ISSUE 16 AUGUST 26, 1999
CANOLA DISEASE SURVEY AN UPDATE
Canola disease survey in northwestern North Dakota, as reported by Jan Knodel, included fields in Bottineau, Burke and Divide counties. Blackleg was mostly low, with a range of 0-15% incidence (percent infected stems) and an average of 4¼%. Sclerotinia was low, with a range of 0-10% incidence and an average of 3¼%.
Survey in central North Dakota, as reported by Greg Endres, included fields in Foster, Stutsman and Wells counties. Blackleg was mostly low, with a range of 0-12½% incidence and an average of 1%. Sclerotinia was low to moderately high, with a range of 0-45% incidence and an average of 13½%. An incidence of 13½% represents a yield loss of 7-10% and an incidence of 45% represents a yield loss of 23-31%.
Survey in Benson County by Jerry Ries and myself revealed low
incidences of blackleg, with a range of 0-7½% and an average of 2%. Sclerotinia was low
to moderate, with a range of 2½%-32½% incidence and an average of 16½%. An incidence of
16½ represents a yield loss of 9-12% and an incidence of 32½% represents a yield loss of
The North Dakota Department of Agriculture issued a state label
(24C) for a 7 day PHI (pre-harvest interval) for the application of Super Tin fungicide to
sugarbeets. Thus, Super Tin can be applied up to 7 days before harvest. This will help
sugarbeet growers control Cercospora leaf spot late in the season without having conflicts
with pre-pile harvest. If warm, humid nights continue into September, as occurs
frequently, late season application will be essential to maintaining late season control
as well as yield and quality of the sugarbeet crop that is delivered to the sugar co-op.
The state label only changes the PHI
from 21 days to 7 days; it does not change the total amount of Super Tin that can be applied in a year.
Extension Plant Pathologist
Some disease may further develop in the approximately 35% of the durum and 10% of the spring wheat crop which is still not mature, especially in the wetter areas of the state. However, our NDSU Extension survey efforts essentially finished this week, due to return of the crop surveyors to their colleges or jobs. I want to thank each of the four surveyors, Amy Dukart, Jerry Ries, Jerry Schneider, and Brittany Sund, for their excellent efforts in 1999! Scott Halley also helped out with surveying some later fields in Towner Co.
These individuals surveyed 878 small grain fields across the state during the 1999 growing season. Of the 878 fields, the majority were wheat (718), but 143 barley fields and 17 oat fields also were surveyed. The survey began at the 1-2 leaf stage of the crops and ended when crops reached physiological maturity. A full report on the survey results will be available later this fall, but a few highlights are summarized here:
Tan spot and Septoria leaf spots of wheat were common throughout the state and were detected early in crop development and became severe in many cases on the flag leaves. Spot blotch was a common fungal leaf spot on barley, and also was detected on wheat, and bacterial leaf spot was common on oats in the southwest and west central counties. Bacterial blight and black chaff were often observed on wheats in eastern counties.
Barley yellow dwarf virus (BYDV) was common on wheats and barley in the eastern half of the state, but also was seen on late planted grain in the northcentral areas. Some evaluations of BYDV in naturally infected variety plots at Langdon (John Lukach and Terry Gregoire), and at Mohall (Kent McKay, Janet Knodel, and Marcia McMullen), indicated that some varieties showed severe symptoms (ACBarrie, Ingot, Majestic, Grandin), others showed much less visible symptoms (Keene, Amidon, Parshall, Reeder, Russ), while a number of varieties were intermediate in response or did not perform similarly at both sites. Durum wheats generally showed fewer symptoms at both sites than the spring wheats.
Wheat streak mosaic virus (WSMV) was recorded in counties in the southwest, west central and northwest districts. About 9% of the fields surveyed in the southwest and west central districts showed symptoms of WSMV. This is a fairly high level and should be of concern for anyone considering winter wheat plantings in that area. Precautions should be taken to avoid WSMV infections this fall in winter wheat, through appropriate planting dates and destruction of volunteers and grassy weeds two weeks prior to planting.
Root rot observations were not a formal part of this survey of leaf and head diseases. However, in 1999, root rot symptoms were very evident in much of the state, with whole plants prematurely whitening, often in patches or in large areas of the field. These symptoms may have been due to the common root rot fungus or due to Fusarium crown rot, plus the shiny blackn lower stems and crowns typical of take-all root rot were observed by Bob Stack, NDSU Plant Pathologist, and me at the Carrington research site. The common root rot fungus, Helminthosporium (Cochliobolus), and Fusarium root rot fungi were isolated from roots and crowns in cultures at NDSU.
Fusarium head blight (scab) was most commonly observed in the eastern half of the state, with very few observations in the western counties this year. Although scab was not uncommon in eastern wheat and barley fields, severities were much lower in 1999 than in recent years, with field severities (# of tillers showing symptoms x severity of infected heads) ranging from less than 1% to 5-6%. The highest field severity of scab recorded in the survey was 10.5% in one wheat field.
Wheat leaf rust was very common in 1999, with observations in
all areas of the state. Barley leaf rust and oat leaf (crown) rust (different
species of leaf rust) also were commonly observed. For wheat leaf rust, survey
detections were made as early as June 8 and June 9 in the eastern half of the state, June
14 in the southwest, and June 28 in the northcentral area. In the southcentral and central
districts, 70.8% of the wheat fields surveyed showed some leaf rust, and severities on the
flag leaf ranged from 2- 100%. In the southeast, east central and northeast districts,
73.4% of the wheat fields surveyed showed symptoms of leaf rust, with severities on the
flag leaf ranging from 0 to 40%. In the southwest and west central districts,
65.7% of the surveyed wheat fields showed leaf rust, with severities on the flag leaf ranging from 0 - 46%. In the northcentral and northwest districts, 37.7% of the surveyed wheat fields showed some level of leaf rust, with severities on the flag leaf ranging from 0 - 26%. Higher severities were recorded in some varieties in research plots in all districts. Some information on spring wheat variety response to leaf rust in 1999 is given in the next section.
A preliminary summary of leaf rust reactions among some spring wheats was provided to me by Jack Rasmussen, NDSU Plant Pathologist. The following values are average coefficients of infection for some selected varieties, averaged over three leaf rust nurseries, at Prosper, Carrington, and Langdon. Coefficient of infection (CI) equals the percent severity of the leaf rust multiplied by the reaction type value (susceptible reactions having the highest reaction type value).
Average CI of Leaf rust in 1999*
20.8 (Esp. High at Carrington)
19.4 (Low at Carrington)
*Source: Dr. Jack Rasmussen, NDSU Plant Pathology Dept.
An evaluation of leaf rust severities on the flag leaves at Renville County plots at Mohall on 8/17 by Kent McKay, Jan Knodel, and me, indicated similar responses for most varieties, except that Reeder and Gunner had noticeably lower levels of leaf rust in these late planted variety trials at Mohall.
Extension Plant Pathologist