Interest rates explain disease epidemics

The term ‘maverick’ often is applied to a person who does not conform to or play by the rules and often takes an unorthodox stand. As often as the word is used, few people know that maverick is associated with a family name.

The origin of maverick comes from an 1800s rancher by the name of Samuel Augustus (S.A.) Maverick. During his time open range ranging was prevalent throughout Texas. To identify what steer belonged to whom, cattlemen would brand their calves for identification. However, S.A. Maverick chose not to brand his cattle, reasoning that if everyone branded cattle than those not branded were his. In some dictionaries one of the definitions given for maverick is “an unbranded calf or yearling.”

In plant pathology the most famous maverick was James Edward Vanderplank, who was born to an English family with a family heritage of more than 200 years, in South Africa. He kept the English spelling of his name for more than 60 years then changed his name to Van der Plank, the Dutch version.

Back in the day this caused graduate students considerable frustration. Now you had to search under multiple names to find his citations. Normally this is not a big problem, but for Vanderplank, who was/is one of the most cited researchers in plant pathology, it was. I’m convinced he knew his name change would cause problems for aspiring researchers.

In the 1950s Vanderplank was a potato breeder and the major disease of potato was late blight. By training he was not a plant pathologist, and actually prided himself on that fact by telling students that he had never taken a plant pathology course. Vanderplank, based on the development of the growth curve or sigmoid shaped curve in the 1940s, proposed mathematically how plant disease epidemics occurred. His early papers in the late 1950s on spore dispersal and such were not well understood. Frankly, no one understood what he was doing. Plant pathologists at the time were focused on looking at weather parameters as they influenced disease epidemics.

However, in 1963 when he released his book, “Plant Diseases: Epidemics and Control,” all that changed. Vanderplank used simple interest and compound interest terms to describe different types of disease epidemics. Simple interest, or monocyclic diseases, were ones that increased mathematically — similar to simple interest on money. Monocyclic diseases develop one generation of infection and rarely does secondary infection occur during the season.

In turf, the diseases that would most likely be considered monocyclic diseases are the soil-borne pathogens. The major soil borne pathogens I would consider are the ectotrophic root infecting fungi that cause diseases. For example, take-all, summer patch and spring dead spot.

Compound interest diseases, or polycyclic diseases, are characterized by multiple generations of spores being produced in a year. These diseases are normally quite explosive compared to a monocyclic disease that, similar to money, will grow much more quickly with compound interest. Polycyclic diseases would include Microdochium patch, gray leaf spot and some of the leaf spotting diseases, to name a few.

Besides predicting or explaining a disease epidemic, Vanderplank also proposed that the variables used in predicting an epidemic could be used to explain control strategies. His mathematical equations included two primary variables: number of the spores or pathogen (N) and the rate of growth of the pathogen (r). Control measures focus on either the N or r. Chemical, biological and genetics (plant resistance or susceptibility) impact N. Effective cultural practices slow the rate of pathogen reproduction. The basic understanding of cultural practices, sanitation practices, chemical and biological controls are described by Vanderplank’s work.

Vanderplank’s seminal book on plant epidemics has stood the test time (with some modification and challenges). He epitomizes the person who is able to “think outside of the box” or, as I prefer, the more admirable term: maverick.