Sugarcane Aphid in Virginia Sorghum
ID
ENTO-334NP
Introduction
The sugarcane aphid (SCA) is a pest of sugarcane, sorghum, and millet. Its origin is thought to be northern Africa and the Middle East and SCA is now widely distributed in the southern US. It was detected in Virginia sorghum in 2015. Sorghum growers must be acutely aware of SCA populations to avoid yield loss and harvest complications.
Pest Description
SCA are small, sap-feeding insects that form clusters or colonies on the undersides of sorghum leaves (Fig. 1). Color ranges from gray in cool weather to creamy yellow in warmer weather. They are never green. SCA can be distinguished from similar-looking aphid species by their light- colored heads, smooth “skin”, and dark-colored feet, antennae, and cornicles, which are the “tailpipe” structures on the rear end of the insect (Fig. 2). SCA nymphs look like smaller versions of adults. Adults can be wingless (typical morphology) or winged (for population distribution) (Fig. 2).
Life Cycle
Populations of SCA in Virginia reproduce asexually and all individuals are female. Females give birth to live young, which molt four times before reaching adulthood, typically in 4-12 days. Adults can live from 10-37 days, depending on the temperature. Groups of females cluster together to form colonies. When conditions are right, females birth offspring that grow wings to spread the colony to new locations. SCA prefer warm, dry weather, and populations can rapidly explode under these conditions. Wind and storm fronts help move winged SCA long distances, after which they settle on the underside of leaves towards the top of sorghum plants.
In warm climates, aphids feed on sorghum in the spring and summer and overwinter in sorghum refuse or Johnsongrass for the colder months. In colder regions (and likely, Virginia), SCA colonies die off in the winter and reestablish the next growing season from winged adults traveling on wind currents.
Damage Caused by SCA
SCA feed on plant sap using their straw-like mouthparts, which are inserted into the plant tissue to draw up liquids. This robs nutrients from the plant and can cause yellowing, wilting, and leaf death. Severe infestations can kill plants.
Aphids secrete sticky, liquid waste called honeydew. This liquid causes lower leaves to appear shiny and creates the perfect conditions for sooty mold to florish. Mold blocks light from reaching the plant surface, reducing or stopping photosynthesis, reducing vigor and causing leaf or plant death, and contaminating finished products (Figs. 3, 4).
Major consequences of SCA infestations:
- In early sorghum (pre-boot to soft dough)
- reduced yield, reduced seed weight, delays in maturity, and even death of young plants - In later, mature sorghum – honeydew on leaves can clog combine, causing reduced harvest efficiency and overall yield
- In sorghum grown for forage – longer curing times, or a finished product contaminated by mold
Management
Every sorghum field in Virginia should be scouted for SCA beginning in August. In uninfested fields, perform a weekly inspection at each edge of the field. Walk about 25 feet into the field and inspect between 15 and 20 plants in 50 ft of row. At each plant, check the underside of leaves with a hand lens. Check also for shiny honeydew on the top surface of lower leaves. Continue until 60-80 plants have been inspected. If aphids are not found, continue weekly monitoring.
If aphids are found, switch to monitoring twice weekly to catch population spikes, especially in warm, dry weather. Because counting individual aphids is impractical, Texas A&M AgriLife Extension and Research has developed a method for visually estimating aphid numbers (https://agrilifecdn.tamu.edu/ccag/files/2016/04/NTO043.pdf). Average the number of aphids counted on the 60-80 inspected plants and compare to the EIL and ET below.
The recommended economic injury level (EIL) for sugarcane aphids in Virginia is 50-125 aphids per leaf when sorghum prices are at $4/bu. The economic threshold (ET; when control measures need to be taken) is 50 aphids per leaf on 25-30% of plants. (Fig. 5).
Control
Biological
Lady beetles, hoverfly larvae, and lacewing larvae are all excellent predators of SCA and tend to closely follow populations as they move into sorghum (Fig. 5).
Several wasps lay their eggs in SCA, creating aphid "mummies," or easily distinguished parasitized aphids (Fig. 6). Aphid mummies are dark blue, black, or light tan and are essentially the dead husks of aphids used by the developing wasp. Unfortunately, aphids reproduce so quickly that their populations can overwhelm natural enemies, and other control methods are usually necessary.
Cultural
Plant sorghum early and in high densities to maximize crop growth stage during infestation. Yield loss ranges from 21% (soft-dough) to 100% (pre-boot). Also, consider planting a SCA-tolerant hybrid varieties of sorghum (see list of available varieties at: http://www.sorghumcheckoff.com/newsroom/2016/03/28/sugarcane-aphid/).
Chemical
Currently (Aug 2019), the only chemical control available for sugarcane aphid management in Virginia is Sivanto Prime (17.09% flupyradifurone, Bayer CropScience, Leverkusen, Germany) and Transform WG (50% sulfoxaflor, Dow AgroSciences, Indianapolis, IN). Transform is allowed by a Section 18 Emergence Exemption that must be renewed each growing season. Contact your local ANR Agent of Virginia Cooperative Extension Office for current labels and restrictions. Remember that all label instructions must be explicitly followed.
References
Bowling, R.D., et. al. 2016. Scouting Sugarcane Aphids in South, Central, and West Texas. Texas A&M AgriLife Extension Publication. https://agrilifecdn.tamu.edu/ccag/files/2016/04/NTO043.pdf
Bowling, R.D., et. al. 2016. Sugarcane Aphid (Hemiptera: Aphididae): A New Pest on Sorghum in North America. JIPM. https://academic.oup.com/jipm/article/7/1/12/2658146
Knutson, A., et. al. 2016. The Sugarcane Aphid: Management Guidelines for Grain and Forage Sorghum in Texas. Texas A&M AgriLife Extension Publication. https://agrilifecdn.tamu.edu/ccag/files/2016/06/2016KnutsonENTO-035-Sugarcane-Aphid-Management-2016.pdf
Malone, S. 2015. Sugarcane Aphid Advisory. Virginia Cooperative Extension Publication. https://blogs.ext.vt.edu/ag-pest- advisory/files/2015/09/SCA_advisory_Sep_18_2015.pdf
Malone, S. 2015. Sugarcane aphids found in sorghum field in Suffolk, Virginia. Virginia Cooperative Extension Ag Pest and Crop Advisory Blog Post. https://blogs.ext.vt.edu/ag-pest-advisory/sugarcane-aphids-found-in-sorghum-field-in-suffolk-virginia/
Texas Invasive Species Institute. 2014. Sugarcane Aphid. http://www.tsusinvasives.org/home/database/melanaphis-sacchari
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Publication Date
September 12, 2019
