Volume 51 Number 17 Date 08/18/2006

Corn rootworm beetle – Northern and western corn rootworm beetles were particularly active in the past week and present in younger fields in high numbers. Counts in fields with brown silks have decreased as the selective beetles move to feeding sites with fresh silks. Preliminary results of the annual corn rootworm survey suggest some multi-year corn in the southwest, south central, southeast, and east central districts will be subject to heavy feeding pressure by corn rootworm larvae next season. In contrast, surveys in the central district found mostly low rootworm beetle populations. Visit the CORN section for preliminary survey results by county.

Corn earworm – Significant captures of corn earworm moths have been registered at nearly all of the 18 pheromone trapping sites since the major flight began in early August. Counts recorded during the August 11-18 reporting period ranged from 10-732 moths with the highest capture reported at Evansville. Larvae are increasing in tips of ears in sweet corn in south central and central fields and growers should prepare to begin or continue treatment programs in the week ahead. As long as nightly moth captures remain high, insecticides may need to be applied and reapplied every 2-5 days (or every 100 GDD) until silks turn brown. Sweet corn fields in the Central Sands with newly emerged silks are highly susceptible to infestation at this time.

European corn borer – Moth captures in black light traps declined to relatively low levels across the state this week, which suggests most of the second flight has emerged. Except for the possibility of very light third flight activity early in September, the summer flight of corn borer moths is essentially finished for the season. Growers can expect a corresponding decrease in egg laying in the week ahead. Small corn borer larvae, on the other hand, should remain very active this week and in the next few weeks. The treatment window for second generation larvae is expected to close in a matter of days in the southeast, east central and northern districts after 2100 DD (base 50F) have accumulated.

*Corn leaf aphi*d – Extremely high populations are present on corn tassels, in the silks and on the leaves in some Central Sands sweet corn fields. Growers may soon expect damaging infestations if heavily infested corn is not scouted and excessive aphid populations are not effectively controlled. Do not treat without first scouting fields as corn leaf aphid infestations are frequently localized and may be reduced with spot treatments. Sample 50 plants consisting of 10 adjacent plants in five separate locations within each field and consider treatment when 50% of the plants have colonies of over 50 aphids per plant.

Bean leaf beetle – Second generation beetles were active in Columbia and Dodge Co. soybeans, where defoliation ranged from 5-20% in the fields sampled this week. Although levels of defoliation did exceed the threshold of 30% in any field checked and sampling found no more than four adults per 10 sweeps, be alert to the possibility of pod feeding and clipping through the month of August.

Two-spotted spider mite – Mite pressure has intensified in many fields in the last two weeks. Exceptional Rock Co. fields were treated recently to control economic populations, though fields examined in south central and central districts contained primarily non-economic populations of this pest. Some northwest Wisconsin fields are also experiencing heavy mite populations. Growers statewide are urged to monitor soybeans for two-spotted spider mites in the week ahead.

Soybean aphid – Populations continued to build slowly in a few isolated fields, despite the general trend toward decreasing densities. Decisions to treat soybean in the week ahead should be carefully considered. Growers are advised to make certain: 1) the threshold of 250 aphids per plant has been exceeded by sampling 20-30 plants per field and covering at least 80% of the field, 2) the population is actively increasing, and 3) soybeans have not reached R6. Aphid populations have begun to decline naturally in south central fields checked two weeks ago and again this week.

Western bean cutworm – Considering that pheromone traps documented the peak period of flight activity during the first week of August, nearly three weeks ago, larvae throughout the southern half of the state should be approaching the mid- or late instars. Scout corn fields closely and continue to watch for larvae in the tips of corn ears in the week ahead.
—Krista Hamilton

Leave a Comment

Name (required)

Email (will not be published) (required)

Website