General Instructions
In order for the simulation to run on your computer, your browser must be Java-enabled.
For a free download of the necessary software and the installation instructions, go to
http://www.java.com/en/download/manual.jsp.
Click the Start Simulation
button to the left. The simulation opens in a new window,
across the top of which is a menu bar. Check each menu and note the
selections in each. The menu at the far right is a Help menu
that gives you an explanation of each command and menu selection.
There is also context-sensitive help for each menu item.
From the Potato menu, you can select cultivars with low, moderate,
and high levels of resistance to Phytophthora, and from the
Environment menu, you can select various weather options to see how
late blight responds to temperature and moisture. In the Inoculum
menu, you can enter values for the numbers of sporangia blowing into the
field from cull piles or from adjacent unsprayed potato fields, and you can
enter values for the number of infected tubers that are in your field from
uncertified seed potatoes or from volunteers from the previous season.
The Management menu allows you to check the weather forecast day by day
and to spray either a protectant fungicide or a systemic fungicide as needed.
Select Begin New in the Simulation menu to start the simulation,
and use the right arrow key or click on the right arrow of the scroll bar to advance
the simulation through time.
The simulation behaves somewhat differently with different browsers and from one
computer to the next. If the model does not load fully on the first try, close it and
open it again. If the scrollbar just below the graph does not appear, increase the
resolution of your monitor and/or enlarge the simulation window. If the help window
will not appear, check to see that the browser's popup blocker is turned off for this application.
Note that the default units of measure are metric. If you prefer to work in acres,
gallons, pounds, hundredweight, etc. select American in the Measure menu.
(Select the desired units at the start of the simulation before clicking on Begin New.
The metric/American conversion is not designed to work while the simulation is running.)
For a detailed description of how the simulation works and how the model is
constructed, see the Lateblight Model Description.
....proceed to EXERCISE 1
Instructors: See
Instructor Answer Sheet.
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Introduction
Late blight
is a disease of potatoes and tomatoes caused by the fungus-like organism,
Phytophthora infestans. Under favorable environmental conditions,
and in the absence of any control measures, this disease can destroy virtually
100% of the above-ground parts of susceptible cultivars.
Inoculum produced
on infected foliage can be disseminated to the tubers, where infections can
also occur. Losses include reduction of photosynthetic area resulting in
reduced bulking of tubers (yield loss), blighted tubers (quality loss),
and decay of tubers in storage (postharvest loss).
Management of potato late blight begins with reducing the initial inoculum by:
- Keeping the numbers of infected seed tubers to very low levels
by planting only certified seed
- Crop rotation to reduce the numbers of volunteer plants (which may
be infected)
- Burying or composting cull piles, or at least keeping them far away
from the potato fields.
Control of late blight by means of potato varieties with a high degree
of resistance to P. infestans has not proven to be very practical
because of the rapid selection of virulent races of the pathogen. Varieties
with moderate levels of resistance, however, have been very useful when
combined with other management tactics, particularly the use of fungicides.
In most potato growing areas, regular fungicide application is an essential
component of late blight management.
Because of environmental concerns, the problem of fungicide resistance, and
the high cost of fungicides and their application, potato growers have been
forced to reduce their overall use of fungicides and to improve the
efficiency of the fungicides they apply. One approach has been to improve
the timing and adjust the dose of fungicide applications according to
environmental conditions. Various kinds of forecasting systems have been
employed to help growers decide when and how much to spray. By using potato
varieties that are partially resistant to P. infestans, it is possible
to markedly reduce the doses and/or frequencies of fungicide sprays.
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Arneson, P. A. 2005. Managing Potato Late Blight: Simulation with Lateblight. The Plant Health Instructor. DOI:10.1094/PHI/A-2005-0722-01.
This version of Lateblight was adapted from the simulation originally written
by J. A. Bruhn et al. (1980)
and modified in various ways over the years by different people working
in the research program of W. E. Fry, Department of Plant Pathology,
Cornell University. We have retained the original structure of the model
wherever possible, but some small modifications have been necessary to
enhance its pedagogical value. While the simulation is sufficiently
realistic for teaching purposes, this version should not be trusted as a
research tool or a management decision making aid. An earlier version of Lateblight
was adapted as a Microsoft Windows application by Barr E. Ticknor and Phil A. Arneson.
It was rewritten into Java and modified
as a web application in 2002 by Joshua M. Goldfarb.
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