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Nursery & Forest

Degree Days

Volume 62 Number 18 Date 08/31/2017

CORN ROOTWORM - Below are two maps summarizing the findings of the 2017 corn rootworm beetle survey, completed two weeks ago. Beetle populations decreased markedly in all nine crop districts as compared to 2016, with district averages ranging from 0.1 to 0.3 per plant. The very low 2017 state average of 0.2 beetle per plant is less than half of last year's average of 0.5 per plant. Only 23 of the 229 (10%) cornfields sampled had above-threshold averages of 0.8-2.9 beetles per plant, while 53 (23%) had below-threshold averages in the range of 0.1-0.7 per plant. No corn rootworm beetles were observed in 153 (67%) of the fields. Results of the survey indicate that adult rootworm pressure has been much lower than expected this season. The substantial decrease in beetle abundance may result in fewer eggs being deposited into cornfield soils, and an overall lower risk of larval root damage to continuous corn next summer.

WESTERN BEAN CUTWORM - Larval infestations were noted in Monroe, Richland and Vernon counties in the past week. An exceptional cornfield near Cashton 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 were reported from Columbia and Dodge counties, while counts at all other monitoring locations were low. The primary late-season migration first accelerated from August 17-23 with the capture of 288 moths in 15 traps and another 351 migrants arrived this week. Egg laying is expected to continue well into September. All susceptible sweet corn fields should be closely monitored until harvest. Moth counts for the week ending August 31 were: Arlington 156, Beaver Dam 129, Coon Valley 14, Cottage Grove 19, Hancock 0, Janesville 8, Madison airport 2, Marshfield 2, Pardeeville 2, Prairie du Chien 0, Sun Prairie 12, and Watertown 7.

-- Krista Hamilton, DATCP Entomologist