Brian Kalmbach, Nutrient Management, Talbot County
Introduction
The sugarcane aphid is a relatively new pest of grain sorghum that will also feed and reproduce on a variety of other species within the Sorghum genus, including Sudan grass, sorghum/Sudan hybrids, and Johnsongrass. Sugarcane aphid was first seen feeding on sorghum in Texas in 2013 and by 2015 the insect was reported in over 400 counties covering 17 states throughout the southeastern United States and in sorghum-producing areas of Mexico. The aphid was found in Charles County, Maryland in the fall of 2016, where a large population was seen feeding on both leaves and grain heads.
Sugarcane aphids spread via wind after overwintering in central and southern Texas and northern Mexico, therefore are likely to occur later in the season in Maryland. Yield loss potential is greatest for infestations at early crop stages, but grain quality and harvest efficiency may be substantially affected by infestations that increase after flowering. Scouting for sugarcane aphid should begin as soon as it has been confirmed in the area.
Life Stages and Biology
For many parts of the year, only female sugarcane aphids are present and they reproduce asexually, giving birth to live young (nymphs). The aphids have four nymphal stages and can complete development from birth to adult in as little as 4 (up to 12) days. Adult sugarcane aphids live for 10-37 days and a single adult aphid has the potential to produce nearly 100 nymphs. Adults may be winged (alate) or non-winged (apteran) (Figure 1).
As temperatures in the southeastern U.S. increase, winged adults from overwintered populations begin to spread both locally and over long distances by wind-aided movement. Populations of sugarcane aphids increase rapidly in warm and dry conditions, typical of many sorghum-producing regions.
Crop Damage
Sugarcane aphids, like other aphids, have piercing-sucking mouthparts and feed by sucking plant sap from the leaves and panicle. Feeding injury is characterized by yellow, purple, or brown leaves as the tissue dies as well as a sticky honeydew present on the leaves. Large infestations can stunt the plant’s growth, cause significant grain loss, and cause uneven panicle emergence (Figure 2). Pre-boot infestations can cause up to 100% yield loss if left untreated. Later season infestations can affect grain quality and harvest efficiency.
The honeydew, containing mostly plant sugars and water, will cause the leaves to look shiny and feel sticky. Sooty mold will often develop on the honeydew, decreasing the plant’s capacity for light absorption (Figure 3). Honeydew may also gum up harvest equipment, thereby decreasing harvest efficiency.
Monitoring/Scouting
Scouting for sugarcane aphid should occur once per week as soon as sugarcane aphid has been confirmed in the area.
- At 4 locations per field:
- Examine plants along 50 feet of row
- Look for honeydew
- Inspect underside of leaves for aphid presence, 20 plants per location
If sugarcane aphid is present in a field, begin scouting twice per week to determine if the infestation has reached the treatment threshold.
At 4 locations per field:
- Estimate number of aphids on a lower canopy leaf and uppermost leaf on 5 random plants
- 4 locations x 5 plants x 2 leaves = 40 leaves total
Currently in Maryland, treatment is recommended when 50-125 aphids per leaf are present on 25% of plants (Figure 4). A scouting guide created by Texas A&M is helpful in determining the number of aphids per leaf, and can be found here.
Presence of sugarcane aphid in Virginia may indicate its potential movement into Maryland. Updates on sugarcane aphid occurrence in Virginia are posted on the Virginia Cooperative Extension Ag Pest and Crop Advisory webpage, which can be found here.
Management
It is currently unknown if sugarcane aphid will cause significant or persistent crop injury in Maryland. The following are management tactics to consider.
Early Planting. It is likely that sugarcane aphid will be a late season pest in Maryland, therefore early planting may help avoid infestations.
Tolerant Hybrids. Research is continuing to identify or develop sorghum hybrids that are tolerant to sugarcane aphid. Tolerant hybrids slow aphid reproduction, potentially delaying the need for treatment or suppressing infestations below the treatment threshold. The Sorghum Checkoff has compiled a list of tolerant hybrids, which can be found here.
Beneficial Insects. Syrphid fly larvae, green lacewing larvae, adult and larval lady beetles, and some parasitic wasps can help to control the expansion of sugarcane aphid populations.
Pesticides. Pesticide treatments can help to control sugarcane aphid. Proper pesticide selection for other sorghum pests can help to keep beneficial insect populations in and around your fields. Specific pesticide information can be found in the April 2017 edition of Agronomy News, which can be found here.
Photo Credits: Figure 1: Raul Villanueva; Figure 2: Robert D. Bowling, Texas A&M AgriLife Extension Service; Figure 3: Sarah N. Zukoff, Dept. of Entomology, Kansas State University; Figure 4: Allen Knutson, Texas A&M AgriLife Extension Service.
