Compared to the abnormal temperatures that have prevailed for significant periods in recent months, the "new temperature normals" listed by Wisconsin State Climatology Office are a fairly mild change.
The second edition of the Wisconsin Pest Bulletin for 2012 reported that the state's degree day tables have been upgraded to represent the 30-year average temperatures for 1981-2010, replacing the tables that covered the 1971-2000 period. The new table increases the state's average temperature by .6 degrees Fahrenheit while the national average was increased by .5 degrees.
As has been amply demonstrated by the record-high temperatures posted in March of this year, temperatures play a crucial role in insect emergence, development, and reproduction as well as that of the vegetation that they infest.
Entomologists rely on temperature degree day accumulations to predict those activities.
In the most recent weekly Pest Bulletin, for example, an accumulation of 300 degree days on a base of 43 degrees was cited to verify the emergence of cabbage maggot flies at places as far north as Green Bay and Wausau.
In addition, an accumulation of 200 to 350 degree days on a base of 50 was used to predict the growth stage of the creeping Charlie weed that leaves it most vulnerable to herbicide treatments.
Another significant timetable variation was the one-month early appearance of June beetles in Walworth, Crawford, and Dane counties, the Pest Bulletin indicated.
Migrating aster leafhoppers found in alfalfa as far north as Jackson County (7 caught in 50 net sweeps) could easily pose a threat to carrots, lettuce, other vegetables, and flowers, it added.
Other concerns for vegetables and fruits were the detection of common asparagus beetle eggs on asparagus in northern and central counties and the continued heavy migration of imported cabbage worm adults.
In addition, other concerns are the migration of overwintered plum curculio adults into southern Wisconsin apple orchards, and the feeding by tarnished plant bugs on the fruit buds of apples, resulting in bud blast and the failure of blossoms to open.
Field Crop Pests
Among field crop pests, entomologists expect damage to corn from black cutworms by mid-May in southern Wisconsin. This is based on their calculation of the heavy moth flight on April and the anticipation of 300 degree days (base of 50) by May 15.
Additional heavy flights of true armyworm moths on the nights of April 15 and 17 continue to raise concerns about outbreaks in field crops in the coming weeks.
Observations in Monroe and Rock counties were documented along with the catches of 79 moths in a trap at East Troy in Walworth County and 30 more near Janesville in Rock County.
Based on the degree day accumulations that are approaching 374 (base of 50 degrees), the Pest Bulletin anticipates the first flight of European corn borer moths by the end of this week. This would apply mainly in the southern and southwest areas of the state.
Alfalfa weevil populations continue to be minimal in most fields but tip feeding on alfalfa was likely to have started this week where larvae are present, the Pest Bulletin stated.
Recent net sweeps found an average of three larvae per 50 sweeps but 18 were collected during 50 sweeps in a field near Darlington in Lafayette County.
Pea aphids were also found in Lafayette and Iowa counties, topped by a catch of 22 in 50 sweeps. Alfalfa caterpillars were falling victim to a parasite wasp, the Pest Bulletin reported.
Property owners and other persons interested in the control of such invasive species as garlic mustard and wild parsnips were advised by weed scientist Clarissa Hammond to monitor the stage of plant growth and take action accordingly.
For garlic mustard, this means pulling the second-year plants before seed sets and disposing of the pulled vegetation in separate bags destined for landfills while the control measure priorities for wild parsnips are herbicide application, manual removal (avoid contact with skin), and burns overseen by trained persons.
Rust on winter wheat has been reported in Southern states this spring. No rust was detected in visits to four fields in Wisconsin's Dodge and Dane counties but there were some outbreaks of tan spot and one of the fields had a high incidence of mildew, the Pest Bulletin reported.