Cucurbits under protected cultivation

Abstract

EPPO BulletinVolume 34, Issue 1 p. 91-100 Free Access Cucurbits under protected cultivation First published: 08 April 2004 https://doi.org/10.1111/j.1365-2338.2004.00702.xCitations: 1 European and Mediterranean Plant Protection Organization PP 2/31(1) Organisation Européenne et Méditerranéenne pour la Protection des Plantes AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Specific scope This standard describes good plant protection practice for cucurbit vegetable crops under protected cultivation. Specific approval and amendment First approved in 2003-09. This Standard on GPP for cucurbits under protected cultivation forms part of an EPPO programme to prepare such guidelines for all major crops of the EPPO region. It should be read in conjunction with EPPO Standard PP 2/1 Principles of good plant protection practice. It covers methods for controlling pests (including pathogens and weeds) of vegetable crops of the family Cucurbitaceae under protected conditions, such as melon Cucumis melo, cucumber or gherkin Cucumis sativus and courgette Cucurbita pepo. Most cucurbit crops are grown in the open (see EPPO Standard PP 2/32 Outdoor cucurbits), but some are produced under protected cultivation, which includes glasshouses, plastic tunnels or houses. Tunnels or row covers are often used in cooler climates to create a warmer environment, which gives young seedlings an early start. Under these conditions, the basic strategies to control pests remain broadly the same. General hygiene standards need to be maintained at a very high level. GPP in cucurbits also implies good management of the protected environment, for the incidence of pests can be much affected by general cultural conditions. This is of particular importance since most of these protected crops are capital- and labour-intensive. With the given intensive cultivation methods, crop rotation is rarely possible and such crops are liable to rapidly spreading pest attacks. However, in Mediterranean countries, crop rotation is considered as a major component of cucurbit production under plastic, affecting both soil conditions and pest cycles. Cultivation of non-cucurbit crops for at least 2–4 years is recommended, depending on the resistance of the cultivar to particular pathogens. Capsicums, tomatoes and aubergines should be avoided in rotation with cucurbits to minimize disease problems. Cultivars resistant or less sensitive to diseases such as mildews and wilts should be used whenever possible. Due to breeding of new cultivars, northern European cucurbits are resistant to Corynespora cassiicola, Cladosporium cucumerinum and Glomerella lagenarium. These pathogens no longer cause significant problems under protected cultivation. The use of resistant rootstocks can provide good protection if available (e.g. Cucurbita ficifolia which is resistant to Fusarium oxysporum f. sp. cucumerinum). Cucurbits have relatively large seeds and, in northern European glasshouses, they are generally direct-seeded into rockwool blocks or grown from seedlings raised in small peat pots (or similar containers) or peat blocks, transplanted as a whole into the final growing medium. The grower frequently buys in the seedlings from another source, but may also produce them himself. Thus, the guidelines for the different pests given below refer separately to the recommended practice for seedlings. Seedlings should be produced in a high-quality compost or in rockwool. They should be raised in an isolated location, away from cucurbit crops. The seeds should meet normal certification standards. Normal precautions should be taken against damping-off diseases, including the use of seed treatments. Cucurbits may also be grown in hydroponic systems. In southern European countries, cucurbits are mostly direct-seeded into the soil. Seeds are planted in rows or in mounds of soil and, after germination, the seedlings are thinned to the desired population. It is GPP to use seed treatments against pests of young plants, especially if such treatments result in fewer spray applications. Cultivation in disease-free soil or sterile growing medium is extremely important. The same applies to pathogen-free water, particularly when using recirculating water in combination with an artificial growing medium. The plants should be well spaced to permit effective air movement and ventilation, as well as to reduce interplant competition for light, water and nutrients. Damage to plants should be avoided. Tools and machinery should be cleaned after use. At the end of the growing season, the irrigation system should be disinfected against pathogens. In empty glasshouses, windows should be cleaned to remove algae and green moss. In winter, screening may be used to limit cost of heating. In early spring, the screens should be removed to avoid excessive humidity and loss of light, and thus prevent disease infections. Netting of windows and ventilation openings is useful in preventing the entry of insects such as aphids, moths, adult leafminers and whiteflies, but screen apertures need to be very small for thrips and other minute insects. Pests should be monitored at regular intervals. A spray programme of different active substances is GPP if certain pests, which can only be chemically controlled, are indeed present or to be expected. Locally established threshold values should be used. Dosages should satisfy the requirements on the label, taking account of the individual effects and possible interactions. Combining or alternating products with different modes of action can help to avoid the development of resistance. It is GPP to use well-maintained equipment. Application of plant protection products is mainly done by spraying, e.g. with power sprayers, or as a space treatment, e.g. with low-volume mist (LVM) applicators or exhaust fogging machines. LVM applicators have the advantage of being set automatically, so there is reduced exposure of personnel. Application through trickle irrigation is also GPP. Applying plant protection products by means of overhead sprinklers or by dusting may cause unreliable effectiveness because of uneven deposition. In glasshouses, it is particularly important to respect safety regulations for workers applying plant protection products, re-entering after spraying, and handling sprayed plants. Any re-entry interval (REI) and harvest interval (HI) specified on the label should be respected. When applying plant protection products, especially for space treatments, windows and doors should be thoroughly closed to avoid emission into the environment. Waste water should be safely eliminated. Soil sterilization is a common practice for pest control (including weed control) in protected crops. It is GPP to use steam sterilization or solarization for this purpose, but it is not considered GPP to use soil sterilants systematically. Such treatments should be limited to what is strictly necessary. In southern countries, soil solarization is an effective control technique for soil-borne plant pathogens, nematodes and some weed species. It is a hydrothermal process of heating moist soil by covering it with transparent plastic film for at least 40 days during the hottest season. Soil should be previously cultivated and irrigated abundantly in order to favour better heat transmission through the soil and to increase susceptibility of the pathogens to heating. Thin plastic film (0.025–0.05 mm) increases the efficacy and reduces the costs at the same time. The solarization technique gives best performance in warm climates, or in temperate ones if applied in closed plastic tunnels or glasshouses. Solarization integrated with other techniques (fumigation with reduced dosages, biological control agents, organic amendments, etc.) may increase effectiveness and reduce the soil coverage period. Solarization has been found to be effective for controlling infections caused by soil-borne pathogens such as Didymella bryoniae, Verticillium dahliae, V. albo-atrum, Fusarium oxysporum f. sp. cucumerinum, Fusarium oxysporum f. sp. melonis. Biological control as part of an integrated pest management (IPM) programme is becoming common practice in the production of protected cucurbit crops. If biological agents are used and the use of plant protection products is necessary, the side-effects of plant protection products on the biological agents should be taken into account for the choice and the time of application of the plant protection product (see, for example, the tables published by Plantenziektenkundige Dienst, 1998). If plant protection products with harmful effects on natural enemies have nevertheless to be used, spraying only part of a crop can be an option to avoid total failure of the biological control system. If honeybees or bumble-bees are used for pollination, care should be taken to protect them when applying a plant protection product. Parthenocarpic cucumber cultivars do not require pollination. The main pests of cucurbit vegetable crops covered by this guideline are given in Table 1. Table 1. Principal pests of cucurbits under protected cultivation considered Pests Crops on which economic damage occurs Damping-off and root rot Cucumber, melon, courgette Sclerotinia sclerotiorum Cucumber, melon, courgette Phomopsis sclerotioides Cucumber, melon, courgette Fusarium and verticillium wilts Cucumber, melon, courgette Didymella bryoniae Cucumber, melon, courgette Pseudoperonospora cubensis Cucumber, melon, courgette Botryotinia fuckeliana Cucumber, melon, courgette Bacteria Cucumbers for pickling (gherkin) Viruses Cucumber, melon, courgette Aphids Cucumber, melon, courgette Noctuids Cucumber, melon, courgette Leafminers Cucumber, courgette Thrips Cucumber, melon, courgette Whiteflies Cucumber, melon, courgette Capsid bugs Cucumber Mites Cucumber, melon, courgette Meloidogyne spp. Cucumber, melon, courgette Weeds Cucumber, melon, courgette Explanatory note on active substances The EPPO Panel on Good Plant Protection Practice, in preparing this standard, considered information on specific active ingredients used in plant protection products and how these relate to the basic GPP strategy. These details on active substances are included if backed by information on registered products in several EPPO countries. They thus represent current GPP at least in those countries. It is possible that, for any of numerous reasons, these active substances are not registered for that use, or are restricted, in other EPPO countries. This does not invalidate the basic strategy. EPPO recommends that, to follow the principles of GPP, only products registered in a country for a given purpose should be used. It may be noted that many active substances currently used in registered products in EPPO countries will no longer be authorized in the EU after 2003-07. Damping-off and root rot General Several Pythium spp. (P. aphanidermatum, P. ultimum) can infect cucurbits during their early stages of growth, causing seed rot, pre- and post-emergence damping-off, root or stem rot. Untreated seeds in infested soil or substrate may develop a soft rot. On germinated plants, before emergence, a dark brown or black water-soaked lesion develops. On the emerged plants, stem becomes constricted or rotted and the plant collapses. An attack of Pythium spp. is stimulated by fluctuations in climate conditions. Under unfavourable conditions, Pythium spp. survive in the soil as oospores in decayed substrates, potentially for many years. Under optimal conditions, this pathogen can grow indefinitely as vegetative mycelium on various organic substrates in the soil. Pythium spp. are favoured by wet soil conditions, freezing and thawing, and nematode damage. Phytophthora cryptogea can also cause a root rot. Thanatephorus cucumeris (anamorph Rhizoctonia solani) is a ubiquitous soil-borne fungus, which causes damping-off, root rot and basal stem root (foot rot) of cucurbits. In cucurbitaceous crops grown in glasshouses, T. cucumeris is of little importance. It survives in soil, compost and infected debris as mycelium and undifferentiated sclerotia. It can invade cucurbit fruits in contact with soil, leading to irregular scabby lesions on the underside of the fruits. Cucumber is the most susceptible of the cucurbits. Basic strategy Cultural control measures including crop rotation, adequate drainage, planting on raised beds and avoidance of sowing or planting in cold wet soils are usually relied upon to reduce the chances of attack. Hygiene is of great importance. Since these organisms are soil-borne, it is important to use pathogen-free soil, substrate, pots, etc. This can be done by using new or steam-sterilized material. Cleaning and sterilization of pots, glass, etc. is also possible with copper sulphate and quaternary ammonium compounds and other disinfectants (e.g. formaldehyde, sodium hypochlorite). In general, damage to the plants should be prevented. Temperature fluctuation should be avoided by using water at the temperature of the root medium. In systems where recirculating water is used, the diseases can spread rapidly, and the water should therefore be disinfected (e.g. by heating, sand filter or UV). Seed treatment is also good practice. Presowing or preplanting incorporation of fungicides can provide early protection of seedlings. Fungus flies (Mycetophilidae) and shore flies (Ephydridae) should be kept at low levels as they are vectors of Pythium. Main fungicides Seed treatment: thiram, carbendazim. Pot soil treatments: captan, etridiazole, propamocarb, tolclofos-methyl. Drenches: Pythium: etridiazole, metalaxyl-M, propamocarb, fosetyl-aluminium. Drenches: Rhizoctonia: iprodione, mepronil, pencycuron, tolclofos-methyl. Sclerotinia sclerotiorum General Sclerotinia sclerotiorum occurs in glasshouses but rarely causes an epidemic level of disease. The fungus is soil-borne and sclerotia survive in the soil for a long time. It is usually first noted on the stem base of the plants or, where the soil is covered with polythene, in dense canopy growth under the vents, where it forms thick, white cottony mycelium. In this mycelium and the diseased parts of the plant, large white, later blackish sclerotia develop. Lesions may girdle the stem and plants wilt and rot. Lesions on leaves also occur but only spread if conditions are very favourable. Basic strategy Transplants should be disease-free or treated by dipping. Plants should be well spaced. Any condition that contributes to poor air circulation and the retention of moisture is likely to aggravate the disease. Infected plants and any plant debris containing sclerotia should be carefully removed and destroyed. There are no resistant cultivars. If infestation is to be expected, the soil should be steam-sterilized. Fungicide sprays give some control. Main fungicides Sprays: carbendazim, diethofencarb, iprodione, procymidone, thiophanate-methyl. Phomopsis sclerotioides General Phomopsis sclerotioides is soil-borne and can infect all cucurbits infecting the roots and causing the condition known as black root rot. It can also appear on artificial substrates but it is mainly a problem in soil-grown crops. When roots are infested, the take-up of water is blocked. Symptoms are black angular spots on roots and wilting of the plants. The roots become yellow-brownish to black and finally rot. The fungus can spread by air, water or soil/substrate. Under unfavourable circumstances, the fungus can survive for years as sclerotia in the soil. Basic strategy If a resistant rootstock of Cucurbita ficifolia is used, the disease presents no problem. Otherwise, steam sterilization of soil or artificial substrate is recommended. Pathogen-free irrigation water should be used and recycling water disinfected. Infested plant material should be removed. To avoid black root rot, soil temperatures should be favourable for the growth of the host. Fusarium and verticillium wilts General Various formae speciales of the soil-borne fungi Fusarium oxysporum (f. sp. cucumerinum, f. sp. melonis) and Verticillium albo-atrum and V. dahliae cause wilting and sometimes death of plants. These fungi parasitize the vascular system. Verticillium wilt is a cool-weather disease. The two Verticillium spp. survive in soil, as dark resting mycelium or microsclerotia, respectively, in debris from infected plants. Infected plants show mild to moderate wilting during the warmest part of the day but recover at night. As the disease advances, some marginal and interveinal chlorosis develops on lower leaflets. Fusarium wilt is a warm-weather disease, most prevalent on acid, sandy soils. Fusarium oxysporum can persist in the soil for several years. Both Fusarium and Verticillium can also cause serious problems on artificial substrate (especially Fusarium). The characteristic symptom of both wilts is brown or black discoloration seen in the vascular tissue in cross-sections of the lower stem. Wilt symptoms are usually one-sided, i.e. individual runners collapse prior to the death of the plant. Invasion of these wilt pathogens occurs through wounds on roots, such as those produced by cultivation or as result of nematode feeding. Basic strategy Only healthy planting material should be used. Resistant cultivars or resistant rootstocks may prevent early infection, but cannot prevent infection completely. Movement of infected plants and infested soil (with machinery, tools, transplants), and of Fusarium-infected seeds, should be prevented. Hygiene solves most problems, and all possible precautions and actions associated with proper sanitation and management should be taken. The soil should be steam-sterilized before planting or transplanting and also after harvest if there were problems with the disease in the previous season. Diseased plants and plant debris should be removed and destroyed. After harvest, the pallets, water hoses, glass walls, etc. should be cleaned thoroughly. The water table should be checked and kept sufficiently low. Irrigation with ditch water or pond water should be avoided, because surface water may be contaminated with the pathogens. High sodium and nitrogen concentrations should be avoided. If possible, resistant cultivars should be used or a resistant rootstock such as Cucurbita ficifolia. Crop rotation can reduce losses, but not eliminate the pathogens because of the wide host range of these fungi. Verticillium spp. have a wide host range, so effective weed control is important. Any problems should be investigated thoroughly and expert advice should be sought concerning the pathogens, because the susceptibility to fungicides of the pathogens varies considerably. Apart from the active substance, the mode of application varies, from spraying to drenching. Seed treatment is also possible. In southern countries, soil solarization is an effective control technique. Main fungicides Seed treatment: carbendazim. Drenches: carbendazim, thiophanate-methyl. Didymella bryoniae General Didymella bryoniae (synonym Mycosphaerella citrullina, M. melonis) is one of the most common above-ground diseases of cucurbits grown under protected cultivation. The disease is known as black-stem rot, or gummy stem blight, due to the masses of black pycnidia and pseudothecia developing on lesions and the gummy exudates oozing from stem and fruit lesions. It is a pathogen of warm wet weather, which attacks through wounds, primarily in older tissue. In cucumber, necrotic areas first appear at the margins of the leaves, and enlarge rapidly until the entire leaf is blighted. Circular, tan to dark lesions may girdle the stem and the plant dies. On fruits, lesions appear as small water-soaked areas, beneath which an extensive rot is found. Fruit infection frequently starts from infected flowers. In melons, symptoms progress from the centre of the plant outwards. Water-soaked spots on leaves, petioles and stems turn light brown to grey and elongate to streaks. Sources of infection are seeds, older plantings, plant residues and volunteer seedlings. Basic strategy Pathogen-free seeds should be used. Infected plant debris, a major source of inoculum, and volunteer seedlings should be removed and destroyed. Removed plants should be placed in bags in situ. It is very important not to handle the lesions, as spores are sticky and can readily be spread by workers or equipment. Excessive humidity should be avoided by heating and opening vents. Guttation of the plants should be avoided by slowly heating the glasshouse in the morning. Application of extra potassium at fruit formation is recommended. When possible, it is best to use long rotations (at least 2-year rotation cycle) with crops other than cucurbits. Fungicides can be applied at the first signs of the pathogen, but control is often inadequate under the heavy disease pressure. A key spray application is to the stem base after planting. No currently available cucurbit cultivars have commercially acceptable levels of resistance. Isolates of D. bryoniae resistant to benzimidazole fungicides have been detected in some glasshouse cucumber culture. Main fungicides Sprays: bitertanol, carbendazim, chlorothalonil, iprodione, tolylfluanid, triforine. Powdery mildews General Two fungi, Podosphaera xanthii (synonym Sphaerotheca fuliginea, S. fusca) and Erysiphe cichoracearum, can cause powdery mildew on cucurbits. The first symptoms are small pale diffuse spots on the upper surface of old leaves, followed by infection of stems and young leaves. These lesions expand and become a white to pale-grey powdery mass composed of mycelium and countless numbers of spores. Severely infected leaves become brown, desiccate and die. As the disease develops, severe infection may cause premature leaf senescence and plant death. Powdery mildew is seldom seen on the fruits, but decreased photosynthesis may cause significant reductions in the quality and yield of fruits. Development of powdery mildew is favoured by moderate temperatures and relative humidity, dry soil conditions, reduced light intensity and abundant plant growth. On cucurbits in the glasshouse, conidium release is triggered by irrigation or air movement, which then disperse conidia from plant to plant. Conidia can survive the winter period on cucurbits in glasshouses and are dispersed by wind from glasshouse to field crops during the spring and summer. Basic strategy Plant debris should be removed and destroyed at the end of the season to reduce overwintering of the pathogen. Crops should be well spaced, and excess nitrogen fertilization should be avoided. Alternating programmes or mixtures are preferred. Several cultivars of pumpkin, cucumber and melon (cantaloupe) have moderate to excellent resistance to powdery mildew. Some common weeds, e.g. Sonchus spp., may become infected and should be removed from the glasshouse and its neighbourhood. Resistance Strains of Podosphaera xanthii resistant to fungicides are readily selected out of the population. These have occurred in the case of MBC (carbendazim) and DMI fungicides (imazalil, fenarimol), bupirimate and, most recently, azoxystrobin. If a fungicide programme is required, different types of product should be alternated to minimize the loss of efficacy due to resistance. FRAC guidelines should be followed (http://www.frac.info/). Main fungicides Sprays: azoxystrobin, bitertanol, bupirimate, fenarimol, fenbuconazole, hexaconazole, imazalil, myclobutanil, penconazole, sulphur, triforine. Pseudoperonospora cubensis General Downy mildew is one of the most important foliar diseases of cucurbits. In heated glasshouses, downy mildew is not a big problem but, in unheated houses or under lower temperatures, it can be a severe problem. High humidity stimulates growth of the pathogen. It first appears as small yellowish areas on the upper side of the leaves. On the lower leaf surface, blackish-purple spore masses appear over the yellow-brown lesions. Downy mildew develops on older leaves first but does not affect stems or fruit. Basic strategy Satisfactory control can be achieved by combining cultural practices, the use of resistant cultivars and fungicide application. Cultural practices include crop rotation, using plant spacing which reduces canopy density and avoiding overhead irrigation, which can prolong the duration of leaf wetness periods. If fungicides are used, they should be applied with high-pressure sprayers to ensure complete coverage of the undersides of leaves. Strains of the pathogen resistant to metalaxyl-M and azoxystrobin have been reported. FRAC guidelines should be followed. Main fungicides Sprays: azoxystrobin, chlorothalonil, copper oxychloride, fosetyl-Al, metalaxyl-M, myclobutanil, propamocarb. Botryotinia fuckeliana General Botryotinia fuckeliana (anamorph Botrytis cinerea) attacks many plants and plant parts, mainly through wounds. All cucurbits are affected. The fungus causes grey rot on every part of the plant. Infected plant parts die and are gradually covered by the grey mycelium (grey mould), or affected areas may dry out. Lesions release millions of spores into the air. The fungus survives as sclerotia or mycelium in dead or living plant tissue or as sclerotia in the soil. Basic strategy Hygiene is very important. Debris and infected plants should be removed. Soil and growing medium should be well drained and a dense stand avoided. The relative humidity should be generally low, without too much water sprinkled over the plants. Wet plants and condensation should be avoided or dried as soon as practicable. As far as possible, wounding should be avoided and pruning wounds kept small and regular. Foliar sprays can be applied to minimize air-borne infection by B. fuckeliana. Problems with resistance Strains of B. fuckeliana resistant to a number of commonly used fungicides can occur. These include benzimidazoles (e.g. carbendazim) and dicarboximides (e.g. iprodione, procymidone). If a programme of fungicide sprays is required, different types of product should be alternated to minimize the loss of efficacy due to resistance. FRAC guidelines should be followed. Main fungicides Sprays: carbendazim, chlorothalonil, diethofencarb, iprodione, procymidone, pyrimethanil. Bacteria General Bacterial diseases are of little importance in cucurbits in glasshouses. Pseudomonas syringae pv. lachrymans is seed-borne and is rarely found in cucumber, melon and courgette in glasshouses. It sometimes causes a problem of angular leaf spot in cucumbers for pickling. Erwinia carotovora subsp. carotovora can cause a slimy soft-rot of the stem base in soil-grown crops. Infection usually follows pest attacks, but can occur through natural growth cracks. ‘Root mat’, caused by rhizogenic strains of Agrobacterium tumefaciens biovar 1, can affect both soil-grown and hydroponic cucumber crops. Infection results in abnormal plant growth, typically upward growth of roots from the surface of the propagation block, and swelling of the stem base. Basic strategy It is very important to use pathogen-free seeds and to ensure good continuous growth. Crop rotation with a non-host is recommended. With all bacterial diseases, good hygiene is essential and plant debris should be removed, tools should be disinfected, etc. Glasshouses should be disinfected with formaldehyde. Steam sterilization of soil or substrate is recommended. The stem base should be kept dry as far as practicable to avoid E. c. carotovora (basal stem rot). In glasshouse-grown cucurbits, reduction of the relative humidity to 80–90% can reduce the spread of P. s. lachrymans. A number of cucumber cultivars and other cucurbits are resistant to this pathogen. Viruses General The following viruses are regularly found in cucurbits grown under protected cultivation: Cucumber mosaic cucumovirus, Cucumber green mottle mosaic tobamovirus, Melon necrotic spot carmovirus, Watermelon mosaic potyvirus, Zucchini yellow mosaic potyvirus. Symptoms may consist of mosaic, leaf yellowing, leaf deformation, leaf curling, growth reduction, chlorotic and necrotic spots, rings and patterns on leaves and fruits. Symptoms and their severity vary with the virus isolate causing the infection, the plant species and the cultivar that is being infected, the plant stage and environmental conditions in which infection takes place. Symptoms are often not sufficiently characteristic for a reliable diagnosis to be made. Additional diagnostic methods may be needed (e.g. mechanical inoculation to test plants, ELISA test). Cucurbit yellow stunting crinivirus has become important in European melon and cucumber crops only recently, and is still of very limited distribution. In some cases, its increased importance has been associated with the spread of newly introduced and indigenous strains of the vector Bemisia tabaci. This virus is under consideration for regulation. To minimize the effects of viruses, it is important to know which virus causes the disease and how it is transmitted. Each virus has its own mode of transmission (Table 2). In addition, all viruses are spread by grafting and by transport of infected plants. Table 2. Viruses attacking cucurbits and their modes of transmission Virus Transmission Crop affected Cucumber mosaic cucumovirus Aphids i