Scouting for Bird Cherry Oat Aphids on Wheat

By John Few, Tyler Mays, and David Drake – Texas A&M AgriLife Extension Agents – IPM Thrall, Hillsboro, and Commerce TX

Rhopalosiphum padi commonly known as Bird cherry oat aphid (BCOA) is an insect pest of cereals and grasses that is readily appearing now in oat and wheat fields in Texas. This insect is usually described as being pear-shaped, yellow-green, dark green, or black in color with red coloration at the base of its abdomen near the cornicles (Image 1). While feeding from this pest usually does not cause economic damage, it is an efficient vector for barley yellow dwarf virus, a disease known to cause economic loss in wheat. Large populations of BCOA can also reduce the plant’s ability to photosynthesize by creating an environment for sooty mold via the sticky honeydew they produce while feeding. There are a few practices that can be done to control BCOA.

Image 1. Bird Cherry Oat Aphids on wheat

One method suggested by Oklahoma State University and Oklahoma Cooperative Extension Service is to scout for parasitized or “mummy” aphids. See Image 2. These aphids are usually tan in color. These aphids are being killed by parasitic wasp that can help prevent or reduce the amount of insecticide that you have to spray. To determine if parasitic wasp are adequately controlling populations in your field collect 25 tillers and count the number of mummy aphids. If you see mummies on 7 of the 25 plants then do not spray as the other aphids are most likely parasitized as well. If this is not the case the additional scouting is needed.

Image 2. Parasitized “mummy” aphids on a wheat leaf. Image Courtesy of David Drake.

To determine an economic threshold in your field, start by counting the number of aphids on 25 tillers. Once that number is obtained follow the flow chart below to determine if you need to make an insecticide application.

Step 1. Estimate yield loss: Total # of aphids:________= average # aphids/tiller ________ /25

Yield loss estimate: =0.00 if aphid counts are <20 per tiller,

0.05 if aphid counts are 20-39 per tiller,

0.09 if aphid counts are ≥ 40 per tiller

Step 2: Estimate Crop Value $________ /acre

Yield potential/acre #________ bushels/acre X value of grain per bushel $________ per bushel

= Crop Value $________ per acre

Step 3: Estimate Control Cost $________ /acre

Insecticide cost $________ /acre + Application Cost $ ________ /acre

= Control Cost $ ________ /acre

Step 4: Estimate Preventable Loss

Crop Value/acre $ ________ X Yield Loss from aphid $ ________

= Preventable Loss $ ________

IF Preventable Loss $________ is greater than Control Cost $________ TREAT

IF Preventable Loss $________ is less than Control Cost $___________ DON’T TREAT

Table 1. shows a method developed by the University of Nebraska Lincoln to determine action thresholds for BCOA by plant growth stage. While these methods are not from Texas A&M and have not been fine tuned for Texas’ environment, they are better than not scouting at all or having economic loss by missing an application window.

The following are insecticides approved to control BCOA: Baythroid 2, Di-Syston 15% G, Dimethoate Dimate, Lorsban 4E, Nofos 4E, Methyl 4EC, Mustang Max, Penncap-M, Proaxis, Thioanex 3EC, Malathion 8, Dimethoate 4EC, and pyrethroids. Apply insecticides according to the label.

Table 1. Action threshold for BCOA

Average # of BCOA per stem needed to meet threshold
Species	Seedling	Boot to Heading	Flowering	Milky Ripe	Milk to Medium Dough
Bird cherry-oat aphid	20	30	>5	10	10