Module 8.1: Insects and Integrated Pest Management

Module 8.1: Insects and Integrated Pest Management jls164 Wed, 02/26/2014 - 12:25

Ecosystems have many trophic levels of organisms including primary producers, herbivores, omnivores, carnivores; parasites, and decomposers. Agroecosystems are ecosystems managed for food and fiber production that have less diversity and typically fewer trophic interactions than natural ecosystems. But diverse organisms and their trophic interactions provide important functions in agroecosystems including, for instance, decomposition and nutrient cycling; plant pollination, and pest suppression. Organisms that reduce agricultural productivity and quality and are referred to as agricultural pests; these include weed pathogens, insects, and other herbivorous organisms. Mammals that graze or browse crops (ex. deer and rodents), and other arthropod species such as mites and slugs (mollusks), can also reduce crop yields through grazing and seed predation.

Natural Ecosystem and Agroecosystem Comparison

Natural Ecosystem and Agroecosystem Comparison azs2 Thu, 01/07/2016 - 11:31

Pest species can be present in agroecosystems, but not cause significant crop yield loss or livestock productivity reductions. Why? What factors prevent pest populations from reducing yield? One explanation may be that the crop or livestock is resistant to the pest. For instance, a crop plant may produce compounds that fend off pathogen infection or deter insect feeding. And if environmental conditions and resources are ideal, the plant may be able to grow and recover from pest infestation. What other ecological processes and factors might contribute to agricultural resilience to pests or other stresses such as climate change?

Activate Your Learning

Question 1 - Short Answer

Draw a food web pyramid and label the trophic levels as categories of organisms with i. primary producers at the bottom, ii. herbivores next, ii. omnivores and carnivores at the top of the pyramid. Chose a natural ecosystem and list all of the species you can think of that are found at each trophic level in the natural ecosystem. Then draw a second food web pyramid for a type of farm that you are familiar with, and list all of the species you might find at each trophic level. Describe how the natural ecosystem and the agroecosystem compare. How do they differ?

Click for the answer.

ANSWER:
You should have many more species at each trophic level in the natural ecosystem. Additionally, the genetic diversity within species in the natural ecosystem is typically greater than in the agroecosystem.

Question 2 - Short Answer

Odum (1997), an Ecologist summarized some of the major functional differences between natural and agroecosystems that are shown in the table below. Consider how your natural and agroecosystem food pyramids offer examples of the below ecosystem differences. How many predatory and parasitic species are there in the natural ecosystem and agroecosystem? How might the presence of predatory and parasitic organisms impact agricultural pests? How might genetic diversity contribute to pest management and ecosystem stability?

Click for the answer.

ANSWER:
Although you may not be familiar with parasitic species such as wasps and nematodes, you likely can think of many predatory species: humans, large and small mammals, predatory birds, rodents, fish, and arthropods (ex. beetles, spiders, ants, etc.)

In natural ecosystems there tend to be more niches and a higher diversity of species compared to most managed agroecosystems that are simpler, have fewer predatory and parasitic species, and less genetic diversity within a species. As the table below indicates with fewer trophic interactions, there are fewer species to reduce pest populations and prevent them from reducing agricultural yield and quality. Further, with low genetic diversity within agricultural species and across the landscape, the agricultural system is more vulnerable to pest outbreaks than natural ecosystems.

Natural Ecosystems and Agroecosystems
Property	Natural Ecosystem	Agroecosystems
Human Control	Low	High
Net Productivity	Medium	High
Species and Genetic Diversity	High	Low
Trophic Interactions	Complex	Simple, Linear
Habitat Heterogeneity	Complex	Simple
Nutrient Cycles	Closed	Open
Stability (resilience)	High	Low

Insects

Insects azs2 Mon, 12/01/2014 - 09:56

Insects are the most diverse group of animals that are found in most environments. In the Animal kingdom, Insects are in the Phylum Arthropoda; Arthropods have an exoskeleton of chitin that they shed as they grow; they also have segmented bodies and jointed appendages. In addition to the Class Insecta, the Arthropoda also includes the arachnids (spiders and mites), myriapods (ex. centipedes), and crustaceans (crabs, lobsters, etc.). Insects are distinguished from the other Arthropod classes by the following features:

As adults and in some species in the juvenile stages, insects have three body parts: the head, thorax, and abdomen. Although in some insect species, some of the three body parts are fused together and may be difficult to distinguish. See this website for images and more discussion of insect anatomy: Purdue University, College of Agriculture, Department of Entomology, 4-H and Youth: Insect Anatomy
The adults have antennae on their heads that they use to sense their environment, and they have three pairs of legs or six legs.
Figure 8.1.1: Honeybees are important pollinator insects. Note the three body parts (head, thorax, and abdomen) two antennae, and three pairs of legs.
Credit: MaryAnn Frazier, Department of Entomology, Penn State University
Most insects undergo a morphological change that occurs between the time they hatch from eggs and develop into adults. The morphological change is called either complete metamorphosis or incomplete metamorphosis referring to how significantly the insect's appearance changes from the early stage of development to the adult stage. Go to these links to see images of the types of metamorphosis and read more about insect metamorphosis: ASU School of Life Sciences: Metamorphosis

Check Your Understanding

Question - Multiple Select

Browse the following websites for two major agricultural crop pests. What kind of organisms are they? In what stage of their lifecycle do they cause the most damage to the crop plants?

Click for answer.

ANSWER:
Both are insects that undergo complete metamorphosis. They do the most crop feeding and damage in the larval stages when they resemble worms, that are sometimes also called caterpillars. Thus, their common names include the name: worm.

Feeding Types

Insects may be herbivores or omnivores. Herbivorous insects may eat plants by directly feeding on plant tissues such as leaves or roots. Herbivorous insects include caterpillars, beetles, grasshoppers, and ants. Some insects pierce plants and suck plant nutrients from the plant vascular system, typically the phloem, (the cells that transport plant carbohydrates and amino acids); although some insects feed on the xylem, the vascular cells that transport water and nutrients. Examples of piercing-sucking insects include aphids and mosquitoes. By contrast, butterflies and moths have siphoning mouthparts for drinking nectar. Omnivore insects consume multiple kinds of food including other insect prey and plant tissues such as leaves and/or nectar and pollen.

Beneficial insects

Although insect pests are major agronomic pests, only about 1% of insect species are agricultural pests. Insects also contribute to important ecosystem processes, including: i. pollination, ii. predation and parasitism (ex. lady beetles, lacewings, praying mantis, parasitic wasps); iii. decomposition of organic materials such as crop residues and manure (Ex. dung beetles) iv. providing food for other organisms, such as fish and birds. Review the photos below for some categories of beneficial insects, and some of their characteristics here: National Pesticide Information Center

Figure 8.1.2: Dung Beetles contribute to decomposing dung or manure. This photo shows a Large Copper Dung Beetle (Kheper nigroaeneus) on top of its dung ball.

Credit: Bernard DUPONT from FRANCE (CC BY-SA 2.0), via Wikimedia Commons

Figure 8.1.3: A beetle (Chlaneius sp.), predating on insect larvae

Credit: Heidi Myer

Figure 8.1.4: Parasitic wasp laying eggs on an alfalfa weevil

Credit: Arthur Hower, PSU

Figure 8.1.5: Caddisflies: An important food source for fish.

Credit: Jason Neuswanger, Troutnut

Activate Your Learning

Read the following website: Omnivorous Insects: Evolution and Ecology in Natural Agriculture Ecosystems.

Then answer the following questions:

What did scientists observe happened to cotton plants and insect herbivores after cotton plants were injured by herbivorous insects?

Click for answer.

ANSWER: The cotton plants produced defense compounds that reduced the plant quality for herbivorous or omnivore insects. The compounds reduced insect feeding on the cotton plants (as indicated by fewer plant scars) and increased insect predation of the eggs of the insects that had been feeding on the cotton.

To conserve or maintain predatory insects, what is required? What can farmers do to attract and conserve predatory insects?

Click for answer.

ANSWER: Habitat that provides alternative food sources and protection from predators is typically needed to attract and maintain predatory and other beneficial insects. Farmers can maintain or plant alternative and diverse plants in fields or around field edges to provide alternative plant food and habitat for beneficial insects and their alternative prey. These plants typically include flowering plants that can provide pollen and nectar.

Pest Management

Pest Management azs2 Wed, 01/06/2016 - 22:24

Humans have developed methods of insect and pest control for centuries.

Reading

Read the following brief history of pesticides and then answer the questions that follow:
Pesticide Development: A Brief Look at the History. Taylor, R. L., A. G. Holley and M. Kirk. March 2007. Southern Regional Extension Forestry. A Regional Peer-Reviewed Publication SREF-FM-010 (Also published as Texas A & M Publication 805-124)

Check Your Understanding - Pesticide Development: Brief History

What chemicals were used to control pests from 1700 to the early 1900s?

Click for answer.

ANSWER: 1750 to about 1880, insecticides from plant extracts were created to control insects, plant diseases, and weeds. Plant extracts included: Pyrethrum, a natural insecticide made from the blossoms of various chrysanthemums; Rotenone from roots of plants to control leaf-eating caterpillars. In the 1800s solutions that contained sulfur and metals, such as copper and arsenic, were created to control plant diseases and weeds. Ex.1807, copper sulfate solution was used to control disease in wheat. Copper & arsenic mixtures, in Europe and the U.S. used dilute sulfuric acid, iron sulfate, copper sulfate (blue vitriol), copper nitrate, and sodium arsenate to control broadleaf weeds in cereal crops.

When was DDT invented and what was it first used for?

Click for the answer.

ANSWER: In 1939, Paul Müller, developed DDT (dichlorodiphenyltrichloroethane) that killed the Colorado potato beetle, a major pest of potato in Europe and the US. In WWII, DDT was also used to kill lice that carried typhus and mosquitoes that carried malaria. This invention of DDT and pests it controlled earned him the Nobel Prize.

When and why was DDT banned?

Click for the answer.

ANSWER: Scientists learned that DDT bioaccumulated in the food chain (insects and their predators). They learned that birds had accumulated DDT which caused eggshell thinning, early termination of bird eggs, and decline in bird populations. In 1970s and 1980s, organochlorine compounds (e.g., DDT) were banned.

Pesticide Resistance

Soon after the development of DDT in 1939 and the dawn of the modern insecticide era in the 1940s, scientists began to understand that pesticides were not the silver bullet of pest control. Particularly when a pesticide or one effective pest control strategy is relied on, the control tactic acts as a strong selective force for the development of resistance to the tactic in the target pest population. With the continuous application of the same pesticide, individuals that are susceptible to the pesticide are killed, leaving the few resistant individuals that survive to reproduce a offspring that are resistant to the pesticide. See the figure below for an illustration of how frequent reliance on one insecticide can select for a resistant insect population. Further, since many early pesticides were broad spectrum pesticides, the natural enemies of agricultural pest populations were also destroyed, contributing to pest population outbreaks.

Image showing how repeated use of a pesticide can result in pest resistance: the resistant individuals survive and reproduce

Figure 8.1.6: How the repeated use of a pesticide results in pest resistance

Source: How pesticide resistance develops. Michigan State University. Excerpt from Fruit Crop Ecology and Management, Chapter 2: Managing the Community of Pests and Beneficials by Larry Gut, Annemiek Schilder, Rufus Isaacs and Patricia McManus

In 1984, the US Board of Agriculture of the National Academy of Sciences organized a committee to explore the science of pest resistance and strategies to address the challenge. A report called "Pesticide Resistance: Strategies and Tactics for Management" was co-authored by the Committee on Strategies for the Management of Pesticide Resistant Pest Populations and published in 1986 by the National Academies Press, Washington D.C. In Chapter 1, G. P. Georghiou (1986) documented the development of pest resistance across multiple pest organisms (see pages 17 and 28 for figure 2 and figure 8), as well as how difficult and costly it was becoming to develop cost-effective pesticides (see figures 12 and 13 on page 36).

In the report, the Committee recommended using Integrated Pest Management or IPM to reduce the evolution of pesticide resistance and provide more long-term, effective pest control. As early as 1959, a team of scientists (Stern et al.) in California had also proposed that pest control that integrated both biological and chemical control approaches, was needed to prevent pest resistance to pesticides and pest control. Stern et al. (1959) defined terms and concepts that are fundamental to IPM today.

Understanding Economic Thresholds

Understanding Economic Thresholds azs2 Wed, 01/06/2016 - 22:32

Read the following two fact sheets for a description of Integrated Pest Management and the terms that Stern and his colleagues defined in 1959, which are still used today (economic injury level, economic threshold, and general equilibrium position). Then watch the following short video and answer the questions below:

The Integrated Pest Management (IPM) Concept. D. G. Alston. July 2011. IPM 014-11. Utah State University Extension and Utah Plant Pest Diagnostic Laboratory
IPM Pest Management Decision-Making: The Economic-Injury Level Concept. D. G. Alston. July 2011. IPM 016-11. Utah State University Extension and Utah Plant Pest Diagnostic Laboratory

Activate Your Learning: IPM Concept and Decision-Making

Describe three things that are integrated into IPM.

Click for the answer.

ANSWER: Pest control strategies are integrated: such as cultural, mechanical, biological, and chemical. The FAO website provides multiple examples of these practices.

On the IPM figure below, which IPM pest population terms from the article could describe the lines labeled A, B, and C?

IPM graph showing the pest population density over time

Figure 8.1.7: Hypothetical pest density over time graph. What IPM pest population term could apply to each line in the above figure?

Credit: Heather Karsten

Click for the answer.

ANSWER:

Line A: Damage- economic injury level (too late for control), Line B: Prevent damage- economic threshold (control needed), Line C: population equilibrium (control not needed) in balance with natural enemies

Figure 8.1.8: Hypothetical pest density over time graph with IPM pest population terms included

Credit: Heather Karsten

How would you describe the damage that the pest had caused to the crop at each of these pest population densities?

Click for the answer.

ANSWER: A: Economic Injury level- the pest damage has caused a significant economic cost or loss in the value and/or quality of the crop; B: Economic threshold: the pest population has reached a density that is cost-effective to control the pest population and prevent economic losses to the crop; it has not yet caused irreversible economic damage; C: The pest population is in equilibrium with natural enemies: pest damage is minor and natural enemies are preventing the pest population from increasing to the density of being an economic threat to the crop.

Watch the first 4.11 minutes of the below video: Integrated Pest Management (IPM) in Apple Orchards, which describes European Red Mite pests and predatory mites in Pennsylvania apple orchards.

Video: Integrated Pest Management (IPM) in Apple Orchards (8.34)

Integrated Pest Management (IPM) in Apple Orchards.

Click here for a transcript of the Integrated Pest Management video

Fruit growers do their best to assure consumers their food is grown in ways that are environmentally, socially, and economically sustainable. Regular field scouting and weather monitoring are key to achieving the production goals of conserving soil and water, reducing pesticide use, and being good responsible employers. In this short video, you will learn some basic orchard scouting principles for common disease, apple scab, and also mite pests and beneficials. Weather stations provide site-specific data on temperature, rainfall, relative humidity, leaf wetness, and degree days, to alert you when conditions are favorable for diseases and insect pests. Routine inspection of trees and the use of pheromone traps to determine thresholds, will help you minimize and better time sprays. Penn State is known for its early work on IPM for biological control of European red mites. European red mite is a major pest of apples, if controlled only with mitacides, With eight to ten generations per year, this pest can build in numbers very quickly and has historically been able to develop resistance to many new mitacides, in only three to five years, if biological control by predators is conserved. European red mite is a sporadic minor pest that is relatively easy to control with only an occasional selective miticide application. And miticide resistance is not an issue. A quick way of determining light levels in your orchards is to use a magnifying hand lens or a headpiece magnifier to determine the percentage of might infested leaves. Select ten trees in the orchard, on the most susceptible variety, and count ten spur leaves from each tree for the presence or absence of mites. Then use this graph to determine the mite threshold level. As a general rule in apples, a spray threshold of only two point five mites per leaf exists early season, before June. The threshold increases to 5 mites per leaf from June through mid-July. Use a threshold level of 7.5 mites per leaf through the rest of the season. If the mites per leaf do not reach these levels, no control action needs to be taken. Orchards with stable populations of T. pyri never reach these thresholds, as long as there's at least one predatory mite for every 10 pest mites per leaf. Our current population of T. pyri probably came to Pennsylvania on Apple bins moved between states, or on nursery stock. A program developed by Penn State, and funded by the USDA conservation programs, move T. pyri from known seed orchards to many new grower orchards, and over eighty percent of Pennsylvania apple orchards have this predator present at some level. Where conserved, T. pyri has reduced the use of miticides by over ninety percent, and some growers have not sprayed mite-susceptible varieties in more than ten years. Establishment of T. pyri into orchards where it is absent is relatively simple and can be accomplished in one to two seasons, once donor orchards with abundant T. pyri populations have been identified as a source. Transfers of T. pyri from these orchards can be successful by physically moving spur leaves in May and June. Transfers after July appear to be less likely to establish populations. If not controlled, apple scab can cause losses of seventy percent or greater where humid, cool weather occurs during the spring months. Losses result directly from fruit infections or indirectly from repeated defoliation, which can reduce tree growth and yield. The pathogen generally overwinters in fallen leaves and fruit on the orchard floor. As a result, orchards are self-infecting. Primary spores develop during the winter and begin to mature early spring. Around bud break, the first mature spores will be released from the infected leaves and or fruit. The length of time required for infection to occur depends on the number of hours of continuous wetness and the temperature during the wetting period. Leaf wetness hours can be calculated by either beginning the count at the time leaves become wet and ending the count when the relative humidity drops below ninety percent, or by adding consecutive wetting periods (hours), if the leaves are again wetted within eight hours from the time relative humidity dropped below ninety percent. For example, if the average temperature is between 61 to 75 degrees Fahrenheit, a minimum of six hours of leaf wetness is required for spores to be dispersed. Once the primary spores have established infection on the plant tissue, and approximately nine to ten days, symptoms can be observed. At that time, secondary spores called conidia, are being produced and will do so the remainder of the season, being dispersed by rain or wind on susceptible tissue. Monitor rainfall and duration of wetness closely, beginning at green tip, since mature spores begin to be released around this time. Peak mature spore release is around bloom time through petal fall. Continue to monitor rainfall and duration of wetness through mid-June, as the final mature spores are released during this time. Start monitoring for lesions (spots) around 10 to 14 days after bud break, which is when the first symptoms can occur, if disease conditions are favorable. For each orchard block, follow a “w” shape pattern within the block when scouting. Evaluate ten trees by examining 20 leaves on each of the five limbs per tree, and record the number of leaves showing any scab lesions. Number one: begin with the flower bud (spur) leaves where early infections are most likely to be noticed. Number two: start with observing the undersurface of leaves, since the undersurface of leaves may become spotted before the top surface. Take notice of early lesions which may be small, light brown, black spots. Number three: as scouting continues during early spring, be sure to observe both the top side and underside of the leaf. Apple scab infection appears as brown velvety lesions, which will become darker as they age. After fruit have set, in addition to leaf observations, examine 20 fruit on each tree and record the number showing any scab lesions. Use this information to better manage scab in the future. It is important to scout and control apple scab early in the season to prevent secondary infections from becoming established. Even if you have a professional consultant who monitors your orchard, it is important to become knowledgeable about basic principles of integrated fruit production. Penn State Extension offers educational programs on current best management practices in nutrition, pruning, tree training, crop load management, farm employee health and welfare regulations, food safety practices, and IPM. For a list of courses, visit the Penn State Extension Tree Fruit Production website. And for timely recommendations, sign up for Penn State Extension, Fruit Times.

Credit: Penn State Pesticide Education Program. "Integrated Pest Management (IPM) in Apple Orchards." YouTube. October 16, 2015.

What are the potential benefits of scouting for the European red mites and predatory mites in Pennsylvania orchards?

Click for the answer.

Answer: If the European red mites have not reached the economic threshold, a farmer can avoid spraying an insecticide and protect beneficial insects that can reduce the pest population and/or provide ecosystem benefits (ex. pollination, nutrient cycling). Avoiding spraying can also save money and time for the farmer and reduce the farmers’ exposure to pesticides.

Formative Assessment: Australian Grain Crop IPM and Determining the Economic Threshold of Potato Leafhoppers in Alfalfa

Formative Assessment: Australian Grain Crop IPM and Determining the Economic Threshold of Potato Leafhoppers in Alfalfa azs2 Thu, 01/07/2016 - 11:05

Part 1: Australian grain crop IPM

Watch the following video that explains IPM adoption in grain crops in Australia; then answer this question:

1. Identify and explain three benefits of utilizing IPM discussed in the Australian video from the GRDC.

Video 1: GCTV2: Integrated Pest Management (5:46)

Integrated Pest Management

Click for a transcript of the Integrated Pest Management video.

Narrator: Now another aspect of the overall push for improved farming practices, is how we control pests; and Jane Drinkwater reports on the latest approach to pest control while looking after the environment.

Jane Drinkwater: Australia's crop production systems are forever improving. A prime example is how we manage insect pests. Where once broad-spectrum, often highly toxic, insecticides were used to blanket eradicate insects, there's a move towards a more holistic approach, and with good reason. Integrated pest management, or IPM, presents a win-win, less damage to the environment and to your hip pocket.

Rowan Peel (Mount Pollock VIC: I love the environment and I want to look after the environment, but I have to make a living. IPM has given us the opportunity to do all of these things, both look after the environment and to make more money.

Jane: IPM uses multiple strategies to manage insect pests. One of the tactics is to let an army of the insects’ natural predators, or beneficials, fight the battle for you, and that means holding off on the use of broad-spectrum chemicals.

Rowan: I've probably learned that nature has its way of handling things its own way. You just have to give those beneficials that time. And when you understand that when you are using a broad-spectrum insecticide that you might control it straight away, but you'll get another flight straight in. But you've killed all your beneficials, and you've killed beneficials for other pests later on. And some of these beneficials don't have the lifecycle of an aphid. You know, their lifecycle might be only once or twice a year. And so you know, economically, if you look at the long-term, you're a long way worse off.

Jane: For insects without natural predators, or where the ratio of pests to beneficials is high enough to affect yield, strategies include the application of pesticides to problem areas only and the use of chemicals which target the problem pests, without damaging the beneficial insects. Rowan: We actually treat the seed for earwig infestation to give ita protection. But if there is a further problem, and that may well only be in certain areas of the paddock, which we tend to know where they will be, we will make up a brew of wheat, a little lawsben, and a little bit of vegetable oil. And we'll go out and spread just on that area. So as the earwigs are attracted to that bait, rather than all the other insects.

Jane: Peter Enkelmann’s been using IBM for more than a decade. While his beneficials successfully control silver leaf whitefly, there are still a few pests without natural predators.

Peter Enkelmann (“Riverview” Byee QLD): The chemistry that we use here, it takes out the beneficial insects. So the attitude is to delay spraying any product at all basically, apart from very few natural viruses, right through until the very last.

Jane: And using IPM means, when you do need to pull out the big guns, they're more likely to work.

Peter: One of the big advantages is that resistance to our traditional chemistry is just dropped dramatically.

Jane: But how do growers know when to take action? Well thanks to research funded by GRDC, entomologists have data on the density of pests in each crop that will lead to economic damage. Growers measure the number of pests in their fields and only take action once they've reached this threshold.

Hugh Brier (Senior Entomologist, Primary Industries and Fisheries, DEEDI QLD): So the short-term gain is you might avoid unnecessary sprays. Another short-term gain is by not spraying when you didn't need to, you might avoid flaring another pest which is more expensive to control, so that's another benefit. Longer term, if you avoid spraying unnecessarily, you build up beneficials in the whole system and the system is much more stable.

Jane: Fundamental to successful integrated pest management is the ability to correctly identify pests and beneficial species, and to regularly monitor both populations.

Hugh: In row crops, we use a bed sheet. So we'll go and we shake the plants from meter of row and that shakes all the insects out, or a lot of them out onto the bed sheet and you can count them.

Jane: With IPM leading to lower costs and better environmental outcomes, GRDC views it as an important step forward. Apart from funding IPM Research, GRDC also provides information and training for growers.

David Shannon (GRDC Southern Region Panel Chairman): We have run a series of workshops, IPM workshops. We also work with the grower groups so that grower groups can scale up their grower members on the use of IPM.

Jane: And it's well worth getting up to speed.

Rowan: I find the system of IPM very easy because it's not an almost do nothing, but you just don't worry about it anywhere near as much.

Jane: With IBM's effectiveness in controlling insects, while reducing costs both financial and environmental, it's here to stay.

Rowan: IPM for us has cut down our chemical usage, insecticide usage a long way and you feel better for not using it.

Credit: Grains Research and Development Corporation (GRDC). "GCTV2: Integrated Pest Management." YouTube. October 14, 2010.

If the video does not load for you, go to GCTV2: Integrated Pest Management

Part 2: Determining the Economic Threshold of Potato Leafhoppers in Alfalfa

Read the Penn State University Potato Leafhopper on Alfalfa Fact Sheet.

Figure 8.1.9: Economic Threshold for Potato Leafhoppers

Credit: Penn State University Potato Leafhopper Alfalfa Fact Sheet

Scenario

Assume that you followed the procedure described in the Penn State fact sheet to scout for Potato Leafhoppers in an alfalfa field by sweeping 20 times with your sweepnet in each of 5 different locations in the alfalfa field. The number of leafhoppers that you found in the 5 different locations was: 15, 12, 16, 7, 13 when the alfalfa crop was about 11 inches tall. You would like the alfalfa to grow about 25-30 inches height before harvesting it for hay, this could require 2 to 3 more weeks of growth, depending on rainfall. Based on current alfalfa hay prices in your region, you estimate your alfalfa hay is worth about $250/Ton, and the insecticide you would spray to control the leafhoppers would cost about $16/A. If you spray the alfalfa field, it cannot be harvest until 7 days after spraying the insecticide; and due to toxicity to bees, the alfalfa should not be sprayed if it is flowering.

Answer the following questions:

Calculate the average number of leafhoppers per sweep. Add the number of potato leafhoppers from the 20 sweeps in each of the 5 locations (20 X 5= 100 sweeps). Divide by 100 to calculate the number of leafhoppers per sweep. Use the Economic Threshold Table from the Fact Sheet for Potato Leafhoppers, shown here. Has the insect population reached an economic threshold for your crop at this height?
Based on the average number of leafhoppers per sweep, what should you do? Why?
If your crop height was 7 inches tall and you had the same number of leafhoppers per sweep that you calculated here, would your pest management decision change and how?
Discuss at least two potential benefits of using the economic threshold decision tool rather than spraying as soon as potato leafhoppers were first visible.

Files to Download

Module 8 Formative Assessment Worksheet

Submitting Your Assignment

Please complete the Module 8 Formative Assessment in Canvas.