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Soybean pests and diseases

How does this crop behave?

The plant Glycine max, commonly known as soybean, is defined by the Food and Agriculture Organization (FAO) as one of the most important world crops. It is often grown as a rotation crop combined with cotton, maize and sorghum.  The stages of this crop can be divided into: initial, crop development, midseason and late season, covering a total period from 100 to more than 130 days.

The commercialized parts of the soybean are the seeds. According to the lastest data, the yield varies between 1.5 and 2.5 tons/ha seed under rainfed conditions. Under irrigation, the yield can reach between 2.5 to 3.5 ton/ha seed. However, not only the water availability can affect the yield but also the nutrient availability. In the SMART Fertilizer Software, we calculate the best fertilization strategy for your soybean crop based on the characteristics of your field which can help you to obtain higher benefits from your plantation.

Soybean field. Image: Meredith Petrick

Know about common pests and diseases

Even if not all the pests and diseases observed in soybean crops are economically important, it is interesting to know about their existence in order to protect the plants. A large number of genetically modified soybean now exisist to reinforce its drought tolerance or pest and diseases resistance. According to the International Service for the Acquisition of Agro-biotechnological Applications (ISAAA) in 2019, soybeans covered 48% of the world surface dedicated to genetically modified crops. This makes it the first transgenic crop in the world, with 91.9 million hectares cultivated. However, the legislation of some countries does not allow farmers to grow them. In any case, we are mentioning in this articles the pests and diseases affecting wild type plants, so please take into account that some of them can be avoided by using resistant varieties.

Although it is most common to observe symptoms caused by pathogens or pests first on the leaves, damage can be done to all parts of the plant, including roots, shoots, stems, pods and seeds. The least common case is that of problems that start at the root. Damage can be caused by various types of organisms such as bacteria, fungi, nematodes, and viruses. Pests also vary greatly, from insects to mammals. In any case, the most effective way to manage and control a disease is based on a proper diagnosis. That is why knowing the possible causes is key.

Sclerotinia blocks the stem flow

Sclerotinia stem rot (SSR) is a significant disease that is difficult to control, and has appeared in over 95 countries. It is caused by the cosmopolitan fungal pathogen Sclerotinia sclerotiorum that induce programmed cell death in the host plant. This infection causes dramatic yield reductions, reducing seed number and weight because of the enclosing of stems that disrupts the xylem and phloem flow. The strategies to deal with this fungus can be addressed from three sides: by cultural practices to avoid the fungus development, by using the appropriate soybean varieties according to the field location or with methods that attack the pathogen directly.

Management strategies against Sclerotinia stem rot disease. Image: Willbur et al. 2018

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Direct to the seeds

Nothing affects the yield more than pest and diseases attacking the seeds and pods. One of these cases is the fungus Diaporthe longicola that causes the classic phomopsis seed decay (PSD) of soybean. This infection can be observed by the naked eye because the seeds are often have a chalky white mold on its surface. Even though the currently available fungicide seed treatments seem to be quite effective against this fungus, it is recommended to control the presence of it and as fast as possible eradicate the infected plants.

The always unwelcome aphids

Aphids are approximately 1.5mm insects that needle the soybean plants to extract plant juices using its sucking structures. Even if they are so small, their reproduction tax is so fast that a plant can be rapidly infected by a large number of them, blocking the stem flow. This disease is not easy to get rid of without using proper insecticides. In addition, the damage they cause on the stems are sometimes the entrance of bacteria, virus and fungus and amplified the damage. In north America, the registered data shows that over 30% of the yield is lost in average when this insect is present.


A general overview

Two very common diseases and a pest have featured  in this article, because its presence has been observed all around world as a cause behind a large drop in yield. Have you found any signs of  infection in your plants? Do not hesitate to upload it at the SMART Fertilizer forum to get the best advice from our experts and the community. Make sure you follow our articles to find more useful information and obtain the highest production from your field.





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