Heavy Dew Research Articles

Potato Leaf Disease Prediction: A Machine Learning Perspective

Potato leaf disease has mostly two categories; early blight and late blight disease. The disease may be more prevalent in certain weather patterns and have a catastrophic effect on potato crops. In summary, warm, humid weather with frequent rain or heavy dew, temperatures between 15°C and 20°C, and a lack of sunshine are the weather conditions that can cause potato late blight. Drier weather conditions favour early blight, unlike late blight. Warm and dry weather with a lack of rain or irrigation, temperatures between 21°C and 29°C, and high humidity in the morning are the weather conditions that can cause potato early blight. A modified dataset is used for climate-influenced prediction, and the testing accuracy using random forest models is 97%. Analysis of experimental results shows that the suggested potato-leaf disease prediction based on the weather data framework outperforms the outcome of frameworks.

Incidence of Black Point on Wheat Seeds in Different Location of Uttarakhand, India

An experiment was conducted to determine the incidence of black point disease in wheat varieties with different locations caused by A. alternata fungal pathogens of wheat grain. Fresh seeds of popularly cultivated wheat varieties, preferably viz., GW 366, GW 496, Lok 1, and GW 1, were collected after harvesting season from the farmers’ fields of wheat growing areas of middle Uttarakhand viz., Sahaspur, Roorkee, Haridwar, and Dehradun. At least 50 samples were collected from each of the districts. Five primary samples were collected and mixed from the harvested seed lot to have composite samples. Working samples were prepared from composite samples by repeated halving method. The black point disease incidence might be due to the inherent boldness of the seeds. Florets remain more open in bold-seeded varieties, enhancing the chances of more seed infection during seed development. Moreover, low night temperatures during the flowering period, severe dew at the seed maturation stage, frequent and heavy crop irrigation, and excessive application of nitrogenous fertilizers may lead to a higher incidence of the black point disease. Besides, infected seeds reveal seed rot, necrosis, and shriveling. High humidity due to prolonged rainfall or heavy dew deposition during seed maturation favors the black point. As our research findings varied, GW366 is significantly the highest incidence of black point disease.

Effect of dew and spray volume on the efficacy of control of asulam on fall panicum (Panicum dichotomiflorum)

Asulam controls fall panicum (Panicum dichotomiflorum Michx.), the most troublesome annual grass weed in Florida sugarcane. This study was conducted to evaluate the effect of dew on asulam efficacy on fall panicum control when applied using different spray volumes. Fall panicum 30 cm tall with 0, 50, and 100% dew on leaves equivalent to no dew, moderate dew, and heavy dew, respectively, were treated with asulam at 3,700 g ha–1 using spray volumes of 94, 140, 187, and 281 L ha–1. Fall panicum control was rated 28 days after treatment, and aboveground biomass was harvested immediately. The presence or absence of dew and spray volume did not significantly influence asulam efficacy on fall panicum control and aboveground biomass accumulation. Fall panicum was controlled from 89% to 94% at the different dew levels and spray volumes. Heavy dew did not diminish the performance of asulam. The presence of dew on fall panicum foliage probably hydrated the cuticle and aided water-soluble asulam to remain in solution for a longer period, thereby enhancing uptake. The water-holding capacity of fall panicum foliage with the heavy dew and spray volumes was probably not exceeded, resulting in no runoff and no subsequent reduction of control. These results indicate that dew deposition under Florida conditions has no effect on asulam efficacy on fall panicum 30 cm tall or less when applied at commonly used spray volumes of 140 and 187 L ha–1.

AscotraceR: An R Package Resource to Simulate the Spatiotemporal Spread of Ascochyta Blight in a Chickpea Field Over a Growing Season.

ascotraceR: An R Package Resource to Simulate the Spatiotemporal Spread of Ascochyta Blight in a Chickpea Field Over a Growing Season.

Investigating the role of evaporation in dew formation under different climates using 17O-excess

With increasing aridity in many regions, dew is likely to play an increasingly important role in the ecohydrological processes in many ecosystems, especially in arid and semiarid regions. Few studies investigated the role of evaporation during dew formation and how it varies under different climate settings. 17O-excess, as a new tracer, could be used to extract information of evaporation dynamics from natural water samples (e.g., precipitation, river, and lake). Therefore, to fill the knowledge gap in evaporation mechanisms during dew formation, we report the isotopic variation (δ2H, δ18O, δ17O, and 17O-excess) of dew and precipitation from three distinct climatic regions (i.e., Gobabeb in the central Namib Desert, Nice in France with Mediterranean climate, and Indianapolis in the central United States with humid continental climate). We examined whether dew formed in different climate settings was affected by different degree of evaporation using observed isotopic values and evaporation models during the formation processes, and modeled the effects of key meteorological variables (i.e., temperature and relative humidity) on 17O-excess variations. The results showed that dew in Gobabeb experienced kinetic fractionation associated with evaporation under non-steady state conditions during dew formation with enriched δ18O and low 17O-excess values. Dew formations with temperatures over 14.7 °C in Indianapolis were also influenced by evaporation under non-steady state conditions. However, dew formation in Nice did not experience significant evaporation. Evaporation processes (equilibrium or kinetic fractionation) occurring during nights with heavy dew under three climate settings were mainly related to the variation of atmosphere relative humidity. The 17O-excess tracer provides a new method to distinguish the different evaporation processes (equilibrium or kinetic fractionation) during dew formation and our result provides an improved understanding of dew formation.

Review of the Current Forage Production, Supply, and Quality Measure Standard in South Korea

Cattle feeding in South Korea has been heavily dependent on domestically produced rice straw and imported grain. Around 42% of domestically produced rice straw is utilized for forage, and the remainder is recycled to restore soil fertility. Approximately 35% of round baleages were made with rice straw. However, higher quality hay is desired over rice straw. Due to increasing stockpiles of rice, there has been an economic burden on the government to store the surplus; therefore production of annual forage crops in rice fields has been further promoted in recent years. Hay import from the USA currently constitutes more than 80% of total imported hays. The main imported hays are alfalfa (Medicago sativa), timothy (Phleum pretense), and tall fescue (Festica arundinacea). The estimated forage required for cattle feeding was approximately 5.4 million MT in 2016. Domestically produced forage sates only 43% of that value, while low quality rice straw and imported hay covered the rest of demand by 33% and 20%, respectively. As utilization of domestically produced forage is more desirable for forage-based cattle production, long-term strategies have been necessary to promote domestic production of high quality baleage. One such strategy has been utilizing the fertile soil and abundance of fallow rice fields of western region of S. Korea to produce forage crops. Italian ryegrass (Lolium multiflorum) is the most successfully produced winter annual in the region and is approximately 56% of the total winter annual forage production. Forage sorghums (Sorghum bicolor), sorghum × sudangrass hybrids, and hybrid corn (Zea mays) produce a substantial amount of warm-season forage during summer. Produced forage has been largely stored through baleage due to heavy dew and frequent rains and has been evaluated according to S. Korea’s newly implemented baleage commodity evaluation system. The system weighs 50% of its total grading points on moisture content because of its importance in deliverable DM content and desirable baleage fermentation; this has proved to be an effective method. Although further improvement is required for the future of forage production in South Korea, the current government-led forage production in rice fields has been able to alleviate some of the country’s shortage for quality hay.

New scientific knowledge in kiwifruit storage using sanitization systems (Ionny®) avoiding postharvest chemical treatments

Loss of produce during commercial kiwifruit storage is so high as to require the adoption of specific techniques and preventive measures. Postharvest curing techniques alone are not sufficient to guarantee valid economic results, particularly when fruits are harvested in high-humidity environmental conditions due to rain or heavy dew. The incidence of rot due to Botrytis spp. penetrating the pulp at the detachment point of the stalk can reach high percentages (10-20% of damaged fruit), and specific postharvest chemical treatment known as drenching is required. As verified in the past, an alternative to the use of chemicals, with air sanitation of the storage environment using an ionizer (Ionny®), is possible. Tests carried out during the 2016-17 season have confirmed the validity of this technique in CA storage conditions (-0.5/-0.7°C, RH>90%, CO2 3-4%, O2 2.5-3%, C2H4<0.02 ppm) alongside curing, with results comparable to those obtained using the chemical treatment fenhexamid in a drencher. A batch of ‘Hayward’ kiwifruit produced in the Trentino (Italy) area was divided into three groups: 1) treatment with fenhexamid + curing + CA; 2) curing + CA in an ionized environment; and 3) no treatment + curing + CA (TEST). The trial found over 15% of fruits infected with Botrytis spp. in group 3, and 100% healthy fruits in groups 1 and 2. These results, as well as confirming the outcome of previous trials, have also highlighted that group 2 (CA storage with air sanitized by Ionny®) produced the best results (firmness, total acidity) both at the end of storage and also after 8 d shelf-life at room temperature.

Dew measurement and estimation of rain-fed jujube (Zizyphus jujube Mill) in a semi-arid loess hilly region of China

Dew is an important water source for plants in arid and semi-arid regions. However, information on dew is scarce in such regions. In this study, we explored dew formation, amount, and duration of rain-fed jujube (Zizyphus jujube Mill) trees in a semi-arid loess hilly region of China (i.e., Mizhi County). The data included dew intensity and duration, relative humidity, temperature, and wind speed measured from 26 July to 23 October, 2012 and from 24 June to 17 October, 2013 using a micro-climate system (including dielectric leaf wetness sensors, VP-3 Relative Humidity/Temperature Sensor, High Resolution Rain Gauge, and Davis Cup Anemometer). The results show that atmospheric conditions of relative humidity of >78% and dew point temperature of 1°C–3°C are significantly favorable to dew formation. Compared with the rainfall, dew was characterized by high frequency, strong stability, and long duration. Furthermore, heavy dew accounted for a large proportion of the total amount. The empirical models (i.e., relative humidity model (RH model) and dew point depression model (DPD model)) for daily dew duration estimation performed well at 15-min intervals, with low errors ranging between 1.29 and 1.60 h, respectively. But it should be noted that the models should be calibrated firstly by determining the optimal thresholds of relatively humidity for RH model and dew point depression for DPD model. For rain-fed jujube trees in the semi-arid loess hilly regions of China, the optimal threshold of relative humidity was 78%, and the optimal upper and lower thresholds of dew point depression were 1°C and 5°C, respectively. The study further demonstrates that dew is an important water resource that cannot be ignored for rain-fed jujube trees and may affect water balance at regional scales.

Enhanced Pest Ant Control With Hydrophobic Bait.

The red imported fire ant, Solenopsis invicta (Buren), left most of its natural enemies behind in South America when it arrived in Mobile, AL, in the 1930s and spread rapidly throughout the southeastern United States, reaching population levels up to 10 times those found in South America. The large population densities and propensity for disturbed habitats led to direct conflict with human activities. Bait control methods were first developed for fire ants in the early 1960s and little has changed in the subsequent decades, despite the drawback that the bait carrier rapidly breaks down when wet. The southeast United States is wet; thus, bait labels have various guidance-restricting applications based on potential wet conditions. Here we compare a hydrophobic fire ant bait to the equivalent standard bait formulation and demonstrate in a paired-mound field experiment under natural wet conditions in Florida (heavy dew on ground), a significant advantage for the hydrophobic bait. An effective hydrophobic ant bait would extend the utility of current bait insecticides to wet conditions and also fill an important gap in our ability to control invasive pest ant species that thrive in wet tropical and subtropical habitats, e.g., Wasmannia auropunctata (Roger), the little fire ant.

First Report of Dollar Spot of Sandbur Caused by Sclerotinia homoeocarpa in Oklahoma.

Sandbur (Cenchrus incertus Curtis) is a warm-season, annual, noxious, grassy weed native to southern North America. It is common in sandy, disturbed soils and can also be found in home lawns and sport fields where low turf density facilitates its establishment. In July 2013, after a period of frequent rainfall and heavy dew, symptoms of dollar spot-like lesions (1) were observed on sandbur plants growing in a mixed stand of turf-type and native warm-season grasses in Logan County, Oklahoma. Lesions, frequently associated with leaf sheaths, were tan and surrounded by a dark margin. Symptomatic leaves were surface sterilized and plated on potato dextrose agar amended with 10 ppm rifampicin, 250 ppm ampicillin, and 5 ppm fenpropathrin. After incubation, a fungus morphologically identical to Sclerotinia homoeocarpa Bennett was consistently isolated. The nuclear ribosomal internal transcribed spacer (ITS) region of two different isolates, SCL2 and SCL3, were amplified using primers ITS4 and ITS5 (2). The DNA products were sequenced and BLAST analyses were used to compare sequences with those in GenBank. The sequence for isolate SLC2 was 869 bp, contained a type I intron in the 18S small subunit rDNA, and was identical to accession EU123803. The ITS sequence for isolate SLC3 was 535 bp and identical to accession EU123802. Twenty-five-day-old seedlings of C. incertus were inoculated by placing 5-mm-diameter agar plugs, colonized by mycelia of each S. homoeocarpa isolate, onto two of the plants' leaves. Plugs were held in place with Parafilm. Two plants were inoculated with each isolate and sterile agar plugs were placed on two leaves of another seedling as control. Plants were incubated in a dew chamber at 20°C and a 12-h photoperiod. After 3 days of incubation, water-soaked lesions surrounded by a dark margin appeared on inoculated plants only. Fungi that were later identified as S. homoeocarpa isolates SLC2 and SLC3 by sequencing of the ITS region were re-isolated from symptomatic leaves, fulfilling Koch's postulates. To our knowledge, this is the first report of dollar spot on sandbur.

Coordinated Mass Movements of Blow Fly Larvae (Diptera: Calliphoridae)

I watched blow fly (Diptera: Calliphoridae) larvae in western Maine that had consumed six animal carcasses so that I could identify patterns relating to when, how, and why they left the carcasses. The blow fly larvae stayed under the carcasses on hot, dry days, and then left them on rainy nights, traveling in random directions. Following several rainless days, the larvae left the carcasses at dawn on days with heavy dew and proceeded in a single 1-2-cm-wide column directly toward the rising sun. Species composition of one larvae column was nearly all or exclusively Phormia regina.

Inheritance of blast resistance and identification of SSR marker associated with it in rice cultivar RDN 98-2

An F2 population was developed from a cross between rice (Oryza sativa L.) genotypes, EK 70 (highly susceptible to blast) and RDN 98-2-3-5-14 (resistant to blast), to study the inheritance of blast resistance and to identify the marker associated with resistance. The F2 population segregated in 3:1 ratio for resistance: susceptible under hot spot conditions for blast suggesting monogenic control of resistance in this population. Bulk segregant analysis conducted using a total of 25 SSR markers identified two SSRs to be polymorphic between the parents and the corresponding bulks. One of these SSR markers RM204 which has been reported to be mapped on the short arm of chromosome 6 and in close proximity of blast resistance gene/QTLs in other studies showed expected segregation ratio (1:2:1) for single gene model in the F2 population. This marker was found significantly associated with blast resistance on regression analysis. Rice is the world’s largest food crop, providing caloric needs to millions of people daily. Rice suffers attack by a large number of pests and pathogens, which under epidemic conditions, cause serious yield losses. Among these, rice blast caused byMagnaporthe grisea (Hebert) Barr. (Barr 1977), synonym M. oryzae is one of the most devastating and destructive diseases of rice worldwide. Under heavy dew, arial plant parts are affected, leaf surface becomes speckled with oval lesions and plants are liable to lodging if nodes are infected. If the panicles are infected, it also results in severe yield losses (Ou 1985). Resistance to the M. oryzae is a classic gene-for-gene system, where a major resistance gene is effective against

Occurrence of False Smut on Date Palm (Phaenix dacyilifera L.) in the Southern Coastal Plain of Yemen

Twelve date palm cultivars were evaluated for resistance to Graphiola leaf spot caused by Graphiola phaenicis (Moug) poit. The disease incidence and number of sori were compared on both surface of leaf, pinnae position on leaves and plant age. Cultivars Gizaz, Tha'al and Khodari showed negligable infection and fewer number of sori on the leaf surface and rachis. Symptom of disease was absent on leaves and rachis in cultivar Sagaee. These cultivars differed significantly from susceptible cultivars Shahree, Soqotree and Khalas (P = 0.01). Abundant distribution of sori caused a drastic reduction of the leaf area covered by the fungus. Adaxial leaf surface trapped more number of sporidia and significant differences were detected among test cultivars (P = 0.05). The temperature ranging between 32°C-38°C in summer and humidity accompanied by heavy dew in the night and early morning favored the development of infection. Correlation of age on cultivar

Mango diseases in Egypt

Mango diseases in Egypt

First Report of Dollar Spot of Seashore Paspalum (Paspalum vaginatum) Caused by Sclerotinia homoeocarpa in South China.

Seashore paspalum (Paspalum vaginatum Swartz), a warm-season perennial grass, is native to tropical and subtropical regions of North and South America (1). Its fine texture and tolerance to low mowing and hypersaline environments make it a commercially promising turfgrass species for coastal regions of south China. In late March 2009, disease symptoms were observed from two golf course fairways in Shenzhen and Foshan, Guangdong Province, China. Small, round patches from 25 to 75 mm in diameter were found to be consisting of bleached, straw color leaf lesions bounded by reddish brown margins. Similar patches had previously been observed on seashore paspalum since 1997 in Guangdong Province, but this turf species has been grown in southern China only since the early 1990s. These symptoms were observed when daytime temperatures were above 25°C and with heavy dew formation at night. Greatest severity was seen in the spring and fall. Several contact and systemic fungicides were applied after first symptoms were observed and they were usually successful in suppressing disease. To confirm the disease as dollar spot, isolates from Shenzhen and Foshan were obtained by plating diseased leaf blades of P. vaginatum (cv. Salam) on potato dextrose agar media. Isolates produced white, fluffy, aerial mycelium, columnar when mature, and usually with a cinnamon base and dark brown or black substratal stroma on and in the agar. One representative isolate from each location was chosen for pathogenicity testing. Six-week-old P. vaginatum (cv. Salam) grown from seed in pots was inoculated, with 5-mm-diameter agar plugs with hyphae from 5-day-old cultures, by direct placement onto leaves and with three replicate pots per isolate. Plants treated with sterile agar plugs served as controls. Inoculated turf was incubated at 25°C with 12-h light/dark conditions. A plastic film was also placed over the pots to retain moisture. Chlorotic leaf lesions started to develop 4 days after inoculation and became a bleached straw color. The same fluffy, white fungus was reisolated from lesions, while no disease was observed on controls, thus completing Koch's postulates. The internal transcribed spacer (ITS) region of the ribosomal DNA was amplified from DNA extracted from two isolates using primers ITS5 and ITS4 (2), and the 610-bp sequences showed 98% similarity with Sclerotinia homoeocarpa F.T. Bennett in GenBank and have been deposited as Accessions GQ386985 and GU002301. Dollar spot on P. vaginatum has been commonly observed in the United States (1). To our knowledge, this is the first confirmed report of dollar spot on P. vaginatum in China or from any host plant in China.

The Use of an Orthotic Casting Foam as a Track‐Plate Medium for Wildlife Research and Monitoring

Track plates are an inexpensive, non‐intrusive and widely used wildlife monitoring tool. Almost all track‐plate media are not suited for use during rainy conditions, because rain or heavy dews can distort tracks or render the medium ineffective for registering further animal visitations. Furthermore, available track‐plate media may also produce tracks of varying quality and hard‐surfaced media produce inaccurate two‐dimensional imprints. We experimented with the utility of using Biofoam™, a phenolic foam used in orthotics, as a track‐plate medium. Domestic animals were utilized to produce track imprints on track plates constructed of casting foam, coarse sand, fine sand, very fine sand and sooted aluminum. Resulting tracks were photographed and images were used in a questionnaire which was completed by expert wildlife trackers who rated the quality of the tracks. Tracks in the casting foam are three‐dimensional, register claws, clearly depict all pads, accurately record shape and size, and convey very fine anatomical details. Track imprints on the casting foam were rated consistently better by experts than track imprints left on the other media. Field trials demonstrated that the casting foam and tracks in the casting foam can endure lengthy periods of inclement weather conditions in the field without being damaged or distorted. In summary, where three‐dimensional, high‐quality prints need to be recorded in variable field conditions, we recommend the use and further experimentation with track plates made of casting foam.

Dew frequency, duration, amount, and distribution in corn and soybean during SMEX05

Dew affects the brightness temperature of vegetation and backscatter from vegetation at microwave wavelengths. Must this effect be taken into account in order to avoid corrupting remotely sensed observations of important ecosystem variables such as soil moisture? As a first step towards answering this question, we report the frequency and duration of dew events, the total amount of dew in the canopy, and the distribution of dew within the canopy for two different types of crop canopy, corn and soybean, during SMEX05, a 21-day field experiment conducted during June and July, 2005, in Iowa, USA. We observed dew to be present more than 50% of the time in both corn and soybean at common satellite overpass times of 1:30 and 6:00 CST. Dew was most likely to be present between 12:00 and 6:30 CST, and as late as 9:00 CST. Two different methods to scale the liquid water measured on single leaves to the entire vegetation canopy produced similar results, and we observed dew amounts that were comparable, and in some cases higher, than those that have been shown to affect the microwave brightness temperature and backscatter. The distribution of dew within the canopy among the top and bottom of a leaf and (for corn) the leaf collar may influence its effect on remotely sensed measurements. We found that this distribution is different for light, moderate, and heavy dew events. A modeling approach will be necessary to estimate dew at larger spatial scales associated with satellite remote sensing. The Atmosphere–Land Exchange (ALEX) model, a land surface process model that accounts for both dewfall and distillation, produced estimates of dew amount and duration that were in agreement with manual observations and observations made with leaf wetness sensors.

Epidemiology of Fusarium head blight on small-grain cereals

Fusarium head blight (FHB) is one of the most serious diseases affecting wheat and barley worldwide. It is caused by Fusarium graminearum along with F. culmorum, F. avenaceum and other related fungi. These fungi also produce several mycotoxins. Though the disease results in reduced seed quality and yield, the toxins which may accompany the disease are often a more serious problem. Pathogen inoculum is usually very abundant, however production and dispersal of inoculum are weather-sensitive processes. An abundance of colonized substrate ( i.e. maize or cereal debris) in a region contributes to airborne inoculum throughout the area. Local residues beneath the cereal crop ( i.e. from previous crop) may have a less obvious effect, particularly in regions where long-distance dispersal is likely due to wind conditions. The host is most susceptible to infection at anthesis and shortly thereafter. A warm, moist environment characterized by frequent precipitation or heavy dew is highly favorable to fungal growth, infection and development of disease in head tissues. As the fungus grows, it produces mycotoxins which are water-soluble and may be translocated between tissues or leeched from source tissues. Important epidemiological issues have arisen recently and include an apparent shift in prevalence of Fusarium species on infected heads in Europe toward F. graminearum; and the presence of multiple chemotypes and aggressiveness variants within a species in a region.

Namaqualand—A brief overview of the physical and floristic environment

This paper provides a brief introduction to the physical environment of Namaqualand as well as an overview of patterns of plant diversity. The diverse array of parent material and geological processes that have shaped the region since the break up of Gondwanaland have created a complex, and sometimes dynamic physical environment, that is partly responsible for the patterns and processes observed in the biota today. The contemporary climate is characterised by relatively reliable, albeit low (50–250 mm pa), winter rainfall (>60% winter precipitation) arriving between May and September. East of the central mountains, tropical thunderstorms penetrate the region in late summer (February–April). The presence of the cold Atlantic Ocean in the west not only moderates temperatures throughout Namaqualand (mean max summer temperature <30 °C), but also provides alternative sources of moisture in the form of coastal fog and heavy dew experienced in winter months. Recent analyses show that the flora of the Succulent Karoo is part of the Cape Floral Kingdom, now termed the Greater Cape Floral Kingdom. It is one of only two desert regions recognised as a global biodiversity hot-spot and contains an estimated 6356 plant species in 168 families and 1002 genera. Namaqualand, which comprises about one quarter of the area of the Succulent Karoo, contains about 3500 species in 135 families and 724 genera, with about 25% of this flora endemic to Namaqualand. This remarkable diversity, however, is not distributed evenly throughout the region, but is concentrated in many local centres of endemism usually associated either with quartzite mountain complexes or lag-gravel plains (quartz-patches). A major exception to the general pattern of centres of diversity is the true Fynbos vegetation of the highest Kamiesberg peaks where rainfall exceeds 400 mm pa. Suggested determinants of the region's exceptional floral diversity include the complex physical environment, a unique past and present climate and the region's diverse fauna, most notably insects. The challenge for the current inhabitants and scientists working in the region is to develop a better understanding of this ecosystem so that they will be equipped to deal with the challenges posed by the demands for land and the prospect of global climate change.

Some epidemiological investigations on Colletotrichum leaf disease on rubber tree

The inoculum of some species of the genus Colletotrichum, responsible for the secondary leaf fall of rubber tree (SLF), is present as conidia on all the organs of the tree. On young lesions, the fungus produces acervuli, but on old lesions kept in prolonged wetness, conidia are produced without acervuli. Acervuli occur frequently on senescent tissues, especially on the epidermis of the fruits, which are infected in the early stages of their development. The fungus can spread from diseased organs to healthy organs and sporulate on them. Conidial production and pathogenicity differ greatly according to the organ of the rubber tree from which the fungus is isolated. The higher the leaf wetness duration and the inoculum concentration are, the greater are fungal sporulation and damage. Although heavy rains and high winds favour conidial dispersal, it can also occur in drizzle. Heavy dew is sufficient to ensure downward dispersal of the conidia. The epidemiological pattern of the disease in a rubber tree plot during 1.5 years agrees with all these observations. The results of these investigations will enable the control of the disease to be improved in the rubber estate of Mitzic (Gabon).