Linda F. Benedict, Schultz, Bruce
In her 1960 book “Silent Spring,” Rachel Carson shook agriculture to its core with a stinging indictment of heavy pesticide use and its effects on the environment. But that book may have actually helped farmers in the long run, according to Rogers Leonard, LSU AgCenter vice chancellor for plant and soil sciences.
“One outcome from that book was the concept of integrated pest management,” Leonard said.
Leonard said the book’s overall message — that farmers were relying heavily on pesticides as a single control tactic to solve their pest problems — persuaded scientists to look at opportunities for pest management in a broader spectrum and reduce overall pesticide use.
“Integrated pest management strategies use a variety of control measures in a holistic system,” Leonard said. “Pesticides can still be an important component in the system, but with an enhanced understanding of the interactions for the cropping system and pest and other management techniques.”
The IPM approach generally combines several tactics such as cultural practices, physical methods, host plant resistance, biological control agents, chemical control and regulatory actions. Cultural practices, such as planting date, variety selection and proper fertilizer use, can often help prevent problems with weeds, diseases and insects. Physical methods work to prevent the pests from infesting the host. Traps, barriers or vacuuming can be used as physical controls.
Plant resistance to pests may include nonpreference or avoidance of the host plant, tolerance in the presence of the pest or having chemicals produced in the plant that negatively affect the pest. Biological control of pests relies on the use of predators, parasites and diseases in a targeted way to suppress pest populations.
Regulatory action refers to government policies that attempt to reduce pest infestations through inspections, quarantines and destruction of infested material. Managed chemical control is used to supplement many of these other practices.
The IPM philosophy requires regular monitoring of a crop and the pest. It also requires clearly defined action thresholds for determining when a farmer should use herbicides, fungicides or insecticides, rather than spraying on a schedule or when a pest is found, regardless of the population or severity.
Leonard said he has realized that many farmers have been using IPM practices because the techniques have become habits, without realizing the true, original reasons.
“We’ve gone through a generation or more of farmers, and they’ve been applying IPM techniques for 30 or 40 years,” he said.
Long before Carson’s book, many farmers were using various components of IPM before the practices had been included in a named strategy. For example, plowing a field before planting has long been a way of controlling weeds as much as it is a seedbed preparation, Leonard said, and eliminating weeds early often rids a field of prime habitat for insects harmful to a crop.
After World War II, the United States saw a heavy adoption of pesticides in agriculture because of the development of inexpensive, broad-spectrum and effective products such as DDT. With these tools, farmers could spray pesticides upon the first sighting of a pest without regard to pest population or the nontarget effects in the environment.
LSU AgCenter plant pathologist Clayton Hollier recalled that the late Mary Grodner, LSU AgCenter pesticide coordinator, often referred to “the judicious use of pesticides.
“The ‘judicious use’ is a perfect phrase,” Hollier said. Before spraying a field, other measures should be used including variety selection for resistance, date of planting and using a recommended seeding rate, Hollier said. Once the crop is established, regular scouting for insects and disease is essential.
Using too much fertilizer can foster disease development. Hollier recalled a field in Vermilion Parish years ago where a pilot applied twice the fertilizer rate on the perimeter, leaving a well-defined strip of blast-infested rice.
Weeds also harbor disease pathogens, he said, and simply mowing the edges of a field can help control disease and insects.
“If you look at the particulars of a lot of pathogens, the hosts often are weeds,” he said.
Hollier said IPM is a balanced approach.
“You don’t want to rely on any one thing,” he said.
Consistent use of the same chemical will foster resistance to a chemical. Persistent use of herbicides with the same mode of action has created populations of resistant weeds.
“Many farmers chose not to vary products due to differences in costs,” Hollier said.
Leonard said control of the boll weevil was a prime example of the potential of IPM. Effective control of this cotton pest usually required multiple applications of insecticides. Even when using effective sampling strategies and action thresholds as prescribed in IPM to initiate treatments, the frequency of sprays was often excessive.
However, eradication of the boll weevil began in North Carolina where farmers used the cultural practice of destroying cotton stalks after harvest to remove overwintering habitat for the insect, Leonard said. Traps were used to monitor the presence of boll weevils.
These practices were used throughout the South, and the boll weevil now has been confined to an area in Texas along the Rio Grande Valley. Many cotton farmers today never had to deal with boll weevil infestations in cotton fields, Leonard said.
Johnny Saichuk, LSU AgCenter rice specialist, said simple practices such as planting early are an important part of IPM. “You combine every tool you have and resort to the pesticide as a last measure,” Saichuk said.
Flooding rice fields is primarily a weed-control measure, but delaying when the flood is applied can help control the rice water weevil.
Scouting fields and using insect population thresholds before spraying is now considered sound crop management. Controlling weeds in a crop is a given for the highest yield, but even weed control on the edge of a field can reduce insect problems, Saichuk said.
Bruce Schultz is an assistant communications specialist with LSU AgCenter Communications.
(This article was published in the spring 2014 issue of Louisiana Agriculture.)