Why Is The Economic Threshold For Aphids Zero Chrysanthemums?

Pests such as thrips, aphids, caterpillars, mites, and flies have significantly affected chrysanthemum crops, causing economic losses. Thrips are small insects of the order Thysanoptera that affect yield and quality, while the economic injury level (EIL) and economic threshold (ET) are tools used to assess the impact of pests on yield and/or quality. The chrysanthemum aphid (Macrosiphoniella sanborni Gillette) is one of the most severe crop pests for cultivated chrysanthemum.

The soybean aphid ET is best viewed as a fixed action or treatment threshold, which reduces lead-time for applications and increases the risk of economic loss from rapidly increasing aphid populations. The goal of the economic threshold is to prevent a pest population from reaching the point where its damage causes monetary losses equal to the cost of control. This “break-even” point is known as an economic injury level, and is computed using the formula: the ET of 250 aphids per plant is the point at which farmers and agricultural professionals should begin preparing to make an insecticide application to prevent the aphid population from reaching the economic injury level.

In this study, an aromatic wild species Chrysanthemum aromaticum was introduced to hybrid with Chrysanthemum nankingense to breed aphid-resistant offspring. Fifty interspecific hybrids were obtained and identified by morphology and SSR test. The chrysanthemum aphid Macrosiphoniella sanborni is one of the most severe crop pests for cultivated chrysanthemum, and it is urgent to find efficient and eco-friendly control strategies to promote the industry’s sustainable development. Economic thresholds (ETs) are a foundational principle of integrated pest management but are not always widely accepted by farmers and agricultural professionals.

Do Aphids Like Chrysanthemums?

Chrysanthemums face several pest and disease challenges, particularly from aphids, including the Macrosiphoniella sanborni, commonly known as chrysanthemum aphids. These pests are unique to chrysanthemums as their sole known hosts in North America and exhibit parthenogenetic reproduction, leading to rapid population increases. Aphids are small, soft-bodied insects that primarily feed on plant sap; they inflict damage by piercing plant tissue, leading to loss of vigor, yellowing, and stunted growth. Infestations can result in premature leaf drop, and other visiting aphid species, such as green peach aphids and melon aphids, can also affect chrysanthemums, distinguished by their coloration.

Effective management requires understanding aphid life cycles, employing preventive strategies, and utilizing both natural predators and chemical controls. These predators include parasitic wasps, lady beetles, and lacewings, which help mitigate aphid populations. Additionally, aphids can transmit various viruses, such as chrysanthemum vein mottle virus and chrysanthemum virus B, further complicating care for these plants.

Recognizing the signs of infestation and maintaining plant health can improve the resistance of chrysanthemums against these pests, ensuring their ornamental value is preserved. Overall, proactive measures and vigilant monitoring are critical to managing aphid populations and protecting chrysanthemum growth and vitality.

What Is The Threshold For Aphids?

To determine if soybean plants have reached the threshold for soybean aphids (Aphis glycines) infestation, scouts need not count or estimate aphid numbers. SDSU recommends a threshold of 250 soybean aphids per plant, applicable on at least 80 examined plants, or the speed scouting method. This threshold is conservative, functioning as a fixed action point for management, rather than an economic threshold subject to variability seen with other pests.

It is crucial to recognize population densities that necessitate insecticide treatment. Peak aphid density typically occurs during soybean growth stages R3 (beginning pod formation) to R5 (full size pod), with the established threshold for insecticide application remaining at 250 aphids per plant, specifically when populations are increasing. Although earlier estimates suggest economic thresholds could be lower at 34–50 aphids per main stem, current recommendations stick with the 250 aphids per plant figure, which has gained acceptance among growers.

Research indicates that yield differences become detectable when aphid populations reach about 485 per plant. It's important for scouts to adhere to the 250 threshold as it is widely recognized and used within the industry, even if higher thresholds may apply in other instances or for other pests. The consistent application of this threshold aids in maintaining effective management strategies for soybean aphids.

What Plants Are Most Susceptible To Aphids?

Melon aphids primarily target various plants, particularly cucurbits like watermelons and cucumbers, alongside asparagus, pepper, eggplant, aster, hollyhock, and lily. Brown ambrosia aphids favor Rudbeckia, coneflower, and sunflower. To combat infestations, it’s crucial to recognize flowers that attract aphids and identify effective prevention strategies. Cabbage and mustard (Brassica spp.) are notably susceptible, with aphids also drawn to tomatoes, cucumbers, leafy vegetables, and some root crops.

Companion planting, trap plants, and attracting natural predators can help repel these pests; marigolds, garlic, and onions serve as effective deterrents near at-risk plants. Dill, fennel, and yarrow attract beneficial insects that prey on aphids. To maintain a thriving garden, explore natural defenses and identify top plants that repel aphids. Discing fields post-harvest eliminates alternate host plants, reducing aphid populations and viruses.

Plant susceptible crops upwind from infested areas. While aphids can infest nearly any plant—ornamentals, vegetables, and houseplants—they are particularly attracted to mustard and nasturtium, which can serve as trap crops.

What Is The Aphid Threshold For Wheat?

When assessing aphids, it's crucial to document the presence of natural enemies, parasitized mummies, or those destroyed by fungi. The economic threshold for cereals lies at an average of 12 to 15 aphids per stem before the soft dough stage, as insecticide applications post-early dough stage may not be economically viable. Scouting should involve estimating aphid numbers per stem across various locations, rather than just in hotspots. The bird cherry oat aphid is notably impactful in transmitting BYDV.

Predominantly, scouts encounter wingless female aphids due to their commonality, utilizing parthenogenesis to reproduce. Among numerous aphid species, the Russian wheat aphid (RWA) and greenbug are particularly damaging, with the English grain aphid (EGA) often appearing as grains mature. Historically, EGA caused damage at 25 aphids per grain head, now estimated at 50 aphids per tiller. The mite, found on wheat and other species, measures about 1/100 inch and can be monitored via methods like sweep nets or visual inspection for pathogens or weeds.

Economic action thresholds indicate treatment should occur when 50% of cereal tillers show 15 or more aphids. Traditionally, sprays were recommended at an average of 5 aphids per ear during flowering. Alternatively, treatment could be considered if over 50% of tillers or 66% of ears with increasing aphid counts are present. A predictive online calculator assists farmers in estimating if aphid density will reach injurious levels by GS50. Aphid thresholds tend to rise with wheat maturity, so younger plants may allow for lower thresholds.

Generally, economic losses were associated with 25 aphids per grain head and a calculated action threshold area. The economic threshold for high-yielding wheat can vary during different crop stages, indicating a need for strategic pest management planning.

What Are Economic Thresholds For Soybean Aphid?

Economic thresholds (ETs) are crucial in integrated pest management but are not universally accepted among farmers. A survey of Minnesota farmers and agricultural professionals assessed perceptions of the ET for soybean aphids (Aphis glycines Matsumura). Findings indicated average soybean aphid populations at 6. 8 ± 0. 8 days (mean ± SEM), with an average ET of 273 ± 38 aphids per plant (mean ± 95% confidence interval, range 111-567).

This ET allows for a seven-day lead time before economic losses due to aphid infestations occur. In 2007, the ET of 250 soybean aphids per plant was established, recommending action when over 80% of plants are infested and populations are rising.

At South Dakota State University (SDSU), this guidance is still applicable, alongside speed scouting methods. The established threshold is intended to mitigate risks of significant crop loss. Current recommendations for late vegetative through R5 stage soybeans state that management should follow the ET of 250 aphids per plant in similar population conditions. These thresholds remain conservative and are adaptable to changing economic situations influencing control costs and market values.

The 2007 ET holds validity as it is set below the economic injury level (EIL), which denotes the crop loss point due to aphid feeding. Recent models have confirmed that populations can indeed be identified as above or below this ET. By adhering to these thresholds, particularly the 250 aphids per plant guideline, farmers can optimize their pest management strategies while minimizing economic impacts.

What Is A Aphid Threshold?

The threshold for insecticide application against soybean aphids (Aphis glycines) aims to prevent their population from reaching the economic injury level (EIL), where pest-induced losses equal insecticide costs. In the North Central U. S., soybean is significantly impacted by these aphids, necessitating management strategies based on economic thresholds (ET). The average EIL and ETL for soybean aphids are calculated at 7. 03 and 2. 26 aphids per spike per feddan, respectively.

The gain threshold is noted at 0. 21 Ardab per feddan. Typically, peak aphid densities occur from soybean growth stages R3 to R5, with the ET for aphid intensity being identified at 15. 61, 22. 06, and 19. 49 aphids per 10 cm terminal central shoot based on certain mustard varieties.

The current ET for effective yield protection in soybeans is set at 250 aphids per plant when 80% of plants are infested and populations are increasing. In comparison to other pests, the soybean aphid ET is characterized as a fixed action threshold. The research supports that even with reduced impacts from natural enemies, this ET can protect yields. For pea aphids in lentils, the nominal threshold varies from 30 to 40 aphids per sweep.

To monitor aphid populations, regular checks, especially on the undersides of leaves where they predominantly reside, are recommended. The threshold for damage is recognized when 20% of flowering heads are infested with aphids. This strategic approach is essential to prevent substantial economic losses in soybean crops due to aphid infestation.

When Should Aphids Be Treated?

Seventy-two percent of participants indicated the need to treat fields for aphids before reaching 250 per plant to effectively manage infestations and avoid economic injury levels. Treating aphids involves spraying a mixture directly on the infested plants, especially beneath the leaves where aphids tend to hide. Prevention is emphasized as the best strategy, which includes indirectly controlling ants. Aphids breed rapidly, complicating eradication, but diligent management can control their population.

A recommended approach is to spray them off with water upon sighting. A step-by-step guide provides techniques to eliminate aphids throughout a plant's life cycle. With their rapid reproduction, immediate action is crucial; removing affected plant parts and applying Plant Soap can be effective. Following this, introducing natural predators like Carna lacewing larvae or Puncta ladybirds can help manage aphids sustainably. While controlling them isn't mandatory as they play a role in garden biodiversity, it's often unnecessary to resort to chemical treatments.

Non-chemical options or low-risk pesticides are effective alternatives. Regularly applying Seasol and using fertilizers like PowerFeed supports plant resilience against stress. Homemade solutions, such as soapy water mixtures, are also prevalent. Late October to early December is an optimal time for applying fall pesticide treatments, contributing to effective aphid control in the following season.

How Many Aphids Are In A Plant?

The most common economic threshold (ET) for managing aphid populations among all groups is set at 250 aphids per plant, although a lower threshold of 100-150 aphids per plant is frequently used, particularly by sales agronomists and farmers. In Britain, over 500 aphid species exist, with some specializing in just one or two plant types, while others can feed on a variety. Aphids, typically small (about 1/8 inch), display various colors and forms, including green and black varieties.

Their presence on plants can lead to issues such as curled and yellowing leaves, especially when populations grow uncontrollably. Most aphids feed on plant sap, which can be detrimental to young plants. They often form symbiotic relationships with ants, feeding on the sugary substances produced by aphids. Although they are considered global pests, not all aphids are harmful unless infestations become severe. Over 4, 000 species of aphids are recognized and the majority are plant-specific, meaning they usually do not migrate between different plants.

High populations of aphids can significantly affect herbaceous plants, but established trees and shrubs can typically withstand them without serious harm. For effective management and damage assessment, it is crucial to identify the specific aphid species present. Overall, understanding their feeding habits and host preferences can help mitigate potential damage to crops and ornamental plants.

Why Are Aphids Bad For The Environment?

Aphids are significant pests that damage a wide range of host plants by feeding on their sap. Their feeding behavior leads to discoloration, leaf curling, yellowing, and stunted growth. With large infestations, they produce honeydew, a sticky, sugary waste that can attract ants and promote fungal growth on plant surfaces. These pests serve as indicators of climate change due to their rapid reproduction and environmental sensitivity.

Direct damage occurs as they pierce plant tissues with their needle-like mouthparts called stylets, extracting valuable nutrients and water, which results in wilting and yellowing of leaves and can severely stunt growth. While some species, like the sycamore aphid, may not cause serious harm, others can lead to extensive damage in gardens and crops, particularly when their populations surge.

Aphids are true bugs classified under Hemiptera: Aphidoidea, known for their specialized mouthparts suited for sap-sucking. They can infest gardens, landscapes, and even houseplants. Their feeding can lead to nutrient depletion, distorted plant growth, and transmission of lethal viruses that infect various crops, such as potatoes and citrus fruits. The honeydew they excrete not only fosters sooty molds but can also dirty surfaces, such as windows and cars.

Aphids carry viruses like the cucumber mosaic virus, which affects numerous vegetables. In high populations, they can significantly impair fruit quality and plant vigor, highlighting their role as both agricultural pests and companions to other unwanted garden nuisances.

What Is The Economic Threshold For Grasshoppers?

The most significant economic harm caused by grasshoppers occurs during their third to fifth nymphal stages, with the economic threshold varying from 8 to 12 grasshoppers per square meter in cereal crops. In rangelands, control measures are instigated once densities surpass eight per square yard, largely regardless of rangeland productivity and forage amounts. Decisions regarding control measures are ultimately at the discretion of the producer, aided by economic thresholds that inform whether insect control may yield economic advantages.

An economic threshold reflects the pest population at which the cost of control becomes justified by the anticipated crop value saved from damage. Evaluating key parameters like ranch type, rangeland productivity, and costs of alternative forage sources for livestock is essential. In most cereal crops, established thresholds depend on various factors, including the insect’s life stage, crop type, and growing conditions.

Integrating these considerations enables effective pest management strategies. Current guidelines suggest that control should be initiated when grasshopper densities reach eight per square yard. This article aims to explore the implications of these economic thresholds. For grasshopper infestations, yield reductions can be significant; for instance, two-striped grasshoppers at a low density can still cause considerable wheat yield loss.

The article also indicates that thresholds for grasshoppers in rangeland can range from 8 to 40 per square yard, shaped by the specific grasshopper species and the economic impact of damage incurred. It is important to adapt thresholds based on the estimated amount and value of forage saved, alongside the costs associated with control measures. Ultimately, accurately assessing grasshopper density is key for effective management and decision-making in agricultural practices.

What Should Farmers Know About A Pesticide Threshold?

For farmers, enhancing education on the conservative nature of pesticide thresholds and their implications is crucial. It is important to understand how these thresholds take into account the effects of multiple stressors and the risks associated with premature or excessive pesticide application. Farmers should critically evaluate the potential biases in their information sources. Pesticide thresholds exist for assessing adverse effects, and they are based on yield loss due to invertebrate feeding, indicating that increased pest densities correlate directly to greater damage.

Research has shown that farms implementing a threshold-based pesticide strategy only treated 25-30% of their cropped land, significantly less than neighboring farms. The list of pesticide residues and their permissible maximum levels will be determined by the Council on the Commission’s proposal. The use of thresholds may be promoted by enhancing the accessibility of pesticide technology. Farmers' views on thresholds often vary, reflecting their subjective interpretations.

Economic thresholds, linked to pest populations and crop yield impacts, are essential for pest management. This threshold indicates the pest density that necessitates intervention to avert economic harm. From 2013 to 2019, pesticide levels surpassed effect thresholds at 13 to 30% of surface water monitoring sites in European water bodies. WHO suggests minimizing pesticide use when feasible, advocating for initial assessments of necessity and encouraging non-chemical solutions. Once thresholds are breached, indicating unsustainable pest levels or damage, prompt control measures are required. Integrated Pest Management emphasizes creating predator habitats and crop diversity while diligently monitoring pest thresholds. Farmers must maintain electronic records of pest management actions, facilitating thorough risk assessments.