Category 1C Agricultural Disease Management

Plant Disease

Any abnormal condition harming plants, which can lead to significant alterations in appearance, function, or productivity or quality of yield. Plant diseases can arise from various causes, including pathogens like fungi, bacteria, and viruses.

Symptoms

Visible effects of a plant disease on plants, which can include leaf spots, wilting, yellowing, stunted growth, necrosis, and abnormal growth patterns. Symptoms vary by disease and can be influenced by plant species and environmental conditions, acting as critical indicators of underlying problems.

Pathogen

A parasitic organism such as a fungus, bacterium, virus, or nematode that causes disease in plants.

Plant Disease Triangle

The three components required for disease: a susceptible host, a pathogen, and a favorable environment.

Fungi

The largest group of plant pathogens, some of which can cause diseases in plants. Most are microscopic and cannot be seen. some can be seen when extension growth occurs.

Viruses

Infectious particles that induce host cells to produce more viruses, primarily transmitted by insects or mechanical means.

Nematodes

Microscopic roundworms that feed on plant tissues or organic matter, some of which are parasitic.

Noninfectious Disorders

Diseases that appear suddenly and can mimic infections, often caused by environmental factors.

Integrated Pest Management (IPM)

A comprehensive approach to managing pests with minimal environmental impact, emphasizing pest prevention.

Disease Resistance

Using resistant varieties to mitigate common diseases.

Cultural Practices

Management practices such as crop rotation and residue management to disrupt pathogen cycles.

Chemical Control

Use of fungicides to manage plant diseases, which should be applied wisely.

Fungicides

Chemical substances used to kill or inhibit the growth of fungi.

Resistance Management

Understanding and applying FRAC codes to manage fungicide resistance.

Host Plant Alteration

Modification of host plants to enhance resistance against pathogens or to improve tolerance to environmental stressors, which can include techniques like genetic engineering or selective breeding. disease resistant varieties

how to reduce pathogens

removing crop debris, rotating crops, controlling insects that carry disease, use fungicides to kill pathogen

make environment less favorable to disease

change row spacing, avoiding overhead irrigation

Hyphae

The thread-like structures that make up the mycelium (the visible mass on plants) of fungi, responsible for nutrient absorption and reproduction.

Fungi lack

chlorophyll and cannot perform photosynthesis.

fungi reproduce by forming

spores, carried primarily by wind and water.

sclerotia

are specialized survival structures made of compacted hyphae formed by some fungi, allowing them to endure harsh conditions.

Fungi Symptoms

leaf spots and blights, root rots, seedling blights, wilts, and stalk rots

Fungal Diseases include

frogeye leaf spot of soybean, anthracnose of corn, leaf spot diseases of alfalfa and small grains

Bacteria

small microorganisms that reproduce by cell division and can cause disease

Colonies

groups or masses of bacteria with characteristic colors, growth habits and shapes that can be used to identify bacteria

Bacteria spread via

primarily wind-driven rain, and gain access via plant wounds or natural openings such as stomata.

Bacterial disease symptoms

leaf spots, water soaking of tissue, soft rots.

common bacterial diseases in Iowa

wilt of alfalfa, blights, pustule of soybean, holcus leaf spot of corn, stewarts wilt of corn

viruses

non-living, infectious particles that consist of DNA in a protein coat. Can only survive in living cells

viral vectors

primarily insects, mostly aphids and leafhoppers. sometimes machinery can spread viruses,

Virus symptoms in plants

mosaic patterns on leaves, tissue deformation, stunting, reduced yield

common viral diseases in iowa

bean pod mottle, dwarf mosaic of corn, barley yellow dwarf

Nematode

threadlike worms found in soil, some are plant parasites that can cause root damage and reduce crop yields.

life cycle of a nematode

includes egg, four juvenile stages, and an adult. Cycle is 60 days. They can be free living or associated with root nodes or knots.

Soybean cyst nematode

include yellowing leaves, stunted growth, and reduced pod and seed development. Most common one in Iowa

Non-infectious disorders

caused by non-living agents such as environmental factors, nutrient deficiencies, or chemical imbalances, leading to poor plant health without the involvement of pathogens.

non-infectious disorder symptoms and patterns

if for example herbicide injury is the cause, injury will appear as a drift pattern or spray pattern and show symptoms such as cupping (2,4-D).

If the entire field or small pockets show symptoms, other factors may be involved.

disease cycle

1. Production of inoculum

2. spread of inoculum to susceptible host

3. penetration of inoculum into host

4. infection

5. secondary cycles

6. pathogen survival between host crops

Inoculum

the part of a pathogen that initiates infection, including fungal spores, bacterial cells, virus particles, nematode juveniles

Plant disease may have more than 1 source of _____

dissemination

how the inoculum spreads and moves to the host

Four Steps of diagnosis

1. Make observations. ID the host, Examine the area for patterns of disease, check for prevalence and severity of the problem, check affected species, consider recent weather conditions, consider time of year.

2. Examine individual plants, comparing healthy to diseased.

3. Collect background or crop hisstory

4. Diagnose problem

IPM

incorporates cultural, biological, and chemical control methods to manage pests and diseases in an environmentally sustainable manner. Emphasizes prevention whenever possible.

EIL, Economic Injury Level

the level at which the cost of pest damage equals the cost of control measures. A pest density measure. It helps determine the threshold for taking action against pests to prevent economic losses.

ET

economic threshold, always lower than EIL, the density at which you should take action

Regulatory control of diseases

prevent import or spread of plant pathogens via regulations and laws, such as quarantines inspections, seed certification, and testing to ensure disease-free plant material.

Biological plant disease Management methods

Resistant Varieties, biological control agents

Cultural disease Management methods

crop rotation, residue management, disease free seed, proper planting, sanitation practices, and proper irrigation techniques to reduce disease incidence.

Fungicides

chemical or physical agents that kill or inhibit the growth of Fungi. Usually effective against specific groups of Fungi, so damaging pathogen ID is important. Fungicides are the most common pesticide for diseased plants.

Bactericides

kill or inhibit bacteria. Not generally used for bacterial management, however copper products are used to kill both fungi and bacteria.

Nematicides

chemical agents that kill or inhibit nematodes, often used in soil treatments to protect crops from nematode damage. spot treatment to determine benfit is recommended

Viricides

used to kill or inhibit viruses, not used in the fieldd but primarily in laboratory, home, and hospital settings.

fungicide movement in plants

very few fungicides are truly systemic, some are upwardly systemic (move upward through xylem) and others are locally systemic (move near treated tissues)

curative or kickback activity

fungicide activity in the plant when applied shortly after infection that cures early infection activity and prevents further disease development.

anti sporulant

fungicide that inhibits the formation of spores, reducing fungal reproduction and spread. Infected plants don’t spread.

chemical classes of fungicides

triazoles, Qo1

FRAC code

represents the mode of action of a fungi

single vs multisite fungicides

the number of metabolic pathway sites a fungicide is active against. Single is less toxic and tends to be systemic.

Fungicide Formulations

Most are solids that are not soluble in water

Fungicide Failure

misdiagnosis, improperly stored product, too high water pH at mixing, improper applicaation rate, incompatible mixing, or environmental conditions affecting efficacy.

order in which to add pesticides to the tank

WP (wetteble powders) ,(F)Flowables, Solubles, Powders, Surfactants, EC’s

FRAC codes

fungicide resistance action committee codes that classify fungicides based on their modes of action to manage resistance. Using different fungicides with different frac codes helps prevent resistance. Single site mode fungicides are more susceptible to resistance.

Captan and Maneb

older, multisite fungicides that need to be applied before infection. still effective.

demethylation compounds (traizoles) and Qo1 (strobilurins)

newer fungicides more prone to resistance due to their single-site modes of action. They are used to manage various fungal diseases but require careful rotation to minimize resistance development.

Additives and Fungicide

most additives like surfactants are should not be used with fungicides unless indicated by the label, particularly fertilizer solutions because they can affect the efficacy and safety of the fungicide.