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Nursery & Forest

Degree Days

Volume 63 Number 17 Date 08/30/2018

CORN ROOTWORM - The annual rootworm beetle survey completed earlier this week documented low counts similar to those recorded in 2017. District averages in the state's nine crop reporting regions remained at or below 0.3 beetles per plant for the second year in a row, while the 2018 state average count of only 0.2 beetle per plant is equivalent to the historically low 2017 average, the lowest since surveys for this pest began in 1971. The only district-level increase recorded this season was in the west-central area, where the average rose from 0.2 beetle per plant in 2017 to 0.3 per plant. Minor decreases occurred in the southeast and central districts. Above-threshold counts of 0.75 or more beetles per plant were found in 21 of 229 (9%) fields surveyed, compared to last year's 24 fields (10%), and no beetles were observed in 127 (55%) of the surveyed sites.

In addition, again this season the northern species outnumbered the western species by a 2:1 ratio. The 2018 total beetle count was 566, with 379 being the northern variety and 187 western beetles. In 2017, a total of 347 northerns, 176 westerns, and 5 southerns were counted, 517 adult rootworms in all.

WESTERN BEAN CUTWORM - Larval infestations were noted in Buffalo, Columbia, Trempealeau, and Vernon counties in the last two weeks. An exceptional cornfield near Pardeeville was 10% infested with 1-2 larvae (-1 inches long) per ear, while infestation rates in other fields were lower and ranged from 1-3%. In all instances, the larvae were located in the ear tips where control is virtually impossible. Most larvae were in the late instars and should enter the pre-pupal overwintering stage by early September.

CORN EARWORM - Locally heavy flights of 193-1,093 moths were reported from Columbia, Dane, Dodge, and Fond du Lac counties in the past week. The primary late-season migration first accelerated from August 9-15 and a cumulative total 5,293 migrants have been captured to date. The count for the week of August 23-29 was 3,357 moths in 12 of 15 monitoring traps. Egg laying is expected to continue well into September. All susceptible sweet corn fields should be closely inspected until harvest.

-- Krista Hamilton, DATCP Entomologist