Weed problems in soybean fields

This information was summarized from a June 22, 1998 teleconference with ISU extension field specialists in crops.

  • Rain and saturated soils continue to hamper fieldwork statewide. Most areas of the state had at least 2 to 4 inches in the past week and parts of north central, northeast, central, and southern areas of Iowa had an additional several inches. Brian Lang (northeast) reported significant hail damage from Saturday's storm running north of Ridgeway through north of Hesper in Winneshiek County.
  • Replanting of crops in hail, flood, insect, and disease-damaged areas has not progressed very quickly. The soybean seedlings are damping-off in some replanted fields. Some fields have been planted for the third time. It is getting too late for further replanting of corn and soybean.
  • Postemergence herbicide applications in soybean are behind in many areas because of wet soil conditions. Some fields are extremely weedy with giant ragweed up to 20 inches tall. Mark Carlton (south central) and John Creswell (central) reported that only 25 percent of post herbicides have been applied in their areas.
  • Soybean damping-off is a problem in many of the wet areas and seems to be worse in hail-damaged fields, high-residue fields, or in conjunction with herbicide injury.
  • Some corn, especially in southern Iowa, has had problems with crown rot and damping-off diseases (see the last week's ICM newsletter, page 116).
  • Up to 25 percent of first-cut hay is not complete. Some has been rained on several times and mostly stems remain. Joel DeJong (northwest) reported that some farmers in his area have started to harvest second cut. Potato leafhoppers on alfalfa are being reported in numbers above the threshold. William Lotz (northeast) commented that the potato leafhoppers are above thresholds, but the fields are too wet to spray. Virgil Schmitt (east), Jim Jensen (southeast), and Mark Carlton (south central) reported common and Leptosphaerulina leaf spot on alfalfa.
  • Wheat is ripening but diseases will reduce yield. Oats are heading and Paul Kassel (northwest) observed some barley yellow dwarf starting to show up.
  • Estimates (see table) of the average growth stages for corn and soybean were reported by the 14 ISU Extension field specialists across Iowa. (Note: V1, V2, etc., refer to the vegetative stage; numerals refer to the number of visible leaf collars on the corn plant. For soybean, V1 and V2 refer to the number of fully developed leaf nodes [i.e., leaflets expanded above the top node]).
Area Corn Soybean
Northwest V9 V3
North central V9-V10 V3
Northeast V8 V3-V4
East central V8-V9 V3
Central V9 V3
Southwest V8 V4
South central V6 V3
Southeast V7 V3

This article originally appeared on page 126 of the IC-480(16) -- June 29, 1998 issue.

Updated 06/28/1998 - 1:00pm