Penncap-M® Insecticide Corn Rootworm Management Program

Corn Rootworms

There are three types of corn rootworms - Northern, Western, and Southern. Northern adults are tan to green, without distinct stripes or spots. Present mostly in North Central states, also scattered east and south of that region.

Western adults are black and yellow. Color patterns may vary from distinct stripes to almost black with a yellow tip on the rear of the wing covers. Present in the Plains states, east of the Rocky Mountains.

Southern adults, also known as spotted cucumber beetles, vary in color from yellow to green, with 12 black spots on the wing covers. Present in most of the United States east of the Rocky Mountains, in southern Canada and Mexico.

Life Cycle

Corn rootworms overwinter as eggs in the soil. Eggs are oval, pale yellow, and very small, about 1/50 inch long. In the spring, the eggs hatch and small larvae begin feeding on the roots of young corn plants, weakening or destroying the root system. Affected plants often lodge because of wind or heavy rain. The greatest injury generally occurs in late spring to early summer. Larvae are slender, white, or pale yellow, reaching a length of 2/5 inch when fully grown. When larvae mature, they pupate in the soil.

This program concentrates on controlling the adult female rootworm beetles when they are gravid (ready to lay eggs) and before they deposit eggs in the soil. There is normally only one generation per season and 95 percent of adult beetles emerge during a 35 day period. Understanding the rootworm life cycle is important to ensure timely scouting and application of PENNCAP-M® Insecticide.

1. Beetle Emergence - Adult beetles usually begin to emerge from mid-June to early July, depending on the temperature. Males generally emerge first, with females emerging 3 to 14 days later. It is important to start scouting now, taking care to note the time of emergence of both male and female beetles.

2. Scouting and Identifying Females - Females generally mate only once, soon after emergence, and begin to lay eggs about 12 days later. During this gestation period, it is important to continue scouting. By scouting on a weekly basis through early September, you can determine the adult rootworm beetle population and the presence of gravid female beetles. The best time to begin scouting depends both on your location and weather conditions. To ensure proper evaluation, scout several randomly selected locations in each field, depending on field size. Female beetles can be easily identified. Hold the beetle between the thumb and forefinger and squeeze the abdomen. If the contents of the abdomen are "t" shaped, the beetle is female. If the contents also contain milky-colored eggs, the female is gravid. After scouting and finding 0.5 beetles per plant, with 10 percent being gravid, the economic treatment threshold has been reached. Remember, one key to determining the threshold is the presence of "gravid" females for the "first" application.

3. Spray PENNCAP-M® Insecticide - On average, female rootworm beetles will lay 13 clutches of eggs. The early clutches generally contain more eggs and each female will lay an average of 1,100 eggs. That's why it's important to spray PENNCAP-M® Insecticide once the economic threshold has been reached and gravid females are present.

4. Let the Residual Action of PENNCAP-M® Insecticide Go to Work - Because it's microencapsulated PENNCAP-M® Insecticide controls insects over an extended period of time. After application, the active ingredient is slowly released. This allows the active ingredient to remain on the crop at effective levels for an extended period of time. After the initial spray of PENNCAP-M® Insecticide you most likely will continue to see beetles during routine scouting. There is no need to be concerned. This is simply due to the emergence of new beetles. As long as the beetle population is not increasing, it means the residual action of PENNCAP-M® Insecticide is working, controlling the beetle population as it continues to emerge. A minimum interval of fourteen days should fall between PENNCAP-M® Insecticide applications.

5. The Key to Success - Scouting should continue on a consistent basis after the first PENNCAP-M® Insecticide application to determine if a subsequent application is necessary. A new treatment threshold is used after the initial application of PENNCAP-M® Insecticide. If you see more than one beetle every three plants, you have reached the treatment threshold of 0.3 beetles per plant. It is necessary to reapply. Remember to wait a minimum of fourteen days between applications of PENNCAP-M® Insecticide. The presence or absence of secondary pests (like European Corn Borer) should not be used to determine the timing of the PENNCAP-M® Insecticide Corn Rootworm Management Program.

Environmental conditions such as weather, insect pressure and timing of application may affect performance.