Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/5/00
Contacts:
Rich Pope, Department of Entomology, (515) 294-1101
Julie Todd, Extension Communication Systems, (515)
294-2405
Corn Flea Beetle Populations Are Large This Spring
AMES, Iowa -- Large corn flea beetle populations have been reported in southern and central Iowa this spring. "These beetles are a concern because they damage corn by feeding on leaves and by transmitting Stewart's wilt (also called Stewart's disease), a bacterial disease of corn," said Rich Pope, Iowa State University Extension program specialist.
The corn flea beetle is a small, shiny black beetle that chews long, parallel lesions in the leaves of seedling corn. Feeding damage first appears as thin, silvery or white streaks. Heavily injured leaves turn brown, wilt and die. Damage is considered severe when one or more leaves of seedling corn are killed. Some heavily damaged fields have a frosted appearance when viewed from field edges. "These flea beetles overwintered as adults and should mate, lay eggs and die in the next week to 10 days. Later emerging corn is not likely to suffer severe damage," Pope said.
Transmission of Stewart's disease to corn plants can be limited by controlling the corn flea beetle with an insecticide because the bacterium is transmitted to corn through leaf feeding by infected beetles. "Stewart's disease is not usually a major economic problem in field corn, but seed corn, commercial sweet corn and popcorn fields are more prone to economic damage," Pope said.
"Economic thresholds are useful in determining treatment options," said Pope. For field corn from emergence to V5 (five leaf collars present), consider treating if 50 percent of plants have severe feeding injury and five or more beetles are found per plant. However, producers should consider other stress factors that might be affecting corn growth, including dry soil or very young (VE to V1) corn developmental stage and drop the treatment threshold to three or four beetles per plant. That decision should be made based on the actual situation in a given field.
For seed corn with inbred lines that are susceptible to Stewart's disease, consider treating when 10 percent of the plants exhibit severe feeding injury and two or more beetles are found per plant.
There are several insecticides registered for flea beetle control. Gaucho is a new systemic insecticide formulated as a seed treatment that has been shown to reduce flea beetle feeding and Stewart's disease. If Gaucho was used at planting, there will probably be some benefit, but Gaucho is not labeled as a rescue treatment. Labeled insecticides and the manufacturer's recommended rates for flea beetle control are as follows: Ambush (6.4-12.8 oz/acre), Asana XL (5.8-9.6 oz/acre), Furadan 4F (1 qt/acre), Lannate LV (12-24 oz/acre), Lorsban 4E (1-2 pt/acre), Penncap-M (2-3 pt/acre), Pounce 3.2EC (4-8 oz/acre), Sevin XLR Plus (1-2 qt/acre) and Warrior (2.56-3.84 oz/acre).
ml: isufarm
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