Cane Blight Research Articles

Paraconiothyrium fuckelii, Diaporthe eres and Neocosmospora parceramosa causing cane blight of red raspberry in Northern Italy

Red raspberry (Rubus idaeus L.) represents a relevant crop which production has largely increased worldwide during the last decade. Cane blight is one of the most common diseases of red raspberry and it can produce considerable losses. During 2019–2021, surveys were conducted in red raspberry orchards in Cuneo province, Northern Italy, to investigate the etiology and pathogen diversity in association with cane blight. Eleven isolates were collected from symptomatic plants of the cultivars ‘Diamond Jubilee’ and ‘Grandeur’, and were identified through multi-locus phylogenies and morphological features. Three fungal species were identified: Paraconiothyrium fuckelii, Diaporthe eres and Neocosmospora parceramosa. Four different genomic regions were included in the molecular analyses: ITS, tef1, tub2 and rpb2. The species pathogenicity was confirmed and P. fuckelii was revealed as the most aggressive. This study provides an insight into raspberry cane blight in Italy and the genomic loci sequencing lay the basis to develop specific diagnostic protocols to monitor the presence of pathogens and to prevent disease spread, adopting effective integrated control strategies.

Phytotoxic metabolites produced by Diaporthe eres involved in cane blight of grapevine in Italy

Grapevine trunk diseases (GTDs) are one of the most serious biotic stresses affecting this important crop. Among them a range of diseases were identified and associated to a plethora of phytopathogenic fungi, including species of Diaporthe. Diaporthe eres was recently identified as one of the species involved in cane blight of grapevine. The ability of a strain of this fungus isolated from infected grapevine plant in Italy to produce in vitro phytotoxic metabolites was investigated. Five phytotoxic metabolites were identified by their physical and spectroscopic properties as 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, nectriapyrone, p-cresol and tyrosol. When tested on grapevine leaf disks and by leaf absorption, 4-hydroxybenzoic acid induced symptoms on both disks and leaves, 4-hydroxybenzaldehyde and p-cresol showed, respectively, phytotoxicity on leaf disks and on the leaf absorption bioassay.

First Report of Diaporthe eres Associated with Cane Blight of Grapevine (Vitis vinifera) in Italy

First Report of <i>Diaporthe eres</i> Associated with Cane Blight of Grapevine (<i>Vitis vinifera</i>) in Italy

Changes in phenolic content induced by infection with Didymella applanata and Leptosphaeria coniothyrium, the causal agents of raspberry spur and cane blight

The phenolic profile of healthy and infected raspberry canes was investigated in three raspberry cultivars: Autumn Bliss, Himbo Top and Polka. The content of total phenols and tannins was determined using spectrophotometric methods, whilst individual phenolic acids, flavan‐3‐ols, ellagic acid derivatives and glycosides of quercetin were analysed using HPLC/MS analysis. The content of secondary metabolites varied considerably among the analysed raspberry cultivars. Moreover, Didymella applanata and Leptosphaeria coniothyrium infection significantly altered the metabolism of phenolic compounds. Flavanols represented the greatest share of all identified phenolics in raspberry canes (90%), followed by glycosides of quercetin (6%), derivatives of ellagic acid (3%) and traces of hydroxycinnamic acid derivatives. Spur and cane blight diseases caused an increase of flavan‐3‐ols and tannins but the levels of hydroxycinnamic acid derivatives, conjugates of ellagic acid and quercetin glycosides were significantly reduced. Cultivars Himbo Top and Polka contained higher levels of hydroxycinnamic acid and ellagic acid derivatives in healthy and infected canes compared to cv. Autumn Bliss. Cultivar Polka also contained the highest level of flavanols and tannins. However, despite high levels of flavanols and total phenols measured in cv. Polka, the canes were highly diseased following infection with D. applanata and L. coniothyrium. The results of the study provide evidence that the level of phenolic compounds in the canes could be causally linked to the differences in disease susceptibility.

A moléstia da cana-de-açúcar na década de 1860: a lavoura em busca das ciências

The Imperial Instituto Fluminense de Cultura (Fluminense Imperial Institute of Agriculture) encouraged debate with a view to eradicating the blight that devastated sugar cane plantations in the State of Bahia. Rural landowners, government officials and men of science participated in the discussions. The article presents the context of the sciences applied to agriculture, especially agricultural chemistry and the repercussions of the 'discoveries' of Justus Liebig in Brazil. The debate at the Imperial Instituto about the sugar cane blight was analyzed, together with the ideas espoused there and the characters involved in the issue. The procedures and solutions presented are studied, as well as the formation of knowledge networks around the agricultural sciences, which was in the process of institutionalization at the time.

High Tunnel and Open Field Production of Floricane- and Primocane-fruiting Raspberry Cultivars

Identical trials were conducted in a multibay high tunnel and an adjacent open field in southwestern Michigan to compare primocane-fruiting cultivars (Autumn Britten, Caroline, Chinook, Heritage) and floricane-fruiting cultivars (Canby, Encore, Heritage, Nova) of red raspberry (Rubus idaeus). Floricane-fruiting plots of ‘Heritage’ were pruned to produce fruit on floricanes and primocanes (double cropping). The most productive cultivars in both environments were ‘Nova’ and ‘Canby’ (floricane) and ‘Caroline’ and ‘Heritage’ (primocane). These cultivars produced annual yields of 5.5 kg·m−1 row in the tunnel and 2.5 kg·m−1 row in the field. The order of primocane harvest (earliest to latest) was the same in the tunnel and field: ‘Autumn Britten’, ‘Caroline’, ‘Chinook’, and ‘Heritage’. Cultivars with the greatest average berry weight in the tunnel and field were Encore and Nova (floricane) and Autumn Britten and Caroline (primocane). ‘Chinook’ and ‘Autumn Britten’ tended to have the highest incidence of gray mold (Botrytis cinerea) of primocane-fruiting cultivars, but incidence was similar in floricane cultivars. Overall mold incidence was 1% in the tunnel and 13% in the field. Leaf spot (Sphaerulina rubi), cane anthracnose (Elsinoe veneta), spur blight (Didymella applanata), and botrytis cane blight (B. cinerea) were common in the field but absent in tunnel. Phytonutritional analyses of primocane fruit indicated that genotype differences were not consistent across the two environments. Relative cultivar characteristics (harvest season, yield, berry quality) were similar in the field and tunnels, but the tunnel environment tended to increase plant vigor, yield, and fruit quality and suppress several diseases.

First Report of Cane Blight on Blackberry Caused by Diaporthe eres in Croatia.

A cane disease of blackberry (Rubus sp.) cv. Thornfree was observed in May and June 2010 in two growing regions in the eastern part of Slavonia in Croatia. Symptoms consisted of bleached areas between and around cane nodes with some canes showing wilt symptoms. Infected areas were covered with numerous, black pycnidia immersed in the epidermal tissue. Disease occurrence in orchards growing cv. Thornfree ranged between 1 and 15%. Thirty disease samples were collected, disinfected (1 min in 70% ethanol and 2 min in 1% NaOCl), and placed in a moist chamber for 4 days. Fungal sporulating structures were then picked off and placed on potato dextrose agar (PDA). Fungal isolates obtained were identified as a Phomopsis sp., the conidial state of Diaporthe (3), on the basis of cultural and morphological characteristics. Alpha conidia were unicellular, hyaline, fusiform, sometimes tapering toward one or both ends, biguttulate (sometimes with several guttules), and 5.2 to 9.7 × 1.4 to 2.7 μm (average 6.5 × 2.1 μm). Beta conidia were hyaline, aseptate, filiform, hamate, and 16.6 to 28.2 × 0.5 to 1.5 μm (average 24.0 × 1.1 μm). The teleomorph was not observed. Biomolecular analysis was performed to identify the fungal species by sequencing the internal transcribed spacer (ITS) region spanning ITS 1, 5.8S rDNA, and ITS 2 of two isolates (Phk1 and Phk2). The amplified product was sequenced (GenLab-Enea, Rome, Italy) and a BLAST search of the NCBI nucleotide database was performed. Sequences from Phk1 and Phk2 (GenBank Accession Nos. HQ533144 and HQ533143, respectively) were identical to authentic and vouchered Diaporthe eres Nitschke (GenBank DQ491514, BPI 748435, and CBS 109767) ITS sequences in GenBank. Fungal isolates for pathogenicity tests were grown on PDA at 25°C for 7 days (12 h light/dark regimen). Inoculations were made on 30 to 40 cm long green shoots of potted plants of the blackberry cv. Thornfree. One-centimeter long wounds were made with a sterile scalpel and mycelia of D. eres were placed in the wounds. Inoculation sites were covered with a piece of wet cotton wool and aluminum foil to retain moisture. Three replications of 10 plants each were inoculated and these plus 10 control plants (inoculated with plugs of PDA only) were maintained in a growth chamber at 25°C. After 25 days, lesions developed on all 30 inoculated plants that averaged 15 mm long and control plants remained symptomless. D. eres was reisolated from inoculated plants, thus completing Koch's postulates. Phomopsis spp. have previously been reported on blackberry canes in Serbia (1) and Yugoslavia (2,4), however, to our knowledge, this is the first report of the occurrence of D. eres (anamorph P. oblonga) on blackberry in Croatia.

BACTERIAL CANE BLIGHT OF ROSE CAUSED BY PSEUDOMONAS SYRINGAE

A disease affecting rose (Rosa spp.) plants with symptoms of cane blight has been observed in southwest Idaho USA, since 1996. The symptoms were commonly observed under cool, wet conditions during spring (March to May) on several cultivars of climbing, floribunda, grandiflora, hybrid tea, hybrid perpetual, miniature and shrub roses. The symptoms usually started at the base of a vegetative bud or at leaf scars or wounds, as reddish brown areas on the bark that later turn dark purple to black and necrotic. The necrotic areas expanded around and along the cane, often involving a major part or even the entire cane. Vegetative buds on the affected parts of the cane turned brown and dried. The surface of the necrotic areas of the bark was glossy, and the tissue beneath the epidermis was brown to dark brown, and moist in the early stages. Microscopic examination of the necrotic tissue revealed profuse bacterial streaming, and isolations on King's B agar plates consistently yielded creamy, whitish-gray, raised colonies that produced a diffusible pigment which fluoresced blue-green under ultraviolet light. Pure cultures were characterized using standard bacteriological tests, including Gram staining, LOPAT tests, Biolog, cellular fatty acid analysis, and inoculation to lemon and cherry fruits. Pathogenicity of the isolated bacterium to rose shoots and canes was confirmed by inoculations, and the bacterium was re-isolated from the symptomatic tissue and characterized. Based on the bacteriological characteristics and pathogenicity, the bacterium causing cane blight of roses was identified as an undetermined pathovar of Pseudomonas syringae. The bacterial cane blight disease described here is distinctly different from the various symptoms on roses previously attributed to P. syringae and/or P. syringae pv. morsprunorum in the literature. Some of the rose cultivars that showed severe symptoms of bacterial cane blight under conditions of natural incidence are listed.

Occurrence of Phoma argillacea on Rubus spectabilis in British Columbia and an evaluation of its potential as a forest weed biological control agent

A survey was conducted on Vancouver Island and in coastal mainland British Columbia of naturally occurring fungal pathogens of salmonberry (Rubus spectabilis), an endemic plant species considered to be undesirable in conifer regeneration sites. Fungi were recovered from necrotic lesions on foliage and stems and identified to genus level. An in vitro pathogenicity test was performed on 281 fungal isolates using detached salmonberry leaves. Nineteen isolates were found to be moderately to highly aggressive, causing >50% leaf area necrosis within 14 days. These included Botrytis cinerea (17 isolates), Phoma sp. (3 isolates), and Septoria rubi (1 isolate). The three isolates of Phoma, identified as P. argillacea, were selected for further testing on salmonberry plants under greenhouse conditions. Mycelial or conidial inoculum were applied to the foliage of plants, which were incubated for 48 h at 20–22 °C and 100% relative humidity (RH) and then grown at 20–22 °C and 55–65% RH, with a 16 h photoperiod, under greenhouse conditions. Extensive necrosis of leaves and stems developed within 14 days for all isolates using mycelia and conidia as inoculum. A minimum of 18 h of continuous leaf wetness and mycelial inoculum of 2.6 × 103 colony forming units/mL was required for infection to occur. In a small host range test, three economically important conifer species, namely Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western red cedar (Thuja plicata), showed tolerance at the seedling stage with <5% disease severity. On red raspberry (Rubus idaeus), P. argillacea caused some initial damage (leaf spots and chlorosis) but failed to cause cane blight. These results demonstrate the pathogenicity of P. argillacea on salmonberry and the conditions required for establishing disease.

Potential Use of Chitosan in the Control of Grapevine Trunk Diseases.

Summary. Due to its fungistatic or fungicidal potential, chitosan, a high molecular-weight polymer that is non-toxic and biodegradable, has become an alternative to conventional fungicides. In addition, chitosan is reported to elicit defense mechanisms in plant tissues. In this study, we explored the in vitro fungicidal effect of chitosan on some of the most important grapevine wood fungi, such as Botryosphaeria sp. (dieback and cane blight), Phomopsis sp. (Phomopsis cane and leaf spot), Eutypa lata (eutypa dieback), Neonectria liriodendri (black foot disease), Phaeomoniella chlamydospora (Petri disease and esca) and Fomitiporia sp. (esca). Inhibition of mycelial growth was evaluated at five concentrations 50, 25, 5, 2.5 and 0.5 mg a.i. l -1 of chitosan. Chitosan was effective in reducing mycelial growth of all the fungi. The lowest EC50 values were obtained with Pa. chlamydospora, Fomitiporia sp. and Botryosphaeria sp., and the highest with Neon. liriodendri. All these were inferior to the maximum recommended field rate (8.33 mg a.i. l -1 ) with exception of the value obtained with Neon. liriodendri. Greenhouse experiments were carried out to evaluate the efficacy of foliar sprays of chitosan on potted grapevine plants (cultivar Castelao) growing in a substrate artificially infested with Pa. chlamydospora or Neon. liriodendri. The effect of chitosan against Neon. liriodendri was similar to that achieved with some selected fungicides (carbendazim+flusilazole, cyprodinil+fludioxonil and tebuconazole). Chitosan significantly improved plant growth (plant height and number of roots) and decreased disease incidence compared with untreated plants. As regards Pa. chlamydospora, chitosan only reduced the disease incidence caused by this fungus.

Fungi Occurring on Aerial Constituents of Cultivated Blackberry ( Rubus fruticosus L.) in Norway

Cultivated blackberry (Rubus fruticosus) was recently introduced in Norway, and most plantings were established in the 1990's. Many of these plantings died back or had severe damage on leaves and stems. Plant pathogens incombination with frost injury were suspected to be the cause of the damage. In 1998-99, field and greenhouse plantings of blackberry were surveyed for the occurrence of plant pathogenic and saprophytic fungi. A total of 33 different fungi were identified in 18 cultivars from 23 plantings (19 field and 4 greenhouse). Of these, 12 were pathogenic fungi, while 21 were non-pathogenic, secondary invaders. The most important pathogens on the canes were (common name in parenthesis) Septocyta ruborum (Purple blotch), Gnomonia rubi (Gnomonia canker) and Sydowiella depressula (Sydowiella canker). Pathogenic fungi of less importance on the canes were Elsinoe veneta (Anthracnose) and Coniothyrium fuckelii (Cane blight). Peronospora sparsa (Downy mildew) was the most important fungus attacking leaves. On fruits Botrytis cinerea (Grey mould) was the most prevalent pathogen. Cladosporium spp. (Cladosporium rot) and Penicillium spp. (Blue mould) were frequently observed on fruits, but did not seem to be of significant importance. Other minor fruit rots were due to Colletotrichum gloeosporioides (Bitter rot) and Mucor sp. (Mucor rot). Phragmidium violaceum (Blackberry rust) was found on canes and leaves, but was of minor importance. G. rubi and S. depressula caused damage mostly in the thornless cultivars, and P. sparsa was found almost exclusively in the thornless cultivar 'Loch Ness'. Both thorny and thornless cultivars were damaged by S. ruborum. In greenhouses the major fungal problem was B. cinerea.

First Report of Pestalotiopsis populi-nigrae on Poplar in North America.

Black acervuli were observed on abaxial surfaces of leaves of hybrid poplar (Populus trichocarpa Torr. & A. Gray × P. deltoides Marsh.) collected during fall 1998 in western Washington. Melampsora uredinia also were present but may be coincidental. When incubated in a moist petri dish, leaves became necrotic, and acervuli produced black masses of fivecelled, appendage-bearing conidia. Average conidia length was 25 µm. Three median versicolorous cells averaged 17.5 µm long and 6 µm wide; the upper two were darker than the lower one. There were typically three apical setulae, averaging 20 µm long. The average basal pedicel was 5 µm long. The fungus fits the description of Pestalotiopsis populi-nigrae (Sawada et Ito) Morelet. Originally described as an opportunistic pathogen on poplar in Japan (1), P. populi-nigrae was subsequently found on poplar in Europe (2). It is also the cause of cane blight of Rosa spp. in Japan (2), but it has never been reported in North America. A specimen has been deposited in the U.S. National Fungus Collections (BPI 746460). I did not observe P. populi-nigrae in 1997 to 1999 collections of rusted poplar leaves from the Southeast, western Kentucky, Minnesota, and Iowa nor in other Pacific Northwest collections. This was not a comprehensive survey for P. populi-nigrae but may indicate that the fungus is rare in North America. It also is possible that BPI 746460 represents an undescribed, uncommon species native to North America that is morphologically indistinguishable from P. populi-nigrae. Further research is required to test this hypothesis.

Excoriose, Cane Blight and Related Diseases of Grapevines : A Taxonomic Review of the Pathogens

The disease of grapevines known as excoriose has been the source of a certain amount of controversy. Much of this concerns the identity of the causal agent and this has been further confounded by the taxonomic problems of the fungal pathogens associated with this disease. Many of these problems have now been resolved and it is clear that excoriose is caused by Botryosphaeria dothidea while cane blight and leaf spot is caused by Phomopsis viticola. However, although at least five different species of Phomopsis are currently known to be associated with grapevines, only P. viticola causes cane blight and leaf spot. The role played by the other species of fungi is not clear, but they may be weak pathogens, saprophytes or endophytes.

Excoriose, cane blight and related diseases of grapevines: a taxonomic review of the pathogens

The disease of grapevines known as excoriose has been the source of a certain amount of controversy. Much of this concerns the identity of the causal agent and this has been further confounded by the taxonomic problems of the fungal pathogens associated with this disease. Many of these problems have now been resolved and it is clear that excoriose is caused by Botryosphaeria dothidea while cane blight and leaf spot is caused by Phomopsis viticola. However, although at least five different species of Phomopsis are currently known to be associated with grapevines, only P. viticola causes cane blight and leaf spot. The role played by the other species of fungi is not clear, but they may be weak pathogens, saprophytes or endophytes.

Resistance to cane and foliar diseases in red raspberry (Rubus idaeus) and related species

Several types of resistance to fungal pathogens of cane fruits have been identified by controlled infection procedures and incorporated into the UK Rubus breeding programme. These are reviewed with a description of the biology of the pathogens involved. Some of them take the form of a mechanical barrier associated with the position and rate of development of suberised periderms. For example, damage to the deep-seated cane polyderm occurs when Leptosphaeria coniothyrium (cane blight) infects the phloem and xylem, but forms of resistance which restrict the expansion of these vascular lesions have been found.

Pruning Practices Affect Yield, Yield Components, and Their Distribution in `Royalty' Purple Raspberry

A factorial arrangement of 48 treatments was used to evaluate the effects of cane density, time of cane density adjustment, primocane tipping, and cane or branch length on yield components in `Royalty' purple raspberry [(Rubus occidentals × R. idaeus) × R. idaeus] over 2 years. Yield was positively related to cane density and length, while fruit size and fruit count per lateral were negatively related to cane and branch length. When branches on tipped canes were shortened in late winter, more buds became fruitful at the proximal end of the branch, but fruiting laterals did not have more flowers or fruit. Fruiting laterals were longer on shortened canes, resulting in a decrease in the fruit: wood ratio. Plants performed similarly whether floricane density was adjusted in late winter orprimocane density was adjusted in late spring. Although potential yield was higher when primocanes were tipped in late spring, harvesting was more difficult because of branch orientation, and the incidence of cane blight infection was higher. Our study suggests that maintaining at least 12 canes per meter of row, avoiding primocane tipping, retaining full cane length, and providing adequate light, moisture, and nutrient levels can result in high yields of large fruit.

Factors affecting the development of cane blight (Leptosphaeria coniothyrium) on red raspberries in Washington, Scotland and Germany

SUMMARYThe effects of cultivar, virulence of isolates of Leptosphaeria coniothyrium, cane maturation and wound healing were examined in a series of inoculation experiments carried out over a 3–yr period in three countries in an attempt to explain why cane blight has caused serious yield losses in machine‐harvested red raspberries in Europe, but not in the Pacific Northwest of America. Three isolates of L. coniothyrium from Puyallup (USA), Dundee (UK) and Dossenheim (FRG) were pathogenic on the three test cultivars Willamette, Malling Jewel and Glen Isla in all the experiments. Isolates and cultivars differed for aggressiveness and susceptibility respectively but their ranking was dependent on the test conditions and the differences were small and unlikely to explain the differences in incidence and severity of cane blight in raspberry fields in Scotland and the Pacific Northwest. Conditions at Dossenheim were most favorable for lesion development. At all sites, canes inoculated in late summer produced shorter lesions than those inoculated earlier. A delay between wounding and inoculation produced shorter lesions than simultaneous wounding and inoculation.

Effects of straddle‐harvester design on cane blight (Leptosphaeria coniothyrium) of red raspberry

SUMMARYA new fruit catching device developed for raspberry straddle harvesters to reduce wounding of young canes and their consequent infection by Leptosphaeria coniothyrium was tested. During picking the young canes were contacted only by the foam rubber on a pair of belts which moved backwards along the harvester at the same speed that the machine advanced. The incidence of canes with cane blight lesions in 1981 was 18% following the use of the new device in 1980, and 79% following the use of a conventional commercial harvester equipped with overlapping metal fruit‐catching plates. In comparison with the latter plates, the new device avoided wounding the cane surface directly: when the belt marks on these canes were inoculated with mycelium, however, the disease incidence was 77%. The new device caused wounds in 1980 by ripping leaves from nodes. In comparison with the commercial harvester the new device led to smaller lesions in 1981 and a lower percentage of canes dead above the fruit‐catching zone.A modified new catching device tested in 1982 made barely detectable pressure marks on the young canes without bruising them. Only 6·6% of these canes developed vascular lesions after inoculation, an incidence similar to that for unwounded control canes (2·5%). The modified new device is advised for regions prone to cane blight where the cropping system has young and fruiting canes growing together.

Didymella applanata . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Didymella applanata . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Rubus idaeus (raspberry), R. fruticosus (blackberry) and R. ursinus var. loganobaccus (loganberry). Also on R . australis . DISEASE: Spur blight (in USA) and sometimes referred to as cane blight (in Europe). Early symptoms are purplish blotches mainly on the epidermis at the nodes round the base of leaves and sometimes between the nodes on the lower portions of the stems. As the disease progresses the blotches increase in size extending upward and downward along the cane and sometimes the lesions coalesce to form a discoloured cane. Didymella applanata has been reported to cause dieback (2, 457; 32, 572; 41, 353) and witches' brooms (2, 457). GEOGRAPHICAL DISTRIBUTION: Africa, Asia, Australasia &amp; Oceania, Europe and North America (CMI Map 72, ed. 3, 1977). New records not mapped are: Europe (Czechoslovakia). TRANSMISSION: By ascospores and conidia released during wet or extremely moist conditions (10, 530; 55, 1875; Wormald, 1939; Converse, 1966). In the UK small numbers of ascospores have been trapped in raspberry plantations throughout the summer and early autumn when RH exceeded 70% and temperatures above 12°C prevailed for at least 12 h (37, 201). It invades both unwounded and wounded tissues (9, 117-118; 10, 531). Entry into canes is also achieved through wounds created by Diplosis (gall fly) in Germany (11, 381) and by Thomasiniana theebaldi (midge) (28, 340; 32, 86; 34, 728; 39, 120; 43, 519). As a rule the fungus invades all regions of the cortex except the cork which acts as a barrier (9, 117-118; 10, 531; 11, 381) but it has been known to cause deeper lesions on midge larval feeding areas and frequently penetrates the stem to the pith and kills the cane (32, 86).

The effect of sprays of thiophanate–methyl on cane diseases and yield in red raspberry, with particular reference to cane blight (Leptosphaeria coniothyrium)

SUMMARYSpur blight (Didymella applanata), cane botrytis (Botrytis cinerea) and cane blight (Leptosphaeria coniothyrium) were studied in two consecutive seasons in unsprayed raspberries and in plots sprayed with thiophanate‐methyl in the first season alone, (a) twice pre‐harvest, (b) twice post‐harvest, or (c) twice pre‐ plus twice post‐harvest. Pre‐harvest, but not post‐harvest sprays, gave moderate control of both spur blight and cane botrytis; both diseases occurred mainly on the lower halves of canes, the latter being the less common.Cane blight occurred at the base of canes where they were wounded by old cane stubs. In the first year it was severe; 37% of canes died before harvest in the unsprayed plots. The three spray programmes all decreased cane death due to cane blight and they all increased yield by c. 45% even in those plots sprayed post‐harvest where spur blight was severe and not controlled. Clearly this last disease, despite its high incidence, had no effect on potential yield in this experiment. In the second year cane blight was common but less severe and the incidence of its lesions was reduced similarly by all programmes, but only 4% of canes died in control plots.Analysis of the potential yield and the sizes of lesions caused by L. coniothyrium in canes inoculated at fortnightly intervals in the previous year showed that potential yield loss occurred only when lesions girdled canes. A bimodal distribution in the lesion sizes, measured by length or girdling, indicated some endogenous control of lesion development which might explain the marked differences in the effect of cane blight on potential yield in two seasons.