First Report of the Sting Nematode Belonolaimus longicaudatus on Soybean in Delaware.

In late July of 2005, several, large, irregular areas of severely chlorotic, stunted, and dead soybean plants were observed in two fields of soybean (Glycine max), 8.05 km apart, in sandy soil (94% sand, 2% silt, and 4% clay) in southwestern Sussex County, DE. The grower also had observed stunted corn the previous year in the same areas and thought the fields had a fertility problem. The morphology of adults and molecular analyses of the juveniles isolated from soil samples established the identity of the species as the sting nematode, Belonolaimus longicaudatus (1-4). The population density was 216 nematodes per 250 cm3 of soil. Morphological characters used for identification included female body, stylet and tail length, shape of head, stylet knobs, tail and tail terminus, number of lines in the lateral field, and vulva percentage in relation to body length. The male characters critical for identification were the following: body, stylet, spicule, and gubernaculum length; shape of head and stylet knobs; and number of lines in the lateral field. Measurements of females (n = 5) included body length (range = 2,035 to 2,120 µm, mean = 2,073.7, standard deviation [SD] = 37.0), stylet (117.0 to 127.5, 123.4, 4.5), V% (48.4 to 52.3, 50.6, 1.5), and tail (109 to 140, 120, 14.2). The lateral field had one incisure. Shape of head, stylet knobs, and tail were also consistent with B. longicaudatus. Males (n = 4) were characterized by the body length (range = 1,500 to 2,070 µm, mean = 1,753.3, SD = 290.2), stylet (117.0 to 127.5, 121.5, 5.4), spicules (41 to 50, 47, 5.2), and gubernaculum (17.0 to 18.5, 17.8, 0.8). Molecular diagnosis as B. longicaudatus was confirmed by sequencing two ribosomal DNA markers from three juveniles. Sequence of the internal transcribed spacer region ITS1 and 2 (GenBank Accession No. GQ896549) from this population was 99% identical to Florida isolate BlCi6 (DQ672368), and the 28S large ribosomal subunit D2-D3 expansion region (GQ896548) was 99% identical to Florida isolate BlCi4 (DQ672344). A high degree of similarity (>98%) was also shared by several other B. longicaudatus sequences (1). This detection represents a new state record in Delaware for B. longicaudatus. Since this detection in 2005, there have been no new reports of other observations of sting nematode or spread from these two fields tilled by the same farm operator in Delaware. Elsewhere, B. longicaudatus is known to occur in subtropical regions of the lower coastal plain, from Virginia to Florida and along the Gulf Coast into Texas. On the east coast, USDA Nematode Collection records document this nematode from Florida, Georgia, New Jersey, and South Carolina. Within Delaware, another sting nematode species, Belonolaimus maritimus, was detected on American beachgrass (Ammophila breviligulata) and bitter panicgrass (Panicum amarum var. amarulum) from Fenwick Island, near the Maryland border. Sting nematodes have also been reported in Burlington County, NJ. References: (1) U. Gozel et al. Nematropica 36:155, 2006. (2). H.-R. Han et al. Nematropica 36:37, 2006. (3) G. J. Rau. Proc. Helminthol. Soc. Wash. 25:95, 1958. (4) G. J. Rau. Proc. Helminthol. Soc. Wash. 30:119, 1963.

Lima Bean Downy Mildew Epiphytotics Caused by New Physiological Races of Phytophthora phaseoli.

Before 1995, race D of Phytophthora phaseoli, the causal agent of downy mildew on lima bean (Phaseolus lunatus), was the prevalent physiological race in the mid-Atlantic region of the United States. Since 1995, however, new physiological races of P. phaseoli have been responsible for downy mildew outbreaks in previously resistant cultivars in this region. Cultivar differential testing of 180 isolates of P. phaseoli collected between 1994 and 2005 from Delaware and the eastern shore of Maryland has confirmed the presence of two new physiological races. The detection of race E in 1995 and race F only 5 years later in 2000, plus the lack of resistant cultivars to manage the epiphytotics in lima bean, have led to millions of dollars of crop losses. Intra- and interspecific genetic variation of Phytophthora spp. and isolates were assessed using amplified fragment length polymorphism DNA fingerprinting. Primer groups EcoRI+AG and MseI+C distinguished P. phaseoli and P. capsici from P. infestans but did not distinguish among different races of P. phaseoli.

First Report of Mefenoxam-Resistant Isolates of Phytophthora capsici from Lima Bean Pods in the Mid-Atlantic Region.

Phytophthora capsici Leonian, the causal agent of lima bean pod rot, was first identified as a pathogen of lima bean in 2002 (1) and poses a new threat to lima bean (Phaseolus lunatus L.) production in the Mid-Atlantic Region. The phenylamide fungicide mefenoxam (Ridomil Gold; Syngenta Crop Protection) is widely used in the region for controlling foliar and soilborne diseases caused by Oomycetes. Isolates of P. capsici were collected from lima bean pods from production fields in Delaware, Maryland, and New Jersey from 1998 to 2004. These isolates originated from survey samples of lima bean fields for another pathogen, P. phaseoli, in 1999 and 2000 and diagnostic samples were submitted to the Plant Disease Clinic. Isolates were from lima bean, except for one from pepper (basal stem). Identification was made on the basis of morphometric characteristics. No known sensitive or insensitive isolates were included in the evaluation. Single zoospore cultures were evaluated for mefenoxam sensitivity on V8 agar plates amended with 100 ppm of mefenoxam, a previously tested concentration (2). Seven-millimeter-diameter agar plugs of each isolate were cut from the edge of actively expanding cultures of P. capsici with a cork borer and transferred to three V8 agar plates amended with mefenoxam and three unamended V8 plates. The plates were arranged in a completely randomized design and incubated at 25°C in the dark for 3 days. After incubation, colony growth was measured in millimeters and averaged for the three replicate plates of each isolate and percent growth relative to the unamended control was calculated. Mefenoxam sensitivity was assigned according to methods of Lamour et al. (2). The experiment was repeated once, and also run with a treatment of 200 ppm of mefenoxam. Of sixteen isolates screened, nine were rated as sensitive, four were intermediately resistant, and three were resistant. There was no difference between the 100 and 200 ppm results, except for a slight increase in sensitivity for one isolate. A subsequent experiment tested five isolates at concentrations of 1, 10, 100, and 1,000 ppm. Results were consistent with previous tests, with resistant isolates exhibiting some growth at the highest concentration of mefenoxam. One resistant isolate was from a field in Delaware previously cropped to slicing cucumbers with a history of mefenoxam applications. The second was from Caroline County, MD, which is heavily cropped to pickling cucumbers and likely to have been exposed to mefanoxam applications for the control of fruit rot; the origin of the third insensitive isolate from lima bean is unknown. Mefanoxam usage on lima bean is usually limited to one foliar application of mefenoxam+copper hydroxide to control downy mildew in the fall crop in wet seasons. This study indicates that mefenoxam resistance is present in populations of P. capsici in lima bean fields in the Mid-Atlantic Region, presumably as a result of mefenoxam applications to other vegetable crops, principally cucurbits, which are planted in rotation with lima beans or from nearby cucurbit fields. Implementing strategies to minimize fungicide resistance in other vegetables is important to slow resistance development associated with this emerging pathogen on lima beans. Lima bean pod rot continues to be seen sporadically each year in fields with a history of P. capsici and abundant rainfall or excessive irrigation. References: (1) C. R. Davidson et al. Plant Dis. 86:1049, 2002. (2) K. H. Lamour et al. Phytopathology 90:396, 2000.

Management of Xiphinema americanum and Soybean Severe Stunt in Soybean Using Crop Rotation.

Soybean severe stunt (SSS), caused by the Soybean severe stunt virus (SSSV), is a soilborne virus disease affecting soybean (Glycine max) first described in Delaware in 1988. Lack of breeding programs directed at incorporating resistance to SSSV in new cultivar releases necessitated alternative methods of SSS control. The effect of crops in 2-year rotations on the dagger nematode (Xiphinema americanum), the putative nematode vector of SSSV, and SSS severity were examined. Two years of continuous corn or grain sorghum, wheat followed by 'HT-5203' soybean, or 2-year fallow, reduced both dagger nematode density in the soil and SSS severity. Crop rotation to the SSSV-tolerant HT-5203 soybean as a single crop for 2 years increased dagger ematode populations and SSS severity. Greenhouse studies indicated that corn, wheat, marigold, castor, and fallow treatments reduced dagger nematodes the most after 14 weeks compared with 'Essex' and HT 5203 soybean.

Anthracnose Caused by Discula fraxinea on the New Host Chinese Fringetree and White Ash in Delaware.

Leaf blight or anthracnose symptoms have been noted on the current year's growth of Chinese fringetree (Chionanthus retusis L.) since the early 1990s in Newark, DE. Symptoms begin as dark, greenish brown, water-soaked lesions on the edges of young leaves. With time, lesions enlarge, turn darker brown, and coalesce with necrotic areas turning dry and light brown. Isolations from infected leaves consistently yielded a golden brown fungal culture on acidified potato dextrose agar. Similar symptoms were observed on white ash (Fraxinus americana L.), from which a similar fungus was isolated. C. retusis and F. americana belong to the Oleaceae, the olive family. Acervuli were inconspicuous on leaves, but conidia were easily observed. Conidia were small, non-septate, ellipsoidal, hyaline, and averaged 5.5 × 3.5 µm. In culture, the fungus formed conspicuous, concentric zones of flocculent mycelium and spherical conidiomata when exposed to diurnal light. Isolates from C. retusis and ash were identified as Discula fraxinea (Peck) Redlin & Stack, the anamorph of Gnomoniella fraxini Redlin & Stack (Gnomoniaceae, Diaporthales) (3). Sequences of the internal transcribed spacer region (ITS) of rDNA indicated that the isolates from C. retusis and white ash (GenBank Accession No. AY455810-AY455818) were conspecific with D. fraxinea isolates from Maryland and Oregon, with six or fewer base pair substitutions or insertion/deletions (indels) across all isolates. Ash anthracnose has been reported from the central and eastern United States and California, the prairie provinces in Canada, and recently from British Columbia, usually under the synonyms of Gloeosporium aridum and G. fraxineum (1,2). Koch's postulates were completed when isolates of D. fraxinea from C. retusis, green ash (F.pennsylvanica Marsh.), and white ash were inoculated onto 3- to 4-year-old trees of C. retusis and F. americana in 2000 and 2001. Seven replicate branches with emerging leaves were sprayed to runoff with a conidial suspension (60,000 conidia per ml) and covered with plastic bags for 24 h. After 20 days, 85% of C. retusis branches inoculated with a C. retusis isolate developed symptoms, and D. fraxinea was isolated from 78.6% of symptomatic leaves. Isolates from green ash in Maryland and white ash in Delaware produced symptoms on 57% of C. retusis branches. Only 37% of white ash branches inoculated with isolates from C. retusis and white ash developed symptoms, but D. fraxinea was isolated from 100% of symptomatic leaves. No symptoms developed on control branches. To our knowledge, this is the first report of D. fraxinea on C. retusis or on any member of that plant genus (1,2). In addition, D. fraxinea has not previously been reported on F. americana in Delaware. Specimens and cultures of D. fraxinea from C. retusis (BPI 746408, CBS 114058) and F. americana (BPI 746411, CBS 114051) were deposited at the U.S. National Fungus Collection and the Centraalbureau voor Schimmelcultures, The Netherlands. References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory, On-line publication. ARS, USDA, 2003. (3) S. C. Redlin and R. W. Stack. Mycotaxon 32:175, 1988.

First Report of Phytophthora capsici Infecting Lima Bean (Phaseolus lunatus) in the Mid-Atlantic Region.

Lima beans are an important crop in Delaware and the Mid-Atlantic Region. In the summer of 2000, five commercial cultivars (3-28, 184-85, C-elite Sel, Butter Bean, and Jackson Wonder) of lima bean in Delaware, Maryland, and New Jersey were observed with white, appressed mycelia on infected pods that appeared distinctly different from signs of downy mildew infection caused by Phytophthora phaseoli. Isolations were made by placing diseased pods between layers of rye media (1). A fungus that produced white mycelia with sporangia was consistently isolated. All Phytophthora isolates from the infected pods were heterothallic, grew at 35°C, had as much as 100 µm long pedicles on varying shapes of caducous sporangia with tapering base and >2 papillae, and were identified as P. capsici (2). Initially, three surface-disinfected pods from cv. Early Thorogreen plants grown in the greenhouse were floated on 20 ml of sterile water in a petri dish, and each was inoculated with a disk of P. capsici. This was repeated for nine isolates obtained from lima bean. After incubation for 7 days at room temperature, all 27 pods were infected, and P. capsici was reisolated from all the pods. A pathogenicity test was performed on the same cultivars from which the original field isolates were collected. Three seedlings and two plants with mature pods were inoculated with a sporangial suspension of each of the nine isolates and placed in a dew chamber for 5 days at 20 to 25°C and 100% relative humidity. White mycelial growth was observed on seedlings and mature pods. One inoculated plant developed brown-to-black stem lesions with white mycelia. All pods on the mature plants showed appressed, white mycelia identical to that observed in the commercial lima bean fields. P. capsici was consistently reisolated from all inoculated plants. In 2000, most infected pods in infested fields were observed low in the plant canopy or touching the soil. However, in 2001, infected pods were mostly in the lower and mid-portion of the plants observed in baby lima bean fields in Kent County, DE. References: (1) C. E. Caten and J. L. Jinks. Can. J. Bot. 46:329, 1967. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora capsici. Page 264 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996.

Two New Races of Phytophthora phaseoli from Lima Bean in Delaware.

Downy mildew, incited by Phytophthora phaseoli Thaxt., is the most important disease of lima bean (Phaseolus lunatus L.) on the east coast of the United States. It has been a serious threat to commercial lima bean production in Delaware, Maryland, and New Jersey for the past 5 years. Growers have attempted to manage this disease using resistant cultivars and copper hydroxide fungicides. In August and September 1995, a new pathogenic race of P. phaseoli was isolated from infected pods of the lima bean cv. Packer in a production field near Milton, DE. Races of P. phaseoli are determined using a modification of a cultivar differential developed by Wester (3). The cv. 184-85, which is resistant to races A, B, C, and D (1), is susceptible to the new race, designated as E. In August 2000, another new pathogenic race of P. phaseoli was isolated from infected pods of cv. 184-85 near Middletown, DE. The lima bean line BG2-408, which is resistant to races A, B, C, D, and E, is susceptible to the new race, designated as F. Symptoms produced on lima bean plants infected by races E and F are similar to each other, and to those produced by all other races. All races of P. phaseoli have the same cultural characteristics on lima bean pod agar. Evaluations of in field weather station data and disease occurrence indicate that races E and F may have temperature maxima greater than 32°C, whereas race D has a maximum of less than 32°C (2). During the 2000 growing season, 118 isolates of P. phaseoli were collected from 44 production fields in Delaware and the eastern shore of Maryland, with 86% characterized as race E and 5% as race F. References: (1) C. R. Davidson et al. Biol. Cult. Tests 2001:V80. (2) R. A. Hyre and R. S. Cox. Phytopathology 43:419, 1953. (3) R. E. Wester. Phytopathology 60:1856, 1970.

First Report of Sudden Death Syndrome of Soybean in Delaware and Eastern Shore of Maryland.

In August and September of 2000, soybean (Glycine max (L.) Merr.) plants from two fields in Sussex County, Delaware, and one field from Somerset County on the eastern shore of Maryland exhibited typical symptoms of sudden death syndrome. The season had been wetter and cooler than normal. Leaf symptoms ranged from small chlorotic spots to elongated regions of interveinal necrosis. Leaflets dropped leaving attached petioles in the upper canopy. Severely infected plants were easily pulled from the soil and had taproots with blue sporodochia, necrotic cortical tissue, and necrosis of secondary roots (2). Initial isolations from the infected plants were made from the basal stems, discolored taproots, vascular tissue, and directly from blue sporodochia. Sections were plated on water agar (WA) amended with neomycin and streptomycin, WA with antibiotics and chloramphenicol, and acidified potato dextrose agar (PDA). The isolates were slow growing on PDA, often staining agar dark maroon, produced little aerial mycelium, and formed macroconidia in blue sporodochia. The fungus was identified as Fusarium solani (Mart.) Sacc. based on spore morphology. Plugs (5 mm) of the fungus from 14-day-old cultures were placed next to the stem just below the soil line of 14-day-old plants of soybean cvs. Essex and Lee 74. Eighteen plants of each cultivar (three per pot) were inoculated and placed on a greenhouse bench for 43 days at 21°C (±2°C). Six noninoculated control plants were also included. Plants were rated for the presence of stem lesions and foliar symptoms. Of the inoculated plants, 70% had mottling, rugosity, and leaf cupping, 6% had severe interveinal leaf necrosis, and 52% had distinct stem lesions at the soil line. Control plants were symptomless. F. solani was recovered from all symptomatic plants and presumed to be F. solani f. sp. glycines based on spore morphology, color, lack of microconidia, and symptoms (1). A more extensive test was conducted to confirm Koch's postulates. Eleven isolates of F. solani f. sp. glycines were grown as before and used to inoculate Essex soybeans as previously described. Inoculated and control plants were randomized on the greenhouse bench and watered using an individual pot irrigation system. Fifty-six days after inoculation plant height was reduced 12% compared with the noninoculated controls. Lesions produced on the lower stem and taproot of the inoculated plants averaged 4.5 cm long. Most plants had mild foliar symptoms that included mottling, rugosity, and leaf cupping. Only three plants had severe foliage symptoms. F. solani f. sp. glycines was recovered from 56% of inoculated plants, completing Koch's postulates for all 11 isolates. Noninoculated controls were symptomless. Sudden death syndrome was not observed in 2001. Soybean is an important crop in the region; 250,000 ha were harvested in 2000 on the Delmarva Peninsula, which includes the three counties of Delaware, nine eastern shore counties of Maryland, and two counties of Virginia. Sudden death syndrome could be a serious threat to profitable soybean production. To our knowledge, this is the first report of sudden death syndrome from this area and represents the most eastern occurrence of this disease reported in the United States. References: (1) K. W. Roy. Plant Dis. 81:259, 1997. (2) K. W. Roy et al. Plant Dis. 81:1100, 1997.