SOUTH-CENTRAL ND CROP SCOUT REPORT (June 25-26)
The NDSU Extension Service annual crop scouting program in south-central North Dakota continued this week with the emphasis on disease and insect presence in small grain. On June 25-26, 28 fields (4 barley, 1 durum, 1 winter wheat, and 22 spring wheat) were checked in Barnes, Stutsman, Logan, McIntosh, Emmons, Burleigh, and Kidder counties. The crops were in the jointing to early heading stages. Tan spot was found in all but three of the wheat fields with more advanced fields having higher incidence (60-100% of tillers) but low severity (1-6% of flag leaf area). A Logan county winter wheat field in the mid-flowering stage showed heavy tan spot including 22% on the flag leaf but little, if any, head diseases at this point. Contributing factors were the wheat-on-wheat ground with high residue and damp conditions. The remaining three wheat fields were showing symptoms of Septoria spot blotch with high incidence but low severity. This disease is distinguishable by its small black specks (called picnidia or fruiting bodies) in the infected area. Leaf rust has finally made an appearance in this region. A field in Emmons county had 16% incidence but the infection was found only on the bottom and middle leaves at low levels. All four barley fields show signs of net blotch with higher intensity (94-100%) but minimal severity. The infections have appeared mostly on the bottom leaves. Young grasshoppers were found in field margins in all scouted fields. A couple fields had fairly high number of young hoppers. Also, the first aphids of the season were seen in the southern part of the scouting area in two fields.
Scouting has also started in the counties for downy mildew in sunflowers (200 plants inspected per field). Downy mildew infection stunts sunflower growth, yellows the upperside of the leaves, and the underside of the leaf has a white ‘fuzz’ present. A couple fields per county have been checked with only one field above 2.5% of plants infected.
POST BROADLEAF WEED CONTROL OPTIONS IN SUNFLOWER
POST broadleaf herbicide options in sunflower are limited to Assert. Assert controls wild mustard and provides fair to good control of wild buckwheat, based on NDSU herbicide efficacy ratings. Mechanical weed control is the only option for other annual broadleaf weeds.
Mechanical weed control includes between-row cultivation for wide-rowed sunflower and use of a harrow or rotary hoe for all row spacings. A harrow or rotary is suggested to be used when sunflower is in the 2- to 6-leaf stage. Some stand reduction likely will occur. In a 2-year NDSU trial at Carrington, sunflower stand was reduced up to 10% with a rotary hoe and 25% with a harrow.
Weed species and stage is important. Weeds need to germinate from a 1-inch depth or less and be ready to emerge or newly emerged (cotyledon to 2-leaf stage). The key is to pull the plants from the soil and allow them to quickly dessicate. Tillage should be done on a dry soil surface and with sunny and warm weather. Annual broadleaf weeds that can be controlled with light tillage include nightshade species, pigweed species, kochia and foxtail. Frequently monitor the crop and weeds during the tillage operation to determine impact on plants. A second tillage pass may be needed for satisfactory weed control.
Refer to NDSU Extension Service circular W-1134 “Mechanical weed control with a harrow or rotary hoe’ for details on this weed control strategy.