Browsing by Author "Nutman, F. J."
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Item Acute Die-back of Clove Trees in the Zanzibar Protectorate(Annals of Applied Biology, 1952) Nutman, F. J.; Roberts, F. M.; Clove Research Scheme, ZanzibarThe most widespread die-back of clove trees (Eugenia aromatica) in the Zanzibar Protectorate is caused by Cryptosporella eugeniae sp.nov. The most noticeable symptom is the death of a branch or a portion of a branch, or, in young saplings, of the entire tree; in mature trees infection eventually leads to the semi-moribund trees now common in almost every clove plantation. The fungus invariably enters through a wound, most often one resulting from harvest damage. Pycnidia, and later perithecia, develop near the point of entry. Internally the infected wood is clearly distinguishable from the healthy by a dark red-brown stain.Item Climatic Conditions in Relation to the Spread of Coffee Berry Disease since 1962 in the East Rift Districts of Kenya(1969) Roberts, F. M.; Nutman, F. J.This paper offers an explanation for the sudden extension in range of coffee berry disease in East Rift districts of Kenya after 1961. The spread was into lower-altitude districts which had previously been disease-free. Climatic conditions in the East Rift before and after 1961 are considered in relation to the known moisture and temperature requirements of the causal agent with the object of finding whether changes in these are adequate to account for the new situation.Item Climatic Conditions in Relation to the Spread of Coffee Berry Disease Since 1962 in the East Rift Districts of Kenya.(1969) Roberts, F. M.; Nutman, F. J.; E.A.A.F.R.O.This paper offers an explana1ion for the sudden extension in range of coffee berry disease in East Rift districts of Kenya after 1961. The spread was into lower-altitude districts which had previously been disease-free. Climatic conditions in the East Rift before and after 1961 are considered in relation to the known moisture and temperature requirements of the causal agent with the object of finding whether changes in these are adequate to account for the new situationItem Coffee Berry Disease(1970) Nutman, F. J.; E.A.A.F.R.O. KenyaCoffee Berry disease is caused by a mutant pathogenic strain of Colletotrichum coffeanum Noack which has spread throughout tropical Africa from its point of origin in Kenya. Fruit is attacked in all stages, and total destruction of the crop can be caused. The disease was confined for many years to the higher altitudes, because suitable conditions of temperature and humidity were infrequent in the lower ones. Following the inception of a wetter and cooler climatic phase in E. Africa in 1961, coffee in the lower altitudes is now attacked. Infection of the fruit is initially by infective conidia produced on the maturing wood of the twigs, where the pathogen "overwinters". When one crop only is on the tree, this inoculum is more important than that from lesioned fruit; but where a series of over-lapping crops is present, the reverse is the case. In the former situation control can be based on reduction of inoculum from the twigs: in the latter, however, this is ineffective, and control can only be achieved by a series of protective sprays. Varieties of coffee vary greatly in susceptibility to berry disease. No commercially acceptable variety is, however, completely resistant, although genetic material embodying resistance is available.Item Coffee Berry Disease: Epidemiology in Relation to Control(1969) Nutman, F. J.; Roberts, F. M.; East African Agriculture and Forestry Research Organization, KenyaIn many instances measures developed for the control of coffee berry disease in East Africa have become less effective since 1961. Changes in the flowering and fruiting patterns of the coffee tree have recently become evident, ascribed in part to the onset of a wetter and cooler climatic cycle in 1961-62, and in part to the effect of the disease itself which, by removing crop, stimulates out-of-season flowering. Consequently, instead of a single main crop in which susceptible and highly ineffective ripe berries are present for a short time only, a series of over-lapping crops results in ripe berries being on the trees for most of the year. This has changed the disease epidemiology: formerly the main source of infection was conidia from the maturing wood, but now conidia from the berries are often predominant. This has greatly affected the efficiency of control measures, and means are suggested for restoring the previous situation.Item The Effect of Fungicidal Treatments on Sporulating Capacity in Relation to the Control of Coffee Berry Disease(1969) Roberts, F. M.; Nutman, F. J.; East African Agriculture and Forestry Research OrganizationThe capacity of the maturing wood of the branches of Coffea arabica to produce conidia of Colletotrichum coffeanum Noack, the causal agent of coffee berry disease, is profoundly affected by fungicidal treatments. The effect differs according to the epidemiology of the disease. When the main source of inoculum is from the wood, the reduction in the sporulating capacity persists throughout the crop-season, and good control of the disease results. When the main source of inoculum is from diseased berries, reinfection of the branches takes place, the sporulating capacity of sprayed branches rises above that of unsprayed ones, and there is indifferent or no control. Evidence from field trials suggests that the correct timing of early season spray schedules may be related to the part of the annual rhythm of sporulating capacity at which they are applied. As this rhythm is determined by rainfall, and varies from year to year and from place to place, the correct time for the start of a schedule should be predictable from meteorological data.Item Foliar Nutrients in Relation to Coffee Berry Disease(1969) Nutman, F. J.; Roberts, F. M.In addition, to insecticidal and fungicidal sprays coffee trees in Kenya are often sprayed with foliar nutrients. These inevitably reach the fruit and, where berry disease is present, may affect the behaviour of the pathogen, or may interact with other chemicals.Item A Note on a Laboratory Technique for Testing Fungicides against Coffee Berry Disease(1970) Roberts, F.M.; Nutman, F. J.Many attempts have been made to evaluate fungicides in the laboratory for their possible use against coffee berry disease. For example, during the period 1957-58, the writers (unpublished data carried out a series of screening tests with over 20 fungicides, using the reduction in germination on both agar films and on berry surfaces; the reduction in formation of appressoria; and the reduction in lesion production on berries, all over a wide range of concentrations of the fungicides used. At the same time Bock (1963 was evaluating the field performance of some of these in an extensive series of comparative field trialsItem The Sudden-Death Disease of Cloves and Its Economic and Agricultural Significance(1951) Nutman, F. J.; Sheffield, F. M. L.; Swainson, O. S.; Winter, D. W.I. As the result of epidemiological evidence on the rate of spread of the Sudden-death disease of cloves in Pemba, the situation was thought sufficiently serious to justify an attempt to control the disease in advance of scientific proof of its aetiology. Although this attempt was eventually abandoned, many data were collected in preparation for it. This article reviews the history of the abortive control scheme, and discusses the data acquired. 2. From the results of a partial survey made in 1948 and another in 1949-50, there is an estimated total of over 2,000 separate outbreaks of disease in Pemba. These vary in size but average 25 dead trees. New outbreaks are constantly arising and the present annual rate of increase in number of outbreaks would seem to be about 14 per cent. Outbreaks increase in size at a highly variable rate but, on the average, the radial rate of spread is approximately constant. An attempt has been made to forecast the probable future development of the disease. 3. The effects of the disease on the economy of the Protectorate is discussed, and on the assumption that direct control is a practical impossibility suggestions are made for rehabilitation in Zanzibar Island, where up to the present the disease has caused much greater destruction than in Pemba. These are based on elimination of residual sources of disease in already devastated areas, followed by planned replanting with cloves and with other crops in order to achieve diversity.Item Valsa Eugeniae In Relation To the Sudden-Death Disease of the Clove Tree (Eugenia Aromatica)(1954) Nutman, F. J.; Roberts, F. M.The sudden-death disease of the clove tree is invariably associated with the fungus Valsa eugeniae. The pathogenicity of this fungus has been investigated experimentally, and it has been shown that it is a primary parasite on mature clove trees, that saplings are resistant to it, and that seedlings are immune. It has been experimentally demonstrated that water-borne spores of the fungus can invade the absorbing and the fibrous roots of the clove tree. The slow-decline disease, which affects clove saplings only, is associated with a slow and progressive root-rot over a period of many years. Valsa is also invariably associated with this disease, which occurs only in areas which have been replanted after the previous stand has been killed by sudden death. It is thought that slow decline is the symptom-expression of Valsa attack on young trees when these still retain some measure of juvenile resistance to it.
