18 Diseases of Apple
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Apples - Chap 18 21/3/03 3:03 pm Page 459 18 Diseases of Apple Gary G. Grove1, Kenneth C. Eastwell1, Alan L. Jones2 and Turner B. Sutton3 1Irrigated Agriculture Research and Extension Center, Washington State University, Prosser, Washington, USA; 2Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan, USA; 3Department of Plant Pathology, North Carolina State University, Raleigh, North Carolina, USA 18.1 Introduction 460 18.2 Diseases Caused by Bacteria 460 18.2.1 Fire blight 460 18.3 Diseases Caused by Fungi 468 18.3.1 Apple scab 468 18.3.2 Powdery mildew 470 18.3.3 Brown-rot diseases 472 18.3.4 Summer diseases 473 18.3.5 Phytophthora crown and root rot 476 18.3.6 European or Nectria canker 477 18.4 Postharvest Diseases 477 18.4.1 Blue mould 478 18.5 Diseases Caused by Viruses, Viroids, Phytoplasmas and Other Virus-like Agents 478 18.5.1 Chlorotic leaf spot 479 18.5.2 Apple decline (on ‘Virginia Crab’) 480 18.5.3 Flat apple 480 18.5.4 Apple mosaic 481 18.5.5 Stem pitting 481 18.5.6 Union necrosis 481 18.6 Diseases Caused by Phytoplasmas 482 18.6.1 Proliferation 482 18.6.2 Chat fruit 482 18.7 Diseases of Apple Caused by Viroids 482 18.7.1 Blister bark 482 18.7.2 Dapple apple 483 18.7.3 Dimple fruit 483 18.7.4 Fruit crinkle 483 18.8 ’Virus-like’ or Graft-transmissible Diseases of Apple with No Known Causal Agents 483 18.8.1 Green crinkle 484 18.8.2 Rubbery wood 484 18.8.3 Dead spur 485 18.9 Control Measures 485 © CAB International 2003. Apples: Botany, Production and Uses (eds D.C. Ferree and I.J. Warrington) 459 Apples - Chap 18 21/3/03 3:03 pm Page 460 460 G.G. Grove et al. 18.1 Introduction Blister bark has been described from South Africa but the pathogen P. s. pv. syringae van Apples are host to over 70 infectious dis- Hall is found as a common epiphyte on eases, the vast majority of which are caused apple foliage worldwide. Crown gall and by pathogenic fungi (Table 18.1). Apples are hairy root are soil-borne diseases caused by also susceptible to diseases caused by bac- two species of Agrobacterium; crown gall is teria, phytoplasma and virus/virus-like the most common of the two problems. agents. The authors discuss several but not In areas where these bacterial pathogens all economically important pre- and posthar- either are not established or are rare, bacter- vest apple diseases in this chapter. Readers ial diseases are often avoided by planting should keep in mind that some of the dis- pathogen-free nursery stock. Where these eases discussed might be major in some diseases are established, they are managed areas and minor in others. Others (e.g. fire through orchard sanitation, wound mini- blight) are of importance or potential impor- mization, the use of resistant rootstocks and tance wherever apples are grown. In most cultivars, site selection, cultural practices apple-producing regions, disease control is a that promote air movement and drying of major annual expense for the grower. For plant surfaces and, in some cases, the use of example, in the eastern USA, the manage- copper and antibiotic sprays. ment of apple scab can require eight to ten protective fungicide applications annually. In those areas, the apple grower must manage 18.2.1 Fire blight early-season diseases, such as apple scab and cedar apple rust, as well as a group of dis- Fire blight is of major concern in all countries eases termed ‘summer diseases’. Conversely, where apples are grown including countries in the arid production regions of the Pacific that are currently free of this disease Northwest, these diseases are non-existent or (Vanneste, 2000). When fire blight is epi- sporadic in nature and powdery mildew is demic, it can cause serious tree loss in nurs- much more problematic. eries and orchards (Plate 18.1), even leading Successful disease management usually to orchard removal. In high-risk areas, fire results from the integration of several meth- blight is limiting the planting of some highly ods of disease control. The use of resistant susceptible apple cultivars and rootstocks. rootstocks and scions, fungicides, bacteri- Strict quarantines and restrictions are main- cides, biological control agents, environmen- tained in countries where the disease does tal modification and site selection are some not currently occur; enforcing quarantine of the means used to control apple diseases. regulations and restrictions and, if necessary, The precise combination and order of control eradicating the disease are very costly. measures are usually disease-specific. The fire blight pathogen kills fruit-bear- ing spurs, branches and entire trees. Infected blossoms are initially water-soaked and 18.2 Diseases Caused by Bacteria darker green; spurs with infected blossoms (Table 18.2) turn brown to dark brown and collapse after 4–5 days. Infected shoots turn brown to Fire blight, blister spot, blister bark, crown black from the tip and bend near the tip to gall and hairy root are diseases of apple resemble a shepherd’s crook (Plate 18.2). caused by bacteria. Fire blight is the most When shoots are invaded from the base, the important of these diseases and is described basal leaves and stem turn brown to black. in more detail below. Blister spot, caused by Leaves may exhibit discoloration of the Pseudomonas syringae pv. papulans (Rose) midrib, followed shortly by a darkening of Dhanvantari, occurs in North America and the lateral veins and surrounding tissues. Europe. It causes a fruit spot on Bark on infected branches and scaffold ‘Mutsu’/‘Crispin’, ‘Fuji’, ‘Redcort’, ‘Sun limbs is darker than normal. When the outer Crisp’, ‘Smoothee’ and a few other cultivars. bark is peeled away, the inner tissues are Apples -Chap1821/3/033:03pmPage461 Table 18.1. Fungal diseases of apples, names of the asexual and sexual stages of the causal fungi and their reproductive stages, the symptoms and damage .(domestica Borkh.) A.L. Jones, primary collator (last update 3/12/93 ן most likely to be encountered and general methods of control. (Malus Disease (distributiona) Fungal pathogen Reproductive stage Common symptomsb Main control method Alternaria blotch (A, Alternaria mali Roberts; = Alternaria Conidia/conidiophores Leaf spots, defoliation Fungicides, AF, NA) alternata (Fr.:Fr) Kessl apple pathotype cultivar selection Alternaria rot (W) Alternaria alternata (Fr.:Fr.) Keissl Conidia/conidiophores Decay of fruit None American brown rot Monilinia fructicola (G. Wint.) Honey Conidia in sporodochia; Decay of fruit (P) Avoid preharvest injury to fruit (A, AF, NA,O) ascospores in apothecia Anthracnose canker Pezicula malicorticis (H. Jacks.) Nannf Conidia in acervuli; Cankers on wood, decay Fungicides and bull’s-eye rot (E, Cryptosporiopsis curvispora (Peck) ascospores in apothecia of fruit (P) NA, O) Gremmen in Boerema & Gremmen [anamorph] Apple scab (W) Venturia inaequalis (Cooke) G. Wint. Ascospores in pseudothecia; Leaf spots, scabs on fruit, Sanitation, fungicides, resistant Spilocaea pomi Fr.:Fr. [anamorph] conidia/conidiophores defoliation cultivars AppleDiseases of 461 Apple ring rot and Botryosphaeria berengeriana De Not. (syn. Conidia in pycnidia; Cankers on wood, decay Fungicides canker (A) Physalospora piricola Nose) ascospores in pseudothecia of fruit Armillaria (shoestring) Armillaria mellea (Vahl:Fr.) P. Kumm. Basidiospores in basidiocarps Decay of roots None, avoid problem sites root rot (W) (mushrooms); rhizomorphs Bitter rot (W) Glomerella cingulata (Stoneman) Spauld. Conidia in acervuli; Decay of fruit Fungicides, sanitation & H. Schrenk ascospores in perithecia Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. [anamorph] Colletotrichum acutatum J.H. Simmons Black pox (NA) Helminthosporium papulosum Berg. Conidia/conidiophores Spots on fruit and leaves Fungicides Black root rot (NA for Xylaria mali Fromme Ascospores in perithecia Decay of roots None X. mali; W) Xylaria polymorpha (Pers.:Fr.) Grev. Black rot, frog-eye Botryosphaeria obtusa (Schwein.) Shoemaker Conidia in pycnidia, Spots on leaves and fruit, Sanitation, fungicides leaf spot and canker Sphaeropsis malorum Berk. [anamorph] ascospores in pseudothecia defoliation, cankers on (AF, E, NA, SA, O) wood Blister canker (nail- Biscogniauxia marginata (Fr.) Pouzar Conidia in a sclerotia-like Cankers on branches Removal of infected branches head canker) (NA) = Nummularia discreta (Schwein.) Tul. & C. stroma, ascospores in Tul. perithecia Continued Apples -Chap1821/3/033:03pmPage462 Table 18.1. Continued. 462 G.G.Grove Disease (distributiona) Fungal pathogen Reproductive stage Common symptomsb Main control method Blotch (NA) Phyllosticta solitaria Ellis & Everh. Conidia in pycnidia Blotches on fruit, leaf Fungicides spots, blisters in bark Blue mould (W) Penicillium spp. Conidia/conidiophores Decay of fruit (P) Packing-house sanitation, P. expansum Link fungicides Brooks fruit spot (NA) Mycosphaerella pomi (Pass.) Lindau Conidia/conidiophores; Spots on fruit, often at Fungicides Cylindrosporium pomi C. Brooks ascospores in pseudothecia calyx end [anamorph] Brown-rot blossom Monilinia laxa (Aderh. & Ruhl.) Honey Conidia in sporodochia Blighting of blossoms, Fungicides blight (A, AF, E, NA, spur dieback SA) Calyx-end rot (NA) Sclerotinia sclerotiorum (Lib.) de Bary Ascospores in apothecium Decay of fruit None Clitocybe root rot (NA) Armillaria tabescens (Scop.) Dennis et al Basidiospores in basidiocarps Decay of roots None = Clitocybe tabescens (Scop.) Bres. Diaporthe canker (A) Diaporthe tanakae Kobayashi & Sakuma Conidia (␣ and ß spores) in Cankers on 1- and Sanitation Phomopsis tanakae Kobayashi & Sakuma pycnidia; ascospores in 2-year-old shoots [anamorph] perithecia et al. Diplodia canker (E, Botryosphaeria stevensii Shoemaker Pycnidia and pseudothecia; Cankers on branches Pruning out of infected NA, O) = Physalospora malorum Shear et al. often in the same stroma branches Diplodia mutila (Fr.: Fr.) Mont. [anamorph] European brown rot Monilinia fructigena Honey in Whetzel Conidia in sporodochia; Blossoms and spur Sanitation, fungicides (A, E, AF) Monilia fructigena Pers.:Fr.