Temperatures Greater than 45⁰ F may Lead to Early Insecticide Spray but First Scout Fields for Aphids Thresholds

Aphids in wheat

Several aphid species are key pests in small grains (wheat, barley, and cereal rye) in Kentucky for their role as vectors of the Barley Yellow Dwarf Virus (BYDV). Among them, the Bird cherry-oat and English grain aphids overwinter as nymphs or adults, and they can start feeding and potentially transmit viruses when temperatures are above 45º F. These aphids start feeding on plants when temperatures are greater than 45º F. Below 45º F, aphids are inactive, lethargic, and sheltered in soil crevices near the bases of wheat stems.

Current Conditions and Management

Since 23 January, to 12 February 2024 there were 13, 12 and 14 days where temperatures were ≥45º F in Lexington, Princeton, and Mayfield in Kentucky (Figure 1), respectively. Thus, during those day aphids might be feeding on plants and if they are carrying the viruses may be spreading them to healthy plants. Under these conditions, it is recommended that farmers and consultants to scout commercial fields before conducting sprays for aphid management. If tallies are above the threshold levels indicated in Table 1, an insecticide spray needs to be considered. Calendar-based sprays or preventative sprays are not recommended as they are not part of integrated pest management (IPM) programs.

Figure 1. Daily average temperatures (Fahrenheit) from January 1 to February 12, 2024 in Lexington, Princeton, and Mayfield. On days where temperatures are >45⁰ F (red ellipses) aphids start to feed on small cereals.

Insecticide spray programs for aphid management should follow IPM practices instead of calendar-based programs. In Kentucky, the rest of the USA, and many other parts of the world, calendar-based insecticide programs continue to be used due to time constraints for scouting and economic savings achieved by reducing trips and conducting combined applications of herbicides and fungicides across fields. However, as mentioned above, the use of IPM is recommended to avoid unnecessary application of insecticides, increase costs of production, reduce insecticide resistance, and kill natural enemies that may be keeping pest populations at low levels.

Table 1. The number of aphids per foot of wheat row required to support an insecticide application for management of BYDV.

By Raul T. Villanueva, Extension Entomologist