Charles M. Benbrook
Ever since clearing the trees and the plowing of native soils, the landscape of the Northern Plains has been changing. Times of change offer hope yet also raise challenges.
When change includes intensification of farming systems and the production of a high-value crop like potatoes, pest management is bound to be among the most important challenges. Indeed, there is a special gear on the pesticide treadmill reserved for potato farmers. This gear has proven hard to avoid for many other farmers around the country, and costly for rural communities and natural resources.
I have been asked to address the possible impacts on pest management and pesticide use of the major new AVIKO USA french fry processing plant in Jamestown. My remarks regarding changes in farming systems are most relevant in Stutsman, Kidder and surrounding counties where the pace of change has accelerated recently as a result of the plant's opening. AVIKO contracted for some 7,500 acres of potatoes in 1996 -- representing about 6 percent of the 131,000 acres harvested in 1996 -- and started production in October.
Impacts on Land Use
According to the December 3, 1996 Jamestown Sun, 6,200 acres of the 7,500 contracted were irrigated. I am told that most of this land was not previously producing potatoes, so the 7,500 acres are predominantly new to the production base. It is interesting to note that statewide, potato acreage rose from 1995 to 1996 by about 10,000 acres -- the plant accounting for nearly three-quarters. This increase is actually modest given the very high potato prices in 1995 -- $8.00 to $9.00 per hundredweight.
Clearly, the AVIKO plant has played a significant role, both in fueling recent growth North Dakota potato acreage and hastening the shift in production practices.
Some of the changes in production practices will have major impacts on pests and pest management, on nitrogen cycling and water quality. For example, in 1993 the average acre of North Dakota potatoes received 110 pounds of nitrogen -- the lowest rate of any major potato growing area. Washington state growers applied 299 pounds; Idaho, 237; Wisconsin, 190; and Minnesota, 213. Today, rates are higher in North Dakota and the difference across states is less great. Within a few years, North Dakota N fertilization rates may about double, on average, compared to the 1993 rate.
Lighter, sandy soils are sought out to produce the preferred varieties and size of potatoes for french fries. Such soils also tend to be subject to drought -- hence the need for irrigation and the increase in potential for nitrates and pesticides reaching groundwater. It is for this reason that the recent expansion in potato acreage is occurring outside the Red River Valley and other parts of the state where potatoes have been grown successfully without irrigation on heavier, higher quality soils.
The shift from heavier to lighter soils is coupled with, indeed largely causes, the shift from dryland to irrigated potato production systems. In 1993, 25.4 percent of North Dakota potatoes were irrigated, according to USDA's cropping practices survey data. Today, well over half are irrigated. The AVIKO plant hopes to double its contracted acreage by 2001. I understand plans are in the mill for other plants if this one proves successful.
If current trends continue, over three-quarters of North Dakota potatoes will be irrigated by the year 2005. If the industry retains its current acreage -- about 130,000 acres -- this would result in over 85,000 irrigated acres. Since a large share of these 85,000 acres will be grown in areas formerly producing small grains and other dryland crops, it is reasonable to expect localized environmental impacts even if great care is exercised in managing erosion, water quality, pests and nitrogen.
Sandier soils are lower in organic matter content, and hence are more prone to leaching. The efficiency of nitrogen uptake on sandy soils is invariably lower than on heavier soils. To cover the capital costs of new irrigation systems, growers will strive for maximum yields, which means farmers will try to assure nitrogen is not a limiting input. Markedly higher rates of nitrogen (N) fertilization will be common on irrigated land -- perhaps as much as 2.5 to 3 times the average rate of N applications on dryland acreage. Hence, many more pounds per acre will leach to groundwater. Given the shallow water table in much of North Dakota's potato producing region, the hydogeological cycle's capacity to assimilate nitrogen without biologically significant consequences is bound to be limited.
Irrigated systems on sandy soils also are prone to special weed management and plant disease problems, which will require heightened skill in the design and implementation of Integrated Pest Management (IPM) systems. In the absence of skillful IPM, reliance on pesticides is likely to rise sharply, with possibly significant impacts on water quality and local wildlife.
These changes will have at least four major consequences in the realm of pest management --
Wherever potatoes are grown, farmers have learned the importance of crop rotations in limiting pest pressure. Most IPM programs call for at least a three year rotation. Four years is often better if the land is available.
North Dakota potato producers have done a good job in sticking to rotations -- a key preventive practice that AVIKO should require as part of its production contracts. In 1993, 77% of potatoes in the state were grown in a three year rotation with row crops and a small grain crop; 13% with hay/pasture; and 10% with continuous row-crops.
Why are crop rotations beneficial? What goal should the farmer strive for when designing a rotation? The benefits of crop rotation arise from the management of habitat both above and below the ground in ways which contribute to profitable crop production. The traditional view of rotations is that they work by breaking pest cycles. Deny a pest the food source it needs and its population will decline. For many potato pests, this is the principle reason rotations work.
But for other key pests -- especially those that live in the soil and attack plants through root systems -- rotations play an additional role. Soil microbial communities adapt and change as a function of the way their environment changes. Any change in a farming system that alters competitive advantage within soil microbial communities is likely to have some impact on pest pressure, reliance on pesticides, yield or quality losses and overall farming system performance.
The benefits of rotations in managing below-the-ground insects and diseases arise largely from microbial biocontrol processes that lead to healthier root systems and stronger plants. The mechanisms generally have little to do with denying a certain pathogen access to its food source. This is because most soil borne pathogens are incredibly durable and persist in the soil at some level for years despite long rotations, recurrent chemical assault or anything else farmers try to get rid of them.
In dealing with pathogens through rotations, the goal is two-fold: first, assuring the presence of a diverse range of microorganisms, especially those known to compete effectively with damaging pathogens or attack them directly, and second, selecting crops, tillage systems and residue management practices that provide beneficial microorganisms a steady supply of food, moisture, and habitat, and indeed an extra boost during those parts of the season when the potato plant is most vulnerable to attack by damaging pathogens.
For decades the goal of the organic farmer has been to feed the soil, which actually means feeding the microorganisms that live within the soil. On many organic farms, this feeding of the soil is carried out generically, through diverse rotations, the planting of cover crops and additions of manure and compost to the soil. Today, science is beginning to identify the characteristics of soil microbial communities that give rise to "disease suppressive soils." This knowledge is critical in designing rotations and farming systems that go beyond just feeding the soil. They do so by preferentially feeding, at the right times, those species of microorganisms that have the ability to protect plants from pathogens through competition, predation, parasitism, antibiosis, or by triggering the plant's immune system (a process called "systemic acquired resistance").
The selection and incorporation of cover crops is another key dimension of crop rotations. Fall seeded cover crops can play a key role in protecting the soil from harsh climatic conditions, while also helping to sustain populations of beneficial soil microorganisms. The timely incorporation of strategically selected cover crops, coupled with irrigation scheduling and nutrient management, is being used by fruit and vegetable growers in many regions to create conditions favorable to organisms typically encountered in known disease suppressive soils.
Rotations and cover crops, then, need to be selected for both agronomic and economic reasons. In general, corn will be a good choice as a rotational crop, since it produces lots of residue. The residues will help lessen the risk of erosion, and also will help sustain higher levels of soil microbial diversity and activity -- the key in managing several potato diseases associated, in one way or another, with nematode damage and activity. A small grain, preceded or followed by a cover crop, will also fit well into many rotations, as may sunflowers and other crops adapted to this region.
I am sure continuous on-farm research will be needed to determine the best way and time to harvest corn and other rotational crops, the best way to manage residues, and carry out fall and spring tillage activities. All these factors will also influence nitrogen management. One key strategy for limiting N-loss to groundwater, for example, is to tie up more nitrogen in organic matter cycling in the soil. But farmers will need help to develop methods to do so that also positively contribute to pest management systems.
It is essential to understand the biology of farming systems, and the ecological interactions and factors that can turn typically innocuous organisms into pests, in order to design optimal crop rotations. Moreover, as soil physical and biological properties change, and they surely will as a result of the shift from dryland grain to irrigated potato production, the interactions of the crop, pests and other organisms will also change. Some changes may be positive in reducing pest pressures, others negative. Crop rotations will need to adapt as a result, enhancing the positive and overcoming negative developments as much as possible. So, rotations and crop residue management practices will be --
So, farmers, AVIKO and the state should do everything possible to assure profitable markets for those rotational crops known to best help enhance the agronomic efficiency of potato production systems.
A second note of caution -- the pattern of crop rotations from grower to grower and field to field across the landscape will significantly influence the benefits from an otherwise well-designed rotation. To the full extent possible farmers and their neighbors need to coordinate crop rotations on each field so that the diversity of crops is maximized across the landscape. If one farmer's three-year rotation ends up placing a potato crop next to a neighbor's field producing potatoes the year before, the full benefits of the three-year rotation may not be realized. Wisconsin farmers have learned from experience to discuss cropping plans with neighbors to assure that the full benefits of rotations are realized, especially in fields with high and/or rising pest pressure.
Pesticide Use
In 1993, North Dakota potato farmers applied, on the average acre, 6.24 pounds of pesticide active ingredients. Only Minnesota farmers applied less -- 6.0 pounds. Growers in other states were much more chemical intensive -- applying as much as 124 pounds a.i. per acre (Washington), including 80 to 100 pounds of a soil fumigant. Other major producing states that do not use fumigation applied 15 to 25 pounds of pesticide per acre.
Herbicides Again to the credit of North Dakota potato producers, 100% of potato ground was cultivated for weed management in 1993, an average of 3.2 passes per acre -- the greatest reliance on this preventive weed management practice in the nation. As a result, only 51.8% of potato acreage in 1993 was treated with a herbicide, by far the lowest percent in the nation and a remarkable achievement compared to other states, and the intensity of herbicide use today on the majority of North Dakota's irrigated potato acreage.
In addition, on the North Dakota potato land treated with a herbicide in 1993, average rates of application were also very low compared to most other states -- 1.08 pounds a.i. per acre, compared to a national average of 2.1 pounds, and some states applying 4 pounds or more.
But today, with a majority of potato land irrigated, herbicide use has mushroomed. The average irrigated acre was treated with at least two herbicides, and at rates generally higher than dryland acreage. The major products are pendimethalin (80% acres treated at 1.1 pounds a.i. per acre), sethoxydim (53% acres treated at .22 pounds a.i.), metribuzin (46% acres at .44 pounds), linuron (31% acres at 1 pound), and metholaclor (11% acres at 2.7 pounds). Compare this level of reliance on herbicides to dryland acres, of which only a little over half were treated with just one herbicide, and typically at somewhat lower rates per acre.
Accordingly, the shift from cultivation-based weed management to reliance on herbicides may emerge as the most significant change in pest management systems as North Dakota intensifies its potato production systems. Growers, rural communities and the state need to carefully monitor herbicide levels in groundwater, since it will probably not take long for contamination to show up. Citizens in the state will then have to wrestle with the tough choices required to set -- and enforce -- safe levels.
Another herbicide-related issue warrants special attention. Potatoes are notoriously vulnerable to a range of root diseases. As noted above, the best way to protect against such diseases is to assure a high level of microbial biodiversity and activity in the rhizosphere -- the region in the soil very close to plant roots. The soil microorganisms that help protect plant roots from pathogens also play an integral role in phosphorous bioavailability and in the promotion of plant health.
There organisms, unfortunately, are highly susceptible to sulfonylurea herbicides often applied to small grain crops. Product labels carry warnings to avoid plant injury. Such rotational restrictions typically are based on the prospect of direct phytotoxicity, but even longer time periods may be needed to avoid adverse impacts on potato production systems -- especially those in which growers are trying to manage root disease with minimal chemical inputs.
Growers and researchers need to look very carefully at the populations of key microorganisms in the root zones of potato fields on land treated within the last two, three or four years with a sulfonylurea herbicide. They should look for overt signs of phytotoxicity, plus evidence of impacts on susceptibility to disease and insect attacks and lowered efficiency in phosphorous uptake.
Insecticides The average potato acre in 1990 was treated 2.1 times with insecticides. By 1995, reliance had risen modestly to 2.6 treatments. But in some states, potato growers have been drawn onto the insecticide treadmill. A combination of resistance and secondary pests can shift the treadmill into that special potato-high gear, and some farmers have had a tough time staying in business as a result. The intensity of use and reliance on insecticides reached high levels -- in Michigan, for example, farmers applied an average 6.4 pounds of five different insecticide active ingredients in 1993.
Just as in the case of herbicides, the average irrigated potato acre in North Dakota was treated with substantially more -- and more toxic -- insecticides in 1995, compared to dryland acreage. The biggest differences in insecticide use were in reliance on some of the most acutely toxic organophosphates still on the market. Only 3.2% of dryland acreage was treated with phorate, compared to 58.6% of irrigated acreage. The average rate of methyl parathion applications on dryland acreage was 1.02 pounds of a.i. per acre but on irrigated land, 2.04 pounds were applied per acre.
In the case of the endocrine disruptor endosulfan, 7% of irrigated acres were treated with 1.88 pounds of active ingredient. On dryland, only .69 pounds per acre were applied per acre. In the case of several other insecticides in 1995, the rate of application and number of applications were markedly higher on irrigated land in contrast to dryland acreage. Since many North Dakota potato producers continue to apply some of the most toxic insecticides available, the implications for wildlife, soil microorganisms and worker-safety are worrisome and will also warrant close monitoring.
A precautionary note is appropriate given how quickly many growers have fallen in love with Admire (imidacloprid). This effective new insecticide works very well and is easy to use. Despite its high per acre cost, too many producers think it is the "final solution," that silver bullet which will forevermore render the Colorado potato beetle (CPB) a harmless distraction.
I am told attention to CPB management through IPM is slipping in some regions. Over 80% of Maine and Pennsylvania potato acreage was treated with Admire in 1995, and almost 80% of Michigan's acreage. Just as with all the wonder pesticides in the past, resistance will soon emerge if growers depend unilaterally on Admire for CPB control. Some experts give it only two or three years in regions where pest managers are now using it almost exclusively for insect control.
This leads me to an important point -- there are a number of new, effective and hopefully safer pesticides, many of them biological in origin, reaching the market, or soon to become available. If managed well within biointensive IPM systems, these new tools will make it possible to reduce pest losses, lessen pesticide use, and dramatically reduce the "toxicity units" required to manage pests within a given farming system. Plus, they will last.
Some people have a cavalier attitude about resistance management, based on the assumption that a steady stream of new compounds will be discovered. Such confidence is misplaced since resistance is an ecological phenomenon which behaves roughly like a human brain or muscle -- the more it is exercised, the quicker it works and the higher it can reach. To a farmer, this means resistance will emerge more quickly to subsequent generations of new pesticide products, and will be more serious when and as it emerges.
Fungicides In most regions potato farmers are facing an increasingly aggressive, tough-to-control mix of disease organisms causing early and late blight, as well as other fungal diseases. Nationwide, the average potato acre was treated 3.2 times in 1990 but by 1995, the emergence of new strains of late blight forced applications up to 7.5 on average.
On both irrigated and dryland potato acres in 1995, chlorothalonil (Bravo) was the fungicide of choice -- nearly all acreage were treated. But irrigated acreage required 4.24 pounds per acre compared to 3.24 on dryland acres. Rates of application also are rising. In the case of Bravo, the average per acre rate of application rose from 1.55 pounds a.i. in 1993 to 3.6 pounds in 1995. Comparable differences occurred on acreage treated with the fungicide metalaxyl (Ridomil) -- almost twice the percent of irrigated ares (60%) were treated compared to dryland acres (35%) at about twice the rate (.45 pound a.i. versus .24 pound) and twice as often (2.24 applications compared to 1.23).
Compared to weed and insect pests, fewer biological control and preventive practices are availability to combat potato plant diseases. Already heavy reliance on fungicides in many potato producing regions threaten sustainability because of economic consequences and food safety concerns. If North Dakota potato growers can intensify production without triggering more serious plant disease problems, lower reliance on fungicides could emerge as a significant regional advantage.
These substantial differences in reliance on fungicides point to the need to assess irrigation management practices from the perspective of plant disease control. Research suggests that moisture from irrigation plays a key role in promoting disease emergence and severity, especially near pivots and other places where more water than average gets applied to a field. Also, it is known that the potato plant can withstand a certain degree of drought stress later in the season, a time which often corresponds to the period when disease severity is most serious.
North Dakota producers need to seek out and use a disease forecasting-irrigation scheduling model like WISDOM to help address these critical management challenges. NDSU researchers need to work with growers and consultants to calibrate such models to the soil types and irrigation systems used in North Dakota's potato producing region, the states climatic conditions, and fertilization practices. Evidence from Wisconsin shows that the use of such models -- if properly calibrated and interpreted -- can cut fungicide and insecticide use in half, while also markedly reducing irrigation and N-loss.
Managing the Colorado Potato Beetle
Experts predict that the Colorado potato beetle (CPB) is likely to remain the dominant insect pest plaguing North Dakota potato producers. For this reason many people are anxious to see how well the NewLeaf potato varieties will do. These new varieties are genetically engineered to express the Bt toxin in plant tissues, thereby hopefully controlling all lepidopteran insects.
I urge growers to proceed with caution in the adoption of this technology, and indeed expect that AVIKO may not wish to be the company shouldered with the task of convincing European consumers that Bt-transgenic potatoes are the next best thing to french fires.
Most entomologists not working for companies involved with the discovery and commercialization of Bt-transgenic plants predict that widespread planting of such varieties will trigger resistance within 3 to 7 years. Given the vital importance of Bt -- one of the safest biopesticides available for lepidopteran control -- to farmers producing a wide array of crops, its loss to resistance would be a major blow to progress toward safe and sustainable pest management systems. While most people who are concerned about the impacts of potato production on North Dakota communities and resources are most worried about water quality impacts, the public debate over the planting of Bt-transgenic varieties may soon dominate the focus of the media and public institutions. (For a fuller discussion of the risk of resistance associated with Bt-transgenic plants, see the "Pest Management at the Crossroads" web site at http://www.pmac.net).
Steering Clear
Several steps are needed in order to help North Dakota farmers steer clear of the pesticide treadmill -- the only way to avoid serious pest management and pesticide-related problems in parts of North Dakota where irrigated potato production is expanding. The most critical steps include --
One key task would be to explore and then develop profitable markets for rotational crops. A second useful initiative would be to sponsor a private monitoring effort to serve as an "early warning" system so that preventive measures can be put in place before problems get out of hand.
Another test will be providing growers a fair price for potatoes that covers the costs of producing the crop using methods that also protect the soil and water quality. Everyone in the industry is concerned with the precipitous drop in market-prices following the record crop in 1996. If the market glut persists, AVIKO may be able to drive down the price of potatoes to below cost of production, but if it does so, corners will be cut in the field, in some situations kicking the pesticide treadmill into high gear. If that happens, more change and new challenges for the region will likely be around the corner.
