Fungicide

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Fungicides are pesticides used to kill parasitic fungi or their spores. [1] [2] Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals. Fungicides are also used to control oomycetes, which are not taxonomically/genetically fungi, although sharing similar methods of infecting plants. Fungicides can either be contact, translaminar or systemic. Contact fungicides are not taken up into the plant tissue and protect only the plant where the spray is deposited. Translaminar fungicides redistribute the fungicide from the upper, sprayed leaf surface to the lower, unsprayed surface. Systemic fungicides are taken up and redistributed through the xylem vessels. Few fungicides move to all parts of a plant. Some are locally systemic, and some move upward. [3] [4]

Contents

Most fungicides that can be bought retail are sold in liquid form, the active ingredient being present at 0.08% in weaker concentrates, and as high as 0.5% for less potent fungicides. Fungicides in powdered form are usually around 90% sulfur.

Major fungi in agriculture

Some major fungal threats to agriculture (and the associated diseases) are Ascomycetes ("potato late blight"), basidiomycetes ("powdery mildew"), deuteromycetes (various rusts), and oomycetes ("downy mildew"). [1]

Types of fungicides

Like other pesticides, fungicides are numerous and diverse. This complexity has led to diverse schemes for classifying fungicides. Classifications are based on inorganic (elemental sulfur and copper salts) vs organic, chemical structures (dithiocarbamates vs phthalimides), and, most successfully, mechanism of action (MOA). These respective classifications reflect the evolution of the underlying science.

Traditional

Captan, a phthalimide, is a major commercial fungicide. Captan Structural Formula V.1.svg
Captan, a phthalimide, is a major commercial fungicide.

Traditional fungicides are simple inorganic compounds like sulfur, [5] and copper salts. While cheap, they must be applied repeatedly and are relatively ineffective. [2] Other active ingredients in fungicides include neem oil, rosemary oil, jojoba oil, the bacterium Bacillus subtilis , and the beneficial fungus Ulocladium oudemansii.

Nonspecific

In the 1930s dithiocarbamate-based fungicides, the first organic compounds used for this purpose, became available. These include ferbam, ziram, zineb, maneb, and mancozeb. These compounds are non-specific and are thought to inhibit cysteine-based protease enzymes. Similarly nonspecific are N-substituted phthalimides. Members include captafol, captan, and folpet. Chlorothalonil is also non-specific. [2]

Specific

Specific fungicides target a particular biological process in the fungus.

Nucleic acid metabolism

Cytoskeleton and motor proteins

Respiration

Some fungicides target succinate dehydrogenase, a metabolically central enzyme. Fungi of the class Basidiomycetes were the initial focus of these fungicides. These fungi are active against cereals.

Amino acid and protein synthesis

Signal transduction

Lipid synthesis / membrane integrity

Melanin synthesis in cell wall

Sterol biosynthesis in membranes

Cell wall biosynthesis

Host plant defence induction

Mycoviruses

Some of the most common fungal crop pathogens are known to suffer from mycoviruses, and it is likely that they are as common as for plant and animal viruses, although not as well studied. Given the obligately parasitic nature of mycoviruses, it is likely that all of these are detrimental to their hosts, and thus are potential biocontrols/biofungicides. [7]

Resistance

Doses that provide the most control of the disease also provide the largest selection pressure to acquire resistance. [8]

In some cases, the pathogen evolves resistance to multiple fungicides, a phenomenon known as cross resistance. These additional fungicides typically belong to the same chemical family, act in the same way, or have a similar mechanism for detoxification. Sometimes negative cross-resistance occurs, where resistance to one chemical class of fungicides increases sensitivity to a different chemical class of fungicides. This has been seen with carbendazim and diethofencarb. Also possible is resistance to two chemically different fungicides by separate mutation events. For example, Botrytis cinerea is resistant to both azoles and dicarboximide fungicides.

A common mechanism for acquiring resistance is alteration of the target enzyme. For example, Black Sigatoka, an economically important pathogen of banana, is resistant to the QoI fungicides, due to a single nucleotide change resulting in the replacement of one amino acid (glycine) by another (alanine) in the target protein of the QoI fungicides, cytochrome b. [9] It is presumed that this disrupts the binding of the fungicide to the protein, rendering the fungicide ineffective. Upregulation of target genes can also render the fungicide ineffective. This is seen in DMI-resistant strains of Venturia inaequalis . [10]

Resistance to fungicides can also be developed by efficient efflux of the fungicide out of the cell. Septoria tritici has developed multiple drug resistance using this mechanism. The pathogen had five ABC-type transporters with overlapping substrate specificities that together work to pump toxic chemicals out of the cell. [11]

In addition to the mechanisms outlined above, fungi may also develop metabolic pathways that circumvent the target protein, or acquire enzymes that enable the metabolism of the fungicide to a harmless substance.

Fungicides that are at risk of losing their potency due to resistance include Strobilurins such as azoxystrobin. [12] Cross-resistance can occur because the active ingredients share a common mode of action. [13] FRAC is organized by CropLife International. [14] [12]

Safety

Fungicides pose risks for humans. [15]

Fungicide residues have been found on food for human consumption, mostly from post-harvest treatments. [16] Some fungicides are dangerous to human health, such as vinclozolin, which has now been removed from use. [17] Ziram is also a fungicide that is toxic to humans with long-term exposure, and fatal if ingested. [18] A number of fungicides are also used in human health care.

See also

Further reading

Related Research Articles

<span class="mw-page-title-main">Plant pathology</span> Scientific study of plant diseases

Plant pathology or phytopathology is the scientific study of plant diseases caused by pathogens and environmental conditions. Plant pathology involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.

<span class="mw-page-title-main">Pesticide resistance</span> Decreased effectiveness of a pesticide on a pest

Pesticide resistance describes the decreased susceptibility of a pest population to a pesticide that was previously effective at controlling the pest. Pest species evolve pesticide resistance via natural selection: the most resistant specimens survive and pass on their acquired heritable changes traits to their offspring. If a pest has resistance then that will reduce the pesticide's efficacy – efficacy and resistance are inversely related.

<span class="mw-page-title-main">Famoxadone</span> Chemical compound

Famoxadone is a fungicide to protect agricultural products against various fungal diseases on fruiting vegetables, tomatoes, potatoes, curcurbits, lettuce and grapes. It is used in combination with cymoxanil. Famoxadone is a QoI, albeit with a chemistry different from most QoIs. It is commonly used against Plasmopara viticola, Alternaria solani, Phytophthora infestans, and Septoria nodorum.

<span class="mw-page-title-main">Powdery mildew</span> Fungal plant disease

Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as the signs of the causal pathogen are quite distinctive. Infected plants display white powdery spots on the leaves and stems. This mycelial layer may quickly spread to cover all of the leaves. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.

A Biopesticide is a biological substance or organism that damages, kills, or repels organisms seens as pests. Biological pest management intervention involves predatory, parasitic, or chemical relationships.

Pythium ultimum is a plant pathogen. It causes damping off and root rot diseases of hundreds of diverse plant hosts including maize, soybean, potato, wheat, fir, and many ornamental species. P. ultimum belongs to the peronosporalean lineage of oomycetes, along with other important plant pathogens such as Phytophthora spp. and many genera of downy mildews. P. ultimum is a frequent inhabitant of fields, freshwater ponds, and decomposing vegetation in most areas of the world. Contributing to the widespread distribution and persistence of P. ultimum is its ability to grow saprotrophically in soil and plant residue. This trait is also exhibited by most Pythium spp. but not by the related Phytophthora spp., which can only colonize living plant hosts.

<i>Alternaria solani</i> Species of fungus

Alternaria solani is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tuber blight on potato. Despite the name "early", foliar symptoms usually occur on older leaves. If uncontrolled, early blight can cause significant yield reductions. Primary methods of controlling this disease include preventing long periods of wetness on leaf surfaces and applying fungicides. Early blight can also be caused by Alternaria tomatophila, which is more virulent on stems and leaves of tomato plants than Alternaria solani.

<i>Plasmopara viticola</i> Species of single-celled organism

Plasmopara viticola, the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition release zoospores. Zoospores are splashed by rain into the canopy, where they swim to and infect through stomata. After 7–10 days, yellow lesions appear on foliage. During favorable weather the lesions sporulate and new secondary infections occur.

<span class="mw-page-title-main">Azoxystrobin</span> Chemical compound

Azoxystrobin is a broad spectrum systemic fungicide widely used in agriculture to protect crops from fungal diseases. It was first marketed in 1996 using the brand name Amistar and by 1999 it had been registered in 48 countries on more than 50 crops. In the year 2000 it was announced that it had been granted UK Millennium product status.

<span class="mw-page-title-main">Sterol 14-demethylase</span> Class of enzymes

In enzymology, a sterol 14-demethylase (EC 1.14.13.70) is an enzyme of the cytochrome P450 (CYP) superfamily. It is any member of the CYP51 family. It catalyzes a chemical reaction such as:

<span class="mw-page-title-main">Plant disease resistance</span> Ability of plants to withstand pathogens

Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathogen growth on or in the plant, while disease tolerance describes plants that exhibit little disease damage despite substantial pathogen levels. Disease outcome is determined by the three-way interaction of the pathogen, the plant, and the environmental conditions.

Copper pesticides are copper compounds used as bactericides, algaecides, or fungicides. They can kill bacteria, oomycetes and algae, and prevent fungal spores from germinating. Common forms of fixed copper fungicides include copper sulfate, copper sulfate pentahydrate, copper hydroxide, copper oxychloride sulfate, cuprous oxide, and copper octanoate.

<span class="mw-page-title-main">Mepronil</span> Chemical compound

Mepronil is a fungicide used as a seed treatment or foliar spray in agriculture to protect crops from fungal diseases. It was first marketed by Kumiai Chemical Industries in 1981 using their brand name Basitac. The compound is a benzanilide which combines 2-methylbenzoic acid with the O-isopropyl derivative of 3-aminophenol to give an inhibitor of succinate dehydrogenase (SDHI).

Early twenty-first century pesticide research has focused on developing molecules that combine low use rates and that are more selective, safer, resistance-breaking and cost-effective. Obstacles include increasing pesticide resistance and an increasingly stringent regulatory environment.

<span class="mw-page-title-main">Cyproconazole</span> Chemical compound

Cyproconazole is an agricultural fungicide of the class of azoles, used on cereal crops, coffee, sugar beet, fruit trees and grapes, and peanuts, on sod farms and golf course turf and on wood as a preservative. It has been used against powdery mildew, rust on cereals and apple scab, and applied by air or on the ground or by chemigation.

<span class="mw-page-title-main">Sedaxane</span> Chemical compound

Sedaxane is a broad spectrum fungicide used as a seed treatment in agriculture to protect crops from fungal diseases. It was first marketed by Syngenta in 2011 using their brand name Vibrance. The compound is an amide which combines a pyrazole acid with an aryl amine to give an inhibitor of succinate dehydrogenase.

<span class="mw-page-title-main">Thiophanate-methyl</span> Chemical compound

Thiophanate-methyl is an organic compound with the formula C6H4(NHC(S)NH(CO)OCH3)2. The compound is a colorless or white solid, although commercial samples are generally tan-colored. It is prepared from o-phenylenediamine. It is a widely used fungicide used on tree, vine, and root crops. In Europe it is applied to tomato, wine grapes, beans, wheat, and aubergine.

<i>Alternaria brassicicola</i> Species of fungus

Alternaria brassicicola is a fungal necrotrophic plant pathogen that causes black spot disease on a wide range of hosts, particularly in the genus of Brassica, including a number of economically important crops such as cabbage, Chinese cabbage, cauliflower, oilseeds, broccoli and canola. Although mainly known as a significant plant pathogen, it also contributes to various respiratory allergic conditions such as asthma and rhinoconjunctivitis. Despite the presence of mating genes, no sexual reproductive stage has been reported for this fungus. In terms of geography, it is most likely to be found in tropical and sub-tropical regions, but also in places with high rain and humidity such as Poland. It has also been found in Taiwan and Israel. Its main mode of propagation is vegetative. The resulting conidia reside in the soil, air and water. These spores are extremely resilient and can overwinter on crop debris and overwintering herbaceous plants.

<span class="mw-page-title-main">Pydiflumetofen</span> Chemical fungicide

Pydiflumetofen is a broad spectrum fungicide used in agriculture to protect crops from fungal diseases. It was first marketed by Syngenta in 2016 using their brand name Miravis. The compound is an amide which combines a pyrazole acid with a substituted phenethylamine to give an inhibitor of succinate dehydrogenase, an enzyme that inhibits cellular respiration in almost all living organisms.

References

  1. 1 2 Dreikorn, Barry A.; Owen, W. John (2000). "Fungicides, Agricultural". Kirk-Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.0621140704180509.a01. ISBN   978-0-471-48494-3.
  2. 1 2 3 Franz Müller; Peter Ackermann; Paul Margot (2012). "Fungicides, Agricultural, 2. Individual Fungicides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.o12_o06. ISBN   978-3-527-30673-2.
  3. ↑ Mueller, Daren. "Fungicides:Terminology". Iowa State University. Retrieved June 1, 2013.
  4. ↑ Latijnhouwers, Maita; de Wit, Pierre; Govers, Francine (2003). "Oomycetes and fungi: similar weaponry to attack plants". Trends in Microbiology . 11 (10). Cell Press: 462–469. doi:10.1016/j.tim.2003.08.002. ISSN   0966-842X. PMID   14557029. S2CID   22200121.
  5. ↑ C.Michael Hogan. 2011. Sulfur. Encyclopedia of Earth, eds. A.Jorgensen and C.J.Cleveland, National Council for Science and the environment, Washington DC Archived October 28, 2012, at the Wayback Machine
  6. ↑ Thao, Hoang Thi Bich; Yamakawa, Takeo (April 2009). "Phosphite (phosphorous acid): Fungicide, fertilizer or bio-stimulator?". Soil Science and Plant Nutrition. 55 (2): 228–234. Bibcode:2009SSPN...55..228T. doi: 10.1111/j.1747-0765.2009.00365.x .
  7. ↑ Pearson, M.N.; Beever, R.E.; Boine, B.; Arthur, K. (2009). "Mycoviruses of filamentous fungi and their relevance to plant pathology". Molecular Plant Pathology (Review). 10 (1): 115–128. doi:10.1111/j.1364-3703.2008.00503.x. PMC   6640375 . PMID   19161358. S2CID   34331588.
  8. ↑ Metcalfe, R.J.; Shaw, M.W.; Russell, P.E. (2000). "The effect of dose and mobility on the strength of selection for DMI (sterol demethylation inhibitors) fungicide resistance in inoculated field experiments". Plant Pathology. 49: 546–557. doi:10.1046/j.1365-3059.2000.00486.x.
  9. ↑ Sierotzki, Helge (2000). "Mode of resistance to respiration inhibitors at the cytochrome bc1 enzyme complex of Mycosphaerella fijiensis field isolates". Pest Management Science. 56 (10): 833–841. doi:10.1002/1526-4998(200010)56:10<833::AID-PS200>3.0.CO;2-Q.
  10. ↑ Schnabel G, Jones AL (January 2001). "The 14alpha-Demethylasse(CYP51A1) Gene is Overexpressed in Venturia inaequalis Strains Resistant to Myclobutanil". Phytopathology. 91 (1): 102–110. doi: 10.1094/PHYTO.2001.91.1.102 . PMID   18944284.
  11. ↑ Zwiers LH, Stergiopoulos I, Gielkens MM, Goodall SD, De Waard MA (July 2003). "ABC transporters of the wheat pathogen Mycosphaerella graminicola function as protectants against biotic and xenobiotic toxic compounds". Mol Genet Genomics. 269 (4): 499–507. doi:10.1007/s00438-003-0855-x. PMID   12768412.
  12. 1 2 "Fungicides Resistance Action Committee website".
  13. ↑ "Fungal control agents sorted by cross resistance pattern and mode of action" (PDF). 2020. Archived from the original (PDF) on 2021-08-16. Retrieved 2020-09-04.
  14. ↑ "Resistance Management". CropLife International . 2018-02-28. Archived from the original on 2020-12-10. Retrieved 2020-11-22.
  15. ↑ Lini RS, Scanferla DT, de Oliveira NG, Aguera RG, Santos TD, Teixeira JJ, Kaneshima AM, Mossini SA (January 2024). "Fungicides as a risk factor for the development of neurological diseases and disorders in humans: a systematic review". Crit Rev Toxicol. 54 (1): 35–54. doi:10.1080/10408444.2024.2303481. PMID   38288970.
  16. ↑ Brooks and, G.T; Roberts, T.R, eds. (1999). Pesticide Chemistry and Bioscience. Royal Society of Chemistry. doi:10.1533/9781845698416. ISBN   978-1-84569-841-6. OCLC   849886156.
  17. ↑ Hrelia P, Fimognari C, Maffei F, Vigagni F, Mesirca R, Pozzetti L, Paolini M, Cantelli Forti G (September 1996). "The genetic and non-genetic toxicity of the fungicide Vinclozolin". Mutagenesis. 11 (5): 445–53. doi:10.1093/mutage/11.5.445. PMID   8921505.
  18. ↑ National Center for Biotechnology Information. PubChem Compound Database; CID=8722, https://pubchem.ncbi.nlm.nih.gov/compound/8722 (accessed Jan. 13, 2019)
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