Malheur Experiment Station Information for Sustainable Agriculture

Seven potato fields in the Treasure Valley, central Oregon, and the Klamath Basin were monitored for temperature, relative humidity, and leaf wetness in the plant canopy. These data and rainfall data were recorded every 10 minutes and the data were forwarded via cellular phone daily to the Malheur Experiment Station. Data were used to estimate real-time late blight risk, using a model to predict potato late blight. Those estimates were distributed four to five times a week via the station web site at http://www.cropinfo.net/Potatoblight/blightcast.htm and by e-mail.

Before the 1995 growing season, potato late blight (Phytophthora infestans) was not a management concern in the Treasure Valley, central Oregon, or the Klamath Basin. During the 1995 season, late blight spread rapidly throughout the Treasure Valley from initial outbreaks in low-lying, humid areas. Treasure Valley growers made three to six fungicide applications in 1995 at great expense. Lack of adequate late blight control in 1995 in the Treasure Valley resulted in yield losses and some losses during storage. Late blight outbreaks in 1997 and 1998 in the Klamath Basin also have caused considerable economic loss.

The ability to predict when late blight is most likely to cause economic loss and when conditions are conducive to its rapid spread would aid in grower decisions as to the necessity and timing of fungicide applications. The refinement of late blight predictions could save growers money by improving the efficiency of control measures. Accurate late blight predictions are needed now for areas both where the disease normally occurs and areas, such as the Treasure Valley and the Klamath Basin, where it has not been a problem in the past.

The Wallin model uses hours of duration of relative humidity above 90 percent along with the corresponding temperature range to calculate the extent to which the daily environment has been favorable for potato late blight disease development. The Wallin model program used at the Malheur Experiment Station accumulates environmental conditions favorable for the development of late blight, which are called "severity values." When the severity value total reaches 18, late blight is predicted and additional fungicide control measures are indicated. The Wallin and other predictive models are being compared to the actual onset and development of late blight. It is essential that instruments are monitoring field conditions from the beginning of potato emergence.

Blitecast is a program module for late blight prediction that is part of the "Wisdom" software for potato crop and pest management from the University of Wisconsin, Madison. Like the Wallin Model, the Blitecast model uses hours of duration of relative humidity above 90 percent along with the corresponding temperature range to calculate the extent to which the daily environment has been favorable for disease development. The Blitecast model also includes rainfall duration and intensity in the risk for late blight, yet rainfall factors are usually not pertinent in arid eastern Oregon. The Blitecast program accumulates environmental conditions favorable for the development of late blight, which are called "severity values." When the severity value total reaches 18, late blight is predicted and additional fungicide control measures are indicated.

2. Help protect growers from economic loss to late blight. Help growers reduce their cost of production by avoiding unnecessary applications of fungicides.

3. Automate the collection of data from weather stations in growers' fields and AgriMet stations. Predictive models for potato late blight need to be adapted to the relatively arid areas of Oregon where potato growers are now suffering economic losses from late blight. Arid summer weather was not originally envisioned in the development of the Wallin model and other models to predict late blight.

During the 2003 season, data were collected from stations in seven potato fields and several AgriMet weather stations. Each of the seven stations in growers' fields consisted of a relative humidity sensor, a temperature sensor, a tipping bucket rain gauge, two Campbell Scientific Leaf Wetness Sensors (237LW, Campbell Scientific, Logan, UT), a portable stand, a data logger with battery and solar panel, a modem, and a cellular phone. Temperature, leaf wetness, and relative humidity in the plant canopy and the rainfall were recorded every 10 minutes. Data were forwarded daily via cellular phone or notebook computer to the Malheur Experiment Station. Weather data from outside of the crop canopy were collected every 15 minutes from seven AgriMet stations closest to the monitored commercial potato fields and forwarded electronically to the Malheur Experiment Station.

Data were used to estimate real-time late blight risk using the same relative humidity and temperature criteria used in the Wallin model, and those estimates were distributed via the station web site and e-mail.

The 2003 season was not conducive to the development of late blight. Late blight was not predicted in 2003 at Klamath Falls, Malin, Culver, Madras, Ontario, Nyssa, or Adrian, and did not occur. During the 2003 season, environmental conditions were favorable for the rapid spread of late blight at Tulelake in the Klamath Basin very late in the season, but late blight was apparently not present. The evaluation of the results of the last couple of years indicates only part of the value of predicting potato late blight. Access to late blight predictions since the program began has helped growers reduce fungicide costs by not making unneeded applications. The prediction of late blight before it has occurred has allowed timely fungicide applications and control of late blight.

Infield data were collected from four stations in 1996 and 1997, three stations in 1998-2002, and two stations in 2003. Starting in 1996, growers had access to late blight predictions.

Environmental conditions at Ontario, Nyssa, and Owyhee Junction near Adrian were particularly dry in 2000-2003. The estimated accumulated severity values did not pass 9 at any location; the threshold value is 18 (Fig. 1). The late blight outbreak was severe in 1995 prior to the beginning of this program (Fig. 2). Late blight was predicted before it occurred in both 1996 and 1997. Late blight was first detected close to Parma, Idaho near the Idaho-Oregon border on August 21, 1996, and on July 17, 1997. Between 1998 and 2003 late blight was not predicted and was not detected in these areas.

Starting in 1997, the data collection in the potato canopy and late blight predictions were extended to Madras. Two stations have collected data near Madras since 1998. The Wallin model did not predict late blight in 1997-2003 and the occurrence of late blight was not recorded. The air in potato canopies was very dry at Culver (Fig. 3) and Madras (Fig. 4), resulting in low accumulation of severity values in recent years.

A single station was set up south of Klamath Falls in 1997, and three stations were used in 1998-2003 (Fig. 5). In 2003 late blight risk accumulated in late July and mid August (Figs. 5 and 8).

In 1997, Wallin model severity values reached 17 at Klamath Falls before late blight was found in Tulelake, California (considerably to the south of the single in-field weather station). In 1998, late blight was found on a few isolated plants on July 10 before it was predicted on July 26. The Klamath Falls late blight epidemic in 1998 occurred later in August after it had been predicted (Fig. 6). The duration of high humidity in 2001 caused the severity index to reach 14 at Henley during 2001, in part due to irrigation patterns during the day that resulted in the potato canopy remaining wet from one night through to the next night on several occasions (Fig. 7). During the 2002 season, high humidity and a high severity index were caused by irrigation patterns. After the irrigation criteria was altered, no more severity values accumulated during the season. In 2003 late blight risk accumulated in late July and mid August (Figs. 5 and 8).

Figure 1. Comparison of two Treasure Valley locations (Ontario and Owyhee Jct. near Adrian) in the accumulation of estimated late blight risk during the 2003 season. Low relative humidity was associated with low accumulation of severity values in 2003; Malheur Experiment Station, Oregon State University, OR.

Figure 2. Comparison of late blight risk estimates over the last 9 years in the Treasure Valley. A severe late blight outbreak in 1995 was followed by a few late blight detections in 1996 and 1997. Late blight has not been predicted or detected the last 6 years; Malheur Experiment Station, Oregon State University, OR, 2003.

Figure 3. Accumulated severity values have remained low at Culver, Central Oregon during the last five seasons; Malheur Experiment Station, Oregon State University, OR, 2003.

Figure 4. Accumulated severity values have remained low the last seven seasons at Madras in Central Oregon; Malheur Experiment Station, Oregon State University, OR, 2003.

Figure 5. Comparison of three Klamath Basin locations in the accumulation of estimated late blight severity values during the 2003 season; Malheur Experiment Station, Oregon State University, OR.

Figure 6. Comparison of late blight risk estimates over the last 7 years in the vicinity of Klamath Falls. Rapid accumulation of severity values in 1997 and 1998 was followed by losses to late blight. Risk estimates were low during 1999-2003; Malheur Experiment Station, Oregon State University, OR, 2003.

Figure 7. Comparison of the accumulation of estimated late blight severity values near Malin over the last 5 years. The severity index reached 18 at Malin only near the end of the 2000 growing cycle, apparently due to irrigation practices; Malheur Experiment Station, Oregon State University, OR, 2003.

Figure 8. Comparison of late blight risk estimates over the last 7 years in the vicinity of Tulelake. Rapid accumulation of severity values in 1997 and 1998 was followed by losses to late blight; Malheur Experiment Station, Oregon State University, OR, 2003.

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Last updated  Tuesday June 28, 2011.