- Author: Mark Bolda
Introduction: The difficulty of controlling Macrophomina, the causal agent in charcoal rot in strawberry, in California has brought about a renewed interest in non-conventional methods for its management.
The following study is an attempt to investigate two soil applied fungicides and their effectiveness in mitigating loss from Macrophomina infection.
Materials and Methods: The trial was done as a randomized complete block design of four replicates of one bed 35 foot long by 4 foot wide per treatment on Monterey variety strawberries in a field known to be infested with Macrophomina in Salinas, California. See the picture below for a demonstration of the disease severity of the disease on one side of the field; the side on which the study was done was unfortunately (for the study, not the grower) not nearly as severe.
Application: Applications of both fungicides were done 3 times in the early part of the year, March 2, April 12 and May 3, 2017. The fungicide Rhyme (which is labeled for soil application for management of charcoal rot), applied at 7 oz/acre and Merivon, applied at 11 oz/acre, were applied in approximately 40 gallons of water per treatment pumped in with a gasoline powered pump hooked up to the double rows of high flow drip tape. Injection consisted priming the irrigation tape, injecting the material and then flushing the lines.
It is important to note that the use pattern deployed here for Merivon is as of this time NOT a labeled application.
Evaluation:
Plant diameters were taken in the early part of the season to gauge any initial differences in plant vigor. One measurement across the widest part of ten plants was taken in each treatment replicate and reported in cm.
Yield of strawberry fruit was the principle measure of plant performance in this trial. Fruit picking commenced in May with weekly picks, and then continued from June through early September with twice weekly picks. Only marketable fruit was included, and it was weighed and counted from each plot.
Since the work here involved two fungicides, one evaluation of powdery mildew was also done on May 9, 2017 but the amount of mildew was insufficient for a significant evaluation.
Results were tested statistically on ARM version 9 using a multiple comparison procedure (Least Significant Difference at the 95 percent level of significance) to determine whether the means of counts and percentages per treatment were significantly higher or lower from the other treatments.
Results and Discussion:
Results are given in Tables 1 and 2 below. While disease was evident with weakening plants from the beginning of May on, it was not as severe as the outbreak on the other side of the field and no plants were lost in any of the treatments.
Table 1: Plant Diameters on Two Dates (in cm) of Strawberry in Plots of Soil Applied Fungicides Rhyme and Merivon Compared to an Untreated Check1
Treatment |
Apr 12 |
May 3 |
Untreated |
32.2 a |
33.1 a |
Rhyme |
32.7 a |
34.7 a |
Merivon |
32.7 a |
35.7 a |
Table 2: Fruit Yield and Size (in g) of Strawberry in Plots of Soil Applied Fungicides Rhyme and Merivon Compared to an Untreated Check1
Treatment |
May totl |
May size |
June totl |
June size |
July totl |
July size |
Untreated |
2214a |
35.6 a |
4408a |
28.4 a |
5636a |
21.0 a |
Rhyme |
2169a |
35.3 a |
4720a |
28.1 a |
5525a |
21.9 a |
Merivon |
2216a |
34.6 a |
4454a |
27.9 a |
6064a |
22.1 a |
Treatment |
Aug totl |
Aug size |
Sept total |
Sept size |
Season total |
Size avg |
Untreated |
3051a |
21.2b |
849.0a |
20.9 b |
16157a |
24.1 a |
Rhyme |
2617a |
22.2a |
784.5a |
21.5 ab |
15816a |
24.8 a |
Merivon |
2752a |
21.9a |
1009a |
22.3 a |
16496a |
24.6 a |
1Method used to discriminate among means Fisher's least significant difference procedure. Treatments followed by the same letter have no statistically significant differences.
As seen in the tables above, use of the soil applied fungicides in this trial did not result in any significant yield differences between any of the treatments. It is interesting to note however, that average fruit size in the later months of the study, those being August and September, was significantly larger in the treated plots than the untreated.
Many thanks to the grower, BASF and FMC for really great support on getting this trial done.
The use of several pesticides is described in this post. As always, before using any of these or other pesticides, consult the label and if there are further questions contact your local County Agricultural Commissioner.
- Author: Sumanth S. R. Dara
- Author: Suchitra S. Dara
- Author: Surendra K. Dara
Charcoal rot, caused by Macrophomina phaseolina, is one of the important fungal diseases of strawberry in California. Macrophomina phaseolina is a soilborne fungus and has a wide host range, including alfalfa, cabbage, corn, pepper, and potato, some of which are cultivated in the strawberry production areas in California. The fungus infects the vascular system of the plant roots, obstructing the nutrient and water supply and ultimately resulting in stunted growth, wilting, and death of the plant. The fungus survives in the soil and infected plant debris as microsclerotia (resting structures made of hyphal bodies) and can persist for up to three years. Microslerotia germinate and penetrate the root system to initiate infection. Plants are more vulnerable to fungal infection when they are experiencing environmental (extreme weather or drought conditions) and physiological (heavy fruit bearing) stress.
Soil fumigation is the primary management option for addressing charcoal rot in strawberry. Crop rotation with broccoli can also reduce the risk of charcoal rot due to glucosinolates and isothiocyanates in broccoli crop residue that have fungicidal properties. Beneficial microorganisms such as Bacillus spp. and Trichoderma spp. are also considered, especially in organic strawberries, to antagonize M. phaseolina and other soilborne pathogens and provide some protection. The role of beneficial microbes in disease management or improving crop growth and health is gaining popularity in the recent years with the commercial availability of biofungicide, biostimulant, and soil amendment products. In a couple of recent strawberry field studies in Santa Maria, some of the beneficial microbial products improved fruit yield or crop health. These treatments can be administered by inoculating the transplants prior to planting, immediately after planting or periodically applying to the plants and or the soil. Adding beneficial microbes can help improve the soil microbiome especially after chemical or bio-fumigation and anaerobic soil disinfestation.
Similar to the benefits of traditionally used bacteria (e.g., Bacillus spp. and Pseudomonas spp.) and fungi (e.g., Glomus spp. and Trichoderma spp.), studies with entomopathogenic fungi such as Beauveria bassiana, Isaria fumosorosea, and Metarhizium spp. also demonstrated their role in improving water and nutrient absorption or antagonizing plant pathogens. The advantage of entomopathogenic fungi is that they are already used for arthropod pest management in multiple crops, including strawberry; now, there are the additional benefits of promoting crop growth and antagonizing plant pathogens. In light of some promising recent studies exploring these roles, a study was conducted using potted strawberry plants to evaluate the efficacy of two California isolates of Beauveria bassiana and Metarhizium anisopliae s.l. and their application strategies against M. phaseolina.
Methodology
About 6 week old strawberry plants (cultivar Albion) from a strawberry field at the Shafter Research Station were transplanted into 1.6-gallon pots with Miracle-Gro All Purpose Garden Soil (0.09-0.05-0.07 N-P-K) and maintained in an outdoor environment. They were regularly watered, and their health was monitored for about 5 months prior to the commencement of the study. Conidial suspensions of the California isolates of B. bassiana and M. anisopliae s.l. were applied one week before, after, or at the time of applying microsclerotia of M. phaseolina to the potting mix. The following treatments were evaluated in the study:
- Untreated control
- Soil inoculated with M. phaseolina
- Soil inoculated with B. bassiana 1 week prior to M. phaseolina inoculation
- Soil inoculated with M. anisopliae s.l. 1 week prior to M. phaseolina inoculation
- Soil inoculated with B. bassiana at the time of M. phaseolina inoculation
- Soil inoculated with M. anisopliae s.l. at the time of M. phaseolina inoculation
- Soil inoculated with B. bassiana 1 week after to M. phaseolina inoculation
- Soil inoculated with M. anisopliae s.l. 1 week after to M. phaseolina inoculation
Entomopathogenic fungi were applied as 1X1010 viable conidia in 100 ml of 0.01% Dyne-Amic (surfactant) solution distributed around the plant base. To apply M. phaseolina, 5 grams of infested cornmeal-sand inoculum containing 2,500 CFU/gram was added to four 5 cm deep holes around the base of the plant. Each treatment had six pots each planted with a single strawberry plant representing a replication. Treatments were randomly arranged within each replication. The study was repeated once a few days after the initiation of the first experiment.
Plant health was monitored starting from the first week after the M. phaseolina inoculation and continued for seven weeks. Plant health was rated on a scale of 0 to 5 where 0=dead and 5=very healthy and the rest of the ratings in between depending on the extent of wilting. Data from both experiments were combined and analyzed by ANOVA using Statistix software and significant means were separated using LSD test. The influence of entomopathogenic fungal treatments applied at different times as well as the combined effect of different applications within each fungus were compared for seven weeks. Ratings for some plants that were scorched from hot summer temperatures and died abruptly were removed from the analyses.
Results
Untreated control plants maintained good health throughout the observation period varying between the rating of 4.3 and 4.9. In general, plant health declined considerably from the 5th week after M. phaseolina inoculation. Plant health appeared to be slightly better in plants treated with entomopathogenic fungi, but there was no statistically significant difference in any except one instance. Plants treated with M. anisopliae one week prior to the application of M. phaseolina had a rating of 3.0 compared to 1.6 rating of plants inoculated with M. phaseolina alone.
When data from different treatments for each entomopathogenic fungus were compared, both B. bassiana and M. anisopliae s.l. appeared to reduce the wilting, but the plant health rating was not significantly different from the M. phaseolina treatment alone.
This is the first report of the impact of entomopathogenic fungi on M. phaseolina with some promise. Additional studies under more uniform environmental conditions and with more treatment options would shed more light on this approach of using entomopathogenic fungi against M. phaseolina. The current study evaluated single application of the entomopathogenic fungi and we plan to conduct additional studies with multiple applications.
Acknowledgements: We thank Dr. Kelly Ivors (previously at Cal Poly San Luis Obispo) for the pathogen inoculum and Dr. Stefan Jaronski, USDA-ARS, Sidney, MT for multiplying the entomopathogenic fungal inocula.
References
Dara, S. K. and D. Peck. 2017. Evaluating beneficial microbe-based products for their impact on strawberry plant growth, health, and fruit yield. UC ANR eJournal Strawberries and Vegetables. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=25122
Dara, S. K. and D. Peck. 2018. Evaluation of additive, soil amendment, and biostimulant products in Santa Maria strawberry. CAPCA Adviser, 21(5): 44-50.
Dara, S. K., S.S.R. Dara, and S. S. Dara. 2017. Impact of entomopathogenic fungi on the growth, development, and health of cabbage growing under water stress. Amer. J. Plant Sci. 8: 1224-1233. http://file.scirp.org/pdf/AJPS_2017051714172937.pdf
Dara, S. K., S. S. Dara, S.S.R. Dara, and T. Anderson. 2016. First report of three entomopathogenic fungi offering protection against the plant pathogen, Fusarium oxysporum f.sp. vasinfectum. UC ANR eJournal Strawberries and Vegetables. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=22199
Koike, S. T., G. T. Browne, and T. R. Gordon. 2013. UC IPM pest management guidelines: Strawberry diseases. UC ANR Publication 3468. http://ipm.ucanr.edu/PMG/r734101511.html
Partridge, D. 2003. Macrophomina phaseolina. PP728 Pathogen Profiles, Department of Plant Pathology, North Carolina State University. https://projects.ncsu.edu/cals/course/pp728/Macrophomina/macrophominia_phaseolinia.HTM
Vasebi, Y., N. Safaie, and A. Alizadeh. 2013. Biological control of soybean charcoal root rot disease using bacterial and fungal antagonists in vitro and greenhouse condition. J. Crop Prot. 2(2): 139-150.
- Author: Sarah Light
A field in Sutter County was confirmed to have charcoal rot, also known as dry root rot or ashy stem blight, which is caused by the fungus Macrophomina phaseolina. The disease generally occurs under dry soil conditions paired with high temperatures and can be especially problematic when irrigation is delayed during periods of drought stress. This pathogen infects the crown and stem of garbanzo plants near the soil line and produces black cankers, which are sunken with distinct margins and often contain concentric rings. The disease is usually scattered in the field and often occurs during the flowering and pod stages (although infection can occur at all growth stages). The pathogen infects the stems of seedlings at the base of the developing cotyledon near the soil line. In older plants, symptoms include stunting, leaf chlorosis, early defoliation, and ultimately plant death. A sudden drying of whole plants scattered in the field is observed. Additionally, a “charcoal dust” can appear near the soil line on the surface of roots and stems of older plants. Canker development may kill the plant's growing tip and weaken the stem, causing stems to break, separating roots from the rest of the plant when plants are removed from the field. Infection can move into the hypocotyl and root region, as well as primary leaf petioles. The plant taproot often becomes dark, necrotic, and devoid of lateral and fine roots.
Management options in California are limited. This disease affects other legumes like common beans, blackeyes, and limas, as well as other crops that may be grown in rotation (like sunflowers). Inoculum survives in both seeds and soil. A 3-year rotation with a cereal grain (except corn and sorghum, which are hosts) is recommended to reduce soil inoculum levels. The dry, warm weather in the winter months earlier this year were conducive to drought stress for garbanzos, which increased the risk of disease. If possible, irrigate to avoid drought stress conditions. Garbanzos grown in soils that are high in organic matter tend to have more problems with this disease, however, garbanzos in other soil conditions are at risk if the plants are stressed and the environment is conducive to disease development.
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