ISSUE 15 August 10, 2000
SMALL GRAIN DISEASE SURVEY
NDSU Extension IPM scouts have finished their survey efforts for the year or are finishing this week. Many thanks to Amy Dukart, Matthew Gregoire, Allison Marsland, Laura Neal, Holly Semler, and Jerry Schneider for the great job they did.
For the past week, the scouts found the following: In the Southwest and West Central areas, Glume blotch was observed on wheat heads in 70% of the wheat fields surveyed. Head scab was observed in 59% of the surveyed wheat fields, with a range of field severity (incidence x head severity) from 1-48% (highest field severity in a durum field in Oliver county). Root rot symptoms were noted in 47% of the fields surveyed. Other diseases included Septoria, tan spot and leaf rust on the flag leaves in all fields, and very low levels of ergot were found in 12% of the fields.
In North Central and Northwest counties, head scab was observed in 55% of the fields surveyed, with average field severity ranging from <1%-30%. Tan spot and Septoria were found on flag leaves in all fields; leaf rust was observed in 40% of the fields surveyed. Loose smut was observed in 27% of the fields, with incidence levels from 2-16%. Root rot, black chaff and barley yellow dwarf symptoms also were reported.
In Central, Southeast and East Central counties of Wells,
Sheridan, Foster, Eddy, Benson, Griggs, Barnes, LaMoure, Dickey and Stutsman, 100% of the
surveyed wheat fields had some level of leaf rust, with severity on the flag leaf
ranging from 1-25%. Septoria leaf blotch was observed in almost all fields
surveyed, with severity on the flag leaf ranging from 4-60%. Glume blotch, the head
infection phase of Septoria, was observed in 93% of the surveyed fields. Head scab
was detected in 63% of the fields, but field maturity made detection difficult in some
fields. Field severity of head scab ranged from 1-22% Other head diseases noted were: black
chaff in 37% of fields, ergot in 19% of fields (but low severity), loose
smut in 15% of the fields, and sooty molds on ripe heads (11% of fields).
In the Northeast counties of Walsh, Grand Forks, Steele, Traill, Ramsey, and Nelson, root rot and head scab were common. Scab was found in all hard red spring wheat and barley fields surveyed, but field severities were relatively low in this weeks survey, from 1-4%. On crops where flag leaves were still green enough to rate, leaf rust averaged from 1-7% in severity. Bacterial black chaff also was observed in several fields.
ROOT ROT AND SEED TREATMENT
Several root rot organisms have been found associated with root rot symptoms this year. Laboratory isolations from plants with brown stem bases and brown subcrown internodes have predominately yielded the common root rot fungus, Bipolaris sorokiniana (more commonly known as Helminthosporium sativum). In some cases the brown discolored root systems also yielded Fusarium spp. Blackened basal stems and roots, as observed by John Lukach at Pekin and Cavalier plot sites, have the characteristic dark runner hyphae and symptoms of take-all (caused by a fungus called Gaeumannomyces). Common seed treatments used by wheat producers would not have controlled the entire range of organisms associated with the root rot symptoms this year.
The following seed treatments registered in North Dakota have labeling for root rot suppression, but some differences exist among them on which root rots are controlled:
Baytan: Suppression or some control of take-all and foot rot (label doesnt specify what organism is associated with foot rot); NDSU research also has showed activity against common root rot (Product must be commercially applied)
Dividend XL RTA: 5 fl oz rate: Partial control of common root rot, Rhizoctonia root rot; 10 fl oz rate: Partial control of common root rot, Fusarium root rot, Fusarium crown rot, take-all, Rhizoctonia root rot.
Imazalil: (FloPro, Double R, Nuzone): control of common root rot
Raxil: Early season suppression of common root rot and Fusarium foot rot
RTU-Vitavax Extra: (has imazalil plus thiabendazole): Protection against the seed and soilborne phases of the common root rot complex
Even with optimum practices for root rot control, including crop rotations away from cereals for several years, and standard root rot seed treatment, the environment played the biggest role in root rot development in 2000, with excessive rains (favoring infection by the fungi and shallow root depth) followed by heat stress.
Extension Plant Pathologist
CANOLA DISEASE SURVEY, PRELIMINARY RESULTS
The canola disease survey was begun last week in Hettinger County. In 8 fields, the incidence of aster yellows averaged 3.8% infected plants (range of 0-17.5%). Incidence of blackleg averaged 0.3% infected plants (range of 0-2.5%). Incidence of Sclerotinia stem rot averaged 1.9% infected plants (range of 0-12.5%). Severity of black spot on the pods averaged 0.04% of pod area affected (range 0-0.125%).
In Pierce County, in 10 fields, the incidence of aster yellows averaged 5.8% (range 0-17.5%); the incidence of blackleg averaged 3.0% (range 0-15.0%), incidence of Sclerotinia stem rot averaged 22.0% (range 5.0-42.5%) and severity of black spot on the pods averaged 0.09% of pod area affected (range 0-0.275%)
In Benson County, in 6 fields in the southern part of the county, aster yellows averaged 2.9% (range 0-7.5%), incidence of blackleg averaged 0.8% (range 0 -2.5%), incidence of Sclerotinia stem rot averaged 35.8% (range 7.5%-65.0%) and severity of black spot on the pods averaged 0.13% of pod area affected (range 0-0.350%).
Surveys are in progress in the central areas (Stutsman, Foster, Sheridan and Wells counties) and in the northwest. Data from these areas will be reported later.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB
This is sunflower week in the diagnostic lab. Most of the samples
coming in have some type of herbicide injury, but one sample and several calls concern a
bacterial disease. The bacterium Pseudomonas syringae pv. tagetis causes a
disease called Apical Chlorosis. According to Dr. Tom Gulya, a USDA research scientist at
Fargo, this is the only bacterial disease of any consequence in the Northern Great Plains.
Symptoms of apical chlorosis are striking, the new leaves are bright yellow to a bleached
The disease only occurs in the vegetative growth stage of the sunflower and is most severe during periods of cool weather and wet soil conditions. The appearance of apical chlorosis differs from nutrient deficiencies such as iron chlorosis or nitrogen deficiency in that the yellowing or bleached white appearance is uniform across the leaves. With nutrient disorders, the veins will often remain green and then green up again once the deficiency is resolved. Plants affected by apical chlorosis will generally recover, producing new green leaves in a few weeks; however, the white leaves will not green up, but remain yellow or white throughout the growing season.
Yield loss is not typically associated with this disease, however young infected seedlings may die if continuously stressed by cool temperatures and water-logged soils. There are no hybrids with complete resistance to apical chlorosis. Rotation to avoid increasing the bacterial population in the soil is the primary management recommendation. Roguing infected plants in seed production fields is reported to eliminate the disease.