ISSUE 15 August 15, 2002
CEREAL RUSTS - END OF SEASON REPORT
The final Cereal Rust Bulletin for 2002 was published by the USDA in St. Paul on 8/7/02. According to this report, stem rust was found throughout the northern Great Plains on winter wheat, barley and oat, but generally developed too late to do major damage. So far, four wheat stem rust isolates from ND have been identified to race by the Cereal Disease Lab in St. Paul. All were race QCCJ, which is virulent on barley cultivars with the Rpg1 (T) gene for resistance. We have identified low levels of stem rust on barley in our NDSU IPM field survey efforts this year. The Bulletin reports some severe levels on oat stem rust in northern states. Severe oat stem rust has been reported in a few fields in North Dakota.
The Cereal Rust Bulletin indicates that wheat leaf rust developed earlier than normal this year and was more widespread and severe than last year. In our NDSU field survey, we first detected leaf rust in the state on June 17 in Richland County, as compared to a first detection on July 5 in 2001. The Cereal Rust Bulletin reports that "in farm fields in the Red River Valley, severity levels of up to 40% were observed on the commonly grown wheat cultivars. High levels of leaf rust were also observed in fields in central and southeastern North Dakota"
Our latest field survey results indicate high incidences of leaf rust in wheat fields. Rust severities were difficult to measure at this time because leaves were dried prematurely due to a combination of leaf rust and high temperatures.
A few fields had severities > 60%. Field scouts also found some substantial leaf rust on some experimental durum lines. Durum varieties typically have a slow rusting reaction.
The Cereal Disease Lab has identified wheat leaf rust races on 241 isolates so far, but these isolates are from southern states. North Dakota samples are still to be characterized. In the central and southern plains, M- races were most common, but there also was an increase in the number of T- races. M and T races vary in their virulence on leaf rust resistant genes used in developing leaf rust resistant wheat cultivars.
FUSARIUM HEAD BLIGHT UPDATE
Wheat fields surveyed during the week of 8/2-8/9 indicated that Fusarium head blight (scab) is present in most fields, but that the field severity index (incidence x head severity) is low (from 0.1 - 5 field severity) in the majority of fields.
A composite map of all wheat scab observations will provided in the last Pest Report. For barley, much fewer observations have been made, but for fields surveyed past heading, the field severity of barley scab also has ranged from 0.1 - 5. The field index is an indication of potential % yield loss due to this disease.
Extension Plant Pathologist
SOYBEAN CYST NEMATODE
Soybean Cyst Nematode (SCN) is a worm_like organism in the animal kingdom that parasitizes plant root tissue. This pathogen has not yet been reported in ND but is known to occur in counties in MN and SD that border our state. This is the time of year when symptoms may become evident. They are only visible on above-ground parts of soybeans when the pathogen population has built up to a significant number. It is particularly important for growers in the SE part of the state, near to SD and MN, to scout for symptoms and have any suspicious fields checked. This can be a devastating pathogen if left unchecked; however it is quite manageable if the grower is aware of the problem and uses appropriate rotation and variety selection.
The host range for this pathogen includes susceptible soybeans, dry and snap beans, peas, and susceptible forage crops such as Sweetclover, Vetch, Lespedeza, and Birdsfoot trefoil. It is called a cyst nematode because the female nematode feeds on the roots, swells, and fills with eggs. As the female matures and dies, she turns a brownish color. This stage is referred to as the cyst, which can survive in the soil and from which eggs are hatched.
Symptoms of SCN usually begin to express themselves later in the season, and only show on above ground parts of the plant. Symptoms may appear similar to iron chlorosis, compaction, drought stress, other nutrient deficiencies, and herbicide injury. Symptoms of possible nematode problems will show up on oval or circular areas on a field, often in an elongated shape that follows tillage patterns. Unlike iron chlorosis where the whole leaf expresses interveinal yellowing, SCN will cause the outer margin of the leaf to yellow and brown, and eventually the whole leaf is affected, not just the area between veins. Plants are usually stunted and rows may not close in affected areas. Symptoms are usually most severe in the center of the affected area and decrease in severity toward the margins. These affected areas are more common at field entrances, where equipment may enter, and along field edges where windblown soil may accumulate. Cysts move most often in soil and soil-peds in seed, and on equipment that might carry soil from an infested field to a new field. Damage is generally more severe on light, sandy soils, but other soil types can be affected as well. It is not uncommon to have both iron chlorosis and SCN symptoms on the same plants.
The NDSU Plant Diagnostic Lab will be cooperating for the third successive year with APHIS on a survey of soybean fields in ND to check for this pathogen; and we can help with identification of potential SCN infestations in your fields. If you suspect an SCN infestation in a field this year, bring or send in a sample that includes the soils. Gently dig out the plant with the root ball and soil intact. This will enable us to check for cysts on the roots. Soil samples can also be assessed after harvest. The cost for this testing is $20.00. Soil samples should be taken from 0-6 inches, from affected areas, or from several areas in the field following a zig-zag pattern. More detailed sampling instructions can be found by calling the NDSU Plant Diagnostic Lab at 701.231.7854 or on the lab website:
NDSU Plant Diagnostic Lab
BACTERIAL DISEASES ON DRY BEANS
A few dry bean leaves and pods are showing symptoms of bacterial diseases. Lesions due to a bacterial disease may appear as water-soaked and shiny. The lesions may develop a reddish margin with age. The common bacterial diseases seen in the Red River Valley are:
The diseases can either start from infected seed or from bacteria that has survived on debris in the soil. Disease is worse under rainy conditions. Splashing rain and wind can spread the bacteria from debris on the soil to the leaves or from plant to plant. The bacteria can only enter the plants through natural openings or wounds, so disease may be more severe after a hailstorm or damaging winds.
Common Blight, caused by Xanthomonas campestris pv. phaseoli.
Halo Blight, caused by Pseudomonas syringae pv. phaseolicola.
Brown Spot, caused by Pseudomonas syringae pv. syringae.
The diseases may be managed by planting high quality certified seed, treating seed with streptomycin, and practicing a 3 to 4 year crop rotation. Some copper fungicides are registered for use on dry beans, but generally have not been effective in North Dakota.
Extension Plant Pathologist