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European corn borer (ECB) is a common pest of corn in Ohio that may cause economic losses during the growing season. European corn borer infestations differ over time and among geographic regions in the state.
European Corn Borer
ECB overwinters as late instar or stage larvae in corn stalks. In the early spring, the overwintering larvae pupate and then emerge as moths that prefer to deposit their egg masses on the underside of leaves of mid-whorl stage corn. Each egg mass appears like a small mass of fish scales and may include 15 to 20 eggs . The eggs hatch into early-instars that initially feed on foliage, causing window-pane injury, and on the tender central whorl, which subsequently leads to shot-hole injury in the emerging foliage.
The larvae become third- and fourth-instars (about 1/2-inch long), they tunnel into the mid-ribs and stalks. There they complete their larval development as fifth-instars and transform into pupae from which adult moths will emerge in midsummer. This larval generation, which occurs in the spring on whorl-stage corn, is called the first brood. During the period of larval development, significant proportions of larvae perish due to natural elements such as heavy rains or predation by beneficial insect predators. Although 15 to 20 larvae may emerge from a single egg mass, it is rare to find one or more mature larvae in a corn stalk or adjacent stalks to which larvae may have migrated.
Life cycle:The European corn borer overwinters as fully grown larvae inside corn stalks or corn cobs. In the spring, they go through the pupal stage and emerge as adults. The adult is a moth. European corn borer moths begin emerging after about 450 degree-days (base 50ï¿½F) accumulate after the start of the new year. In central Ohio, this is usually the third week of May. Emergence is a few days earlier in southern Ohio and a few days later in northern Ohio.European corn borer moths spend most of their time in moist grassy areas, where they rest during the day and mate at night. After sundown, female moths fly to nearby fields of young corn and lay eggs on the underside of corn leaves. The first generation of larvae rarely damages peppers unless the crop was planted unusually early. Eggs hatch into larvae that feed on corn leaves then bore into tassels, stalks, and ears. Larvae go through five instars with a molt after each instar. After feeding for about 4 weeks, from early June until early July, larvae are fully grown then they pupate in corn stalks or ears.
The pupal stage takes about 2 weeks.New adults begin to emerge in July, usually in the third or fourth week of July. These moths lay eggs on either corn or peppers. If there is corn in the fresh silk stage nearby, the moths are more likely to lay eggs on corn than on peppers. If nearby corn is past the fresh silk stage, then moths are likely to lay eggs on peppers. Egg masses are laid on leaves of the pepper plant. Eggs hatch in about 4 to 7 days. Larvae crawl immediately to fruit more than 1 inch in diameter, and bore in at the edge of the fruit cap. Second generation larvae feed inside peppers throughout August and early September.In approximately two of every three years in Ohio, this pest has only two generations per year, with first generation larvae active in June and second generation larvae active in August. In approximately one of every three years, there is a warmer than average summer, which allows an additional generation to develop in September. This third generation causes severe injury to peppers.
Damage:A corn plant goes through a series of phenological stages during its growth and development. During these stages, the plant uses its resources in rapid growth areas and for general plant maintenance. Because the plantâ€™s ability to withstand stress varies during plant growth stages, the stage(s) at which it is attacked influences its ability to deal with injury from the European corn borerâ€™s feeding and subsequent yield reductions. The corn plant is susceptible to European corn borer attack and injury after the 6th-leaf stage through physiological ear maturity. In general, during vegetative growth, the majority of photosynthate (energy) and nutrients produced by the plant is used for leaf development, root growth, and stem elongation. During the reproductive growth period, the photosynthate and nutrients are used for tassel development, ear formation, and kernel fill.
Corn plant developmental stage during European corn borer egg laying must be determined in order to account for differences in yield loss caused by whorl-stage leaf feeding (Figure 15) or sheath and collar feeding (Figure 16) and subsequent stalk boring. This information will contribute to more economically accurate decisions. Researchers have conducted many studies to assess the impact of European corn borer feeding at various stages of corn plant development on the yield of corn.
European Corn Borer
Control:ECBs in pepper can be adequately controlled in Virginia with multiple applications of insecticides beginning at early fruiting through final harvest. There are several insecticides currently labeled for ECB control in pepper. However, not all of them are proven to be effective. Table 1 lists selected products that Virginia Tech and other university researchers have tested and shows their overall effectiveness against ECBs. In Virginia, European corn borer trap catches above 2 per night with pepper fruit 1/2 inch in size or larger should be treated on a 7- to 10-day schedule. In fields with no fruit present, chemical applications should begin when trap catches are above 10 ECBs per week to prevent newly hatched larvae from feeding on leaves and then tunneling into the petioles and stems.
Biological control agents such as Trichogramma ostriniae Pang et Chen (Trichogrammatidae: Hymenoptera) , a tiny parasitic wasp newly imported from China, may reduce the need for chemical control in bell pepper. Research conducted in Virginia has demonstrated that approximately 100 to 170 T. ostriniae per plant/per week can significantly reduce the number of ECB-damaged peppers by over 70 percent. This is a significant reduction of damage. It is the result of the female T. ostriniae parasitoid wasp depositing her own eggs in the egg masses of the ECB. Once the female T. ostriniae locates an ECB egg mass, she will sting each of the eggs in the mass with her ovipositor, thus destroying the ECB larvae within.
After about 4 days the egg mass will turn black, indicating that it has been parasitized . At the end of 10 days, a new adult Trichogramma parasitoid will emerge from each ECB egg to begin the parasitization cycle again. Although control of ECBs with T. ostriniae has shown to be effective for control of the ECB in bell pepper, further work needs to be done to evaluate the use of insecticides with biological control organisms like T. ostriniae. Work is now being done to evaluate a spinosad product in combination with T. ostriniae releases to further increase control of the ECB in bell pepper.
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