About Soybean Cyst Nematode
Soybean cyst nematode disease is caused by Heterodera glycines, which is a plant parasite that can be devastating to soybean plants worldwide. This nematode will infect the roots of a host plant and reproduce sexually. Similar to other nematodes, they go through 6 different life stages: egg, juvenile stages (4), and adult. Typically it takes a nematode 3 or 4 weeks to run through the entire life cycle, depending on climate conditions. The nematode will remain in the confines of the eggshell until they have molted into the second juvenile stage, which is when they will leave the protection of the shell and penetrate soybean roots. They will travel in the soil and find a suitable root, often infecting right above the tip. It will move in the roots vascular system and the enzymes they create will begin to deteriorate the cell walls. They create a feeding site as their secretions modify the plant cells; development from juvenile stage 2 will not continue unless this feeding site is developed. From this stage with proper feeding, the females will begin to swell and lose mobility. This is when the females begin protruding from the plant, with only their head remaining in the root to continue feeding. Eggs that remain in the cyst can wait until a new growing season to emerge from their shell. A female can produce 200-600 eggs, where most remain in the cyst. However, some may be placed in a secretion the female produces outside of the body from their posterior. The cysts will likely detach from the plant roots and remain in the soil. Males do not feed on the roots when they are adults; they are just required for egg fertilization. When mature, adults are fairly long compared to their earlier juvenile stages. Soybean cyst nematodes can have up to 3 generations each year.
Soybean Cyst Nematode Identification and Habitat
Males and females are dissimilar; during adulthood, males are in the shape of a worm and are capable of motion, whereas the females are immobile and are shaped similar to a lemon. The only time this nematode is viewable by the naked eye is when the females are present on the surface of plant roots in their swollen lemon-shape. Adult males and both immature males and females (in their juvenile stages) must be viewed through a microscope. The female adults will first appear as white with their head in the root to feed and will be approximately 750 µm long and 450 µm wide. They have a stylet that sticks out of the head which is used to feed on and pierce plant tissue. As they age, they will change to yellow and when they die their bodies turn brown. After death their bodies become cysts that protect eggs inside. This disease is easy to diagnose when the females are protruding from the roots. However, plant systems can sometimes be confused with other plant conditions such as iron deficiency, stress, nutrient deficiency, etc. Typically when a plant is infected with soybean cyst nematodes, the leaves and stems will begin to yellow with stunted growth. While roots may also be stunted, this is often misdiagnosed as plant stress. Seed yield can greatly be reduced and shoot growth will slow. Symptoms of this disease are more common in areas where the plants are experiencing environmental stress.
Soybean plants in fields with soil that has either extremely high or low moisture levels will have a greater prominence of nematodes. If there is no environmental stress, the nematodes may only be noticed when they have high populations. If proper sanitation methods are not used, soybean cyst nematodes can easily move from field to field from infected equipment or small soil clumps that are transported. The nematode cannot travel via seed. The cysts that are formed when females die are quite durable and can survive for up to 9 years in the soil and can travel by water and wind. Favorable conditions for this nematode include soil temperatures of about 75 degrees Fahrenheit for the eggs to hatch, approximately 82 degrees for second stage juvenile nematodes to penetrate roots, and anywhere between 82 and 89 degrees for development past the second juvenile stage. Development will cease to take place if temperatures reach below 59 or above 95 degrees Fahrenheit.
Soybean Cyst Nematode Management and Control Methods
Early detection of this disease is important for effective control. It is important to note that once this nematode has infected an area, eradication is impossible. If soybean cyst nematodes are present in the field, use resistant varieties with an integration of other management methods such as practicing frequent crop rotation with plant types that are not susceptible such as corn. Additionally, keep plants healthy with ensure proper moisture and nutrient levels are met so that they can better withstand infection. Keep soil fertile and minimize other pests or weeds that could damage the plants’ vigor. While these methods will not eradicate soybean cyst nematodes, they will help in keeping the damage to yield at a minimum.
For chemical control, use nematicides. Dichloropropene as a fumigant has been known to effectively decrease nematode populations. Additionally, nonfumigants such as oxamyl, and aldicarb have also been proven effective. That being said, the overall success of these nematicides will depend on current weather and soil conditions. These applications are toxic and should only be used after careful consideration and can only be applied by a licensed applicator. Labels should always be read for cautions and proper application before use.
Alternative Soybean Cyst Nematode Names