Soybean stem canker is one of the most common fungal diseases in the United States and Canada. The root system of the plant becomes infected as a result. The fungus genus Diaporthe causes this disease. The exact fungus that causes soybean stem canker has little effect on the diagnosis and management of the condition. Stem canker shares symptoms with other late-season diseases such as white mold, Phytophthora stem, root rot, Sudden Death Syndrome, and brown stem rot. In the field, the signs of soybean stem canker may be mistaken for those of prematurely maturing plants. Soybean stem canker is frequently misdiagnosed due to its striking similarities to a number of other conditions. It is essential for farmers and scouts to be able to identify these late-season diseases and problems.
What is Soybean
The soybean is one of the most important sources of oil and protein from plant sources. This legume was initially consumed in China before being exported to Europe and the United States. The United States, Brazil, Argentina, China, and India are the leading producers of soybeans at this time. South American countries Uruguay, Paraguay, and Bolivia also cultivate soybeans in addition to Brazil and Argentina. The total amount of soy produced in South America in 2018 was 194.907.867 metric tons. More than 135 plant diseases impact soybeans around the world; at least 30 of these plant viruses are considered commercially significant and can result in considerable yield losses.
Multiple nations have initiated breeding programs for disease resistance because, when accessible, genetic resistance is the most effective method for boosting global food security by reducing the need for chemical control. Several different species of the fungus genus Diaporthe Nitschke can cause severe diseases such as seed decay, pod, stem blight, and soybean stem canker. All of these diseases have an effect on soybean output. The Diaporthe/Phomopsis complex is a commonly used term for these conditions. Both Phomopsis logically and Diaporthe sojae are responsible for pod and stem blight, although Phomopsis logically is primarily responsible for seed rot.
Soybean Stem Canker
Although soybean stem canker is moderately widespread, it is likely underreported since it affects only a small percentage of soybean crops. Plants as a whole, not just their individual sections, are vulnerable to stem canker\’s destructive effects. Similar to Phytophthora rot, it may cause confusion. The northern and southern soybean stem cankers are different types of this disease, but their distribution zones may overlap. It is possible to grow soybeans that are resistant to stem canker disease by selecting a resistant genotype. While this disease may only appear to be killing or hurting a few plants here and there, in reality, it can wipe out entire regions and result in significant losses of yield.
Symptoms of Disease
Symptoms of soybean stem canker Lesions of a reddish brown hue first appear near the base of the branch or leaf petiole. Small early lesions can develop into cankers that are long, deep, and dark brown in color and can spread up the stem. On the stems of plants killed by stem canker, tiny black spots known as perithecia are frequently dispersed or aggregated. Plant tissue above lesions may wither and perish. It is possible for the interior of the stem to turn rusty brown and pods to fail to form. It is conceivable for necrosis and chlorosis to develop between the veins of a dead leaf, and the leaf may still be attached to the stem. Phytophthora rot is commonly mistaken for a condition characterized by the formation and persistence of darker lesions at nodes, which can progress to the soil line.
Stem Canker In Soybeans
Stem canker in soybeans is a plant disease caused by the fungal pathogen Diaporthe aspalathi (formerly known as Diaporthe phaseolorum var. meridionalis). It primarily affects soybean plants and can cause significant yield losses if not properly managed.
Stem Canker Is Caused by
Actually, the term soybean stem canker refers to two distinct disorders. We have only found the fungus Diaporthe phaseolorum var. caulivorum, which causes northern stem canker, in Nebraska. The fungus typically overwinters on contaminated agricultural waste and has been related to seed. There is evidence that diseased crop waste is a major disease reservoir in the environment. During the initial stages of a plant’s vegetative growth, spore formation and infection occur. The diseased soy plant will remain dormant until it enters reproduction.
Favorable Weather Conditions for Soybean Stem Canker
The severity of soybean stem canker is significantly influenced by climate conditions throughout the early periods of plant development. Wet and wet conditions facilitate the transmission of disease. Researchers have noticed that hail-damaged crops are more susceptible to stem canker.
Disease Cycle of Soybean Stem Canker
The fungus spends the winter in the soil on dead plants that have been infected. It can do this for several years. When it rains, the fungus makes spores, which can be splashed onto the lower stem of the plant and spread there. Soybean stem canker grows best in wet springs and early summers, and most infections happen when the plant is just starting to grow leaves. Seeds can be infected by fungal spores, but spores from infected waste are usually the main source of inoculum.
Management of Soybean Stem Canker
Planting resistant varieties of soybean are the most efficient control method. If you want current information regarding stem canker-resistant varieties, you should visit a seed retailer. By rotating to a non-host species between harvests, soybean inoculum can be maintained to a minimum. After a severe disease infestation, it is recommended to rotate soybeans with nonhosts such as corn, wheat, or sorghum for at least two years. Based on the results of efficacy testing, fungicides may not be effective against soybean stem canker when susceptible cultivars are used. However, stem canker can be treated using fungicides in cultivars with only moderate resistance.
When the plant is young and growing, spray it with pesticides. Stem canker is more prone to occur in low- or no-till agricultural areas due to the presence of greater crop residue. Before the next planting season, incorporating diseased crop debris into the soil can help avoid soybean rust. The practice of planting fields with a known history of stem canker last is another method for preventing the spread of disease. The agricultural areas with the highest amounts of soil organic matter or fertility are among the most vulnerable. Maintain a healthy level of fertility to prevent the spread of disease.
Biological Control of Soybean Stem Canker
Microplots of fields were divided into no-till, minimum-till, and shallow-plowing categories, and an antibiotic-producing Chaetomium globosum isolate was tested for its ability to inhibit the spread of Diaporthe phaseolorum f. sp. meridionalis in soybean stubble. Before any tillage was performed, mature soybean stem canker colonized in vitro with Dpm were disseminated on the soil surface and a nutrient-free C. globosum ascospore suspension was sprayed across the entire plot. The stems canker of soybeans were monitored for 180 days, the average time between harvest and sowing, in order to track the formation and survival of DPM perithecia with C. globosum colonization.
Contrary to the positive correlation between C. globosum occupancy and the proportion of soybean stem canker segments occupied by Dpm, the quantity of perithecia generated dropped linearly over time. The conclusion of the study corresponded with the beginning of the soybean planting season, by which time the soybean stubble had been overrun by C. globosum and no longer contained viable Dpm. C. globosum was equally as effective at eliminating the pathogen from surface-borne residue or harrowed-in residue as it was in shallow-plowed microplots, but at a much slower rate. C. globosum succeeded despite the fact that Trichoderma, Nigrospora, and Fusarium were formidable competitors for the colonization of the soybean stems above and below the soil. The use of an antibiotic-producing C. globosum strain in the control of soybean stem canker disease is supported by evidence.
Soybean Stem Canker Fungicide
- Triazoles: Fungicides such as triazoles (e.g., azoxystrobin, propiconazole) are commonly used for managing fungal diseases in soybeans. They provide broad-spectrum control.
- Strobilurins: Strobilurin fungicides (e.g., pyraclostrobin) are another group of fungicides effective against soybean diseases, including stem canker.
- Mixtures and Rotations: To minimize the risk of resistance development, it’s advisable to rotate or mix fungicides with different modes of action.