Technical
Agrostis canina canina plots - January 2012
levels of disease incidence but, importantly, the application of potassium phosphite reduced the incidence of the disease by more than 50%.
The treatment which was most effective at reducing M. nivale incidence was the combination of iprodione (Chipco Green) and potassium phosphite. These fully inhibited M. nivale incidence on the majority of plots, this total inhibition indicating either differing modes of suppression or a possible synergistic effect.
Turfgrass quality
Turfgrass quality at the beginning of the trial periods was uniform for all plots. As the trials continued, the quality of all plots not receiving phosphite became progressively poorer. By comparison, the quality of all plots receiving the PK Plus phosphite applications improved each month. Interestingly, the Chipco treated plots, even with significantly less disease incidence than the phosphite treated plots, produced a poorer quality sward of less density than the phosphite treatments.
By the end of the trial periods, the quality and density of all phosphite treated plots were far superior to all other treatment regimes.
What has been concluded from these trials is that sequential applications of
potassium phosphite significantly reduced Microdochium nivale incidence and led to an enhancement in turfgrass quality.
Means of suppression
Phosphite mediated reduction of M. nivale has now been established, but the question remains how does this occur? There are two possible methods:
- Direct, which means phosphite acts as a fungicide and kills or stops the growth of the pathogen
- Indirect, by stimulating the turfgrass plants natural defence mechanisms.
To test whether phosphite acted directly on the pathogen, we carried out a range of studies. This involved propagating M. nivale samples taken from infected golf greens. This was then used for a range of laboratory studies which assessed phosphites effect on Microdochium mycelial growth. The fungal mycelium was grown on petri dishes which had been amended with various concentrations of phosphite. We then compared growth to mycelium grown on phosphate and unamended controls.
Phosphite effects on mycelial growth
What we found was that phosphite amended samples, with concentrations of 100µg/ml and above, fully inhibited mycelial growth. Phosphate amended
samples caused no inhibition. Microscopic analysis of the individual fungal hyphae showed distinct irregularities when grown on the phosphite amendments.
What has been learned to date with this section of the research is that phosphite, when in contact with M. nivale, directly inhibits the mycelial growth and conidial germination and causes disruption of hyphal morphology. In the plant, this means phosphite slows the growth of the pathogen, causes release of stress metabolites, thereby allowing for increased time for the plant to initiate defence responses.
What happens when phosphite is applied to turfgrass?
Whilst we knew how phosphite inhibited the fungal growth in the laboratory, we wanted to know if the same happens in the field - in other words, what happens when phosphite is applied to turfgrass. We needed to measure the assimilation rate, track translocation and determine accumulation amounts of phosphite when used as a foliar application on golf greens.
We did this by applying the phosphite in spray, collecting leaf, crown and root samples over a period, and then analysing them using a laboratory procedure which separated and quantified the individual ions of
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