Downy Mildew (Plasmodium viticola) decision support tool
viticolR
A mechanistic compartment model to assist in fungicide decision support for downy mildew (Plasmodia viticola) primary infections in grapevines.
Adapted from scientific literature by Dr Paul Melloy, while working at The University of Queensland
Funding for this project was provided through the Agrifood Kickstarter grant funding in partnership with Cauldron distillery
Disclaimer:
This app is to be used as a guide in making more informed fungicide management decisions. Individual circumstances and conditions may vary, and local conditions should be also concidered when deciding on the appropriate fungicide application
Always apply fungicide according to the label recommendataions
Model estimates primary innoculum dispersal only:
This model uses weather inputs to estimate the steps in primary inoculum dispersal and therefore is influenced by the AWS accuracy. The closer the weather station to the vineyard, the more accurate the estimations. By default missing rainfall observations are filled with 0
This model does not account for secondary infections. If downy mildew is already present on the leaves, an alternate fungicide approach should be considered as this decision support tool would be misleading Once downy mildew is established in the vineyard disease can develop rapidly. Use of this model should be used to prevent primary leaf infections
This model is translated and adapted from the published paper 'A mechanistic model simulating primary infections of downy mildew in grapevine' authored by Vittorio Rossi, Tito Caffi, Simona Giosue and Riccardo Bugiani. This paper was first published in Ecological Modelling in 2008. 10.1016/j.ecolmodel.2007.10.046
Input vineyard details
Submit an issue on github to request the addition of an extra BOM AWS weather station
Weather observations
Downy mildew infection process:
Primary innoculum is the source of the first infections in a crop. The source of which is usually from downy mildew resting structures called oospores residing in leaf litter from the previous season. Overwintered oospores germinate 'sporangia' progressivly through grape growing season when there is suffifient moisture. If conditions remain suitable for sporangia development and survival, zoospore mature within the head of the sporangia. When zoospores are mature rainfall events are required for dispersal to a living host leaf. Environmental conditions, and leaf moisture, need to remain suitable for infection following dispersal for infection to be successful. Following a successful infection the pathogen incubates during the 'latent' period', the time between infection and visible symptoms in the form of 'oilspots'
Figure reproduced from Rossi et al. (2008), 'A mechanistic model simulating primary infections of downy mildew in grapevine'
Seasonal progress of residual oospores germinating
According to Rossi et al. (2007) The germination of oospores, the overwintering downy mildew inoculum, is best explained by Gompertz's equation published in the book 'Introduction to Plant Disease' by Campbell and Madden (1990). Gompertz's equation uses 'Hydrothermal time', a compbination of temperature, rainfall and vapour pressure deficiet (VPD) to estimate conditions in the the soil-leaf layer that would lead to the germination of oospores into sporangia. Here we calculate hydrothermal time from 10 days after the winter solstace. Approximately 3% and 97% of oospores are estimated to have germinated at hydrothermal time of 1.3 and 8.6 respectivley. This is shown by the blue shading on the graph below. When hydrothermal time is outside this range there is a low probability of downy mildew infection from primary innoculum sources.
Primary zoospore dispersals from oospore sporangia
Blue lines show the maturation of soil-borne sporangia, when they reach '1' sporangia are mature and dispersal is possible.
Beige areas show times when sporangia are mature and dispersal is possible.
Light red lines show a zoospore dispersal event, if no recent protective fungicide has been applied, apply ASAP or Agriphos which can provide some curative activity.
Red lines show zoospore likely infection events.
You can use this plot to determine the approximate next dispersal event.
The number of germinated oospore cohorts over the whole season. Sporangia germinate from oospores following rain and survive for some time.
Number or cohorts which have germinated and not survived until conditions were suitable for a dispersal event.
Sporangia survival time range in hours for this site.
Number of times primary infection events in this season. This is when zoospores have successfully been dispersed by rain splash from sporangia onto leaves and conditions have been suitable enough for zoospores to survive and infect.
Number of germinated sporangia cohorts which could lead to a zoospore spread event if it rains
Most recent time when surviving sporangia contained mature zoospores ready for dispersal. It is likely that any rain within 1 - 48 hours of this time will lead to a dispersal event
When zoospores have been spread and caused infection, however have yet to produce symptoms. During this period there is an oppotunitiy to apply fungicide to treat the infection
This plot shows how many 'cohorts' or events where oospores have germinated sporangia (GEO_h), which have then released zoospores (zoo_release_ind). If a rain event occurs when the zoospores have been released before the zoospores dry out and die then the zoospores have a chance to disperse to grapevine leaves (zoo_dispersal_ind). Zoospores can then infect the leaves if conditions remain suitable for infection (zoo_infection_ind). Then the infections are latent for a period before infections present as oilspots between INC_h_lower and INC_h_upper.