It’s not always easy to identify the primary cause of early crop maturity in soybeans, as it can be simultaneously induced by a range of environmental factors, including common diseases. However, a close examination of the plants can reveal the presence of rot around the roots and stems, which could indicate something unusual.
To help you put in place effective management practices and get a clearer picture of the situation, here are the main symptoms for some of the diseases that commonly attack soybean.
Sudden death syndrome
The sudden death syndrome is caused by a pathogen that affects seedlings early in the season. The appearance of little chlorotic spots on the leaves is the first symptom of the disease. These speckles then quickly spread and transform into yellow patches between the veins of the leaves that eventually necrotize.
Rot is present on the roots of soybean plants infected by the sudden death syndrome. When splitting the stem of an infected plant lengthwise, the cortex will appear brown while the centre pith will remain white.
Phytophthora can develop at any time during the season, regardless of the plant’s growth stage. This disease often causes damages to plants under significant stress. Soybeans seeded near the entry points of the field are more likely to become infected by the disease, because of the poorer drainage of the compacted soil in these heavy traffic areas.
Soybean plants affected by phytophthora are easy to pull from the soil because of root rot, which is an early sign of the infection. Diseased roots (that are smaller than ones found on healthy plants) and a brown discolouration moving up 6 to 12 inches from the soil line are usual indications of the disease. Leaves wilting then clinging to the petioles and stem of the dying plant also point to this type of infection.
Pod and stem blight
Sometimes confused with early crop maturity of soybean, pod and stem blight is a disease that can practically destroy an entire field.
The disease may be detected in soybeans from the first reproductive stage. It presents itself as reddish-brown lesions around the base of branches or petioles. As they progress, the lesions will change colour and turn dark brown or black. Symptoms on the leaves may include the development of chlorosis above or below the canker, causing the plant to wilt and eventually die.
Stem blight is not a chronic disease and does not cause root rot.
White mould develops during periods of high humidity and hot weather. It may start at mid-season, but mostly happens during flowering. Symptoms of this disease generally emerge early in the reproductive stage and are characterized by the white mould that appears on the lower part of the stem. Other symptoms, such as leaves and top stems wilting and dying, can also be signs of the disease.
Narrow spacing between the rows, high fertility and earlier appearance of white mould are all factors that may contribute to the occurrence of the disease.
As is the case with white mould, stem rot disease starts developing on soybean plants from mid-season until the end. Infected plants show no signs of the disease on the leaves before pods start forming.
However, when symptoms on the leaves appear, they take the form of yellow-brown spots between the veins. The best way to confirm the presence of brown stem rot disease is to cut the stem in half lengthwise. If the pith shows signs of a dark brown discolouration, odds are that the plant is infected by the disease.
The importance of keeping an eye on soybean fields
The pathogens that cause most of the diseases described above can survive in the soil. Identifying the diseases affecting your soybean, walking the fields and checking the plants one by one will help you manage your crops. Improved drainage and the right fertilization program can also curb the progression of certain diseases.
Have a good summer!