This is to announce the inaugural season of Blightcast - a forecasting system for spray decision timing in potato for Late blight (caused by Phytophthora infestans).  Blightcast- linked weather stations have been in place since April and alerts are available to interested growers and ag professionals by calling 1-888-335-8636.  Daily Severity Values are also posted on a new website at http:\\blightcast.coafes.umn.edu   A network of 26 locations have been established that cover the major production regions of the state.

In 1995, a new strain of the late blight fungus was introduced into Minnesota.  This strain (commonly referred to as US-8) is thought to have originated in Mexico and has spread throughout the United States and Canada in the past 8 years.  This strain is unaffected by Ridomil (the fungicide metalaxyl, used to control outbreaks of the original US-1 strain in the early 1990's).  In addition, all major potato cultivars are susceptible to the new strain, and intensive fungicide spray programs are required to prevent catastrophic losses due to late blight (losses that were intensely severe in 1997 and 1999).

At present, the management of late blight requires complete coverage with protectant fungicides.  Unprotected foliage exposed to the late blight fungus will die at a rate of 6 % per day.  Uncontrolled late blight will also result in the infection of tubers causing them to rot in the field before harvest and also in storage.  Infected tubers represent one source of primary inoculum.  Infected sprouts in cull piles near warehouses or washing plants represent another potential source.  Volunteer potato plants may also play a role in initiating new outbreaks.

Efforts are underway to develop potato varieties that are resistant to the new strain of Late blight.  Sources of resistance have been identified among several wild species of Solanum and the evaluation of crossed materials has been the focus of accelerated efforts to develop new resistant varieties of red, white and russet potato types throughout North America and Europe.  Some efforts were initially directed towards the development of resistance through transgenic approaches although most of these have been abandoned (in favor of traditional crossing methods using wild species sources) as a result of market pressures against the purchase GMO’s in potato.

Current Situation Summary:

Wet weather this spring has created the potential for late blight development.  Growers are urged to establish adequate fungicide protection in potato canopies prior to row closure.  The wet weather has also caused a staggering of planting dates in many regions of the state.  The accumulation of severity values that trigger the initiation of protective spray schedules is a function of the number of hours of high humidity ( > 90%) that accumulate following 50% emergence of the crop. 

I ask that you be alert to possible outbreaks of Late blight in your county.  I ask that you visit our website and examine closely the posted dates for 50% emergence of the crop.   These are our best estimates.   If you feel that they do not reflect your county average, please contact us by e-mail using the links provided at the website.  In future years, we hope to develop a dialog box within each suite that will allow growers to input emergence dates and auto-calculate the severity values on a field-by-field basis.  For now, a local average will have to suffice.

The management of Late blight changes once disease is found in close proximity to production fields.  Increased rates and shortened intervals of protectant fungicides are recommended when Phytophthora infestans has been positively identified within 5 miles of a commercial field.  Your assistance in reporting any positive outbreaks would be greatly appreciated.  Outbreaks may be identified in commercial fields or they may be the result of disease developing in home gardens from either potato or tomato (tomatoes are also host plants for the Late blight fungus).

Attached to this correspondence is a spread sheet with the Blightcast station locations and the local contact (with phone numbers).  A map of the station distribution throughout Minnesota is also attached.   Most stations are Cambell Scientific CR-10 stations.  Many of these are maintained by the U of M.  We are also using four stations in the Red River Valley that are maintained by NDSU (part of the NDAWN network).  We have also arranged to purchase weather data for 6 sites from AWIS (Agricultural Weather Information Service).  The utility of this data (as stations are not located in-field) is being examined this season.

This project is supported by a grant from the Rapid Agricultural Response Fund (an initiative of the College of Agriculture, Food and Environmental Sciences).   Feel free to inform the citizens of your county about our efforts to manage the current problems facing potato growers in Minnesota.   Our website also contains links to regionally significant projects in Michigan, North Dakota, and Wisconsin.  Individuals interested in the history of the Irish Famine, those who are interested in protecting their tomatoes, or even those wondering about all the spray planes working potato fields around their lake home this summer can find more information through links provided at http:\\blightcast.coafes.umn.edu.