April 2012
Disease & pest control By Bill Schaefer

Always an issue somewhere: Disease and pest management remain a precarious balance

The rise and fall of the potato has been inextricably linked to the diseases and pests that feast on the tuber.

The repercussions of late blight on the country of Ireland in the 19th century extended across the Atlantic Ocean, forcefully impacting the very development of the United States. Every March 17, you can witness the Irish impact from Boston and New York westward to Chicago and further west to Butte, Montana.

Growers today have a better handle on disease and pest management, but it is a tentative and precarious balance of power that is constantly being challenged by disease and pest resistance.
Over a century ago, growers were using sodium chloride, lime and sulfur to try and control late blight. Their efforts proved to be more futile than practical. In the 1880s, the first effective compound, composed of copper sulfate and lime, was called a Bordeaux mixture.

In the 1930s, copper-based products were used against late blight. By the 1940s, ethylene bisdithiocarbamates (EBDC) were developed. Zineb, metiran, mancozeb and others came onto the market.

Duane Preston recalls that when he began working in the Red River Valley in the 1970s, growers were just beginning to use new chemistries like the chemiks. Aldacarb and Thimet were two popular brands used by growers. These were followed by the pyrethroids.

“They (pyrethroids) came out and worked very good,” said Preston, “but they had such short lives. The Colorado potato beetle is the main insect that we have up here (RRV) and they built up resistance so quick that we had to come up with new chemistries.”

Insects are constantly adapting, said Preston, citing current problems with aphids and the spread of PVY as an example of the resulting problems growers encounter when pests build up a resistance to popular insecticides.

“We don’t have a lot of aphidcides left for aphids and that’s whey we’re getting so much PVY,” said Preston. “When we had Pygran and Monitor, some of those were very effective killing aphids and now we don’t have that class of family.

“The soil systemic ones we used were Chemik and Thymek. Then we went to the Admires, which is a different family…but we’re starting to build resistance to them as well.”

Preston said it was during this time that growers began to rotate chemistries to prevent insects and diseases from developing resistance.

“We had different families we could rotate with – like for the pathology part, we had the EDBCs like Maneb and Dithane….and you had the chlorothalanils known as the Bravos of the era, then you had the tin products, they were pretty popular in the ’80s and ’90s,” he said.

Preston cited other advances: more monitoring and scouting of fields; proper application timing; and advance information on the Internet, enabling growers to track insect movement or when conditions are right for disease.

Farther west in southern Idaho in the early 1960s, growers were dealing with early dying complex attributed primarily to verticilium, according to Bob Thornton, professor emeritus at Washington State University. “Spudded out” was the term commonly used to describe the condition.

“Chloropicrin and some of the telon-type materials were just coming on to the scene,” said Thornton. “Chloropicrin never caught on. It was effective, but it was a nasty bugger to handle. It is tear gas, so if you got a snort of it, you didn’t like it.”

With the introduction of the telon chemistries, the areas that had been “spudded out” were reinvigorated. They once again became – and remain – productive potato-growing areas.

Moving west to Caldwell, Idaho, and the Treasure Valley region, one of the first issues Thornton had to confront was nematodes. They weren’t as widespread as they are today, so growers could select production sites to avoid the pest until they would impact those fields.

At the time, some fumigants were available. However, growers would often opt to plant on another field instead of treating the infected field.

According to Thornton, early blight was the major foliar disease in the ’60s.

“You had some fungicides, you had the tin compounds that had come on board, you had EDBCs that were reasonably effective,” said Thornton. “Part of the problem was that we hadn’t worked out the effective timing of those applications to best combat the occurrence of early blight at a minimal cost.”

Thornton’s first experience with late blight occurred around 1992, after he had moved to the Columbia Basin. At that time, it was such a rare occurrence that it was believed it wouldn’t happen again. But by the late 1990s, that thinking changed.

“In the late 1990s, it became an issue someplace every year,” said Thornton. “We had to get on the train and figure out what to do about it.”

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