Identification of tea foliar diseases and pest damage under practical field conditions using a convolutional neural network

Lesions of tea (Camellia sinensis) leaves are detrimental to the growth of tea crops. Their adverse effects include further disease of tea leaves and a direct reduction in yield and profit. Therefore, early detection and on-site monitoring of tea leaf lesions are necessary for effective management to control infections and prevent further yield loss. In this study, 1,822 images of tea leaves with lesions caused by three diseases (brown blight, Colletotrichum camelliae; blister blight, Exobasidium vexans; and algal leaf spot, Cephaleuros virescens) and four pests (leaf miner, Tropicomyia theae; tea thrip, Scirtothrips dorsalis; tea leaf roller, Homona magnanima; and tea mosquito bug, Helopeltis fasciaticollis) were collected from northern and central Taiwan. A faster region-based convolutional neural network (Faster R-CNN) was then trained to detect the locations of the lesions on the leaves and to identify the causes of the lesions. The trained Faster R-CNN detector achieved a precision of 77.5%, recall of 70.6%, an F1 score of 73.91%, and a mean average precision of 66.02%. An overall accuracy of 89.4% was obtained for identification of the seven classes of tea diseases and pests. The developed detector could assist tea farmers in identifying the causes of lesions in real time.     

Agricultural and Horticultural Fungicides - Past,Present and Future

Abstract

Maize is produced primarily in temperate and warm-temperate zones of the world, but its production is increasing in many tropical regions. Some diseases are common to both of these environmental zones even though their importance may vary greatly. Other diseases are confined to a single zone. The important factors influencing the geographical distribution of maize diseases and some of their vectors are temperature, moisture, cultural practices, and the type and diversity of maize germplasm used. Within tropical zones maize diseases may be segregated into those in humid environments and those favoured by drier, upland climatic conditions. Elevation within the tropics, as this influences temperature, is a factor in distribution of maize diseases.

Late wilt, banded leaf and sheath blight, and Rhizoctonia, Botryodiplodia and grey ear rots occur only in the tropical zone and the warm, temperate areas, while the Sclerospora-incited downy mildew diseases, southern rust, Pythium and bacterial stalk rots, Curvularia leaf spot, and ear rot caused by Diplodia macrospora are much more prevalent there, occurring only occasionally beyond latitudes 34°N and 34°S. Conversely, bacterial wilt, eye spot, and yellow leaf blight have been found to occur only in the temperate zones. Ergot has been found only in a few locations at high elevation (250–270 m) in Central Mexico. Northern leaf blight, common rust, and stalk and ear rots caused by Diplodia maydis and Gibberella zeae prevail in the temperate zones and at high elevations and in winter seasons within tropical latitudes.     

Diseases of the Oil Palm

Abstract

Thirty two diseases and disorders affecting the oil palm in Africa, Southeast Asia and South America are described with their distribution, economic importance, etiology and control. Of these, nine diseases are considered to be of major economic importance, 19 are of minor importance, and four are due to nutrient deficiencies. The major diseases causing serious economic losses are freckle (Cercospora elaeidis), blast (Pythium splendens and Rhizoctonia lamellifera), vascular wilt (Fusarium oxysporum f. sp. elaeidis). Ganoderma trunk rot (Ganoderma spp.) and Armillaria trunk rot (Armillariella mellea) in Africa; Ganoderma trunk rot, Corticium leaf rot (Corticium solani). Marasmius bunch rot (Marasmius palmivora) in S.E. Asia; sudden wilt and spear rot in S. America. Some of the diseases and disorders of minor economic importance recorded in these areas are anthracnose (Botryodiplodia palmarum, Melanconium sp. and Clomerella cingulata), dry basal rot (Ceratocystis paradoxic), patch yellows (Fusarium oxysporum), crown disease, Cylindrocladium leaf spot (Cylindrocladium macrosporum), algal spot (Cephaleuros virescens), bronze streak, ring spot and little leaf in Africa; Curvularia leaf blight (Curvularia eragrostidis), Leptosphaeria leaf spot (Pestalotiopsis spp.) infectious chlorosis, upper stem rot (Phellinus noxius), stem wet rot, charcoal base rot in S.E. Asia and Leptosphaeria leaf spot and coconut wilt disease in S. America. Little is known, however, about the disease problems in the smaller but rapidly expanding oil palm growing areas of Thailand, Papua New Guinea, India and Sri Lanka. Infectious chlorosis, bronze streak and ring spot have a suspected virus etiology; little leaf, spear rot and stem wet rot are attributed to bacteria and leaf chlorosis, mid-crown yellowing, orange frond and hook leaf to nutrient deficiencies. The etiology of some minor disorders including brown germ, crown disease and several miscellaneous abnormalities is unknown.

Effective control measures, based on the application of various chemicals, have been devised for the leaf diseases but other than precautionary cultural operations, there are no such effective and practical control measures for the root and stem diseases. For this latter group of diseases field transplanting or resistant or tolerant varieties seems to be the best method of control. Seeds selected for tolerance to vascular wilt are being produced on a commercial scale at the Nigerian Institute for Oil Palm Research, Institut de Recherches pour les Huiles et Oleagineux in Ivory Coast and the Unilever Plantations in Cameroun Republic. These efforts need to be supplemented by breeding for resistance to the other major diseases.     

A survey of rice diseases in Bangladesh

Abstract

A survey conducted during 1979–81 in Bangladesh revealed 20 rice diseases, including two viral, two bacterial, 13 fungal, two nematode and one micronutrient deficiency problem. Of these diseases. 16 appeared as major during the period under report. The number of diseases were 17, 16 and 16 during the Boro. Aus and transplant Aman seasons, respectively, with 12 common in all three seasons. Thirteen diseases including bacterial blight, bacterial leaf streak, sheath blight, sheath rot, blast, brown spot, grain spot, stem rot and leaf scald were classified as major; and tungro, bakanae, cercospora leaf spot and zinc‐deficiency were classified as either major or minor, and were common to all regions. Diseases not common in all regions were stack burn, root knot, and ufra classified as major or minor, and false smut, seedling blight. Yellow dwarf and damping off which were always classified as minor. Diseases which were typical for Boro. Aus and transplant Aman seasons were seedling blight and damping off. Yellow dwarf, and false smut respectively. Aus the most humid and warmest season, and the coastal humid areas experienced more major diseases. Seasonal and regional differences in the disease incidence appeared related to agro‐climatic variations.     

Biological control of botrytis leaf blight of onion byGliocladium roseum applied as sprays and with fabric applicators

Gliocladium roseum (5×10⁶ conidia ml^–1) and chlorothalonil (Bravo 500) were compared in two field tests for effectiveness in suppressing leaf blight caused byBotrytis squamosa in cooking onions. The biological control agent and fungicide were applied with sprayers and with specially designed fabric applicators that were mounted interchangeably on an aluminium carriage with bicycle wheels. In the applicators, inoculum and fungicide gravitated from a reservoir down curtains of denim strips and onto portions of onion leaves contacted by the strips. Initial applications were timed using a leaf blight forecasting system (BOTCAST) and three or four subsequent applications were made at weekly intervals. When compared to water checks,G. roseum applied as sprays or by applicators reduced density of leaf spots by about 50–58% during middle and late stages of epidemics. The antagonist was about half as effective as chlorothalonil in suppressing density of spots, regardless of application method. The applicators delivered inoculum in similar densities to proximal and distal halves of leaves, and used at least 35% less volume of inoculum compared to the sprayers. Density of inoculum on leaves treated by applicators was about the same as in spray-treated leaves when canopies were sparse, but less when canopies were dense. It is concluded thatG. roseum has good potential for controlling leaf blight sufficiently to avoid economic yield losses.     

The effect of Cryphonectria parasitica on water relations of American chestnut

Chestnut blight has commonly been regarded as a phloem disease due to conspicuous stem cankers that result from infection by the fungal pathogen Cryphonectria (Endothia) parasitica. Stomatal conductance (g_s), transpiration rate (E) and leaf water potential were measured throughout the day on leaves distal to naturally-occurring virulent (sunken bark with abundant stromata) or hypovirulent (swollen bark lacking stromata) cankers and cankers induced by inoculation with virulent or hypovirulent strains of C. parasitica. Relative to control stems, hydraulic conductivity (K_h), g_s and E were reduced significantly (α = 0·05) for both natural virulent cankers, and cankers that were induced by a virulent strain. These effects were less pronounced for both natural and induced hypovirulent cankers. Isolation experiments revealed that the percentage of xylem tissue chips yielding C. parasitica was greater for virulent than for hypovirulent cankers. The data provide evidence that the localized presence of C. parasitica in cankers of American chestnut results in stomatal closure, possibly as a direct result of xylem dysfunction.     

First report of coriander leaf blight diseases caused by Cladosporium tenuissimum in China and analysis of metabolic alterations related to pathogenic processes

Coriander (Coriandrum sativum) is a medicinal and aromatic plant. From November 2017 to March 2020, leaf blight disease on coriander plants was frequently observed in commercial coriander cultivated fields of Haikou, Sanya and Wanning City, Hainan Province, China. Leaves with symptoms showed irregular chlorotic to dark brown necrotic lesions at the edges of leaves, and the leaves were curled and covered with a layer of grey mould. Based on morphological characteristics, pathogenicity testing and concatenated sequences of the internal transcribed spacer region (ITS), actin (ACT) and translation elongation factor-1α (TEF) genes, the pathogen was identified as Cladosporium tenuissimum. Untargeted metabolomes of the coriander leaves were analysed by gas chromatography-mass spectrometry (GC-MS). Score plots of principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) showed clear discrimination between infected and control treatments. The levels of l -threonic acid, hexadecanoic acid and myo-inositol in the control treatment were 3.45-, 1.81- and 2.44-fold, respectively, those in the infected treatment. To our knowledge, this is the first report of C. tenuissimum causing coriander leaf blight disease in China. Furthermore, this study indicates that C. tenuissimum infection of coriander causes a significant decrease in l -threonic acid, hexadecanoic acid and myo-inositol levels, indicating that these metabolites may be involved in the plant's response to coriander leaf blight disease.     

A new bacterial leaf blight disease of oat (Avena sativa) caused by Pantoea agglomerans in China

A new leaf blight disease of oat (Avena sativa) was observed in many oat fields in Huan county, Gansu Province of China, during 2018–2019. Typical symptoms appeared as yellow necrotic and water-soaked lesions. The lesions developed from tip to base of leaves and eventually resulted in leaf withering. Disease incidence on plants (leaves) was approximately 36%–100%. A gram-negative bacterium was isolated from the necrotic lesions of all samples. Coupled with multigene sequence (16S rRNA and gyrB gene) analyses, Biolog Gen III MicroStation, morphological, physiological, and biochemical characterization identified the pathogen as Pantoea agglomerans. Pathogenicity tests by wounding and injection inoculations in the greenhouse established that P. agglomerans could induce typical symptoms as observed in the field. The infection rate in leaves was 44%–71% after 14 days. In addition, host range tests showed that P. agglomerans could infect other plant hosts, including Sorghum sudanense, Medicago sativa, Fagopyrum esculentum, Setaria italica, and Zea mays. This is the first report of P. agglomerans causing bacterial leaf blight disease (LBD) on oat in China. The current study can provide a foundation for the prevention of this disease in the future.     

水稻白叶枯病杂草带菌和传病的研究

水稻白叶枯病自发现到现在已有90年的历史。由于发生地区广泛,为害严重,各国对此病曾做了大量研究。日本对它已研究了半个多世纪,我国也有二十多年的研究经历。但对其侵染来源和传播途径,仍有不同看法。我国最初认为种子传病是首要的。但在病区单抓种子处理还不能收到预期效果,又认为病稻草是病区次年的主要菌源。近年来,又发现在严格处理病革、病种子的情况下,仍然发病,故怀疑除上述两种传播途径外,还有其它传播途径。关于杂草传病问题,日本已进行了多年的研究,但和我国国内一样,对杂草带菌传病问题,意见很不一致。我们认为对这一传播途径有彻底弄清的必要,它不仅关系到一个病的侵染循环问题,而且直接关系到对白叶枯病的彻底防治。如果这一传播途径确实存在,我们若不承认它,在防治上就会出现大的漏洞。如果白叶枯病确与杂草无关,盲目地采用相应的措施,也是多余而毫无意义的。这次试验是采用较直接的“离心浓缩针刺接种法”,其结果:第一年证实有马唐等六种杂草、黄豆和水稻根部能够带菌;第二年证实有车前等三种杂草和水稻根不仅带菌,而且可越冬并存活到次年五月;第三年又证实在不同地区有马唐,狗牙根等四种杂草能够带菌越冬,并存活到次年五月中旬。另外,用病区杂草和水稻健苗混栽,结果稻苗上发病,而对照的不发病。通过三年来的试验研究,证实有数种杂草的根茎部不仅带菌,而且能传病。     

A broad diversity survey of Rhizoctonia species from the Brazilian Amazon reveals the prevalence of R. solani AG-1 IA on signal grass and the new record of AG-1 IF on cowpea and soybeans

Leaf blight, sheath blight, and web blight are major diseases caused by Rhizoctonia species on both Fabaceae and Poaceae plant hosts in the Brazilian Amazon agroecosystem. To determine the diversity of Rhizoctonia species associated with foliar diseases on fabaceous (cowpea and soybean) and poaceous (rice and signal grass [Urochloa brizantha]) hosts, a broad survey was conducted in Pará, Rondônia, Roraima, and Mato Grosso, in the Amazon, from 2012 to 2013. We extended our survey to Cerrado areas of Mato Grosso, and the lowlands of Paraíba Valley, in São Paulo, where these Rhizoctonia foliar diseases have not been reported so far. Our findings revealed that these diseases are caused by a diversity of Rhizoctonia solani AG-1 complex. We detected that R. solani AG-1 IA (sexual phase Thanatephorus cucumeris) was the predominant pathogen associated with signal grass leaf blight and collar rot diseases in the Amazon, especially in Rondônia and northern Mato Grosso. In addition, a subgroup of R. solani (AG-1 IF), not previously reported in Brazil, was associated with leaf blight on cowpea and soybean, in Roraima. Another subgroup (AG-1 ID) was also detected in Roraima. In Mato Grosso Cerrados we did not find any of the major Rhizoctonia foliar pathogens. Instead, R. oryzae (Waitea circinata) was the predominant species associated with a collar rot on U. brizantha. In the lowlands of São Paulo, R. oryzae-sativae (Ceratobasidium oryzae-sativae) was the predominant pathogen detected causing the rice sheath spot disease.     

Maize resistance to northern corn leaf blight is potentiated by nickel

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum, is one of the most devastating diseases affecting maize yield worldwide. A foliar spray of nickel (Ni) to potentiate maize resistance against NCLB was investigated by examining alterations in the photosynthetic apparatus (leaf gas exchange and chlorophyll [Chl] a fluorescence parameters), production of ethylene and reactive oxygen species as well as activities of defence and antioxidant enzymes. Mycelial growth of E. turcicum was inhibited by Ni in vitro. Inoculated plants sprayed with Ni exhibited higher foliar Ni concentration, reduced NCLB symptoms, and lower concentrations of malondialdehyde and hydrogen peroxide. In inoculated leaves of plants not sprayed with Ni, concentrations of Chl a, Chl b, and carotenoids were lower and the photosynthetic apparatus was impaired at the biochemical level due to high NCLB severity. The activities of antioxidant enzymes were not affected by Ni, except an increase in glutathione reductase activity for noninoculated plants sprayed with Ni. High lipoxygenase and polyphenoloxidase activities, lower ethylene production, as well as elevated production of phenolics and lignin helped decrease NCLB severity in the leaves of Ni-sprayed plants.     

Characterization of Lasiodiplodia species causing leaf blight,stem rot and fruit rot of fig (Ficus carica) in Malaysia

Fig (Ficus carica) is an exotic deciduous plant that is grown worldwide. Fungal diseases pose a major threat to fig plants, affecting their fruit quality and production. This study was conducted to characterize the fungal isolates associated with leaf blight, stem rot and fruit rot of F. carica in Malaysia through morphological analysis, DNA sequencing, multigene phylogenetic analysis and pathogenicity tests. From September 2018 to March 2019, 30 blighted leaves and 30 rotted stems and fruits of F. carica were collected from several nurseries in Malaysia. Thirty fungal isolates that belonged to Lasiodiplodia theobromae (27 isolates) and L. brasiliensis (three isolates) were identified based on morphological characteristics, comparison of DNA sequences and phylogenetic analysis of the internal transcribed spacer (ITS), elongation translation factor 1-α (tef1-α), β-tubulin (tub2) and DNA-directed RNA polymerase II subunit (rpb2). Among the 27 isolates of L. theobromae, nine isolates were obtained from leaves, eight isolates from stems and 10 isolates from fruits, whereas the three isolates of L. brasiliensis were obtained from stems (two isolates) and a leaf (one isolate). The results of pathogenicity tests revealed that L. theobromae and L. brasiliensis isolates were responsible for leaf blight and stem rot of F. carica, whereas fruit rot was caused by L. theobromae isolates. The present study highlighted two different species, L. theobromae and L. brasiliensis, as the causal agents of leaf blight and stem rot of F. carica. Additionally, L. theobromae caused fruit rot of F. carica in Malaysia.     

First report of leaf blight disease of <Emphasis Type="Italic">Gloriosa superba</Emphasis> L. caused by <Emphasis Type="Italic">Alternaria alternata</Emphasis> (Fr.) Keissler in India

Leaf blight disease was found on Gloriosa superba L. (Liliaceae), an endangered, herbaceous, perennial, climbing lily that produces colchicine, in West Bengal, India in 2004. Small brownish spots on leaves developed into concentric rings, which eventually darkened and coalesced to blight the entire leaf. The causal fungus was morphologically identified as Alternaria alternata (Fr.) Keissler. This is the first record of A. alternata on G. superba.     

The Recent Spread of Some Tropical Plant Diseases

Abstract

The recent spread of coffee rust, sugarcane rust, black leaf streak of banana and Alternaria blight of wheat are recorded and the implications of new disease records are discussed.     

布朗李叶枯病病原鉴定及药剂筛选

布朗李叶枯病在湖南布朗李树上一般株发病率为20％～35％,叶发病率10％～25％,病情指数10～25;严重地区株发病率达100％,叶发病率50％～70％,病情指数25～35。病原菌为Macrophoma kawatsakai Hara。病菌从叶尖或叶缘侵入,形成叶枯或半圆形的病斑。实验室药剂筛选证实,抑制该菌菌丝生长效果良好的化学药剂有:70％代森锰锌可湿性粉剂、40％菌克星可湿性粉剂、50％退菌特可湿性粉剂、55％疫霜锰锌可湿性粉剂、80％新万生可湿性粉剂等;抑制孢子萌发效果良好的化学药剂有:70％代森锰锌可湿性粉剂、55％疫霜锰锌可湿性粉剂、50％退菌特可湿性粉剂、80％新万生可湿性粉剂、70％甲基硫菌灵可湿性粉剂、45％石硫合剂可湿性粉剂等。     

Integrated management of late leaf spot and rust diseases of groundnut (Arachis hypogaea L.) with Prosopis juliflora leaf extract and chlorothalonil

Abstract

Late leaf spot (LLS, Phaeoisariopsis personata) and rust (Puccinia arachidis) are the two major biotic constraints of groundnut (Arachis hypogaea L.) of global importance. To identify economic and eco-friendly disease management options, we evaluated extracts of 38 plant spp. of 23 families, for their antifungal activity. Aqueous leaf extracts (20%, w/v) of Prosopis juliflora and Lycopersicon esculentum completely inhibited the in vitro germination of P. personata and P. arachidis, and extracts of Achras sapota, Cyamposis tetragonolobus, Piper betle and Tagetus patula were inhibitory by >95%. In the greenhouse, the severity of LLS and rust corresponded with the time interval between the foliar application of leaf extract and fungal inoculum. Extract of P. juliflora (2%, w/v) in simultaneous application reduced the lesion frequency of LLS and rust by ～75%, and 35.7% and 50.7% in a prophylactic spray of 96 h before the pathogen inoculation. The extract had no effect on the phenolic content of groundnut leaves both during LLS and rust infections. In the field, P. juliflora extract applied four times at 15-day intervals, was effective against LLS and rust up to 95 days after sowing (d.a.s.). Foliar application of P. juliflora extract at 45, 75 and 90 d.a.s. and chlorothalonil at 60 d.a.s. effectively reduced foliar diseases severity and increased the pod yields by 81–98%. This study identified P. juliflora extract as a significant component for the integrated management of groundnut foliar diseases.     

Role of ascospores and conidia in the initiation and spread of South American leaf blight in a rubber tree plantation

Microcyclus ulei, the fungus causing South American leaf blight (SALB) on rubber tree leaves, produces two main types of spores: ascospores and conidia. To assess their respective epidemiological role, a field experiment was conducted in French Guiana over 3 years. Tree phenology, disease severity and climate variables were recorded while airborne spores were trapped and quantified. Ascospores were shown to play an essential role in the perpetuation of the disease outside the host's growth periods, in the resumption of epidemics, and in the spread of the disease to disease‐free zones. Conidia were trapped in visibly infected plots only, during periods of host growth. Disseminated over short distances and present only temporarily on leaves, the conidia enabled the disease to spread stepwise when the climate was conducive. Segmentation analysis revealed that the duration of high relative humidity was the climatic variable most related to ascospore trapping. Ascospore release did not require low temperatures. Considering the essential role of the ascospores in the initiation and spread of disease, artificial defoliation as a means of reducing the inoculum pressure during tree refoliation is proposed to control SALB. To check the validity of this method, a survey over several years of natural defoliation–refoliation in relation to climate and other leaf diseases is needed.     

Pathogenicity and toxigenicity of <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> isolates collected from maize roots,stems and ears in South Africa

Sunflower (Helianthus annuus L.) is an important oilseed crop in South Africa, and is grown in rotation with maize in some parts of North West, Limpopo, Free State, Mpumalanga and Gauteng provinces. Alternaria leaf blight is currently one of the major potential disease threats of sunflower and is capable of causing yield losses in all production regions. Alternaria helianthi was reported as the main cause of Alternaria leaf blight of sunflower in South Africa; however small-spored Alternaria species have been consistently isolated from leaf blight symptoms during recent surveys. The aim of this study was to use morphological and molecular techniques to identify the causal agent(s) of Alternaria blight isolated from South African sunflower production areas. Alternaria helianthi was not recovered from any of the sunflower lesions or seeds, with only Alternaria alternata retrieved from the symptomatic tissue. Molecular identification based on a combined phylogenetic dataset using the partial internal transcribed spacer regions, RNA polymerase second largest subunit, glyceraldehyde-3-phosphate dehydrogenase, translation elongation factor and Alternaria allergen gene regions was done to support the morphological identification based on the three-dimensional sporulation patterns of Alternaria. Furthermore, this study aimed at evaluating the pathogenicity of the recovered Alternaria isolates and their potential as causal agents of Alternaria leaf blight of sunflower. Pathogenicity tests showed that all the Alternaria alternata isolates tested were capable of causing Alternaria leaf blight of sunflower as seen in the field. This is the first report of A. alternata causing leaf blight of sunflower in South Africa.     

Effect of SS-toxin,a metabolite of <Emphasis Type="Italic">Stemphylium solani</Emphasis>, on H<Superscript>+</Superscript>-ATPase activity and standard redox system in plasma membranes from seedlings leaves of garlic (<Emphasis Type="Italic">Allium sativum</Emphasis>)

Leaf blight of garlic (Allium sativum) is a severe disease in garlic-growing regions. SS-toxin is a newly described non-proteinaceous toxin produced by the phytopathogenic fungus, Stemphylium solani, the cause of garlic leaf blight. In this study, the effects of SS-toxin on the H⁺-ATPase activity and standard redox activity in the plasma membranes isolated by aqueous polymer two-phase partitioning from garlic seedling leaves were studied in vitro. The H⁺-ATPase activity, NADH oxidation rate and Fe(CN)₆³⁻ reduction rate of the plasma membranes isolated from susceptible and resistant cultivars were all inhibited in a dose-dependent manner. Our results suggest that, under in vitro conditions, the plasma membrane H⁺-ATPase and standard redox system can be both the cellular targets of SS-toxin.     

Accumulation and distribution of pp′-DDT and related compounds in an apple orchard. II. Residues in trees and herbage

DDT residues in or on the roots and leaves of the herbage and the roots, bark, leaves and fruit of the trees are given for an apple orchard sprayed annually (1953–1969). The distribution of DDT in both the grass and the grass roots was in circular areas of residues, with maximum values at each trunk and decreasing radially to each alley. Of the spray applied at the green cluster stage 80% was deposited on the grass sward and very little, if any, directly on the soil surface. The pp′-DDT content of the grass fell rapidly with successive mowings (from which the cuttings remained in situ) from 400 μg/g at spraying to 2 μg/g after nine months. 33 g/ha pp′-DDT was found in the herbage roots (0.87% of the total residues in the soil). The residues in the bark (87.5 g/ha) were much lower than expected after 13 years spray application. There were increased amounts of pp′-DDE, pp′-TDE and pp′-TDEE relative to pp′-DDT, indicating some breakdown on the bark, but the chief losses were attributed to volatilisation and to removal by wind and rain. The residue content of root bark varied from 3 μg/g near the emerging trunk to 0.05 μg/g at a depth of 90 cm. The pp′-DDT content of leaves at leaf fall rose from <1 ng/g after a single spring spray to 8.33 μg/g following an additional spray in late June. There was a large loss of DDT from the canopy between the June spray and leaf fall (440–480 g/ha down to 25 g/ha), attributed to volatilisation. The amount of pp′-DDT on the fruit, after a single spray, was 3 ng/g fresh weight (80.9 mg/ha out of a total of 1.0–1.5 kg/ha used).