|
|
|
|
|
 |
|
|||||||||||||||||||||||||||||
Corn Rootworm Corn Rootworm Corn rootworm are some of the most damaging corn pests causing up to 80% of yield loss and affecting as much as 32 million acres per year. There are three different species of corn rootworm: Western corn rootworm: The adult western corn rootworm is approximately 5/16 inch long and yellow with a black stripe on the outside of each wing cover. The male has more black on the wing cover than the female. The female's stripes generally are more pronounced than the male's. Female beetles also have larger abdomens than males. Northern corn rootworm: The adult northern corn rootworm is ¼ inch long and yellow to pale green with no stripes or spots on the wing cover. Newly emerged adults are cream or light brown, but gradually turn green with age. Female beetles have longer and larger abdomens than males. Mexican corn rootworm: Mexican corn rootworm beetles are similar in appearance to northern corn rootworm, but can be distinguished by a black stripe on the femur. Also, Mexican corn rootworm and northern corn rootworm regions do not overlap.
Damage The USDA estimates that corn rootworms cause $1 billion in lost revenue each year, which includes $800 million in yield loss and $200 million in treatment costs for corn growers, making it the costliest pest in corn. Current estimates show that 30 million acres of corn (out of 80 million acres grown) are infested with varying levels of corn rootworm, and 12 million acres are treated annually with soil insecticides. Larval corn rootworm feeding can cause:
When corn rootworm larvae feed on and in the roots of a corn plant, they can disrupt the movement of water and nutrients, which in turn can slow plant development and stunt plants, ultimately leading to yield loss. This is especially true during dry years, where conditions suppress root regeneration after feeding and amplify the damage. A telltale sign of corn rootworm damage is goosenecking. When plants lean due to insufficient root mass then try to right themselves, they end up with a curved stalk. Under certain conditions, plants may fall over and lodge on the ground due to rootworm feeding damage. Lodged and misshapen plants often pollinate poorly and can slow harvest. Severe root pruning and damaged brace roots make plants more susceptible to strong winds. Damaged roots also provide pathways for infection by pathogens, potentially leading to root and/or stalk rots. Larval damage is usually most severe after the secondary root system is well established and brace roots are developing. Root tips will appear brown and are often tunneled into and chewed back to the base of the plant. In some fields, entire nodes of roots may be pruned severely. Larvae may be found tunneling into larger roots and occasionally in the plant crown.
Two unique corn rootworm challenges. Historically, corn rootworm adults deposited their eggs in cornfields. Unless the field was planted to corn the following year, larvae would quickly starve to death. However, corn rootworm populations have evolved and developed new survival techniques. Soybean variant western corn rootworm In some regions of the Midwest, corn rotation is no longer a management tool available to stop corn rootworm. A variant of the western corn rootworm has evolved with a reduced attraction to corn. This is causing a steady and substantial increase in larval damage in first-year corn that has followed another crop. While corn was its only host, the soybean variant western corn rootworm now can migrate to neighboring crops, such as soybeans, where it then lays eggs. These eggs hatch the next year when the field rotates back to corn. Extended diapause northern corn rootworm Another survival adaptation of corn rootworms is when the northern corn rootworm lays its eggs, which are capable of remaining dormant, or in diapause, through two winters and one growing season before hatching in the second season. In a rotation where corn is planted every two years, the eggs hatch when corn is back in rotation, resulting in damage to first-year corn. A small portion of the eggs will actually undergo a three-year extended diapause, making even a three-year rotation ineffective. Damage can be extensive, but varies from year to year, even in fields with a history of the problem. Extended diapause has only been observed in northern corn rootworm.
|
||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||
