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Made available in DSpace on 2022-04-28T19:30:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 Florida Education Fund Pestalotiopsis-like species have been reported affecting strawberry worldwide. Recently, severe and unprecedented outbreaks have been reported in Florida commercial fields where leaf, fruit, petiole, crown, and root symptoms were observed, and yield was severely affected. The taxonomic status of the fungus is confusing because it has gone through multiple reclassifications over the years. Morphological characteristics, phylogenetic analyses, and pathogenicity tests were evaluated for strawberry isolates recovered from diseased plants in Florida. Phylogenetic analyses derived from the combined internal transcribed spacer, b-tub, and tef1 regions demonstrated that although there was low genetic diversity among the strawberry isolates, there was a clear separation of the isolates in two groups. The first group included isolates recovered over a period of several years, which was identified as Neopestalotiopsis rosae. Most isolates recovered during the recent outbreaks were genetically different and may belong to a new species. On potato dextrose agar, both groups produced white, circular, and cottony colonies. From the bottom, colonies were white to pale yellow for Neopestalotiopsis sp. and pale luteous to orange for N. rosae. Spores for both groups were five-celled with three median versicolored cells. Mycelial growth and spore production were higher for the new Neopestalotiopsis sp. isolates. Isolates from both groups were pathogenic to strawberry roots and crowns. However, the new Neopestalotiopsis sp. proved more aggressive in fruit and leaf inoculation tests, confirming observations from the recent outbreaks in commercial strawberry fields in Florida. Gulf Coast Research and Education Center University of Florida Corteva Agriscience São Paulo State University College of Agricultural Sciences São Paulo State University College of Agricultural Sciences

The effects of within-row plant spacing and cultivar on the incidence of Botrytis fruit rot (Botrytis cinerea) and marketable yield of annual strawberry were evaluated during the 1997-98 and 1998-99 seasons. Three cultivars (Camarosa, Rosa Linda, and Sweet Charlie) and four plant spacings (23, 30, 38, and 46 cm) were evaluated. Marketable yield and the incidence of Botrytis fruit rot were determined twice weekly. Cultivar and spacing effects were analyzed for three periods each season (early, late, and whole season). In 1997-98, spacing effects were observed on weekly incidence of Botrytis rot for the late period (P = 0.0925) and on cumulative incidence for the whole season period (P = 0.0795). Further analysis of the late and whole season periods revealed a spacing effect for Camarosa (P = 0.0102). Spacing also had a dramatic effect on cumulative and weekly Botrytis incidence for the late and whole season periods during the 1998-99 season (P ≤ 0.0014), when narrower spacings had higher incidence of Botrytis than wider spacings. Marketable yields were higher at narrower spacings during the early period for both seasons. Whole season marketable yields were also higher at the narrower spacings despite higher incidence of Botrytis. There were significant differences in susceptibility among cultivars.

Epidemics of Botrytis fruit rot (Botrytis cinerea) and powdery mildew (Sphaerotheca macularis f. sp. fragariae) in annual strawberry were compared in large plastic tunnel and field production systems during the 1998-99 and 1999-2000 seasons. Treatments were factorial combinations of two main plots (field and tunnel) and four subplots, including combinations of two cultivars (Camarosa and Sweet Charlie) and two captan schedules arranged in a split-plot design with three replications. The mean incidence of Botrytis fruit rot was 88 to 94% lower in tunnels than in the field. The incidence of Botrytis fruit rot for the untreated control in tunnels was less than 2%, which was 89% lower than that of the 7-day captan schedule in the field. This indicates that Botrytis fruit rot can be controlled effectively without fungicides in a tunnel cultural system. Powdery mildew was severe on susceptible cultivar Camarosa in tunnels. Early season yields of cultivar Sweet Charlie were significantly higher in tunnels than in the field. Shorter periods of leaf wetness and higher temperatures in tunnels may have contributed to a lower incidence of Botrytis fruit rot and a higher incidence of powdery mildew on fruit in tunnels compared with open field plots.

During the 1999-2000 and 2000-2001 growing seasons, field experiments were conducted to identify the developmental stage(s) of strawberry flowers and fruit that requires fungicide applications to control Botrytis fruit rot. Fenhexamid, a protectant fungicide, was applied to individual newly opened flowers or fruit of cultivar Sweet Charlie at defined intervals after anthesis. In 1999-2000, a single application of fenhexamid at anthesis controlled Botrytis fruit rot as well as multiple weekly applications beginning at anthesis. During both seasons, disease control deteriorated as applications were delayed 7 and 14 days after anthesis. This trend was described by linear regression equations relating the time of application to Botrytis fruit rot incidence. Additional treatments tested the effects of emasculation and petal removal 3 to 7 days after anthesis. Emasculation significantly reduced disease incidence in 2000-2001. Petal removal produced modest but significant reductions in 1999-2000, but not in 2000-2001. These results demonstrate that strawberry flowers are more susceptible to Botrytis cinerea than green fruit, and suggest that stamens are the principal infection court. Fungicide applications should focus on peak bloom periods to minimize fungicide use and optimize control of preharvest Botrytis fruit rot. During these periods, applications should be made at close intervals (≤7 days) to minimize losses to Botrytis.

Mertely, J. C., and Legard, D. E. 2004. Detection, isolation, and pathogenicity of Colletotrichum spp. from strawberry petioles. Plant Dis. 88:407-412. The herbicide paraquat is used to kill plant tissues and accelerate the growth of quiescent fungal colonists. In this study, freezing was investigated as an alternative to paraquat for the detection of latent infections of Colletotrichum spp. on strawberry petioles. Apparently healthy petioles from field-grown plants and inoculated petioles from greenhouse-grown plants were killed by freezing or exposure to 0.3% paraquat, and incubated in petri dish moist chambers. Previously frozen petioles were treated with 0.525 or 0.0525% sodium hypochlorite and Tween 20 at 18 µl/liter for selected intervals to test the effects of surface disinfestation on detection frequency. After 5 to 7 days of incubation, Colletotrichum acervuli developed much more frequently on freeze- and paraquat-treated petioles than on washed petioles which were not killed. Detection frequencies were similar for paraquat and some freeze treatments, but the latter were negatively affected by prolonged surface disinfestation. Using the petiole freeze method, Colletotrichum acutatum, C. gloeosporioides, and Glomerella cingulata (the teleomorph of C. gloeosporioides) were detected on symptomless petioles of field-grown plants. In addition, C. acutatum and C. dermatium were detected on apparently healthy transplants from northern nurseries. All of these fungi are reported pathogens of strawberry, but not all C. gloeosporioides isolates from frozen petioles were pathogenic in greenhouse bioassays. Freezing is a viable, nonhazardous alternative to paraquat for the detection of latent Colletotrichum infections on strawberry.

Wax myrtle (Morella cerifera (synonym Myrica cerifera) (L.) Small) is a native tree used in Florida landscapes. In the summer of 2005 and spring of 2006, small necrotic spots were observed on young leaves in two commercial nurseries in central Florida. Lesions were dark brown-to-black and eventually coalesced to form large, irregular necrotic areas. Leaves with large lesions abscised prematurely, defoliating the entire plant. Conidia formed on acervuli were observed on the surface of the largest lesions and were tentatively identified as a Colletotrichum sp. Isolations from the edges of lesions were made on potato dextrose agar (PDA) after surface disinfestation of leaf pieces in 0.6% NaOCl for 30 sec. Red chromogenic colonies developed after 5 days of incubation at 24°C. Colonies produced hyaline, oblong conidia with pointed ends averaging 14 × 4 μm and were identified as Colletotrichum acutatum J.H. Simmonds (1). The sequence from internal transcribed spacer regions 1 and 2 and the 5.8s rRNA gene of the rDNA repeat for an isolate (GenBank Accession No. DQ839609) was 100% identical to sequence from the same region of 36 C. acutatum isolates in the NCBI database. These isolates came from at least 16 different hosts, including seven ornamental hosts. There were three isolates from blueberry among the matches (Accession Nos. AB219029, AJ301911, and AJ301905), and the rDNA sequence was also identical to the sequence obtained in our laboratory for a chromogenic C. acutatum isolate from blueberry. Three single-spore isolates were tested for pathogenicity on potted plants in the greenhouse. Two young shoots were spray inoculated with a suspension (1 × 106 conidia/ml) of each isolate. Shoots were covered with a plastic bag for 24 h and maintained at 26.5°C. Two shoots were sprayed with sterile water as a control and similarly covered. All isolates produced brown spots on the youngest leaves 3 to 5 days after inoculation; no symptoms developed on control shoots. The fungus was reisolated from all inoculated shoots. To our knowledge, this is the first report of C. acutatum on wax myrtle in Florida. The disease has a potential to spread and become a significant problem for the cultivation of this species in ornamental nurseries in Florida. Reference: (1) J. H. Simmonds. Qld. J. Agric. Anim. Sci. 22:437, 1965.

Evidence that Colletotrichum fragariae causes disease on hosts other than strawberry is limited. In the fall of 2006, fungal isolates from silver date palm with leaf spot symptoms and from cyclamen with leaf spot and stem rot symptoms were identified as C. fragariae. After confirming the pathogenicity of the isolates on their host of origin, a representative isolate from each host was compared to C. fragariae and to C. gloeosporioides/Glomerella cingulata isolates from strawberry. Date palm and cyclamen isolates bore conidia on setae, and conidia were tapered and in the size range of C. fragariae reference isolates. Sequence data from the combined internal transcribed spacer (ITS) regions 1 and 2 and the gene for the 5.8 ribosomal RNA from the cyclamen and date palm isolates matched the sequence for C. fragariae reference isolates. Based on these characteristics, it was concluded that the C. fragariae species designation was correct for both isolates. However, the date palm isolate was a weak pathogen on strawberry compared with other isolates and had a distinct AT-rich DNA banding pattern. The ability of the cyclamen isolate to cause crown rot on strawberry was comparable with the strawberry reference isolates, and the AT-rich DNA banding pattern of the cyclamen isolate was identical to the C. fragariae isolates from strawberry. The results indicate that C. fragariae is a pathogen on hosts other than strawberry and that there is more diversity among C. fragariae isolates than previously reported.

MacKenzie, S. J., Mertely, J. C., and Peres, N. A. 2009. Curative and protectant activity of fungicides for control of crown rot of strawberry caused by Colletotrichum gloeosporioides. Plant Dis. 93:815-820. The ability of fungicides to control Colletotrichum crown rot of strawberry caused by C. gloeosporioides was examined over three seasons. A single application of each fungicide was made 2 days before inoculation (2 DBI) or 1 day after inoculation (1 DAI) with conidial suspensions of C. gloeosporioides. The proportion of plants collapsed on one date at the end of each season was evaluated. In a combined analysis, there was a significant fungicide treatment-season interaction (P = 0.004). Percent mortality was 64% over 3 years in control plots that were inoculated with C. gloeosporioides but not treated with fungicide. Captan applied 2 DBI consistently reduced plant mortality (mean mortality = 17%). However, it was not as effective when applied 1 DAI (mean mortality = 46%). Azoxystrobin, pyraclostrobin, and thiophanate-methyl all reduced plant mortality relative to the control if applied 2 DBI (mean mortality = 46% for azoxystrobin, 37% for pyraclostrobin, and 41% for thiophanate-methyl) or 1 DAI (mean mortality = 29% for azoxystrobin, 27% for pyraclostrobin, and 32% for thiophanate-methyl). Results indicated that these fungicides were more effective when applied 1 DAI; however, lower plant mortality was not always observed with postinoculation applications. Cyprodinil + fludioxonil reduced mortality relative to the control, but there was no consistent evidence that it was more effective when applied at 2 DBI (mean mortality = 39%) than when applied 1 DAI (mean mortality = 40%). Similarly, mortality in plots treated with thiram 2 DBI (mean mortality = 30%) or 1 DAI (mean mortality = 32%) was not different. Potassium phosphite did not affect mortality, regardless of the timing of application (2 DBI mean mortality = 61%, 1 DAI mean mortality = 67%). The results indicated that an effective strategy for controlling Colletotrichum crown rot caused by C. gloeosporioides should be based on weekly applications of captan throughout the growing season. Azoxystrobin, pyraclostrobin, or thiophanate-methyl applications should be applied when weather conditions are highly favorable for disease development and the activity of contact fungicides such as captan or thiram might be compromised.

Crop phenology and epidemiological information were used to design a reduced use fungicide program for control of Botrytis fruit rot in winter annual strawberry. Fungicide spray programs during early and late periods of the season using high and low rates of captan were evaluated with or without second peak bloom applications of fenhexamid during the 1999-2000 and 2000-2001 seasons. During the early harvest period, low rates of captan were as effective as high rates for controlling Botrytis fruit rot and maintaining yield. Late in the season, treatments with fenhexamid over the peak bloom period significantly improved control of Botrytis fruit rot and increased marketable yield. Application of both captan and fenhexamid during the second peak bloom did not reduce Botrytis fruit rot incidence or improve yield compared with fenhexamid alone during this time period. Late season applications of captan may be reduced or eliminated when bloom applications of fenhexamid are being applied without affecting Botrytis fruit rot control. The study generated new recommendations for use of low-rate applications of captan during the early season and applications of fenhexamid during the second peak bloom period for winter annual strawberry production in Florida.

MacKenzie, S. J., Xiao, C. L., Mertely, J. C., Chandler, C. K., Martin, F. G., and Legard, D. E. 2003. Uniformity of strawberry yield and incidence of Botrytis fruit rot in an annual production system. Plant Dis. 87:991-998. A plant yield and disease incidence uniformity trial was conducted to provide information concerning the efficiency and precision of field trials used to evaluate Botrytis fruit rot control methods on strawberry. Fruit yield and Botrytis fruit rot incidence were recorded for individual strawberry plants of cultivars Sweet Charlie and Camarosa grown in an annual production system over two growing seasons. A nested analysis of variance model was used to measure plot edge effects and to obtain variance components to describe the relationship between plot size and plot variance. Mean seasonal yield for Sweet Charlie was 599 g/plant and for Camarosa 972 g/plant. Mean seasonal fruit rot incidence was 10.3% for Sweet Charlie and 3.0% for Camarosa. Plants growing on the edge of plots next to aisles had higher yields (637 versus 577 g/plant for Sweet Charlie and 1047 versus 923 g/plant for Camarosa), but there was no edge effect for disease incidence. Smith’s equation was used to determine the relationship between plot size and plot variance within mulched beds. Smith’s index was relatively high for yield (0.92 and 0.95) and Botrytis fruit rot incidence (0.91 and 0.69) for Sweet Charlie and Camarosa, respectively. This suggests a relatively uniform distribution of seasonal yield and disease incidence among plants within beds. Using plot variances estimated from Smith’s equation, the power of hypothesis tests to discriminate hypothetical treatment effects of different magnitudes was examined for each cultivar. Power analysis suggests that treatment effects ranging from 11.3 to 21.3% of the mean seasonal yield observed for Sweet Charlie and 8.6 to 16.5% of the mean seasonal yield observed for Camarosa can be detected with a power of 0.80 using four replicates of each treatment group and plot sizes ranging from 32 to eight plants/plot. For Botrytis fruit rot incidence, a power of 0.80 is achieved with treatment differences ranging from 24.9 to 44.1% of mean seasonal Botrytis fruit rot incidence for Sweet Charlie and from 44.1 to 64.9% of the mean observed for Camarosa using plot sizes ranging from 32 to 8 plants/plot. Before planting, the crown diameter and leaf number of transplants were recorded. There was no consistent significant correlation between any of these growth traits and seasonal yields or Botrytis fruit rot incidence. However, there was a consistent positive correlation for both cultivars between yield and crown diameter and also yield and leaf number during the months of December and January in the early part of the season (0.151 r 0.314 for crown diameter and 0.106 r 0.264 for leaf number).

The management of Botrytis fruit rot on annual strawberry by fungicides was evaluated in Florida during the 1995-96, 1996-97, and 1997-98 seasons. Weekly applications of captan or thiram, bloom applications of iprodione applied twice during each of two peak flowering periods, and weekly applications of captan combined with iprodione bloom applications were evaluated. Significant treatment effects (P ≤ 0.05) on the incidence of Botrytis fruit rot were detected for the early, late, and whole-season periods each season. Weekly applications of captan or thiram controlled Botrytis fruit rot, reducing disease incidence by more than 41% compared to the untreated control. These treatments also affected marketable yield during two seasons, with a 42 to 127% increase in yield compared to the control. Weekly fungicide applications did not reduce the incidence of Botrytis fruit rot until at least the fourth week of harvest, 9 to 10 weeks after applications began. Bloom applications of iprodione alone reduced the incidence of Botrytis fruit rot during the second peak bloom period, and the reductions in incidence occurred 1 to 3 weeks after the start of bloom applications. This suggests that iprodione applications control infections at flowering or early stages of fruit development. However, early-season bloom applications did not reduce the incidence of Botrytis fruit rot. The control of Botrytis fruit rot by weekly captan applications was not improved by the addition of iprodione bloom applications. These data suggest that early-season fungicide applications for the control of Botrytis fruit rot in annual winter strawberry are of limited efficacy, and that bloom applications of Botryticides such as iprodione should be focused on the second peak bloom period.

To determine the effects of sanitation on yield and incidence of Botrytis fruit rot (Botrytis cinerea) in annual strawberry, replicated experiments were conducted during the 1995-96, 1996-97, and 1998-99 seasons. Leaf sanitation (removal of senescent and necrotic leaves) and fruit sanitation (removal of unmarketable fruit from alleys between beds) were compared to a standard fungicide control program (weekly applications of captan plus four bloom applications of iprodione) and combined sanitation and fungicide treatments. Leaf sanitation reduced Botrytis fruit rot incidence from 12.6 to 8.2% over the entire 1996-97 season, and from 17.6 to 11.8% during the latter half of the 1998-99 season, compared to untreated controls. However, sanitation did not increase marketable yield. Supplementing fungicides with leaf sanitation or leaf and fruit sanitation did not improve disease control and frequently reduced yield. Fruit sanitation had no significant effect on Botrytis incidence or yield. Losses to Botrytis fruit rot in the sanitation treatments were significantly higher (P ≤ 0.05) than in the fungicide treatments each season; marketable yields were significantly lower in 1996-97 and 1998-99. Under Florida conditions, fungicides control Botrytis fruit more effectively and economically than does sanitation.

The effects of pre-plant dips and post-plant treatments on the infection by Colletotrichum acutatum, survival, and yields of strawberry plants were evaluated over two seasons in Florida using naturally infected transplants imported from northern nurseries. Handling practices such as washing, refrigerating, and dipping plants in water had no effect on infection, survival, or yield. Pre-plant dips with the fungicide Switch 62.5 WDG (cyprodinil + fludioxonil) and, in some cases, with Abound 2.08F (azoxystrobin), reduced infection and plant mortality, and increased yield. Pre-plant dips with Oxidate (hydrogen peroxide) were ineffective and, in some cases, increased plant mortality and reduced yield. Fertilizer treatments, such as dipping and spraying plants with Brotomax (8-0-0 plus micronutrients) or application of slow-release Osmocote (15-9-12 plus micronutrients) after planting, had no effect or reduced plant survival and yield. Post-plant application of Surround WP, a kaolin clay intended to reduce heat stress and control mites and insects, had little or no effect on infection, survival, or yield. In summary, strawberry transplants infected with C. acutatum can be dipped in Switch or Abound at planting to reduce infection and increase survival and yield, but other treatments and practices examined are unlikely to have beneficial effects. Accepted for publication 6 October 2009. Published 25 January 2010.

Preharvest fungicide applications for postharvest control of Botrytis fruit rot were evaluated over four seasons on annual strawberry in Florida. In the 2002-2003 season, applications of Switch or Elevate immediately prior to harvest were ineffective for controlling Botrytis fruit rot postharvest. In the 2003-2004 season, applications of Captevate or Switch made immediately prior to harvest reduced postharvest Botrytis fruit rot, but not as much as applications made during the flowering period. Similarly, in the 2004-2005 season, Captevate and Pristine provided some control of postharvest Botrytis fruit rot when applied immediately before harvest. In both the 2003-2004 and 2004-2005 seasons, applications made during the flowering period were more effective for postharvest Botrytis fruit rot control than those made prior to harvest. In the 2006-2007 season, applications of Captevate, Thiram, Scala plus Captan, or Switch alternated with Captan during the flowering period provided good control of postharvest Botrytis fruit rot. Although not as effective as bloom applications, fungicides applied immediately before harvest may have some benefit for controlling Botrytis fruit rot if the sprays during the bloom period were not made. Accepted for publication 21 July 2009. Published 21 September 2009.

PP 242, a 2-page illustrated fact sheet by N.A. Peres and James C. Mertely, describes this new crown-rot disease in Florida -- causal agent and symptoms, disease development and spread, and control. Published by the UF Department of Plant Pathology, November 2007. PP242/PP161: Charcoal Rot of Strawberries Caused by Macrophomina phaseolina (ufl.edu)

PP-230, a 4-page illustrated fact sheet by J. C. Mertely and N. A. Peres, describes the symptoms, disease development, and control of one of the most important diseases of strawberry worldwide. Includes table of fungicides used to control Botrytis fruit rot of strawberry in Florida. Published by the UF Department of Plant Pathology, July 2006. PP230/PP152: Botrytis Fruit Rot or Gray Mold of Strawberry (ufl.edu)

Botryotinia fuckeliana de Bary (anamorph Botrytis cinerea Pers.) is an ubiquitous plant pathogen causing gray mold disease on more than 200 crops grown in the field or in greenhouses. Eucalyptus seedlings originating from three different greenhouses showing stem lesions were submitted to the Gulf Coast Research and Education Center Disease Clinic in June 2012. Ten single spore isolates of B. cinerea were obtained and tested for sensitivity using spore germination and germ tube elongation assays described previously (4). Fungicides tested were pyraclostrobin at 100 μg/ml (Cabrio, BASF, Research Triangle Park, NC), thiophanate-methyl at 100 μg/ml (Topsin-M, UPI, King of Prussia, PA), fenhexamid at 1 and 50 μg/ml (Elevate, Arysta Life Sciences, Cary, NC), fludioxonil at 0.1 and 10 μg/ml (Medallion, Syngenta Crop Protection, Research Triangle Park, NC), and iprodione at 5 and 50 μg/ml (Rovral, Bayer CropScience, Greensboro, NC) on 1% malt extract agar (MEA, 10 g malt extract and 15 g agar), and to cyprodinil at 1 and 25 μg/ml (Vanguard, Syngenta Crop Protection) on 0.5% sucrose agar (4). Sensitivity to the succinate dehydrogenase inhibitors (SDHIs) boscalid at 5 μg/ml (Endura, BASF), penthiopyrad at 1 and 3 μg/ml (Fontelis, DuPont Crop Protection, Willington, DE), and fluopyram at 3 μg/ml (Luna Privilege, Bayer CropScience) was evaluated on yeast bacto acetate agar (YBA) (3). The discriminatory dose for boscalid was adapted from (2) whereas those used for penthiopyrad and fluopyram were developed in this study. Isolates were grown on malt yeast extract agar for 7 to 10 days and spore suspensions were prepared in sterile distilled water and diluted to 106 conidia/ml. Respective media in 9-cm petri dishes were seeded with 7-μl droplets from each isolate allowing testing for all isolates on one plate. Two plates were used for each fungicide and sensitivity tests were repeated twice. Germination and germ tube growth were assessed microscopically after 16 to 24 h incubation at 22°C. The frequency of isolates resistant to two, three, and four fungicides was 90, 60, and 10%, respectively. Nine isolates (90%) were resistant to thiophanate-methyl and pyraclostrobin, simultaneously, whereas six (60%) and two isolates (20%) were resistant to boscalid and fenhexamid, respectively. All boscalid-resistant isolates were also resistant to pyraclostrobin and thiophanate-methyl, but one fenhexamid-resistant isolate was sensitive to the other three fungicides. Eight isolates that germinated at 5 μg/ml iprodione but not at 50 μg/ml were considered sensitive. All isolates were sensitive to the SDHIs penthiopyrad and fluopyram as well as to cyprodinil and fludioxonil. To our knowledge, this is the first report of resistance to pyraclostrobin, thiophanate-methyl, fenhexamid, and boscalid in B. cinerea from eucalyptus seedlings in Florida. The absence of resistance to fludioxonil and iprodione is likely because these fungicides are not registered in nurseries as well as fluopyram and penthiopyrad which were developed only recently. Management practices should be developed to limit the selection and spread of additional resistant populations in eucalyptus nurseries as has occurred in Florida strawberries where multi-fungicide resistance is widespread (1). References: (1) A. Amiri et al. Plant Dis. 97:393, 2013. (2) M. Leroch et al. Appl. Environ. Microbiol. 79:159, 2013. (3) G. Stammler and J. Speakman. J. Phytopathol. 154:508, 2006. (4) R. W. S. Weber and M. Hahn. J. Plant Dis. Prot. 118:17, 2011.

On standard two-row black polyethylene covered beds, `Camarosa', `Rosa Linda', and `Sweet Charlie' strawberry plants were grown at 23, 31, 38, or 46 cm within-row spacing during the 1997–98 and 1998–99 seasons at Dover, Fla. Ripe fruit were harvested twice weekly from December through March. The first 8 weeks of harvest was considered the early period; the late period consisted of all harvests after the first 8 weeks. The effect of spacing on early marketable yield was consistent across seasons and cultivars. The 23-cm spacing resulted in the highest marketable yield per unit area, followed by the 31-, 38-, and 46-cm spacing. The percentage of fruit that were small (unmarketable) was higher at the 23-cm spacing than at the wider spacings (40% vs. 35% or 36%), but spacing did not affect the percentage of fruit that were misshapen. For the late harvest period, a spacing effect on marketable yield occurred in 1998–99, but not in 1997–98. The 23-, 31-, and 38-cm spacings in 1998–99 resulted in similar late period yields, which were 15% to 21% higher than the yield resulting from the 46-cm spacing. These results indicate that marketable yields per plant during the late period were higher at the wider spacings.

Strawberry (Fragaria × ananassa Duchesne) is produced as an annual winter crop in raised, plastic-mulched beds on 2,800 ha in west central Florida. In December 2001, a grower submitted collapsed and dying strawberry plants from a commercial field to the University of Florida in Dover. The cut crowns of affected plants revealed dark brown necrotic areas on the margins and along the woody vascular ring. Macrophomina phaseolina was isolated from pieces of infected tissue cut aseptically from the crowns and placed on a medium containing 12 g of Difco potato dextrose broth, 17 g of Bacto agar, 250 mg of ampicillin, and 100 mg of streptomycin sulfate per liter of water. The fungus produced numerous, dark, oblong sclerotia in the isolation medium after 4 to 5 days incubation at 24°C under constant fluorescent lighting. In 10-day-old cultures, sclerotia ranged in size from 55 to 190 μm long by 50 to 135 μm wide (average 105 × 74 μm). Ostiolate pycnidia bearing relatively large, broadly ellipsoidal, hyaline conidia occasionally developed on the host tissue after 8 to 10 days of incubation (2). During the 2003-2004 season, M. phaseolina was isolated from dying strawberry plants taken from the original field and two additional farms. Affected plants were often found along field margins or other areas inadequately fumigated with methyl bromide. Two single-spore isolates from different fields were tested for pathogenicity on nursery runner plants (cv. Strawberry Festival) grown for 4 weeks in the greenhouse on artificial potting soil. The fungal isolates were grown on corn meal agar at 24°C for 4 days and allowed to colonize sterile wooden toothpicks placed on the medium for an additional 5 days. Prior to use, the toothpicks were sterilized by autoclaving twice in deionized water and a third time in V8 juice. Six plants were inoculated with each isolate by inserting a colonized toothpick into each crown. Sterile, V8-infused toothpicks were inserted into the crowns of corresponding control plants. The plants were incubated in a greenhouse in a randomized complete block design with two replicates of three plants each. After 3 days, 33 to 100% of the inoculated plants developed wilting in one or more leaves. All inoculated plants collapsed or died within 2 weeks of inoculation, while the control plants remained healthy during the observation period. The pathogen was readily reisolated from inoculated plants. Charcoal rot disease caused by M. phaseolina has been reported on strawberry in France, India, and Illinois (2,3). To our knowledge, this is the first report from Florida. M. phaseolina may be an emerging threat as the Florida strawberry industry transitions from methyl bromide to other fumigants in 2005. References: (1) J. Maas. Macrophomina leaf blight and dry crown rot. Page 26 in: Compendium of Strawberry Diseases. 2nd ed. J. L. Maas, ed. The American Phytopathological Society, St. Paul, MN, 1998. (2) G. S. Smith and T. D. Wyllie. Charcoal rot. Pages 29–31 in: Compendium of Soybean Diseases. G. L. Hartman et al., eds. 4th ed. The American Phytopathological Society, St. Paul, MN. 1999. (3) B. Tweedy et al. Plant Dis. Rep. 42:107, 1958.

Monosporascus cannonbollus ascospore populations in the soils of three south Texas muskmelon fields were quantified at planting and at harvest in 1992. Sampling was conducted along eight-row segments (transects) within a 100×50 m area in each field according to a stratified random design. In a preliminary study (June 1991), ascospore counts were higher in-beds than between-beds and at a moderate depth of 10-20 cm in field A (annually cropped to muskmelon in fixed, plastic-mulched, drip-irrigated beds). Ascospore numbers were significantly lower in adjacent field B (rotated land, bare soil, and furrow irrigation). In 1992, ascospore counts in A were again significantly higher than in B and also higher than in C, a field similar to B

The pathogenicity of Monosporascus cannonballus to nine cucurbit and eight noncucurbit species was evaluated in the greenhouse by direct seeding into infested soil. Six of the cucurbit species were also tested under simulated field conditions in artificially infested microplots. In the greenhouse, M. cannonballus was isolated from 70-100% of the cucumber, muskmelon, and watermelon plants and from 33-70% of the bean, corn, sorghum, and sugar beet plants 8-9 wk after planting. Perithecia of the fungus were observed on the roots of all cucurbits tested but only rarely on roots of noncucurbits. Discrete brownish lesions, general light discoloration, and necrosis were characteristic symptoms of cucurbit root infection

A disease of muskmelon (Cucumis melo L.) characterized by a vine decline and a cortical root rot was first observed in the Lower Rio Grande Valley of Texas in 1986. In 1990, isolations from diseased plants collected from four commercial production fields yielded the fungus Monosporascus cannonballus. Pathogenicity tests with eight isolates confirmed Koch's postulates; however, there were differences in aggressiveness observed among isolates. M. cannonballus is an ascomycete fungus that typically produces only one (rarely two), round, jet-black ascospore per ascus. There is no known asexual stage. Temperature optimum of one isolate was 35 C. The optimum pH for growth was 6-7, but it grew well up to pH 9. M. cannonballus was first reported on muskmelon in 1970 from Arizona and recently was found in Japan under glass house culture. The presence of this fungus in Texas marks only the third report of this species worldwide, although a similar species (M. eutypoides) is the cause of a collapse of melon plants in Israel.

A serious disease of muskmelon (Cucumis melo) caused widespread losses in theLower Rio Grande Valley of Texas in 1986 and has persisted through the 1990 crop season. Primary symptoms on the roots include extensive browning and necrosis of the taproot and lateral roots, vascular discoloration, and discrete brown to red cortical lesions. Secondary vine decline symptoms are characterized by a dieback of older crown leaves, which advances distally to younger leaves as the plants approach maturity