Scout for European Corn Borer (07/08/21)
European corn borer (ECB) Z-race moths (univoltine) have started emerging in ND (Table 1). This past week, ECB-Z have started emerging in east central, north central and northeastern ND. Trap catches increased for the univoltine Z-race ECB moth in Ransom County near Shenford and Shelton. We also detected the first E-race ECB moth (bivoltine) in Ward county near Minot. Corn crop stages were V4 to V8.
Now is a good time to start monitoring for ECB in corn fields, especially conventional corn or Bt corn without Bt-traits for ECB control. When corn is about 17 inches tall, fields should be scouted weekly for corn borers and continue scouting for another five weeks. Inspect plants for the presence of egg masses, whorl feeding (Figure 1), and active larvae. Pull up and unroll the whorls to find ECB larvae. Presence of shot-holes or pinholes (Figure 1) on leaves indicates ECB larval feeding. Observing moth (Figure 2) activity around field margins or within the field may alert you about possible ECB infestations in your field.
See the following Table for the Economic Threshold (E.T.) for corn borer per plant based on corn crop value and control costs. Using an expected yield of 125 bu per acre and the current price of corn at U.S. $5.70 per bu (MYA price for 2021/22), the value of the corn crop is $712 per acre. Using $12 per acre for the control costs, the E.T. is 0.43 corn borer larvae per plant (red square).
The accumulated degree days (ADD; base 50⁰F) for univoltine ECB-Z development range from 900 in northern area to >1300 ADD in southern area of ND (see map below). This indicates that the univoltine ECB moths are 10-90% emerged depending on your location.
Although corn is the preferred crop of ECB, moths (Figure 2) are polyphagous and can infest other crops like dry bean, hemp, millet, potatoes and more. ECB infestations in dry beans and millet have been observed in ND in the past. Last week, a millet field in Pembina County observed high numbers of ECB moths in field (Source: M. Smith, Pembina County Extension Agent). Millet is often used by ECB moths as an aggregation site to congregate and mate. ECB larvae tunnel into the stem causing serious stem lodging (Figure 4) and yield loss in millet. Scout millet and dry bean fields for potential ECB infestations and treat when populations are high in field (sweep millet fields for ECB moths) or if nearby corn is infested above threshold. There are no developed scouting protocols or thresholds for ECB in millet or dry beans.
Extension Crop Protection Specialist
NDSU North Central Research Extension Center