ISSUE 8 July 1, 2010
North Central ND
Wheat Streak Mosaic Virus in Spring Wheat: Wheat streak mosaic virus (WSMV) symptoms were observed in spring wheat fields in the Kenmare (NW Ward County) and Sawyer (McHenry County) areas. The fields in the Sawyer area had flag leaf infections and the Kenmare field was in the jointing stage. Similar to Barley yellow dwarf virus, yield loss is approximately 5% with infections at the flag leaf stage and 20% at the jointing stage (Marcia McMullen, Extension Plant Pathology).
The wheat curl mite that spreads this virus completes an entire life cycle in as little as 7 days when temperatures are in the 70ís. The combination of the warm weather and a maturing winter wheat crop increases the likelihood of the virus being spread from field to field. As green wheat tissue turns brown, the wheat curl mite moves out of protected areas of the wheat plant to volunteer wheat or adjacent wheat fields. The wheat curl mite is primarily spread by wind. Although mites can be spread by wind distances greater than one mile, the highest risk is to adjacent fields one-quarter to one-half mile from severely infected fields. Insecticides registered on wheat are not an effective tool for wheat curl mite management. Mites are in protected areas of the plant and reproduce rapidly so populations recover quickly from insecticides and miticides that are well below the 100% efficacy necessary for control. The best management practice for reducing the spread of WSMV is to eliminate the volunteer wheat food source for the mites through herbicide use or tillage. In addition, avoiding wheat on wheat rotations will reduce the spread of WSMV from one season to the next.
The counties in our area are at or near the start of wheat midge flight. Burke, Divide, Mountrail, Rollette, and NW Ward counties are at 1150-1200, Bottineau, Renville, and Williams counties are at 1200-1250, and McHenry, McLean, Pierce, and central Ward county are at 1300-1350 midge degree days (http://ndawn.ndsu.nodak.edu ). Wheat is at greatest risk when it is at heading to early flowering during peak emergence (1475 degree days). For more information on thresholds and risk, see Jan Knodelís article in the June 24th Crop and Pest Report or refer to the wheat midge section in the 2010 Field Crop Insect Management Guide (www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm).
Peas, Lentils, and Chickpeas:
Peas and Lentils are in bloom in the region. Fields should be scouted during full bloom for pea aphids and Lygus bugs. Pea aphid and Lygus bug numbers are increasing but are not yet above threshold in the fields we have observed. Ascochyta has been found in commercial pea fields and is best controlled during bloom.
Many of the fields in the area are in bloom. The recommended timing for Sclerotinia control is at 20 to 50% bloom. Based on the risk maps from June 26th, the highest risk areas are in Bottineau, Burke and portions of Mountrail and Rollette Counties with low to moderate risk in the rest of the area. Updates can be found at http://www.ag.ndsu.edu/sclerotinia/.
Bertha army worm trap catches have remained very low, however, diamond-backed moth (DBM) trap catches have increased recently to as high as 59 moths per week. Trap catches of greater than 100 moths per week are indicative of populations that cause economic damage. Canola is most susceptible to injury from DBM at bloom to early pod development. Insecticide applications are justified when two or more larvae per plant are found throughout a field. Insecticide applications during bloom should be applied early or late in the day when bees are not out actively foraging for pollen. Some studies have indicated a benefit to canola pollination from insects.
Sunflower maggot, sunflower receptacle maggot, and sunflower seed maggot flies were observed in sunflower fields in Bottineau and Renville counties. The sunflower maggot is a stem feeder that is common in sunflower fields but does not cause economic damage. The sunflower receptacle maggot is the largest of these three species, but like the sunflower maggot, it is not an economically significant pest. The sunflower seed maggot is the smallest of these three species and tends to hold its wings together unlike the other two species. Of the three sunflower maggot species, the sunflower seed maggot has the most potential for crop injury and economic damage. For pictures and more information please visit: http://www.ag.ndsu.edu/pubs/plantsci/pests/e1457.pdf.
North Central Research Extension Center
According to NDAWN (North Dakota Ag Weather Network) data, the region received a trace (Fingal) to 1.2 inches (Lisbon) of rain during June 23 to 2. The regionís soil moisture continues to be at adequate to excess levels. Hail damaged crops in the southwest portion of this region including Logan and Emmons counties.
Winter wheat is in the seed dough growth stage. April-seeded small grain is in the heading to early-seed development stages. Currently, fungicides for control of scab and leaf disease, and foliar N for increasing protein are the two common inputs being considered or used in spring wheat. Timely-planted corn is in at least the 6-leaf stage, which means the growing point is above ground. Accumulated growing-degree day units for April 25 planted corn to June 29 ranges from +28 units at Fingal to -70 units at Linton compared to the past 5-year average. Some of the regionís corn will be waist-to-shoulder high by July 4. Weed spraying continues in row crops. Soybean planting may finally be completed but most timely-planted soybean is in the 3-trifoliate leaf (V3) to early-flowering (R1) stages. Cool-season broadleaf crops are in the flowering to early-pod development stages including canola, field pea, and flax.
Upcoming crop tours for the general public conducted by the NDSU Carrington Research Extension Center (CREC) and cooperators including county extension agents include:
*Tri-county (Wishek area), July 6, 7 p.m.
*Barnes County (Dazey area), July 7, 6:30 p.m.
*Pulse - primarily field pea (CREC), July 8, 9 a.m.
*Field Day (CREC), July 20, 9 a.m.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center