Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Aphid Numbers Rising

Posted by romeethredge on December 24, 2013

I’m finding a good many aphids in some grain fields, others have moderate to low numbers. I’ve mainly been looking at wheat and oats. In the photos below that I took you can see 2 types of aphids. Also you can see that they are reproducing.  The green aphids are usually greenbugs and they cause discolored lesions on the leaves.
Dark reddish-brown aphids are most likely bird-cherry oat aphids.  These aphids do
not cause feeding lesions but they do transmit barley yellow dwarf.  Aphids suck juices from the leaves and cause some growth problems.

_DSC1895 _DSC1907

Aphids vector a viral disease named barley yellow dwarf (BYD) and a related disease called cereal yellow dwarf. Wheat and barley can be severely damaged, but oats are most susceptible to this disease. BYD is present in most fields in most years throughout Georgia. Yield losses of 5-15% are common but losses can exceed 30% during severe epidemics. Infection can occur from seedling emergence through heading, but yield loss is greatest when plants are infected as seedlings in the fall. Although all aphids can potentially transmit certain strains of the virus, infections in the Southeast are mostly associated with infestations of bird cherry-oat aphid and rice root aphid. Planting date is the single most important management practice, with early plantings generally have greater aphid numbers and greater BYD incidence than late plantings.

A single, well-timed insecticide application of the insecticide lambda cyhalothrin (Karate Zeon, Silencer, and similar products) or gamma cyhalothrin (Declare) also can control aphids, reduce the incidence of BYD and increase yields.  In southern Georgia, the best treatment time usually is at full-tiller stage in early to mid-February. But, scout fields for aphids at 25 – 35 days after planting and during warm periods in January to determine if an insecticide application is needed. A lambda cyhalothrin or gamma cyhalothrin treatment at full tiller can be applied with top-dress nitrogen. OP insecticides, such as dimethoate and methyl parathion, also will control aphids but are not effective in preventing barley yellow dwarf infection.

To sample aphids, inspect plants in 12 inches of row in fall and 6 inches of row in winter. In spring, inspect 10 grain heads (+ flag leaf) per sample. Count all aphids on both the flag leaf and head for making control decisions. Sample plants at 8 to 16 locations per field. Treat when populations reach or exceed the following thresholds:

Seedlings: 1 bird cherry-oat aphid per row foot, or 10 greenbugs per row foot.

2 or more tillers per plant: 6 aphids per row foot.

Stem elongation to just before flag leaf emergence: 2 aphids per stem.

Flag leaf emergence: 5 aphids per flag leaf.

Heading emergence to early dough stage: 10 aphids per head.

Do not treat for aphids after mid-dough stage.

 

Thanks to Dr. David Buntin, UGA Entomologist, for the aphid information.

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