Cercospora leaf spot (CLS) has long been problematic to sugar beet production throughout the eastern and Great lakes production areas of the United States. In western Nebraska, it has been sporadic, but not a consistent issue. However, when it does occur, it can be very destructive.

The disease has played a pivotal role in Nebraska’s agricultural history, particularly influencing the locations of cultivation and processing of sugar beets within the state.

CLS is caused by the airborne fungal pathogen Cercospora beticola, and disease development is strongly dependent upon very specific environmental conditions. These include periods of high humidity or extended leaf wetness (more than 11 hours) and warm temperatures (higher than 60 degrees F at night and 80-90 degrees during the day). Without these conditions, disease spread and damage to beet crops is greatly reduced or inhibited.

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Sugar production in Nebraska began in 1890, with the first factory being established in Grand Island by the Oxnard Beet Sugar Co. Other factories in Nebraska were started in Norfolk and Ames later in the 1890s, but interest began to wane in these locations as growers discovered there was more money in raising corn and livestock than sugar beets.

Around 1900, interest in sugar beet production began to shift westward and was concentrated first in central Nebraska near the established Grand Island factory. Although much of the production moved to the Panhandle after 1910 with the construction of the factory in Scottsbluff, the production and processing of sugar beets continued in Grand Island until 1964.

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One major factor encouraging westward migration of sugar beet production was the increasingly severe problems with Cercospora leaf spot in the more humid areas of eastern Nebraska. Although the disease was commonly found in central Nebraska, it was of minor importance until the late 1950s and early 1960s.

The 1950s were characterized by a series of dry years. That fact forced farmers to dig thousands of new irrigation wells, with a subsequent increase of center pivot irrigation systems throughout central Nebraska for improving yields and profitability with controlled irrigation.

Furthermore, fungicides were routinely utilized to help reduce losses, but this system was apparently not sustainable. Sugar beet production ceased in central Nebraska after 1964 and eventually shifted again further west.

The more arid climate of the Panhandle discouraged many disease problems (including Cercospora leaf spot). However, a pattern similar to that of central Nebraska developed in the Panhandle with CLS. The disease was not considered an economic problem until the mid-1980s, when it began causing significant yield and sugar losses. This also coincides closely with the reduction of furrow irrigation and the rapid increase in sprinkler irrigation systems in the west.

Growers in the Panhandle then adopted fungicidal spray programs similar to those used earlier in central Nebraska. Sprays were based on the assumption that disease would increase over the growing season. In western Nebraska, it was noted that sometimes the disease would not become more severe, thus fungicide spraying was not necessary every year.

This observation spurred the development of the Cercospora alert system by UNL Plant Pathologist Eric Kerr and Extension Climatologist Albert Weiss in the late 1980s, which is still in use today. The alert system predicted the likelihood of CLS outbreaks, based on daily measurements of local environmental conditions (temperature and relative humidity) that might favor the disease.

Today we are uncertain as to the specific reasons for the dramatic increase in disease pressure in the 1950s and 1980s in central and western Nebraska, respectively. However, it is curious that the escalation of CLS disease problems in both these regions accompanied a simultaneous increase in sprinkler irrigation systems.

Even in the more arid climate of western Nebraska, center pivot systems create and efficiently maintain a humid microclimate within crop canopies, which then enhances conditions favored by the disease. Perhaps this explains how and why CLS became more problematic in two distinct areas of Nebraska sugar beet production?

Nevertheless, the history of the sugar beet industry in Nebraska has been strongly driven and altered by this single plant disease.

— Robert M. Harveson, extension plant pathologist, Panhandle Research and Extension Center, Scottsbluff.