Effects of fungicides on apple crown rot caused by Phytophthora cactorum

The mycelial growth of Phytophthora cactorum on corn meal agar was completely inhibited by metalaxyl or mancozeb at 50 or 100 μg ml^?1, but not by fosetyl-aluminium at the same concentrations. Soil drenches with metalaxyl, followed by metalaxyl+mancozeb, around the base of naturally infected trees under orchard conditions, prevented the growth of P. cactorum in the infected bark of the tree. Soil drenchs with metalaxyl, followed by metalaxyl+mancozeb, also prevented the infection of apple trees with P. cactorum under orchard conditions. The trunk circumference and spur length were not significantly affected by any of the fungicide treatments in all the trials over 2 years, except in one of the four orchards used in the study. Soil drench with metalaxyl alone, or followed by metalaxyl+mancozeb, may provide an effective control method for crown rot of apple trees.     

Crown rot caused by Phytophthora cactorum in Norwegian strawberry production

Crown rot of strawberry, caused by Phytophthora cactorum , was detected for the first time in Norway in 1992. This paper reports on surveys for P. cactorum in Norwegian certified strawberry plant production and on the distribution of the pathogen in regular strawberry production. In 1996 and 1997, samples of plant material from all certified strawberry plant growers in the country were investigated by isolation on artificial growth medium and using an enzyme-linked immunosorbent assay (ELISA). P. cactorum was not detected in any of the samples. A total of 171 isolations from plants with symptoms resembling crown rot were made from plants in a survey of the distribution of Phytophthora fragariae var. fragariae and from other samples. P. cactorum was detected at 35 different strawberry-producing farms in 11 of the 19 counties of Norway. The fungus was most frequently isolated from cv. Korona (at 18 locations), followed by cv. Inga (at 10 locations).     

Control of crown rot (Phytophthora cactorum) of apple trees with the systemic fungicides metalaxyl and fosetyl-aluminium

Four fungicides were evaluated as combined soil drench and trunk treatments for the control of crown rot, caused by Phytophthora cactorum, in naturally infected apple trees. In a 3-year preliminary study, metalaxyl at 1 and fosetyl-aluminium at 8 g a. i. per tree, applied twice a year, prevented death of infected trees showing only initial, but not more severe, symptoms of crown rot. This indicates that these fungicides have the ability to arrest further symptom development in naturally infected trees if they are treated as soon as symptoms appear. Healthy trees remained free of infection if they were treated with these fungicides, suggesting a preventative action. Repeated bi-annual application of metalaxyl or fosetyl-aluminium should be sufficient to prevent the loss of trees to crown rot.     

Phytophthora crown rot of almonds in Australia 1

Phytophthora crown rot, caused primarily by Phytophthora cambivora, has caused considerable losses in almond orchards in the Willunga and northern plains areas approximately 50 km north and south of Adelaide (AU), respectively. Other Phytophthora species including P. citrophthora, P. cryptogea, P. megasperma and P. syringae have also been associated with diseased trees. Tree losses have been associated with P. cactorum isolated from trunk cankers on scaffold limbs on trees in the Riverland almond-growing area approximately 350 km north-east of Adelaide. The Al mating type of P. cambivora was the most pathogenic to almond seedlings. Cvs Mission and Chellaston, which are commonly used as rootstocks, were highly susceptible to crown rot whereas peach cv. Nemaguard was resistant. An excised twig assay has been developed to screen micropropagated shoots for resistance to P. cambivora. Metalaxyl applied at 5 g active substance per tree in spring, winter and autumn in a shallow trench close to the trunk prevented the development of trunk cankers. Foliar sprays of phosphonate (H₃PO₃) at 2 g active substance per litre in autumn and spring also inhibited canker development.     

Phytophthora rot of alpine delphinium caused by Phytophthora sp. kelmania

Severe stunting and root rot were observed on alpine delphinium plants (Delphinium elatum) from Aomori Prefecture, Japan, in 2010 and 2011. A Phytophthora isolate from the diseased crown was identified as Phytophthora sp. kelmania based on morphological characteristics and DNA sequence data. Inoculation of alpine delphinium plants with the isolate produced a similar root rot. Pathogenicity of the isolate on four species of plants that are known hosts for P. sp. kelmania was confirmed. We propose the name “Phytophthora rot” (eki-byo in Japanese) for the present new disease on alpine delphinium.

     

Root rot of lavender caused by Phytophthora nicotianae

Lavender (Lavandula angustifolia) plants with rotted roots and discoloured vascular systems consistently yielded cultures of fungi that were identified as Phytophthora nicotianae van Breda de Haan (= P. parasitica). Inoculation experiments using either zoospore suspensions or mycelial fragments were successful in reproducing symptoms originally observed on wilting and dying plants. Lavender is a new host for P. nicotianae.     

Root rot of cabbage caused by Phytophthora drechsleri

A root rot of cabbage is reported from South Africa. The causal pathogen was identified as Phytophthora drechsleri , based on morphological characters and electrophoretic patterns of soluble proteins.     

Phytophthora root and crown rot of raspberry in Bulgaria

Root and crown rot of raspberry (Rubus idaeus L.) was observed in a plantation at the experimental station of small fruits in Kostinbrod, Bulgaria. Isolates ofPhytophthora spp. were obtained from diseased plants. Colony morphology, growth rates, features of asexual and sexual structures were studied and as a result twoPhytophthora species were identified:Phytophthora citricola Saw. andPhytophora citrophthora (R.E. Sm. & E.H. Sm.) Leonian. Their pathogenicity was confirmed in artificial inoculation experiments. The isozyme (-esterase) patterns ofP. citrophthora andP. citricola isolates from raspberry and from the collection of the CBS, Baarn the Netherlands were compared, using micro-gel electrophoresis. Both species are reported for the first time as pathogens of raspberry in Bulgaria. This is only the second report in phytopathological literature ofP. citrophthora on raspberry, the first being from Chile [Latorre and Munoz, 1993].     

Root rot of tree lucerne caused by Phytophthora nicotianae

Phytophthora nicotianae Breda de Haan was consistently isolated from rotted roots and discoloured vascular tissues of tree lucerne ( Chamaecytisus palmensis ). It was identified with the aid of total DNA restriction fragment length polymorphisms and morphological characters. Pathogenicity was demonstrated by inoculation. This is the first record of P. nicotianae on tree lucerne in South Africa.     

Storage rot of swede caused by Phytophthora sp.

During long-term storage trials of swedes ( Brassica napus ) carried out during five seasons between 1982 and 1987, storage rots caused by a Phytophthora sp. were observed, the first report of the disease in the UK.     

The occurrence of Fusarium crown and root rot of tomato in Israel

Based upon symptomatology and the results of pathogenicity tests, it has been shown that the Fusarium crown and root rot organism of tomato — previously reported only from North America and Japan — is present in Israel.     

Evaluation of selective media and bait methods for estimating Phytophthora cactorum in apple orchard soils

Soil plating, with a specially devised selective medium, gave estimates of Phytophthora cactorum in an East Mailing Research Station apple orchard soil up to three times those obtained by dilution and baiting with apple seedlings or cotyledons and using the most probable number analysis.
When the same techniques were applied to a range of soils from apple orchards in south-east England with a history of P. cactorum diseases the plating method failed in most instances, mainly because Pythium spp. rapidly swamped the plates. The dilution/baiting method was applicable to all soils though there was a tendency to underestimate because of anomalous results at lower soil dilutions.
Oospores were the only propagules which could be confirmed as sources of P. cactorum colonies on soil isolation plates.     

The occurrence in Denmark of black root rot of pea caused by Thielaviopsis basicola

Thielaviopsis basicola has been shown to be a root pathogen of pea of considerable importance in Denmark. The fungus is only found in fields with one or more previous pea crops in the field history. In the dry and warm growing season of 1989 the fungus was found in 0·6% and 3·2% of the fields in two separate areas in Denmark. In the fields where T. basicola was detected the average disease severity index in plant samples was 51·8, whereas the average disease severity index in plant samples without the fungus was 27·0. The average yield of green peas was reduced from 5167 to 4171 kg/ha when T. basicola was present. For detection and isolation of T. basicola it is important to use a technique combining microscopic examination, a semi-selective medium and a dilution plate method.