Section C: Horticulture Crops in the agro-ecosystem
- Projected Outcomes
- Background / Lessons
- The Ground Beneath Our Feet
- Ecological question 1: What are the nutrient and water flows in the system?
- Ecological question 2: What are the sources and sinks of pollutants in the system?
- Ecological question 3: What are the interactions of living organisms in the system?
- Ecological question 4: What are the energy flows in the system?
- Career Pathway content standards
- Students will begin to apply ecological analysis to vegetable and fruit production systems
- Students will learn about some key agro-ecological management practices, including soil and fertility management, crop rotation, and pest management.
- Students will gain an appreciation of the complexity and variety of the agroecology of horticultural crops.
Like natural ecosystems, agro-ecosystems are characterized by nutrient flows and cycles, energy flows, and the interactions of living organisms with each other and the physical environment. However, agro-ecosystems differ from natural ecosystems in two key ways:
- First, we expect them to export particular biological goods for our use.
- Second, we deliberately manipulate them to get them to produce those goods in abundance.
These two special qualities of agro-ecosystems in turn affect their key ecological processes. Sustainable agriculture seeks to take advantage of ecosystem processes by designing an agricultural system that works with them rather than against them to achieve its production goals.
This section begins with a quick look at the role of the soil in the agro-ecosystem and then encourages students to think about the ecology of horticultural production by posing four ecological questions.
- What are the nutrient and water flows in the system?
- What are the sources and sinks of pollutants in the system
- What are the interactions of living organisms in the system
- What are the energy flows in the system?
Horticultural crops vary widely in their ecological characteristics, from row-cropped annual vegetables to fruit trees that may be productive for more than 30 years. Moreover, while some fruit and vegetable farms specialize in producing one or two crops, others produce dozens of different kinds of plants. This unit will provide some indication of the variety of sustainable horticultural systems in Iowa and Wisconsin, but it cannot cover it all. Classes are encouraged to apply the four agro-ecological questions to crops grown in their areas.
The Ground Beneath Our Feet
|“The nation that destroys its soil, destroys itself.” – Franklin Delano Roosevelt
Essentially, all life depends upon the soil …. There can be no life without soil and no soil without life; they have evolved together.” – Charles E. Kellogg, USDA Yearbook of Agriculture, 1938
Vist the Natural Resources Conservation Service site for more soils quotes
Every farmer knows that soils are important. But different farmers (and scientists) think about soils in different ways.
One way to look at soils is as a physical medium. It needs to serve a variety of mechanical functions: provide a substrate for plant roots to grow in, allow water to drain so plant roots have access to oxygen, but hold on to enough water that roots have access to water. The soil is also where plant nutrients are stored, transferred to roots, and sometimes lost.
Many sustainable farmers think about soils as a living system. They value the mechanical functions of soil, but they look beyond those properties to biological and ecological services. These farmers seek to build and maintain good soil health, rather than simply avoiding damaging the physical structure of the soil.
Our understanding of soil biology is still quite rudimentary, but we are learning more and more about how the multitude of living organisms in the soil affect soil quality and processes and about how our actions in turn affect the life of the soil.
Key groups of soil organisms include:
Bacteria (single-celled organisms that are neither plants nor animals)
Fungi (neither plants nor animals, typically grow in long chains of cells called hyphae)
Protozoa (single-celled animals such as amoebae)
Nematodes (tiny non-segmented worms)
Arthropods (invertebrates such as insects, spiders, millipedes, etc.)
Each of these groups contains a wide variety of species, and the different species do very different things. For example, one gram of soil may contain 11,000 different species of bacteria. Some bacteria help decompose organic matter, some fix nitrogen, some prey on living organisms causing disease, and a few bacteria photosynthesize.
Together, soil organisms perform critical ecological functions such as decomposing organic matter, changing soil structure, moving, stabilizing, and transforming nutrients, altering chemicals such as pesticides, and eating or helping each other.
Short videos on soil quality, including a number of farm case studies.
Scientists are just beginning to explore life in the soil and how it interacts with agricultural management. As you move through the four ecological questions below, keep the role of the soil and of soil organisms in mind.
Ecological question 1: What are the nutrient and water flows in the system?
Several factors influence the nutrient and water flows in horticultural production.
- All plants require nutrients to grow. Because they take nutrients away from a site when they harvest crops, farmers have to replace those nutrients to keep that land productive.
- However, different crops have different nutrient needs. For example, spinach and sweet corn require lots of nitrogen to yield well, while beans, peas, and many fruits do well with little added nitrogen but may have special water or micronutrient requirements.
- The growth habit of the crops is also important. A “crop” such as turfgrass, with year-round ground-cover, requires different nutrient and water management than for example tomatoes, which only grow in summer and are generally surrounded by bare soil or possibly a non-living mulch.
- Even within a crop type, different management approaches can have significant impacts on nutrient and water flows.
Let’s take a look at nutrient and water impacts of two crops: sweet corn and cranberries.
Nothing symbolizes the taste of summer quite like fresh early, sweet corn. Customers seek out the varieties they like – early, sweet “Sugar Buns” or elegant white “Silver Queen.” But most don’t think beyond appearance and flavor to how the corn was raised.
Sweet corn grows best with lots of sunshine, enough but not too much water, and lots of nutrients in the soil, especially nitrogen. Because corn responds well to high fertility, it can be tempting to add generous amounts of fertilizer. But excess nitrogen can leach into groundwater, and phosphorus can run off into surface water, damaging aquatic communities and drinking water supplies. (Visit EPA’s nutrient pollution page, or The University of Missouri State Extension) In addition, money spent on unneeded fertilizer cuts into farm profits.
Farmers can use a variety of practices to reduce the need for purchased fertilizer in sweet corn production:
- Recognize that sweet corn needs less nitrogen than grain corn, because it is harvested earlier. On most soils, a rate of 130 lbs of N per acre is recommended for sweet corn. On soils with less than 2% organic matter a rate of 150 lbs/acre is optimal. For more information see page 275 of J.B. Colquhoun et al., Commercial Vegetable Production in Wisconsin 2022.
- Use realistic yield goals when calculating nutrient needs.
- Supply N through crop rotation. If the corn follows a good stand of alfalfa or clover, it will need no supplemental nitrogen. If it follows soybeans, potatoes, or a small grain, N applications can usually be reduced by about 30 to 40 lbs per acre. (Crop rotation also benefits sweet corn by reducing some pests.)
- Use a late spring soil nitrate test to measure available nitrogen already in the soil, rather than assuming the crop will need all its nitrogen supplied by fertilizer applications. (See 2 Soil Nitrate Tests for Corn Production in Wisconsin and remember to use sweet corn rather than grain corn rates for the starting point.)
- Side-dress N applications while the crop is growing and can use the nutrients right away, rather than relying on fall or pre-plant applications. Fall N applications are likely to leach significant amounts of N. See “How to properly apply nitrogen fertilizer” for more information.
- Use composted manures to supply the phosphorus, potassium, and part of the nitrogen needs of the corn.
- Plant a cover crop such as winter wheat or rye after harvest to prevent runoff and leaching of nutrients.
- Use conservation tillage to minimize runoff and erosion .
Compared to most crops, cranberries require very little fertilizer, in part because as perennial plants they do not have to grow new stems every year and can store nutrients over the winter. The recommended rates are from 20 to 40 lbs of N and 20 to 45 lbs of P2O5 per acre per year. Compare these guidelines to recommended rates of 80 to 150 lbs/acre N and 0 to 100 lbs/acre P2O5 per year for sweet corn and 40 to 100 lbs/acre N for broccoli.
Moreover, unlike most crops, cranberry yields decline quickly when too much nitrogen fertilizer is applied. So you might think that should make sustainable nutrient management for cranberries easy. But it is not so simple. The way cranberries grow provides some special challenges.
Because of the extremely acidic soils in which cranberries grow (4.5-5.5 pH, compare with 6.2-7.0 for corn), many nutrients are not available in the forms that you may be familiar with from other crops. Whereas most plants will take up both ammonium and nitrate, in the presence of extra H+ ions in acidic soils, nitrate converts quickly to ammonium. Cranberry plants, due to their evolutionary history, only uptake the ammonium form of nitrogen. Cranberry plants are very picky about what kinds of nutrients they will take up. The acidic conditions also make iron and aluminum more available than in neutral soils, while binding other essential micronutrients.
On top of that, cranberry marshes are regularly flooded to help with harvest, provide a non-chemical method of killing insects, and to protect against winter kill. This flooding means that if nutrients have not been incorporated into the soil before a flood is applied, there is a risk of nutrients entering surface waters. Cranberry growers mitigate this risk by timing their floods carefully, and using reservoirs to ensure nutrients have time to settle out before water is returned to sources.
These features mean that many of the usual tools for sustainable nutrient management (use of manure, compost, legumes, and cover crops) don’t work for cranberry production. The main approach that most cranberry growers have for improving the sustainability of nutrient use is to fine tune the amount and timing of nutrients applied, using:
- plant tissue testing to determine nutrient needs over the next 15 months,
- fertilizer selection to target P and N ratio and type to cranberry needs,
- careful monitoring of developmental stages and appearance of the plants to determine optimum timing for fertilizer application, and
- accurate fertilizer delivery equipment. These tools can help maximize the amount of fertilizer taken up by the plants and minimize loss to surface or ground water.
- Visit Cranberry Resources for more information on fine-tuning nutrients for cranberry production.
In recent years, with the growth of the organic market, some growers have started producing cranberries organically. Organic growers rely on organic fertilizers, like chicken litter and fish meal to add nutrients. These materials do not provide the rapid release of plant available N that synthetic ammonium and urea do, and the difference in nitrogen availability is thought to be the main reason why organic cranberry yields are typically much lower than conventional yields. Growing a perennial crop organically is also challenging because of insect pests and weed pressure from a lack of being able to use mechanical tilling and chemical controls. (Visit UW-Madison CIAS’ Overview of Cranberry Production.) Nevertheless, with good management and the price premium for organic products, organic production is proving viable for a number of growers. Research, breeding, and experimentation with organic management may improve yields considerably.
Because irrigation and flooding are such important practices in commercial cranberry bogs, cranberry production also has special impacts on water cycling. Cranberry growers store water in natural and constructed wetlands. On average, in Wisconsin each acre of producing cranberry marsh has about ten acres of support lands, both for water storage/purification and to support wildlife. Cranberry growers point out that these support lands provide habitat for a variety of wetland plants and animals, considering they are a native wetland plant.
Critics note that cranberry irrigation and water storage for harvest can exacerbate the impacts of drought on natural wetlands by withholding water that normally would contribute to stream recharge. There also may be implications on surrounding water quality from nutrient runoff and pesticides, although these are monitored closely by growers as well as by the EPA, DATCP, DNR, and WPS.
Climate change is one of the biggest threats to cranberry production in Wisconsin. The layer of ice atop the cranberry beds in winter is one of the most important tools to protect the crop from freezing temperatures. However, temperatures have become more variable and can oscillate above and below freezing, which makes making and maintaining the layer of ice difficult. “False springs” have become more of an issue as well. A “false spring” is when temperatures are above normal for an extended period of time in winter, tricking the plant into breaking winter dormancy (state in which the plant is not growing and therefore protected from freezing temperatures). This premature growth and worse, premature bloom, puts much of the crop at stake because a freeze following these events can kill the growth and blooms that would have become the fruit. To combat these problems, researchers are working to find a cultivar with better cold hardiness and frost tolerance, and farmers can grow supplemental crops to lessen the economic impact of bad cranberry production years. (From the WICCI Agriculture Working Group Report, p. 38, 2021)
Compost is one of the most important nutrient management tools for sustainable fruit, vegetable, and flower growers. Composting is the controlled decomposition of biological materials. (Visit The Art and Science of Composting.)
Compost offers several advantages:
- Nutrients tend to be stable and bound to organic matter, so they are less likely to run off or leach than nutrients in raw manure or synthetic fertilizers.
- Compost is much more homogeneous than raw manure, making it easier to spread on cropland.
- Compost has a mild “earthy” odor, unlike the unpleasant odor of manure.
- Compost acts as a soil amendment as well as a nutrient source, adding organic matter and improving soil tilth.
- The composting process greatly reduces or eliminates pathogens that are harmful to human health.
- Many types of compost contain far fewer viable weed seeds than uncomposted manure.
- Compost can help suppress certain plant diseases.
Compost also offers some challenges:
- Up to half of the nitrogen contained in the material being composted is lost to the atmosphere during the composting process. However in many trials, plants gown with compost yield more than expected at low levels of soil N.
- Compost can be highly variable, depending on the materials composted and on the composting process. Growers need to either analyze composts or request an analyis to be sure the compost they have will meet their needs.
- Compost is much bulkier and therefore harder to transport, store, and apply to large areas than synthetic fertilizers.
- Composting requires careful management, and depending on the composting system chosen, may require expensive equipment.
How do soils relate to nutrient and water flows?
- Water and nutrients move easily through sandy soils. Nitrogen can quickly leach to groundwater. Much of Wisconsin ‘s sweet corn is grown on sandy soils, which makes sustainable nutrient management both more critical and more challenging.
- Organic matter improves the ability of soils to retain both water and nutrients. Composted manures and incorporation of green manures can help raise soil organic matter over time.
- Nitrogen fertilizers such as urea and anhydrous ammonia can change the composition of soil organisms.
Ecological question 2: What are the sources and sinks of pollutants in the system?
A sustainable system will minimize the amount of pollutants introduced into the environment.
What is a pollutant? It is a chemical that is damaging to human health or the environment.
Just as a weed is a “plant out of place,” so whether something is a pollutant depends in part on context. For example, soil particles are a valuable resource in the crop field. However, if those same soil particles are carried from the field to a stream or river by erosion, they become sediment—a pollutant that can severely damage aquatic communities.
Also, whether a chemical is a pollutant may depend on concentration. For example, nitrogen is a critical plant nutrient. However, if it is present in excess, it can be toxic to plants or can degrade marine systems. Similarly, greenhouse gases like carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) occur naturally in our atmosphere and support photosynthesis and keep temperatures from freezing every night. However, when the concentrations of these gases is too high, the resulting climate change harms agriculture and increases risks of catastrophic events, including hurricanes, floods, and forest fires. Each greenhouse gas is a byproduct of modern agriculture, and has a different heat trapping strength and persistence in the atmosphere. So in order to evaluate their impact scientists compare them using CO2 equivalents (CO2e), or how many tons carbon dioxide released would have the same warming potential over 100 years as a ton
s of nitrous oxide or methane. Nitrous oxide has a CO2e of 298 (in other words, just 1 ton of N2O has the same global warming effect as 298 tons of CO2 and methane has a CO2e of 25). For more information on comparing greenhouse gases see the Overview of Greenhouse Gases and Understanding Global Warming Potentials.
Thus, the source of many agricultural pollutants is deliberate application of inputs such as fertilizers and pesticides. Another source is beneficial resources such as soil or manure, which turn into pollutants when mismanaged and displaced. A sink is where the pollutant winds up. Surface waters, including rivers, lakes, and the ocean, are a common sink for agricultural pollutants.
The broad categories of pollutants in horticultural crops include:
- excess nutrients running off or leaching to surface and ground waters
- soil erosion degrading wetlands
- pesticides harming non-target organisms
What are the pollution sources in apple production, and what sustainable practices can reduce pollution?
The main pollution concern for apple growers is pesticides.
Key apple pests in the Upper Midwest include plum curculio, codling moth, and apple maggot. Leafrollers, aphids, leafminers, leafhoppers, scale insects, and spider mites can also cause damage in apple orchards. And diseases such as fire blight, apple scab, and powdery mildew can destroy the crop or make it unmarketable. (Visit Urban Phytonarian Series Common Fruit Insects, or Apple Pest Management for Home Gardener.)
For decades, apple growers have used a wide array of pesticides to control these insects, diseases, and weeds. But since the 1970s scientists, farmers, and consumers have all become increasingly aware that pesticides can cause both environmental and human health problems. As a result, some apple growers are seeking ways to grow apples using fewer and less toxic pesticides.
The array of techniques and tools farmers use to get a good crop with minimal use of pesticides is called Integrated Pest Management, or IPM.
Fertilizer recommendations for tree fruits are low in comparison to most other agricultural crops, so runoff and leaching from nutrient applications are not generally considered to be problems of apple production in Wisconsin and Iowa. In addition, fruit quality can deteriorate when too much nitrogen is applied. Thus, most mature Midwestern orchards are not fertilized unless tissue testing indicates a nutrient deficiency.
Visit Michigan State University Extension Fertilizing Fruit Crops, Growing Apples in Wisconsin, or Spectrum Analytic Inc. Fertilizing Apples for information on nutrient recommendations for apple production. Including legumes such as clover in the cover crop for the orchard floor can further reduce the need for nitrogen fertilizer.
Soil erosion is a possible source of pollution from apple orchards. Apple trees yield better when they do not compete with other vegetation within two or three feet of the tree trunk. Most Wisconsin and Iowa orchards maintain 5 foot wide strips of bare ground in the tree rows and 6 to 10 foot wide strips of grass groundcover between tree rows. If the strips of groundcover are well maintained and planted along the contours, erosion can be minimized. Some sustainable growers use mulch to suppress competing plant growth in the tree row. Mulching reduces reliance on herbicides and the potential for soil erosion. Although mulch can potentially provide cover for rodents and other pests, a 6 year study of a cherry orchard in Michigan found that mulching increased yields over conventional orchard floor management.
How do soils relate to pollution sources and sinks?
- Soil itself can be a pollutant if it is allowed to erode.
- Soil organisms can break down some pollutants, such as disease-causing organisms and some pesticides.
- Other pollutants, such as metals and persistent pesticides, can accumulate in soils and can be taken up by plants that are later eaten by people.
- Pollutants can change the composition of organisms in the soil.
Ecological question 3: What are the interactions of living organisms in the system?
Typically, sustainable agro-ecosystems will try to work with species interactions and will favor species and genetic diversity.
Everything in an ecosystem affects other parts of the ecosystem. Typically, production agriculture has focused on the negative impacts of organisms other than the crop. In this worldview, all non-crop plants are seen as weeds that compete for water, nutrients, and sunlight, and all non-crop animals from insects to birds and mammals are seen as useless at best and crop-destroying pests or disease carriers at worst.
There is some truth to this outlook. Weeds do compete with crop plants, and many types of animals eat parts of the crop and can cause substantial yield losses. Agro-ecosystems differ from natural ecosystems in that we require them to export a good portion of their production for off-site human consumption. So farmers cannot afford to give weeds, crop predators, and diseases a free hand.
On the other hand, it turns out that many non-crop organisms benefit crop production in a variety of ways, such as by improving nutrient cycling and availability to the crop, pollinating the crop, eating crop pests, providing habitat for beneficial species, and reducing disease. Practices such as heavy use of synthetic fertilizers and pesticides and mono-cropping may harm beneficial organisms as much as or more than pests.
The number of different species of plants, animals, and microorganisms in an ecosystem is referred to as species diversity. There is also a different kind of variation, which is the genetic diversity within a species or population (the individuals of one species in an ecosystem).
Let’s take a look at both species diversity and genetic diversity in fresh market vegetable production.
A popular model for sustainable vegetable production is the community supported agriculture operation or CSA. (University of Iowa Iowa CSA Farms)
CSAs promote diversity by:
- Planting a wide variety of crops. Because they try to supply most of the vegetable needs for shareholders during the growing season, CSA farms grow a wide variety of vegetables, herbs, flowers, and fruits. Over the course of one year, a typical CSA farm will grow more than 30 different crops on less than 50 acres. CSAs can have varying acres in production, from small operations like Vitruvian, McFarland, WI (5 acres) to some of the largest CSAs in the Midwest like Angelic Organics, Caledonia, Illinois (35 acres) and Tipi Produce, Evansville, WI (45 acres), which still have less than 100 acres in crops.
- Rotating crops. CSAs rotate crops to reduce disease and insect pressures. At least a 4-year rotation is recommended.
- Planting cover crops to reduce erosion, reduce weed pressure, and manage nutrient cycling.
- Avoiding use of broad-spectrum pesticides that can harm non-target species.
- Deliberately encouraging beneficial organisms, from birds to insects, to help with pest control.
- Preserving and restoring natural habitats on the farm. Habitat preservation can help make the farm more attractive to CSA members, and it also fits with the values of most CSA farmers. Natural habitats usually contain far greater species diversity than crop fields.
- Planting numerous varieties of each crop, including open-pollinated and heirloom varieties. CSAs usually value genetic diversity for several reasons. First and most important, their customers value diversity and look for varieties that look interesting and offer special flavors. In some cases, using several different varieties may decrease the chance that a particular disease or pest will damage the whole crop. Third, different varieties can often be harvested at different times, extending the harvest season . And finally, like their customers, many growers take pleasure in the many different forms and flavors one species can provide.
>For example, in 2005 Harmony Valley CSA grew 16 varieties of tomatoes: 3 paste (a.k.a. Roma) tomatoes, 2 standard reds, 4 small cherry (a.k.a. grape), 2 gold, and 4 heirlooms out in the field, and Sungold cherry tomatoes. August 20 newsletter, p. 2.
Comparison of plant communities
Pre-agricultural / “natural
- Mix of perennial and annual species
- Variety of communities depending on soil type, climate and micro-climate, and site history (prairies, savannahs, wetlands, forests, etc)
- Large number of species at one site, typically little or no exposed soil year-round
- Substantial genetic variation within most species
Conventional horticulture (vegetable production)
- Sequential mono-cultures (usually 2 or at most 3 species in rotation, sometimes only one species)
- Mainly annual row crops, with bare soil between the rows and completely bare soil exposed for 6 months of the year or more
- Little genetic variety within the species; often just one or two varieties grown of a crop and high value placed on consistency of size and appearance
Sustainable horticulture in Wisconsin and Iowa
- Sequential mono-cultures (usually 3 to 6 species in rotation)
- Annual row crops rotated with perennials and small grains. Use of cover crops to minimize amount of bare soil exposed in winter
- Interest in increasing genetic variety, including reintroduction of heirloom varieties as well as breeding new varieties for diversity of flavor, appearance, and agronomic traits such as disease resistance.
- Restoration of complex natural or partly natural plant communities around crop fields
Ecological question 4: What are the energy flows in the system?
Sustainable agro-ecosystems rely more on solar energy rather than on fossil fuels. Sustainable systems minimize energy waste.
It is difficult to get recent detailed information about energy use in modern agriculture, and most of the work that has been done on energy used in agricultural production looks at field crops and livestock production rather than horticultural farms. Most modern fruit and vegetable production relies on fossil fuels in a variety of ways, such as:
- Fuel and electricity to power equipment such as tractors
- Fertilizers and pesticides made from or with fossil fuels such as natural gas
- Fuel or electricity to heat greenhouses
- Plastic to cover hoophouses, act as mulch, and package produce
- Fuel to transport produce to market
- Electricity to keep produce cool
- Fuel and electricity to process produce
Certain farming and food system practices can provide substantial savings in fossil energy use.
- Minimize use of nitrogen fertilizer and pesticides (see strategies recommended in the nutrient cycling and pollution prevention segments)
- Recycle nutrients and resources on the farm
- Minimize transportation costs by selling to and buying from local sources
- Use renewable energy sources such as wind, solar, or biomass-fueled power
More than half of the energy in our food system is used not on the farm, but in transportation, processing, storage and packaging, and home cooking. (Energy Use in the U.S. Food System)
Sustainable practices for the consumer
- Buy local foods, when possible
- Avoid excess packaging
- Use energy-efficient appliances and techniques when possible
- Use renewable energy sources, if possible (solar and wind power)
Career Pathway content standards
|National Agricultural Education Standards
Performance Element or
(in this section)
|1. Apply ecological analysis to vegetable and fruit production systems.
|PS.03.04 Apply principles and practies of sustainable agriculture to plant production.
ESS.01 Use analytical procedures to plan and evaluate environmental service systems.
ESS.01.01 Analyze and interpret samples.
|2. Describe key agro-ecological management practices, including soil and fertility management, crop rotation, and pest management.
|PS.02 Prepare and implement a plant management plan that addresses the influence of environmental factors, nutrients and soil on plant growth.
PS.02.03 Develop and implement a fertilization plan for specific plants or crops.
PS.03.02 Develop and implement a plant management plan for crop production.
PS.03.03 Develop and implement a plan for integrated pest management.
PS.03.04 Apply principles and practices of sustainable agriculture to plant production.
|3. Identify and perform environmental monitoring techniques.
|ESS.03 Apply scientific principles to environmental service systems.
CS.11 Utilize scientific inquiry as an investigative method.
|4. Show how feedstocks change compost recipes.
|5. Apply basic math skills to develop compost recipes.
|6. Identify organic waste streams at school.
|ESS.04.02 Manage safe disposal of all categories of solid waste.
|7. Define IPM.
|PS.03.03 Develop and implement a plan for integrated pest management.
|8. List economic thresholds in IPM.
|PS.03.02 Develop and implement a plant management plan for crop production.
PS.03.03 Develop and implement a plan for integrated pest management.
|9. Describe how IPM is used in some Wisconsin apple orchards.
|PS.03.02 Develop and implement a plant management plan for crop production.
PS.03.03 Develop and implement a plan for integrated pest management.