About Sorghum Webworm
Reproduction and Life Cycle
The sorghum webworm will typically go through 2 to 4 generations annually, depending on climate conditions. They make cocoons and remain in them as larvae throughout the winter. They do this underneath dead leaves and plant debris near the stalk of a host plant. They pupate in the spring when temperatures reach an average of 58 degrees Fahrenheit. They will remain pupae for 5 to 9 days. The adults surface later in the spring and are only active during the night with a lifespan usually between 10 and 20 days. During the female’s lifetime they will lay approximately 88 eggs on and around the blooms or seeds of a host plant within the area. The eggs are placed individually and will hatch 3 to 4 days later. When the eggs hatch the larvae will go through 5 instars, usually taking 13 days to complete. The entire process from egg to moth will take about 24 days. By the middle of summer, this pest’s population tends to grow quite quickly.
Sorghum Webworm Identification and Habitat
The adult is a moth and has a wingspan of 12 to 18mm. Their white forewings have slight shading along the outer margin that is yellow-brown. They have 4 clusters of scales that are found down the costa. These scales are noticeable on some and indistinct on others. The eggs are 0.5mm long and 0.3mm wide, can be either oval or round in shape, and are somewhat flattened. When they are first laid, the eggs are white with a hint of yellow, and will then change to a deeper yellow or sometimes a brown colour over the next 48 hours. When the larvae hatch, they are tiny (about 0.7mm) and hairy with 4 brown stripes running lengthwise down their back. Their main body colour is green-yellow and has 8 prolegs. As the larvae mature, they can reach to be about 14mm long. They are not overly active. The pupa is pale yellow, or sometimes brown with its upper side being closer to red in colour. They are about 6 to 10mm long. The cocoon is white.
This pest can often be spotted in the southeastern areas of the United States. They are common in grassy areas, especially in sorghum fields. The larvae will cause the most damage as they eat the sorghum seed heads. The young larvae often just feed on sorghum buds, but the more mature larvae eat the kernels, keeping the outer hull undamaged. During severe infestations, yield losses can be anywhere between 30 and 80 percent. However, these bad infestations are unlikely to occur if the summer has been hot and dry. This pest is able to dangle from the plant with silk strands that they spin. This webbing can be noted if there is an extensive amount of larvae present.
Sorghum Webworm Management and Control Methods
To help suppress the sorghum webworm population, fall plowing is advised. This buries any plant debris that remained from harvest and will lower the number of larvae that uses that area to overwinter in. There are also sorghum hybrids available that are “open headed”. This variety of grain will allow larvae that feed on the sorghum to be exposed to insecticide sprays and other predators of the sorghum webworm. An early planting can also help reduce their population. However, it is important to note that having satisfactory control is often dependent on using an integrated management system that includes the use of both cultural and chemical methods.
When there are approximately 5 larvae per plant, chemical treatment may be warranted. Some insecticides that are recommended: Lannate SP or LV, Lorsban 4E, Sevub XLR, Tracer, Warrior T, Baythroid 2, and Mustang Max. Be sure to carefully read the label for cautions and proper application. It is extremely important to never spray on days that are windy. After applying insecticides, it is important to irrigate sprayed area to increase the insect control. That being said, a large rainfall or irrigation soon after the application can reduce the concentration insecticides.
Latin / Alternative Sorghum Webworm Names