrations were much lower in the new crop than they had been in the old crop.There was no effect of a trash blanket on grub response to BioCane in bins. Death of grubs following contact with BioCane may be slower at lower temperatures (<24?C), but the apparent difference was small. Spore concentrations in soil were not significantly affected by trash blanketing in most experiments. Overall, we were unable to conclude that trash blanketing will influence the efficacy of BioCane in commercial fields.There was no deleterious effect of the insecticides suSCon Plus, Confidor CR (controlled release) or Confidor SC (liquid), or of the fertilisers sulphur, gran-am or urea, on the survival of spores on BioCane granules in PVC rings. This is in agreement with field observations, where there have been no complaints from farmers who have applied BioCane close to some of these other products in commercial practice. However, abnormally low concentrations of spores in the rings indicate technical problems with the product that reduce confidence in the results.