Showing papers on "Leaf spot published in 1994"

Managing Turfgrass Pests

Abstract: Turfgrass Weeds and Their Management (T.L. Watschke) Introduction Managing Summer Annual Grasses: Crabgrasses. Goosegrass. Foxtail. Barnyardgrass. Fall Panicum. Dallisgrass. Sandbur. Managing Winter Annual Grasses: Poa annua. Managing Perennial Grasses and Sedges: Creeping Bentgrass. Tall Fescue. Orchardgrass. Timothy. Smooth Brome. Quackgrass. Nimblewill. Bermudagrass. Zoysiagrass. Nutsedge. Rescuegrass. Managing Summer Annual Broadleaf Weeds: Oxalis. Knotweed. Spotted Spurge. Purslane. Prostrate Pigweed. Lambsquarters. Puncturevine. Ragweed. Carpetweed. Kochia. Florida Pusley. Sow Thistle. Brass Buttons. Managing Winter Annual Broadleaf Weeds: Common Chickweed. Henbit. Shepherd's Purse. Corn Speedwell. Bedstraw. Dog Fennel. Peppergrass. Managing Biennials: Yellow Rocket. Wild Carrot. Black Medic. Managing Perennial Broadleaf Weeds: Wild Garlic. Dandelion. White Clover. Plantain. Buckhorn. Mouse-Ear Chickweed. Mallow. Ground Ivy. Sheep Sorrel. Canada Thistle. Chickory. Curly Dock. Bull Thistle. Healall. Ox-Eye Daisy. Hawkweed. Thyme-Leaf Speedwell. Creeping Speedwell. Violet. Stitchwort. Bindweed. Bellflower. Cinquefoil. Yarrow. Moss. Betony. Beggarweed. Bur Clover. English Daisy. Oxalis (Creeping). Weed Management IPM References Turfgrass Diseases and Their Management (P.H. Dernoeden) Introduction Monitoring Disease and Establishing Thresholds Relationship of Environmental Conditions and Cultural Practices to Disease Biological Control of Turfgrass Diseases Winter Diseases: Pink Snow Mold or Fusarium Patch. Gray Snow Mold or Typhula Blight. Yellow Patch or Cool Temperature Brown Patch. Low Temperature Pythium or Snow Blight. Diseases Initiated in Fall or Spring that May Persist into Summer: Red Thread and Pink Patch. Helminthosporium Leaf Spot and Melting-Out. Take-All Patch. Necrotic Ring Spot. Spring Dead Spot. Large Patch of Zoysiagrass. Pythium Root Rot. Dollar Spot. Stripe Smut and Flag Smut. Powdery Mildew. Anthracnose. Ascochyta and Leptosphaerulina Leaf Blights. Yellow Tuft or Downy Mildew. Diseases Initiated During Summer that May Persist into Autumn: Bermudagrass Decline. Brown Patch or Rhizoctonio Blight. Pythium Blight. Summer Patch. Fusarium Blight. Southern Blight. Helminthosporium Leaf Spot, Melting-Out and Red Leaf Spot. Curvularia Blight. Nigrospora Blight. Copper Spot. Fairy Rings. Superficial Fairy Ring. Localized Dry Spot. Yellow Ring. Gray Leaf Spot. Cercospora Leaf Spot. White Blight. Slime Mold. Rust. Seedling Diseases and Damping-Off. Virus Diseases: St. Augustine Decline and Centipede Mosaic Bacterial Diseases: Bacterial Wilt Plant Parasitic Nematodes Algae and Black-Layer Factors Associated with Fungicide Use: Fungicide Use in Lawn Care. Fungicide Use on Golf Courses. Types of Fungicides. Fungicide Application. Turfgrass Insect and Mite Management (D.J. Shetlar) Goal of Insect and Mite Management in Turf: Pest Identification. Pest Life Cycles. Turf, A Unique Habitat. Monitoring. Selecting Appropriate Controls. Leaf and Stem Infesting Insect and Mite Pests: Bermudagrass Mite. Clover Mite. Banks Grass Mite. Winter Grain Mite. Greenbug. Sod Webworms (Lawn Moth). Cutworms and Armyworms. Other Turf Infesting Caterpillars. Stem and Thatch Infesting Insect and Mite Pests: Chinch Bug and Hairy Chinch Bug. Southern Chinch Bug. Twolined Spittlebug. Rhodesgrass Mealybug. Bermudagrass Scale. Billbugs. Annual Bluegrass Weevil. Cranberry Girdler. Burrowing Sod Webworms. European Cranefly or Leather Jacket. Frit Fly. Thatch and Root Infesting Insect and Mite Pests: Mole Crickets. Ground Pearls. White Grubs. Black Turfgrass Ataenius. Asiatic Garden Beetle. European Chafer. Green June Beetle. Japanese Beetle. Northern Masked Chafer. Southern Masked Chafer. Oriental Beetle. May and June Beetles, Phyllophaga. Nuisance Invertebrate, Insect, and Mite Pests: Earthworms. Slugs and Snails. Spiders and Tarantulas. Chiggers. Ticks. Sowbugs and Pillbugs. Centipedes. Millipedes. Earwigs. Bigeyed Bugs. Leafhoppers. Ground Beetles. Rove Beetles. Fleas. March Flies (Bibionids). Ants. Fire Ants. Cicada Killer. Nuisance Vertebrate Pests: Common Grackle. Starling. Redwinged Blackbird. Moles. Pocket Gophers. Skunks and Civet Cats. Raccoon. Ninebanded Texas Armadillo. References. Index

Nitrogen and Fungicide Effects on Yield Components and Disease Severity in Wheat

Abstract: Spring N applications increase wheat (Triticum aestivum L.) grain yields in the Mid-South. The interactive effect of increased N rates and foliar fungicide applications on the common Mid-South winter wheat foliar diseases ― leaf blotch (Septoria tritici Rob. in Desm.), glume blotch and leaf spot [S. nodorum (Berk.) Berk.], and leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici) ― is not clearly understood. Research was initiated in 1984 on a Collins silt loam soil (coarse-silty, mixed, acid, thermic Aquic Udifluvents) and continued each year through 1987 to evaluate the effect of N rates and fungicide applications on disease severity in wheat. Spring N rates of 0, 30, 45, 60, 90, and 120 Ib/acre were applied at Feekes' growth stage (GS) 3

Diallel cross analysis of resistance to gray leaf spot in maize

Abstract: Diallel cross analysis of resistance to gray leaf spot (caused by Cercospora zeae-maydis) in an inbred set of diverse heterotic types revealed marked differences in general and specific combining abilities. The former component was of greater relative importance in maize breeding material largely unselected for resistance to this disease, although nonadditive effects were recognized as playing a significant part in the resistance mechanism. Inbreds KO54W and SO507W, representing the F arid M heterotic groups, respectively, exhibited the highest resistance and inbred SP713W (P heterotic group) the lowest resistance. Major dominant effects for resistance were associated with KO54W, which makes it particularly suitable for use in backcross recovery programs for gray leaf spot resistance

Characterization and Pathogenicity of a New Anastomosis Subgroup AG-2-3 of Rhizoctonia solani Kühn Isolated from Leaves of Soybean

Abstract: During July to August in 1992, a unusual foliar blight disease was observed on soybean plants intercropped between rows of winter wheat in an upland field converted from a paddy field at Tohoku National Agricultural Experiment Station in Morioka, northern part of Japan. The symptoms appeared as primary lesions consisting of small, circular necrotic spots, 1-mm or less than 1-mm in diameter, followed by secondary lesions showing circular to irregularly-shaped and large-sized areas of necrosis around the primary lesions under humid conditions. All the isolates of Rhizoctonia solani Kuhn consistently recovered from leaves with the primary and secondary lesions (hereinafter referred to as leaf spot isolates) formed anastomoses in a high frequency (>75%) with the tester isolates of the anastomosis subgroup AG-2-1 but in a low frequency (<16%) with those of the AG-2-2 IIIB and IV and anastomosis group AG-BI. Among the 66 leaf spot isolates, 64 were auxotrophic for thiamine, whereas the isolates of the AG-2-1 were autotrophic for thiamine. The remaining 2 isolates could not grow even in the presence of thiamine. Culture appearance and optimum growth temperature of the leaf spot isolates were similar to those of the AG-2-1 rather than to those of the AG-2-2 IIIB and IV subgroup. Inoculation tests revealed that the leaf spot isolates were highly pathogenic to soybean, adzuki bean and kidney bean and caused severe pre-emergence and post-emergence damping-off, but were not pathogenic to rape and radish. The isolates caused foliar blight on soybean. These results indicated that most of the leaf spot isolates of AG-2 from soybean did not fit to either the AG-2-1 or AG-2-2 subgroup. Hence, we assigned these isolates to a new subgroup 3 in AG-2 (designated as AG-2-3).

Epiphytic bacteria antagonistic to Curvularia leaf spot of yam.

Abstract: Curvularia eragrostidis yam leaf spot is a serious concern among the northeast Brazilian yam growing areas. In order to study its biocontrol, bacterial isolates from the yam phylloplane were tested against the pathogen. They were evaluated with respect to the following parameters: (1) inhibition of C. eragrostidis mycelial growth by using paired culture and cellophane membrane methods, (2) inhibition of conidium germination by using a paired suspension test, (3) reduction of disease severity and, (4) persistence of antagonistic action, on plants under greenhouse conditions. From a total of 162 bacterial isolates, 39 showed antagonism to the pathogen in paired culture. The bacteria produced extracellular, nonvolatile, and diffusible metabolites in the membrane cellophane test. Seventeen isolates resulted in more than 75% inhibition of C. eragrostidis mycelial growth. Among them, IF-26 showed the greatest antagonism. The isolates IF-82, IF-88, and IF-109 inhibited pathogen conidial germination, with average inhibition levels of 99.2, 98.2 and 96.2%, respectively. Under greenhouse conditions the antagonists were applied at three different time intervals relative to C. eragrostidis inoculation: 3 days before, at the same time, and 3 days after. IF-82 and IF-88 applied at the same time as pathogen inoculation both reduced disease severity 75%. IF-82 showed the best persistence of antagonistic action, with an average of 96.3%. IF-82, identified as Bacillus subtilis, was the best biocontrol agent for the yam leaf spot disease in this study.

Genetic Resistance, Fungicide Protection and Variety Approval Policies for Controlling Yield Losses from Cercospora Leaf Spot Infections

Abstract: Cercospora (Cercospora beticola Sacc.) leaf spot infections can result in significant losses in many sugarbeet producing areas of the United States. The principal means of controlling losses is the use of resistant varieties and/or fungicide protectants. Currently available resistant varieties significantly outperform non-resistant genotypes under severe Cercospora infections, but may be 10070 or more lower yielding in the absence of disease. Thus, in some areas of potential heavy infestation, Cercospora leaf spot is managed primarily through the use of triphenyltin fungicides. However, Cercospora isolates resistant to the triphenyltin compounds were reported in Greece in 1978. U.S. sugarbeet researchers are concerned that strains of Cercospora resistant to the triphenlytin compounds may develop, resulting in an epidemic similar to that which occurred in Southern Minnesota in 1981 when benomyl resistant strains of Cercospora emerged. Furthermore, the use of triphenlytin products has become restricted by the EPA and may even be discontinued due to human safety considerations. No replacement fungicides with a similar efficacy appear forthcoming. Resistant levels currently required for variety approval vary from region to region depending on potential disease severity and grower experience with fungicides. It is recommended that variety approval policies anticipate this potential loss of chemical protection and implement a gradual increase in the genetic resistance.

Relationships between temperature and latent periods of rust and leaf-spot diseases of groundnut

Abstract: The effect of temperature on the latent periods of rust, late leaf spot and early leaf spot diseases of groundnut caused by Puccinia arachidis, Phaeoisariopsis personata and Cercospora arachidicola. respectively, was studied. The latent periods (LP) of rust, late leaf spot and early leaf spot ranged from 12-49 days, 13-38 days and 13-39 days, respectively, between 12 C and 33 C An equation relating the rate of pathogen development (1/LP) to temperature was fitted using daily mean temperatures to provide three cardinal temperatures: the minimum (7"m,n), optimum (r^pc), and maximum (Tm,,). T^,^ was about I2°C for rust and about 10°C for the two leaf-spot diseases. Top, for all three diseases was close to 25 C. 7"max was Bl'C for early leaf spot, and extrapolated values for late leaf spot and rust were about 35 and 40°C, respectively.

GLS1 - a major gene for resistance to grey leaf spot in maize.

Abstract: Grey leaf spot of maize, caused by the fungus Cercospora zeaemaydis Tehon and Daniels, is a disease that has become of increasing agricultural importance in the warmer, humid regions of the United States, South Africa, and presumably other countries having favourable conditions for its development. This trend has been associated in the main with conservation tillage practices, which increase the post- harvest plant debris in the field and hence favour the over-wintering and subsequent spread of this serious yield-reducing disease.

Leaf spot and stem blight of sweetpotato caused by Alternaria bataticola: a new record to South America.

Abstract: A severe leaf spot and stem blight disease was observed on several sweetpotato genotypes at an experimental field and in commercial plantings of the cultivar Brazlandia Roxa in the Brasilia-DF area. An Alternaria sp. was consistently isolated from the lesions. Pathogenicity tests were done under greenhouse conditions (air temperature, 18-40 C) using a spore suspension adjusted to 5 × 10 4 conidia per milliliter. The same Alternaria sp. was reisolated from leaf and petiole lesions. Even though identified as A. bataticola, the Brazilian isolates completely lacked the forked beaks in the conidia that are characteristic of this species. This is apparently the first report of A. bataticola in South America, extending the geographic range of this pathogen to the New World

Partial replacement of local common bean mixtures by high yielding angular leaf spot resistant varieties to conserve local genetic diversity while increasing yield

Abstract: Summary The effect of replacing proportions of local farmer bean (Phaseolus vulgaris) mixtures with varieties resistant to angular leaf spot on grain yield was evaluated under local disease pressure in the Kivu region of Zaire. Local bean mixtures in on-station and in multi-locational trials containing respectively 25%, or 50% of Centro Internacional de Agricultura Tropical (CIAT) breeding lines BAT76, or A285, resistant to angular leaf spot yielded significantly more than the local mixture alone. Yields exceeded expected values in three seasons of on-station testing and in two seasons of multi-locational trials. Yield over the expected was found to be a property of new mixtures not protected with fungicide and were attributed to disease control. Relative to expected yields non-protected farmer mixture components performed 17% and 16% better than in protected plots and A285 components yielded 24% and 16% better at respectively 25% and 50% A285 supplementation levels. A285 increased yields of the local mixture components and benefitted from the local mixture when not protected by fungicide. Yield increases in multi-locational trials were largely attributed to the higher yield potential of the resistant variety A285, although angular leaf spot severity was significantly reduced. It was concluded that high yielding, resistant varieties were able to increase bean yield in the region, but probably at a substantial cost in genetic diversity in farmer bean mixtures. That said, a partial replacement strategy is preferable to strategies which encourage complete replacement of local germplasm with one or few high yielding varieties.

Effect of Application Techniques on Performance of Propiconazole for Peanut Disease Control

Abstract: Propiconazole (Tilt®) was applied to Florunner peanut by injection into irrigation water (chemigation) or as a foliar spray. At rates of 0.12-0.25 kg/ha of propiconazole control of both Rhizoctonia limb rot (Rhizoctonia solani AG-4) and stem rot (Sclerotium rolfsii) was inconsistent. Chemigation resulted in the lowest incidence of stem rot, but the incidence of stem rot was only 26% less than the control. Yields from plots receiving chemigation were greater than expected based on disease ratings, indicating that some effects of the fungicide were not being evaluated. Where foliar sprays of chlorothalonil were applied for late leaf spot (Cercosporidium personatum), supplemental applications of propiconazole via chemigation improved leaf spot control. However, substituting chemigated propiconazole for foliar sprays of chlorothalonil consistently resulted in more severe leaf spot and, in one year, decreased yields. Propiconazole is most effective against leaf spot when applied as a foliar spray, whe...

Effects of previous cropping and fungicide timing on the development of light leaf spot (Pyrenopeziza brassicae), seed yield and quality of winter oilseed rape (Brassica napus)

Abstract: Summary Light leaf spot, caused by Pyrenopeziza brassicae, was assessed regularly on double-low cultivars of winter oilseed rape during field experiments at Rothamsted in 1990-91 and 1991-92. Previous cropping and fungicide applications differed; seed yield and seed quality were measured at harvest. In each season, both the initial incidence of light leaf spot and the rate of disease increase were greater in oilseed rape crops sown after rape than those sown after cereals. The incidence of diseases caused by Phoma lingam or Alternaria spp. was also greater in second oilseed rape crops. In 1991-92 there was 42% less rainfall between September and March than in 1990-91, and much less light leaf spot developed. However, P. lingam and Alternaria spp. were more common. Only fungicide application schedules including an autumn spray decreased the incidence of light leaf spot on leaves, stems and pods, as indicated by decreased areas under the disease progress curves (AUDPC) and slower rates of disease increase. Summer sprays decreased incidence and severity of light leaf spot on pods only. In 1990-91, all fungicide treatments which included an autumn spray increased seed and oil yields of cv. Capricorn but only the treatment which included autumn, spring and summer sprays increased yields of cv. Falcon. No treatment increased the yields of cv. Capricorn or cv. Falcon in 1991-92. Fungicide applications decreased glucosinolate concentrations in the seed from a crop of cv. Cobra severely infected by P. brassicae in 1990-91, but did not increase yield.

Sources ofCycloconium oleaginum (Cast.) conidia for infection of olive leaves and conditions determining leaf spot disease development in the region of Sétif, Algeria

Abstract: In the region of Setif, peacock leaf spot disease caused byCycloconium oleaginum was found to be most prevalent in the period from late autumn to spring and of minor significance in the period from the beginning of July until the middle of November. Severity of infection on the lower parts was greater than on the upper parts of the trees. Damage on leaves facing north was much greater than on those facing south. Production of conidia leaf spots was found to be high in spring and late autumn but very low in summer and early autumn. Temperatures from 15 to 18°C were found optimal for the growth of the fungus. Reduced growth was seen at 3, 1 and 25°C with total inhibition at 30°C. Our results suggest that fallen leaves play no role in new infections and the role of the remaining spots on the tree during summer is of little importance. Four phases for the infection of new leaves were determined. In the first, during late spring, three newly opened pairs of leaves were infected, this infection remains hidden until late autumn. The second phase occurs in early autumn after rain. The third stage in late autumn and in the beginning of winter is characterized by the occurrence of new leaf spots which are usually concentrated on the basal pair of newly grown leaves. The fourth phase of infection, at the beginning of spring, is the most important of all. The infected leaves at this stage, comprise the infection source for all the following stages.

Production of a Host‐Specific Toxin by Germinating Spores of Alternaria tenuissima Causing Leaf Spot of Pigeon Pea

Abstract: Production of a host-specific toxin by Alternaria tenuissima, the cause of pigeon pea leaf spot, was investigated in spore-germination fluids (SGF). The SGF selectively induced necrosis on pigeon pea leaves in a deteched leaf assay. Necrotic lesions were observed when a toxin from SGF was applied onto detached young leaves of the pigeon pea cultivar Bahar at concentration as low as 5 ng/ml. The resistant line Tanzania and nonhosts tolerated at least 20,000 times higher concentration of the toxin. The differential activity of the toxin on hosts and nonhosts of the fungus, as well as on susceptible and resistant cultivars or lines, suggested host-specific property of the toxin. At a concentration of 10 ng/ml, the toxin induced susceptibility of pigeon pea leaves to a non-pathogenic isolate of Alternaria alternata. The toxin possibly plays a role as a disease determinant of A. tenuissima, because the toxin was released from germinating spores as early as 3 h of incubation andthe, amount detected within 9 h was about 6 times of the concentration required for necrotic toxicity.

Mulberry diseases in India and their control

Abstract: The following diseases are reviewed. Major diseases: powdery mildew (Phyllactinia corylea), leaf rust (Cerotolium fici and Aecidium mori), leaf spot (Cercospora moricola), bacterial leaf blight (Pseudomonas mori), root knot nematode (Meloidogyne incognita); minor diseases: Phleospora leaf spot (Phleospora maculans), Fusarium leaf spot (Fusarium concolor and Fusarium solani), tar spot (Myrothecium roridum), stem canker (Botryodiplodia theobromae), Fusarium leaf blight (Fusarium padilliroseum), stem blight and collar rot (Phoma exigua and Phoma murorum), Sclerotium wilt (Sclerotium rolfsii); viral diseases: leaf mosaic, yellow net vein; new records: Alternaria leaf blight (Alternaria alternata), sooty mould (Chaetotyrium and Curvularia affinis)

Rapid identification of Xanthomonas fragariae in infected strawberry leaves by enzyme-linked immunosorbent assay

Abstract: An indirect enzyme-linked immunosorbent assay using the F(ab') 2 fragment as a trapping antibody for Xanthomanas fragariae was developed. The pathogen was detected in extracts of single 4-mm leaf disks containing a 4- to 5-day-old lesion obtained by artificial inoculation or lesions in field collections from plants showing symptoms of angular leaf spot disease. Our antiserum reacted positively with 14 strains of X. fragariae but not with 16 of 17 pathovars of X. campestris and strains of Agrobacterium spp., Erwinia amylovora, Pseudomonas spp., Rhodococcus fascians, and nonpathogenic bacteria isolated from strawberry plants

Early and Late Leaf Spot Resistance and Agronomic Performance of Nineteen Interspecific Derived Peanut Lines

Abstract: Nineteen selected interspecific peanut lines with resistance to leaf spot [ Cercospora arachidicola Hori and/or Cercosporidium personaturn (Berk. and Curt.) Deighton] were field tested 3 yr for disease reaction and productivity with and without foliar fungicide protection. Measurements included severity ratings of leaf spot every 2 wk based on the Florida leaf spot disease rating scale, and pod yield. Area under disease progress curves (AUDPC) and pod yield losses were calculated. Ilifferences among the interspecific lines in AUDPC values were significant, and one line had values equal to or lower than that of Southern Runner. One-half of the lines were equal in yeld (P=O.Ol) to Southern Runner. Yields among lines averaged 1 to 50% higher with, as compared to without, chlorothalonil application. Yield losses of individual entries varied significantly from 1 yr to another and incongmous with the AUDPC pattern. Correlations between the AUDPC and yield loss were significant (P=O.Ol) forthe 1989and 1990, but not forthe 1988 data. Results ofthe study indicate that resistance to both C. arachidicola and personaturn were incorporated from the wild species parents into productive, runner-type breeding lines, and that the resistance to personaturn was equal to or better than that of Southern Runner. Additional effort will be required to transfer levels of leaf spot resistance observed in the wild species parents into successful cultivars.

2,3-Di-(E)-caffeoyl-(2R,3R)-(+)-tartaric acid in terminals of peanut (Arachis hypogaea) varieties with different resistances to late leaf spot disease (Cercosporidium personatum) and the insects tobacco thrips (Frankliniella fusca) and potato leafhopper (Empoasca fabae).

Abstract: Peanut (Arachis hypogaea L.) terminals (partially opened vegetative quadrifoliate leaf buds) of varieties with varying levels of resistance to the late leaf spot disease (LLSD) fungus [Cercosporidium personatum (Berk. & M. A. Curtis) Deighton] and the insects tobacco thrips [Frankliniella fusca (Hinds)] and potato leaf hopper [Empoasca fabae (Harris)] were analyzed for their polyphenolic content. All varieties confined only one major polyphenol, which was isolated and identified as 2,3-di-(E-caffeoyl-(2R,3R)-(+)-tartaric acid (levorotatory chicoric acid), previously reported in only one other plant species. Levels of 1-chicoric acid were highest in newly emerged terminals (0.25% fresh wt) of Florunner (susceptible to LLSD) and Southern Runner (resistant) varieties and showed a steady decline (to 0.019%) as the leaves matured over 18 days

Application rates and spray intervals of ergosterol-biosynthesis inhibitor fungicides for control of Entomosporium leaf spot of photinia

Abstract: The ergosterol-biosynthesis inhibitor (EBI) fungicides myclobutanil, tebuconazole, diniconazole, and flusilazole were compared with chlorothalonil and triforine for the control of Entomosporium leaf spot on photinia. Applied weekly, myclobutanil (0.15 g a.i./L) was equal to or better than chlorothalonil (1.35 g a.i./L) for control of leaf spot, and these two fungicides were superior to triforine. Tebuconazole and diniconazole provided good disease control but reduced growth of plants. Application of myclobutanil at 2-wk intervals was efficacious in controlling disease. All of the fungicides tested controlled Entomosporium leaf spot, but only myclobutanil caused no phytotoxicity to photinia

Stability of bacterial leaf spot resistance in peach regenerants under in vitro , greenhouse and field conditions

Abstract: Phenotypic stability of bacterial leaf spot resistance in peach (Prunus persica (L.) Batsch) regenerants, either selected at the cellular level for insensitivity to a toxic culture filtrate of Xanthomonas campestris pv. pruni or screened at the whole plant level for resistance to X. campestris pv. pruni, was investigated. A detached-leaf bioassay was used to evaluate the original regenerants again after three years in the greenhouse and also after a two to three year cycle of tissue culture propagation. Peach trees derived through micropropagation from the original regenerants were also evaluated after one to three years growth in the field. Although leaf spot resistance was retained in some regenerants over time in the greenhouse, following in vitro propagation, and under field conditions, resistance was either lost or not expressed in others. Regenerants # 19-1 and #156-6, derived from embryo callus of bacterial spot susceptible ‘Sunhigh’, were significantly more resistant than ‘Sunhigh’. High levels of resistance were exhibited in greenhouse plants and field-grown trees of regenerant #122-1, derived from embryo callus of moderately resistant ‘Redhaven’. This research provides additional evidence that selecting or screening for somaclonal variants with disease resistance is a feasible approach to obtaining peach trees with increased levels of bacterial spot resistance.

Gray Leaf Spot of Corn

Abstract:  Gray leaf spot can become severe in favorable environmental conditions: 70-90° F, high relative humidity, and prolonged leaf wetness from rain, dew, or irrigation.  Yield loss is attributed to a reduction in photosynthetic leaf area due to blighted leaves; the severity of yield loss depends on the location of the damaged leaves and the growth stage of the plant at which infection occurs.  Management strategies include host resistance, fungicides, residue management, and crop rotation.

The effect of moisture and sunlight on the severity of dogwood anthracnose in street trees

Abstract: The effect of supplemental irrigation and sunlight on the severity of dogwood anthracnose was evaluated on Cornus florida street trees in New Jersey during 1989 and 1990. Fewer leaf spot and twig blight symptoms were observed on trees that received supplemental irrigation in the summer during periods of drought. In addition, those trees placed in full or partial sun were less diseased than trees grown in the shade.

Choanephora blight and alternaria leaf spot of Amaranth in Tanzania

Abstract: A leaf blight incited by Choanephora cucurbitarum and a leaf spot incited by Alternaria amaranthi on cultivated amaranth, Amaranthus cruentus, are described. This is a new host record for C. cucurbitarum, and A. amaranthi is a new record for Tanzania. Additional hosts of C. cucurbitarum are listed.

Seasonal occurrence of foliar fungal and bacterial diseases of mulberry in South India

Abstract: A survey on the incidence and severity of foliar fungal and bacterial diseases of mulberry was conducted during 1990-92 in selected mulberry growing areas under different agroclimatic zones located in Andhra Pradesh, Karnataka, Kerala and Tamil Nadu. Disease incidence was recorded twice in each season at a regular interval of two months on leaf spot, leaf rust, powdery mildew, leaf blight and bacterial blight diseases. The survey was conducted in 5-10 farmers gardens in different villages at Anantapur, Mysore, Madivala, Sirsi, Chamarajanagar, Kanjirapalli, Palghat, Coimbatore and Coonoor. Incidence and severity of diseases were more during rainy season followed by winter and summer. All the diseases were indexed in most of the places of survey during rainy and winter seasons. However, leaf rust and bacterial blight were not recorded at Coonoor in any of the survey periods. The incidence and severity of various diseases in different seasons are discussed.