|
|
Light rain showers and summer heat during the last week of July benefited maturing row crops in Wisconsin. Weekly average temperatures ranged from 2.0°F below normal in the southeastern counties to 4.0°F above normal in the northwest. Accumulated precipitation varied from 0.05-1.50 inches, with most of the state receiving less than an inch of rain during the week. Warm overnight temperatures in the 60s to lower 70s were conducive for activity by nocturnal pest insects, including the western bean cutworm moth, which appeared in high numbers in survey traps for the third consecutive week.
DATCP Pest Survey activities included conducting seed field inspections, assessing soybeans for insect pests, checking western bean cutworm traps, and beginning the annual corn rootworm beetle survey, which will continue throughout the month of August. Additional weekly weather and climate information is available from the University of Wisconsin Extension Crops and Soils Division.
__________________________________
|
|
Field surveys across the southern half of Wisconsin indicate that the most advanced soybeans are at the R5 beginning seed growth stage and soybean aphid pressure has generally been low. Of the 168 sites surveyed as of July 31, only two fields had an average count exceeding 25 aphids per plant (see map below). The highest count recorded was 76 aphids per plant on 84% of the plants, in Waushara County.
The vast majority of soybeans scouted by DATCP for economic pests this month have had aphid infestations in the range of 1-20 aphids per plant on less than 50% of the plants throughout the field. In addition, natural enemies such as ladybeetle larvae, green lacewings, and parasitoids are abundant in many fields. |
|
|
Soybean aphid populations often increase rapidly from late July to early August, and scouting and insecticide treatment decision-making will be most critical in the next two weeks. To qualify for treatment to control aphids, a soybean field must meet the following three criteria:
- The average aphid count is greater than 250 soybean aphids per plant
- More than 80% of plants are infested with soybean aphids
- The aphid population is increasing
Soybeans should be evaluated not only for aphids, but also for two-spotted spider mites and defoliation caused by Japanese beetles, green cloverworm, and assorted caterpillars. Defoliation that meets the 20% threshold between the bloom and pod-fill stages and 30% in the pre-bloom stages may warrant control. Scouting several areas in the field interior, in addition to field edges where Japanese beetles are most numerous, is required for an accurate assessment.
|
|
 __________________________________
|
|
Preliminary results of the 20th annual western bean cutworm trapping survey show a cumulative state count of 11,871 moths in 69 traps, or an average of 172 per trap. This season’s current average moth catch is below last year’s all-time record high capture of 223 moths per trap (9,351 moths in 42 traps), although there are still three more weeks of monitoring left and the flight has not yet peaked in parts of northern Wisconsin. Peak activity should occur August 2-8 in areas north of Wausau, as western bean cutworm growing degree day (gdd) accumulations reach 2,704. The modified base 38°F column in DATCP’s degree day table shows Wausau has accumulated 2,677 gdds as of July 31, Medford has 2,631 gdds, and Crandon is at 2,451 gdds.
For the week ending August 1, the total catch was 4,660 moths, an increase from 3,658 moths July 19-25. This week’s high individual trap count was 367 moths near Taylor in Jackson County, while seven monitoring locations reported catches above 200 moths per trap.
Counts across southern and central Wisconsin are expected to drop off sharply next week as the flight subsides. Western bean cutworm trapping network participants are asked to continue reporting counts through August 22. |
|
 __________________________________
|
|
|
Apple maggot emergence continued for the fifth week but has been variable so far this season. A few orchards have reported very high weekly counts of 15 flies per trap, while many sites have not yet caught a single apple maggot fly. Economic counts were reported from 11 of 27 reporting locations July 26-August 1.
Peak emergence of adult flies is approaching and egg laying on apples can be expected throughout August. Apple growers should continue to apply sticky coating to traps each week (or as needed) and maintain apple maggot controls as long as counts exceed the following economic thresholds:
- One fly per trap per week for unbaited traps
- Five flies per trap per week for baited traps
|
|
 __________________________________
|
|
Corn leaf aphids are prevalent in corn this summer but their presence does not necessarily indicate damage is inevitable. This species appears annually in Wisconsin, usually in July, and can interfere with ear development if corn tassels and upper leaves become saturated with aphids. However, densities seldom reach economic levels and aphids are a larger concern in drought years when plants are moisture stressed. Although aphids appeared early this season and have been noticeable in corn throughout the state, in most cases, fieldwide counts have not been high enough to justify treatment.
The most critical period for aphid build-up is during the late-whorl to pollen-shed stages (when high populations may interfere with pollination) and scouting should begin two to three weeks before tassel emergence. If populations are high, meaning more than 50% of corn leaves or tassels are infested with 50 or more aphids per plant, spraying may be advisable for corn still in the early tassel stages.
Once fields have tasseled and pollination is complete, the benefits of insecticides are less clear. Corn leaf aphid populations may continue to increase through the R3 corn and often build up in the ear zone, but no research exists to verify if post-pollination treatment provides economic return. University of Minnesota Extension specialists conclude that late-season corn leaf aphid sprays are probably not advantageous. |
|
 __________________________________
|
|
|
|
|
