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Significant Aphid Infestations Showing Up

Thresholds are quickly being breached in South Dakota winter and spring wheat.

Significant aphid infestations in wheat are being reported in Brown, Davison, Hand, Hughes, Hyde, Jerauld, Roberts and Sully counties of South Dakota.

Mike Catangui, SDSU Extension entomologist, issued a warning this morning that wheat should be scouted now.

Economic thresholds can be reached quickly, he says.

Spraying is already underway in a number of counties.

Aphids are insects with syringe-like mouthparts and feed on the sap of plants. Although small in size (1/16 to 1/8 inch), they multiply very fast and their collective feeding can reduce crop yields. They are also known to transmit diseases such as barley yellow dwarf virus.

The two aphid species currently being found are the bird cherry-oat aphid and the English grain aphid, Catagnui says.

Bird cherry-oat aphids are dark olive green and broadly oval in form. English grain aphids are bright green in color, with dark skinny legs antennae and cornicles or “tail pipes.”

Bird cherry-oat aphids can be found mainly underneath the leaves while English grain aphids congregate on the head at flowering.

Economic thresholds

The economic thresholds for bird cherry-oat aphids are 20 aphids per tiller during the seedling stage, 30 aphids per tiller from boot to heading stage, 5 aphids per tiller during the flowering stage.and 10 aphids per tiller from milky ripe to dough stage.

The economic thresholds for English grain aphid are similar to the bird cherry-oat aphid except for seedling and boot to heading stages when its economic thresholds are 30 and 50 aphids per tiller, respectively.

Catangui provided the following list of Insecticides labeled for use against aphids on wheat in South Dakota and their recommended rates and pre-harvest intervals (PHI):

Baythroid XL (1.8 to 2.4 fluid ounces per acre, 30 day PHI).
Lorsban 4E (0.5 to 1.0 pint per acre, 20 day PHI).
Mustang Max (3.2 to 4.0 fluid ounces per acre, 14 day PHI).
Penncap-M (2 to 3 pints per acre, 15 day PHI).
Proaxis (2.56 to 3.84 fluid ounces per acre, 30 day PHI).
Warrior (2.56 to 3.84 fluid ounces per acre, 30 day PHI).

Always read and follow label directions.

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