Jan 31, 2011Crop protection has entered a new era: IPM
Before examining the ways crop protection techniques have changed over the last half-century, George Bird wanted to go back a little further – 12,000 years or so.
Bird, 72, doesn’t go back that far, but with his long background in fruit production, nematology, pest management, soil biology, entomology and plant pathology, the retired Michigan State University professor felt that would be the appropriate place to start.
Bird, who still teaches classes and gives presentations, separates the history of pest management into three eras: the pre-synthetic era, the synthetic pesticide era and the Integrated Pest Management (IPM) era.
The first era was, by far, the longest. Records of insect pests are as old as human farming, which originated in the Fertile Crescent about a dozen millennia ago. Back then, farmers probably just moved when pest pressure became too intense, Bird said.
About 8,000 years later, there were signs that crop protection was becoming more sophisticated. By then, sulfur was being used as a pesticide. A few thousand years after that, Chinese farmers were using mercury and arsenic to control insects. In classical Greek times, Homer mentioned burning to control locusts. Nearly 1,800 years ago, China started using ants to control lepidopterous larvae that fed on orange leaves – the first biological control.
Bird jumped ahead to the European Renaissance, when scientific books about pests first made an appearance. The Irish potato famine of the 1840s opened people’s eyes to the fact that a fungus could be responsible for disease. In 1870, a French grower mixed lime and sulfur together to keep local schoolboys away from his grapes – inadvertently inventing Bordeaux mixture.
The first U.S. record of biological control came after the California gold rush of 1849. Some of the prospectors ended up becoming citrus growers, and a pest called cottony cushion scale nearly wiped out their crop. The U.S. government sent some scientists to Australia, who brought back a beetle that helped control the pest and pretty much saved the citrus industry, according to Bird.
In 1912, the U.S. government enacted the Plant Quarantine Act in an effort to regulate pests that came with foreign plant imports. Between 1915 and 1935 or so, U.S. growers controlled pests with inorganic pesticides like sulfur, copper, arsenic, lead and mercury, he said.
It was during the 1940s that growers started using DDT and similar tools to protect their crops. Those practices ushered in Bird’s second era of pest management: synthetic pesticides.
Fifty years ago, the use of broad-spectrum, synthetic pesticides was widespread. There were unexpected consequences, however. Pests started developing resistance, and potential damage was being done to human health, the environment and non-target organisms, according to Bird.
Things changed in the 1970s, when environmental and other concerns led to stricter rules for the application of pesticides. The federal government created the Environmental Protection Agency in 1971, which took over the regulation of pesticides from USDA. That led to a more structured regulatory program, said John Jachetta, president of the Weed Science Society of America (WSSA).
The 1970s also saw the rise of the crop consulting industry – particularly in California, said Frank Zalom, a professor of entomology at the University of California-Davis.
Pest control advisers have been licensed in California since the mid-’70s. Before then, growers had to make pest management decisions on their own. Now, there are plenty of professionals they can go to for advice, Zalom said.
In 1988, the federal government amended the Federal Insecticide, Fungicide and Rodenticide Act. In 1996, it enacted the Food Quality Protection Act. Those actions led to a major reevaluation of crop protection products. Older pesticides, like organophosphates, lost many of their uses and started to be phased out. Newer, “reduced-risk” pesticides started gaining favor and took over the marketplace.
Pesticides now are the most thoroughly evaluated products ever available, Jachetta said, but all that scrutiny tends to drive up costs – which drives research dollars toward larger commodity crops (corn, soybeans, wheat, etc.) that can afford them, Jachetta said.
Specialty crops are the “low man” when it comes to pesticide research, but they do get help from a federal program, the Interregional Research Project Number 4. Since 1963, IR-4 has developed and submitted regulatory data to EPA to support the registration of pest control products for specialty crops, said associate director Dan Kunkel.
Second only to weather, weed pressure is the most significant threat to agricultural productivity – more so than any other pests, Jachetta said.
The discipline of weed science was formally established in 1956, with the founding of WSSA and the institution of several journals. Before that, Jachetta said, weed management consisted mainly of cultivation and crop rotation. Those labor-intensive practices are still the backbone of weed management, but growers today can complement them with more sophisticated tools.
The use of chemical herbicides started in the 1940s with 2,4-D. The decades after that saw the discovery of many herbicides that are now used extensively. 2,4-D mimicked a unique plant product involved in the regulation of plant growth, but additional tools have targeted other plant-only processes such as photosynthesis, essential fatty acid and amino acid biosynthesis, Jachetta said.
As growers relied less on hoeing and pulling weeds and more on chemical tools, manual labor decreased and cropping systems became more productive. In the 1920s, for example, a grower using a newly invented tractor instead of a horse-drawn plow could feed approximately eight people; by 1990, a single grower was feeding 75 others, according to Jachetta.
But the use of herbicides is not without problems. In some cases, weeds started developing resistance to certain herbicide families.
“Continuous use of a single mode of action tends to select resistance to that mode of action, in the same way use of an antibiotic would select resistance to that antibiotic,” Jachetta said.
Every time that happens, however, steps are taken to mitigate resistance; usually with a combination of agronomic practices that include the judicious use of herbicides with alternative action – either concurrently or sequentially, he said.
“We do tend to make the same mistakes over and over, but we also find ways to develop new approaches once that occurs.”
For a long time, fruit growers were left out in the cold when it came to the invention of new herbicides. Orchards and vineyards don’t contain enough acres to make it profitable for manufacturers to develop herbicides for them. However, new chemistries exist today that are expanding into the horticultural market, Jachetta said.
Fruit growers started using the herbicide glyphosate extensively in the 1990s, because it was inexpensive and effective. But some weeds commonly found in orchards, like ryegrass, marestail and fleabane, have developed resistance to glyphosate and need to be managed with combination products containing more than one mode of action, he said.
All the environmental, health and safety concerns of the last few decades have ushered in George Bird’s third era of pest management: IPM.
In a 1979 message to Congress, President Jimmy Carter defined IPM: “A systems approach to reduce pest damage to tolerable levels through a variety of techniques, including predators and parasites, genetically resistant hosts, natural environmental modifications and, where necessary and appropriate, chemical pesticides.”
Bird thinks that definition holds up quite well today.
Pest management is more complicated now than it was 50 years ago. A grower has to monitor everything – orchard, fruit, pests, beneficials, temperature, rainfall, leaf wetness, etc. – and weigh it all before making a final decision. And the economic margin is smaller, so there’s less room for error. Mistakes can be disastrous, Bird said.
There seems to be more pests to fight these days, too. Zalom doesn’t have hard evidence to back it up, but he could swear he’s dealing with more invasive species these days. Increased travel and international trade has something to do with that, along with cutbacks in inspections, he said.
“In the last 10 years, it seems like half the things I’ve worked on have been recent invaders. It wasn’t like that before.”
− By Matt Milkovich
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