Crop pest activity follows season's pattern

Ray Mueller
Now Media Group


With on and off spurts to the growing season during the early weeks of spring this year, activity by pests has also begun as crops emerge from dormancy or are newly seeded.

Pest activities and timetables are tracked by the Wisconsin Pest Bulletin, which began issuing its weekly updates in late April.

Input to the WPB is a cooperative venture of the University of Wisconsin Extension Service, private sector crop consultants and the Department of Agriculture, Trade, and Consumer Protection. The weekly online report is edited by DATCP entomologist Krista Hamilton, who is based in La Crosse.

Migrant pest arrivals

The first report for 2016 highlights the arrival of high numbers of migrating black cutworm moths in Wisconsin's southern counties. Starting in late March and greatly increasing during the third and fourth weeks of April, that migration resulted in the catch of 676 months in 39 pheromone traps, the WPB indicated.

A major migration detected on April 17 could lead to larvae cutting corn seedlings by as early as May 20, the WPB predicted. It explained that the moths are laying eggs on annual weeds such as common chickweed, yellow rocket and peppergrass and that fields with minimum or no tillage are most vulnerable.

During the third week of April, seven true armyworm moths were captured near Janesville in Rock County. In the following week, the number of catches jumped to 136 in black light traps near Janesville and Sparta in Monroe County.

Eastern tent caterpillar egg hatches were already beginning by late March, the WPB observed. It advised insecticide treatment of recently hatched larvae before mid-May.

Alfalfa field insects

On April 25, WPB surveyors found alfalfa weevil adults in fields in Dane and Rock counties. Based on that finding, they estimate emergence of larvae by May 7 in far southern Wisconsin and within the following two weeks in central and north central parts of the state.

A hatch of pea aphids was noticed in Richland County on April 17. Visits to alfalfa fields in several counties yielded an average of 14 aphids per 100 net sweeps.

The net sweeps in alfalfa fields also brought in an average of four tarnished plant bugs per 100 sweeps. The WPB points out that the concern with them is not for damage to alfalfa rather to infestations on strawberries and other fruits.

Corn and soybean pests

The early outlook indicates low populations of pests that have a history of infestation in corn and soybeans, the WPB noted. Based on larvae counts going into the past winter, the tabulation for European corn borers was the lowest in 74 years.

Similarly, the WPB expects a relatively low population of soybean aphids — a total less than in 2015. It noted the appearance of eggs on host buckthorn trees by April 4 but also cited the low populations going into the winter, attributing a portion of the population control to the efforts of the predatory multi-colored Asian lady beetle.

A more localized and potential major threat to soybeans along with sweet corn, tomatoes, green beans, apples and grapes is the establishment of an overwintered population of brown marmorated stink bugs, especially in Dane County, the WPB stated. It cited more than 20 confirmations of the bug's presence this spring.

Another concern with the continuation of cool and wet oils is potential damage to slow germinating seeds from the seed corn maggot, the WPB indicated.

Contrary to reports from states to the west, Wisconsin does not have a problem with stripe rust or leaf rust with its winter wheat. Fields surveyed in Jefferson, Green and Dane counties were found to be 'remarkably healthy' with only a few cases of a minimal amount of septoria leaf blotch being the exception.

Fruit crop update

Growers of fruits in Wisconsin and beyond are now being served with the new fruit.wisc.edu website, which will be updated at least every two weeks. It features a listing of events along with updates on threats to the crops. Growers are invited to subscribe in order to receive regular updates.

Fruit sector insects mentioned in the first edition of the WPB are the spotted tentiform leafminer, redbanded leaf roller, thrips, green fruit worm, grape leaf beetle and the obliquebanded leaf roller.

The report also noted that the common asparagus beetle began laying eggs during the last week of April in southern areas.