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PotatoesD

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Information about PotatoesD
Education

Published on February 28, 2008

Author: Dorotea

Source: authorstream.com

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Potato Diseases:  Potato Diseases Common Scab - Streptomyces scabies Early Blight - Alternaria solani Late Blight - Phytophthora infestans Rhizoctonia Canker - Rhizoctonia solani Silver Scurf - Helminthosporium solani Verticillium Wilt - Verticillium albo-atrum and V. dahliae Bacterial Black Leg and Soft Rot - Erwinia carotovora pvar. carotovora and pvar. atroseptica Bacterial Ring Rot - Clavibacter michiganensis subsp. sepedonicus Early Blight:  Early Blight Alternaria solani:  Alternaria solani Early Blight:  Early Blight Tuber symptoms:  Tuber symptoms Hygrothermograph:  Hygrothermograph Potato Diseases - Early Blight Key Points:  Potato Diseases - Early Blight Key Points Pathogen: Alternaria solani Symptoms: Leaf lesions frequently have "bulls-eye" or "target spot" appearance Advanced lesions usually have angular margins because they are limited by leaf veins As infection progresses, entire leaf becomes chlorotic, then dies The fungus persists in the soil, infected debris, and tubers The disease is more severe when potato plants are under stress, have been injured or have poor nutrition Potato Diseases - Early Blight Control Strategies:  Potato Diseases - Early Blight Control Strategies Protectant fungicides apply according to blight forecasting systems for maximum efficacy Allow tubers to mature in ground before digging wait at least 7 days after vine kill before harvest. Avoid injury of tubers during harvest Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Late Blight:  Late Blight Potato Diseases - Late Blight Key Points:  Potato Diseases - Late Blight Key Points Pathogen: Phytophthora infestans Symptoms: leaf lesions initially small, water-soaked expand rapidly to large brown to purplish-black lesions killing entire leaflets and spreading through petiole to stem, eventually killing entire plant under moist conditions white velvety area of sporangia and sporangiophores visible around edge of lesions (mainly on underside of leaf) Disease progresses very quickly under optimum conditions. Fungus overwinters in infected tubers (cull piles or infected seed tubers) Also infects tomato and other solanaceous crops and weeds such as hairy nightshade Potato Diseases - Late Blight Control Strategies:  Potato Diseases - Late Blight Control Strategies Eliminate cull piles Control weed hosts Eliminate volunteer potatoes Plant disease-free seed Treat crop with currently registered fungicides Combine with disease forecasting Soil coverage by means of adequate hilling can reduce infection of tubers Kill vines two weeks before harvest so sporangia on infected plant tissue die Check and remove infected tubers at harvest Monitor stored potatoes for decay Rhizoctonia Canker:  Rhizoctonia Canker Rhizoctonia Canker:  Rhizoctonia Canker Potato Diseases - Rhizoctonia Canker Key Points:  Potato Diseases - Rhizoctonia Canker Key Points Pathogen: Rhizoctonia solani Symptoms: plants most severely damaged in spring just after planting stem lesions are reddish-brown, may girdle stem leading to: death of shoot (before or after emergence) stunting of plant aerial tubers leafroll symptoms discoloration of foliage, chlorosis tuber symptoms: black or dark brown sclerotia on surface Can overwinter as sclerotia on tubers or in the soil, or as mycelium on plant debris. Low soil temperatures and high soil moisture favor infection Potato Diseases - Rhizoctonia Canker Control Strategies:  Potato Diseases - Rhizoctonia Canker Control Strategies Crop rotation Use disease free seed pieces Plant on well drained soil Deep planting increases risk of stem infection Silver Scurf:  Silver Scurf Silver Scurf:  Silver Scurf Potato Diseases - Silver Scurf Key Points:  Potato Diseases - Silver Scurf Key Points Pathogen: Helminthosporium solani Symptoms: light brown, circular spots with indistinct borders may enlarge to cover considerable area of tuber affected areas have distinct silvery sheen tubers more likely to shrivel in storage Disease found world wide wherever potatoes are grown. Transmission is primarily from infected seed pieces The disease continues in storage as long as conditions are favorable Potato Diseases - Silver Scurf Control Strategies:  Potato Diseases - Silver Scurf Control Strategies Use disease free seed Treat with with currently registered fungicides Harvest tubers as soon as they are mature Avoid free moisture on tubers Verticillium Wilt:  Verticillium Wilt Verticillium Wilt:  Verticillium Wilt Verticillium Wilt:  Verticillium Wilt Potato Diseases - Verticillium Wilt Key Points:  Potato Diseases - Verticillium Wilt Key Points Pathogens: Verticillium albo-atrum and V. dahliae Symptoms: early senescence of plants - leaves become yellow, die single stems or one side of stem often affected first brown vascular discoloration Soil fungi that infect many species and can survive in the soil in the form of microsclerotia Wilting first occurs on hot dry days Inoculum can be distributed by movement of contaminated soil which adheres to seed tubers or equipment Incidence of Verticillium Wilt is increased with the presence of parasitic nematodes Potato Diseases - Verticillium Wilt Control Strategies:  Potato Diseases - Verticillium Wilt Control Strategies Rotate with non-host crops such as cereals, grasses and legumes Control weed hosts Treat soil with a currently available fumigant if pathogen population is above economic threshold Avoid over irrigation during period of emergence to tuberization Common Scab:  Common Scab Common Scab:  Common Scab Potato Diseases - Common Scab Key Points:  Potato Diseases - Common Scab Key Points Pathogen: Streptomyces scabies Most common on soils with pH 5.5-7.5 Warm, dry soils and early season stress favor infection and lesion development Soil borne and tuber borne May be introduced on seed potatoes Limited host range - carrot, beet, parsnips, radishes, rutabagas, spinach, sugar beets, turnips Tubers susceptible as soon as they form Infection through lenticels Once periderm forms, tubers no longer susceptible Survives digestive tract of animals, distributed in manure Potato Diseases - Common Scab Control Strategies:  Potato Diseases - Common Scab Control Strategies Manure applied to soil may favor scab infection Consider 3-5 year rotations - alfalfa, corn, peas, rye, snap beans, soybeans Adjust soil pH to 5.2-5.8 Avoid moisture stress especially at tuber initiation and early tuber growth Some cultivars with high tolerance: e.g. Frontier Russet, RedDale, Russet Burbank, Superior Treatment of seed with mancozeb fungicide dust reduces scab In-furrow application of Mocap granular insecticide reduces scab Bacterial Black Leg & Soft Rot:  Bacterial Black Leg & Soft Rot Black Leg:  Black Leg Bacterial Soft Rot:  Bacterial Soft Rot Potato Diseases - Bacterial Black Leg and Soft Rot - Key Points:  Potato Diseases - Bacterial Black Leg and Soft Rot - Key Points Pathogens: Erwinia carotovora pvar. carotovora and pvar. atroseptica Symptoms: Soft rot: wet, slimy cream to tan colored decay, with distinct margins. May become brown to black, foul smelling with ropy consistency with invasion of secondary organisms Black leg: black, wet looking decay of stem, moving from seedpiece up stem. Plants commonly stunted, wilted Bacteria overwinter on or in tubers in storage Primary inoculum is in the tuber seed piece Bacteria enter lenticels, wounds or growth cracks Bacteria can move in soil water Tubers can become infected in storage if inoculum runs onto clean potatoes and enters through lenticels or wounds Potato Diseases - Bacterial Black Leg and Soft Rot - Control Strategies:  Potato Diseases - Bacterial Black Leg and Soft Rot - Control Strategies Plant in well drained soil Do not over irrigate Cut tuber seed pieces 3-5 days before planting, keep at 55-60° F and 90% RH to allow cut surfaces to suberize before planting. Disinfest seed piece cutting tools Harvest tubers only when mature and when soil temperatures are less than 68° F Do not wash tubers before storage Keep storage temperatures from 34° to 40° F in a well ventilated area Bacterial Ring Rot:  Bacterial Ring Rot Bacterial Ring Rot:  Bacterial Ring Rot Potato Diseases - Bacterial Ring Rot Key Points:  Potato Diseases - Bacterial Ring Rot Key Points The pathogen - a bacterium, Clavibacter michiganensis subsp. sepedonicus (formerly Corynebacterium sepedonicum) Symptoms: wilting of leaves and stems after midseason often affects only one or two stems of a plant lower leaves, slightly rolled at the margins and pale green usually first to wilt milky white exudate can be squeezed from vascular system of tubers Symptom expression is most common following warm dry weather Overwinters in tubers either in storage or left behind in the soil Contaminated knives or picking equipment can disseminate the inoculum Infection occurs through wounds of any plant part Potato Diseases - Bacterial Ring Rot Control Strategies:  Potato Diseases - Bacterial Ring Rot Control Strategies Use certified, disease free seed and follow careful sanitation procedures Dispose of all tubers if the disease is found in the crop Disinfest all equipment used for growing and harvesting the crop Use clean new bags for each new year’s crop

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