Pecan scab

Last updated

Pecan scab is the most economically significant disease of pecan trees (Carya illinoinensis) in the southeastern United States. [1] Venturia effusa is a fungal plant pathogen that causes pecan scab. The fungus causes lesions and tissue death on pecan twigs, petioles, leaves, nuts and shucks beginning in early spring, with multiple cycles of infection repeating until late summer. Wind and rain spread the fungus to a susceptible host. Control of the disease is achieved by fungicide, sanitation and, in some cases, quarantine. [2]

Contents

Pecan scab lesions caused by Venturia effusa on pecan husks Pecanscab.jpg
Pecan scab lesions caused by Venturia effusa on pecan husks

Since its first description in 1882, the pecan scab fungus has been reclassified ten times, [3] with other names such as Fusicladium caryigenum, Cladosporium effusum and Cladosporium caryigenum commonly associated with the fungus. [4]

Pecan scab lesions caused by Venturia effusa on pecan leaves Pecan scab.jpg
Pecan scab lesions caused by Venturia effusa on pecan leaves

Host and symptoms

Venturia effusa has a narrow host range, and its most economically significant host is the pecan, Carya illinoinensis. The pathogen can also infect other trees in the genera Carya and Juglans (walnut). [5] Common symptoms of pecan scab disease include light brown to black lesions on stems, leaves, shucks and nuts. [1] [6] Visible circular lesions begin to develop 7 to 14 days after infection, and first appear on young tissue as olive-green spots that turn black as they age. [1] Older lesions may crack and fall out of the leaf-blade creating a shot-hole effect. [4] Lesions range in diameter from a pinpoint to about one-quarter inch, and occur most numerously along leaf veins. [1] Numerous lesions can coalesce into larger dead areas on infected tissue and can cause early leaf loss. Lesions on nuts may look sunken and distort nut morphology. They may also cause nuts to shrivel or drop prematurely. Lesions are amphigenous, meaning they grow on both sides of leaves. [7]

Disease cycle

Venturia effusa over-winters in plant debris, such as shucks, leaf petioles and stems, as well as in lesions on the tree from the previous season. It survives as stromata, a tight mat of fungal material that lives within tissue. In the spring time, hyphae in the stromata germinate to produce solitary or loosely fasciculate conidiophores which produce conidia (asexual spores) in simple or branched chains. [5] Conidia are dentical-like and have unthickened walls. [7] Conidia are moved by wind and water to a susceptible host, but they cannot germinate and infect without several hours of sustained wet weather. Afternoon rain storms and wet conditions overnight provide ideal conditions for germination. [1] Conidia germinate and form germ tubes which enter the host through stomata or through the cuticle, before forming intramatrical mycelia which moves through the plant and establishes the new infection. [5] These mycelia give rise to further conidiophores and conidia, allowing for many infection cycles in each season.

Venturia effusa commonly reproduces asexually via conidia, but it may also produce a teleomorph stage like other Dothideomycetes in which pseudothecia carrying asci and sexual ascospores grow out of the hyphae. This allows for sexual reproduction and genetic recombination of the pathogen. [4] The teleomorph stage, however, is very rare and literature on its characteristics are lacking.

The severity of infection depends in part on the timing of inoculation. A study by Gottwald and Bertrand in 1982 found that trees inoculated after late June, when the endocarp (shell) begins to form, suffered much less damage to nuts than those inoculated in May or early June during nut set. Trees in the latter category experienced the greatest disease severity around mid-season (mid-July through August), roughly 1.5 to 2 months after inoculation. [8]

Environment

A conducive environment for the propagation of pecan scab requires wet weather. For the spores to inoculate the host, there must be a period of wet weather in order for the infection to occur. [9] The amount of rainfall is not as important as the frequency of rainfall and length of time that the leaves and fruit stay wet. [1] For example, the optimal time for a rain would be right before dusk because the plant will stay wet overnight, thus increasing the period of time the pathogen has to infect the plant. The temperature is not as critical of a factor in the environment. [10] The pathogen thrives in adequate temperatures of spring and summer ranging from 20–30 °C (68–86 °F). [9] When there is a pecan orchard, cultural practices that increase the humidity levels also provide a good environment for the pathogen. [1] These practices include close tree spacing, low limbs, and dense ground vegetation.

Management

Although resistant varieties of pecan trees are available, such as the Elliot Pecan tree, historically the pathogen has overcome the resistance due to its ability to quickly change over time. [10] Because resistance has been ineffective, the main control of the pathogen is fungicide application for commercial farming. Some commercial fungicides used are Pristine, Sovran, Quash, and Headline SC. [2] For the fungicides to be effective, they must be sprayed before inoculation/infection period. The exact time for the first spray depends on the chemical used, but an example time periods is when the buds are bursting and the first leaves begin to show. [2] The fungicide should be sprayed sufficiently in order to completely cover the tree. The rates per acre of application range from 2–5 fluid ounces on developing trees to 8–12 fluid ounces on mature trees. [2] They are protectant fungicides, meaning that they work best to prevent disease from happening when sprayed before any disease is detected. The idea of "getting ahead" of the pathogen is key to preventing a large loss of production. [11]

After this initial spray, the plant tissue is still susceptible to infection making it necessary for multiple sprays to occur during a growing season. The number of applications during a season depends on the weather, amount and virulence of the pathogen, and susceptibility of the cultivars. [1] Generally, the cultivars are sprayed about every two to four weeks of its growing season in spring and summer. This ends up being about 5–7 sprays per growing season. The fungicide needs to be sprayed in a concentration high enough to prevent infection and to completely cover the trees. [11] The fungicides have not been shown to have any adverse effects outside of the warnings of all chemical control impacts on environmental and human health. [12]

Although fungicide application is effective in the commercial setting, the cost of the chemicals and equipment is usually not practical for noncommercial farming such as orchards and small farms. In the noncommercial case, good sanitation practices may help prevent the disease. Removal and destruction of all fallen leaves, shucks, and nuts each winter or early spring helps reduce tissue that is often involved in the primary infection. [10] Also, selective pruning of infected tissue during the dormant season may help reduce the level of scab disease.

A recent study has been done to test if phosphite, a chemical with the potential to induce systemically acquired resistance (SAR), could be used as a potential control for pecan scab. [13] The results showed that in the early stages of the growing season, phosphite was comparable to current fungicide control, however may not be as effective in providing elongated protection in the later growing season. [13]

Importance

Pecan scab disease is the most economically damaging disease of pecans in the Southeastern United States, which is one of the major pecan producing regions in the world. [14] It infects the leaves, shucks, and nuts thus reducing crop yield. In addition, the cost of fungicide application reduces the profitability of pecan production. Because of the cost of fungicides, pecan scab also prevents small orchards and yard trees from producing high quality nuts. [1] The average cost of pecans ranges from $2.86–$3.50 per pound. [15] Prices may fluctuate slightly with demand. An average tree will yield 40–50 pounds of nuts, thus equating to roughly $135 per tree. At 27 trees/acre, the total profit would be $3,645 per acre. [16] [17] Pecan scab is a devastating disease that can significantly impact the amount of quality pecans produced in a year. For example, during the summer of 2013, the estimated potential for the year was around 90 million pounds; however, the weather conditions were conducive for pecan scab growth and the actual total went down to 65 to 70 million. [18] Pecans are valuable crops that are economically valuable to the farmer and also the farming industry. Devastating diseases like pecan scab can result in major financial loss that can hurt growers and also economic development.

Related Research Articles

<span class="mw-page-title-main">Apple scab</span> Plant disease caused by fungus

Apple scab is a common disease of plants in the rose family (Rosaceae) that is caused by the ascomycete fungus Venturia inaequalis. While this disease affects several plant genera, including Sorbus, Cotoneaster, and Pyrus, it is most commonly associated with the infection of Malus trees, including species of flowering crabapple, as well as cultivated apple. The first symptoms of this disease are found in the foliage, blossoms, and developing fruits of affected trees, which develop dark, irregularly-shaped lesions upon infection. Although apple scab rarely kills its host, infection typically leads to fruit deformation and premature leaf and fruit drop, which enhance the susceptibility of the host plant to abiotic stress and secondary infection. The reduction of fruit quality and yield may result in crop losses of up to 70%, posing a significant threat to the profitability of apple producers. To reduce scab-related yield losses, growers often combine preventive practices, including sanitation and resistance breeding, with reactive measures, such as targeted fungicide or biocontrol treatments, to prevent the incidence and spread of apple scab in their crops.

<span class="mw-page-title-main">Black rot (grape disease)</span> Species of fungus

Grape black rot is a fungal disease caused by an ascomycetous fungus, Guignardia bidwellii, that attacks grape vines during hot and humid weather. “Grape black rot originated in eastern North America, but now occurs in portions of Europe, South America, and Asia. It can cause complete crop loss in warm, humid climates, but is virtually unknown in regions with arid summers.” The name comes from the black fringe that borders growing brown patches on the leaves. The disease also attacks other parts of the plant, “all green parts of the vine: the shoots, leaf and fruit stems, tendrils, and fruit. The most damaging effect is to the fruit”.

<i>Diplocarpon rosae</i> Species of fungus

Diplocarpon rosae is a fungus that creates the rose black spot disease. Because it was observed by people of various countries around the same time, the nomenclature for the fungus varied with about 25 different names. The asexual stage is now known to be Marssonina rosae, while the sexual and most common stage is known as Diplocarpon rosae.

<i>Venturia inaequalis</i> Species of fungus

Venturia inaequalis is an ascomycete fungus that causes the apple scab disease.

<i>Monilinia laxa</i> Species of fungus

Monilinia laxa is a plant pathogen that is the causal agent of brown rot of stone fruits.

<i>Mycosphaerella coffeicola</i> Species of fungus

Mycosphaerella coffeicola is a sexually reproducing fungal plant pathogen. It is most commonly referred to as the asexual organism Cercospora coffeicola.

<i>Cladosporium caryigenum</i> Species of fungus

Cladosporium caryigenum is a synonym of Fusicladium effusum, the plant pathogen which causes pecan scab. Pecan scab is the most economically significant disease of pecan in the southeastern United States. In 2010, Seyran and colleagues used sequencing of the mitochondrial gene for cytochrome b to conclusively classify the pecan scab fungus as Fusicladium effusum.

<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>Peronospora manshurica</i> Species of single-celled organism

Peronospora manshurica is a plant pathogen. It is a widespread disease on the leaves of soybeans and other crop plants. The fungi is commonly referred to as downy mildew, "leafspot", or "leaf-spot".

Elsinoë mangiferae, common name "mango scab", is also known Denticularia mangiferae or Sphaceloma mangiferae (anamorph). It is an ascomycete plant pathogen native to tropical regions and specific for survival on only one host, the mango. Originally described in 1943 from Florida and Cuba specimens, this pathogen has since spread worldwide and is becoming a pathogen of great concern for the mango industries in Australia and India. The species was first described formally in 1946.

<i>Elsinoë ampelina</i> Species of fungus

Elsinoë ampelina is a plant pathogen, which is the causal agent of anthracnose on grape.

<i>Cercospora melongenae</i> Fungal disease of eggplant leaves

Cercospora melongenae is a fungal plant pathogen that causes leaf spot on eggplant. It is a deuteromycete fungus that is primarily confined to eggplant species. Some other host species are Solanum aethiopicum and Solanum incanum. This plant pathogen only attacks leaves of eggplants and not the fruit. It is fairly common among the fungi that infect community gardens and home gardens of eggplant. Generally speaking, Cercospora melongenae attacks all local varieties of eggplants, but is most severe on the Philippine eggplant and less parasitic on a Siamese variety.

<i>Botrytis fabae</i> Species of fungus

Botrytis fabae is a plant pathogen, a fungus that causes chocolate spot disease of broad or fava bean plants, Vicia faba. It was described scientifically by Mexican-born Galician microbiologist Juan Rodríguez Sardiña in 1929.

This article summarizes different crops, what common fungal problems they have, and how fungicide should be used in order to mitigate damage and crop loss. This page also covers how specific fungal infections affect crops present in the United States.

Pecan anthracnose is a fungal disease of pecan trees caused by the ascomycete Glomerella cingulata (Stoneman) Spauld. & H. It is a widespread disease found wherever pecan trees are grown. Pecan anthracnose has been reported as far back in time as 1914, and as far away as Argentina. Glomerella cingulata has two anamorphs which cause disease on pecan trees, Colletotrichum gloeosporioides and Colletotrichum acutatum. The occurrence of Colletotrichum on pecans has contributed to a significant decline in pecan production in various years. An increase in the incidence of pecan anthracnose is highly correlated with heavy rainfall, especially heavy rainfall occurring in early spring. The severity of symptoms increases as the season progresses, often culminating in leaf drop in the late autumn. This defoliation is linked to lower yield and poorer quality of nuts.

<i>Taphrina caerulescens</i> Species of fungus

Taphrina caerulescens is a species of fungus in the family Taphrinaceae. It is a pathogenic Ascomycete fungus that causes oak leaf blister disease on various species of oak trees. The associated anamorph species is Lalaria coccinea, described in 1990. This disease causes lesions and blisters on Oak leaves. Effects of the disease are mostly cosmetic. Although not taxonomically defined, strains of T. caerulescens have been shown to be host specific with varying ¬ascus morphology between strains. There are differences in strains' abilities to metabolize various carbon and nitrogen compounds. This has been proposed as a method of taxonomically defining subspecies within T. caerulescens.

<span class="mw-page-title-main">Phomopsis blight of juniper</span> Species of fungus

Phomopsisblight of juniper is a foliar disease discovered in 1917 caused by the fungal pathogen Phomopsis juniperovora. The fungus infects new growth of juniper trees or shrubs, i.e. the seedlings or young shoots of mature trees. Infection begins with the germination of asexual conidia, borne from pycnidia, on susceptible tissue, the mycelia gradually move inwards down the branch, and into the main stem. Management strategies mainly include removing and destroying diseased tissue and limiting the presence of moisture on plants. Junipers become resistant to infection as they mature and the young yellow shoots turn dark green. Preventive strategies include planting only resistant varieties and spraying new growth with fungicide until plants have matured.

<span class="mw-page-title-main">Peach scab</span> Fungal disease of stone fruits

Peach scab, also known as peach freckles, is a disease of stone fruits caused by the fungi Cladosporium carpophilum. The disease is most prevalent in wet and warm areas especially southern part of the U.S. as the fungi require rain and wind for dispersal. The fungus causes scabbing, lesions, and defoliating on twig, fruit, and leaf resulting in downgrade of peach quality or loss of fruits due to rotting in severe cases.

<span class="mw-page-title-main">Cherry leaf spot</span> Plant fungal disease

Cherry leaf spot is a fungal disease which infects cherries and plums. Sweet, sour, and ornamental cherries are susceptible to the disease, being most prevalent in sour cherries. The variety of sour cherries that is the most susceptible are the English morello cherries. This is considered a serious disease in the Midwest, New England states, and Canada. It has also been estimated to infect 80 percent of orchards in the Eastern states. It must be controlled yearly to avoid a significant loss of the crop. If not controlled properly, the disease can dramatically reduce yields by nearly 100 percent. The disease is also known as yellow leaf or shothole disease to cherry growers due to the characteristic yellowing leaves and shot holes present in the leaves upon severe infection.

<i>Spilocaea oleaginea</i> Species of fungus

Spilocaea oleaginea is a deuteromycete fungal plant pathogen, the cause of the disease olive peacock spot, also known as olive leaf spot and bird's eye spot. This plant disease commonly affects the leaves of olive trees worldwide. The disease affects trees throughout the growing season and can cause significant losses in yield. The disease causes blemishes on the fruit, delays ripening, and reduces the yield of oil. Defoliation and in severe cases, twig death, can occur, and the disease can have long-term health effects on the trees.

References

  1. 1 2 3 4 5 6 7 8 9 Sanderlin, R. S. (n.d.). Pecan scab disease. Retrieved from http://www.lsuagcenter.com/NR/rdonlyres/A30CB512-CDB1-4DFB-8D41-9E6086DEF9EE/70679/ScabDisease_CorrectedName.pdf
  2. 1 2 3 4 Smith, S., & Vann, S. (2013). Arkansas plant disease control products guide. Informally published manuscript, Division of Agriculture, University of Arkansas, Little Rock, AR, Retrieved from http://www.uaex.edu/Other_Areas/publications/PDF/MP154/pecan-diseases-commercial.pdf
  3. ↑ Seryan, M; et al. (2010). "Phylogeny of the pecan scab fungus Fusicladium effusum G. Winter based on the cytochrome b gene sequence". Mycol Progress. 9 (2): 305–308. doi:10.1007/s11557-009-0638-9. S2CID   6396142.
  4. 1 2 3 Gottwald, T. R. (1982). "Taxonomy of the pecan scab fungus Cladosporium caryigenum". Mycologia. 74 (3): 382–390. doi:10.2307/3792959. JSTOR   3792959.
  5. 1 2 3 Schubert, K (2003). "A monograph of Fusicladium s.lat. (hyphomycetes)". Schlechtendalia. 9: 1–132.
  6. ↑ Demaree, J. B. (1928). "Morphology and taxonomy of the pecan-scab fungus, Cladosporium effusum Wint". USDA Agricultural Research. 37: 181–187.
  7. 1 2 Mycobank. (2013). Retrieved from http://www.mycobank.org/BioloMICS.aspx?Link=T&TableKey=14682616000000063&Rec=14612&Fields=All
  8. ↑ Gottwald, T. R. (1982). "Effect of inoculation with Cladosporium carygenum on pecan scab development and nut quality" (PDF). Phytopathology. 73 (5): 714–718. doi:10.1094/phyto-73-714.
  9. 1 2 Latham, A. J. (1982). "Effects of some weather factors and Fusicladium effusum conidium dispersal on pecan scab occurrence". Phytopathology. 72 (10): 1339–1345. doi:10.1094/phyto-72-1339.
  10. 1 2 3 Vann, S. (n.d.). Home pecan diseases and control. Informally published manuscript, Division of Agriculture, University of Arkansas, Little Rock, AR, Retrieved from http://www.uaex.edu/Other_Areas/publications/PDF/FSA-7540.pdf
  11. 1 2 Smith, D. (2010). Pecan scab update. Informally published manuscript, Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK, Retrieved from http://entoplp.okstate.edu/pddl/pddl/2010/PA9-27.pdf
  12. ↑ European Union, Invasive Species Compendium. (2013). Fusicladium effusum. Retrieved from CABI website: http://www.cabi.org/isc/?compid=5&dsid=13719&loadmodule=datasheet&page=481&site=144
  13. 1 2 Bock, C. H.; Brenneman, T. B.; Hotchkiss, M. W.; Wood, B. W. (2012). "Evaluation of a phosphite fungicide to control pecan scab in the southeastern usa". Crop Protection. 36: 58–64. doi:10.1016/j.cropro.2012.01.009.
  14. ↑ Andersen, P. C. (2011). Pecan cultivars in north Florida. Informally published manuscript, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, Retrieved from http://edis.ifas.ufl.edu/pdffiles/HS/HS10600.pdf
  15. ↑ Rafanan, M. U.S. Department of Agriculture, (2013).Pecan report (XXXI-7). Retrieved from Agricultural Marketing Service website: http://www.ams.usda.gov/mnreports/fvwtvpcn.pdf
  16. ↑ Call, R., Gibson, R., & Kilby, M. (2006). Pecan production guidelines for small orchards and home yards. Informally published manuscript, College of Agriculture and Life Sciences, University of Arizona, Tucson, AZ, Retrieved from http://ag.arizona.edu/pubs/garden/az1400.pdf
  17. ↑ Nesbitt, M., & Wells, L. (n.d.). Estimation of pecan tree value. Unpublished manuscript, College of Agriculture and Environmental Sciences, University of Georgia, Athens, GA, Retrieved from http://www.caes.uga.edu/commodities/fruits/pecan/growers/documents/pecantreevalue.pdf
  18. ↑ Thompson, C. (2013). Pecan crop hurt by summer rainfall. Unpublished manuscript, College of Agriculture and Environmental Sciences, University of Georgia, Athens, GA, Retrieved from http://georgiafaces.caes.uga.edu/index.cfm?public=viewStory&pk_id=4934
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.