ISSUE 5 June 10, 2010
WHEAT VOLUNTEERS AND VIRUSES
Wheat streak mosaic continues to be confirmed in wheat samples coming to the NDSU Diagnostic Lab. Barley yellow dwarf virus (BYDV) also was confirmed in winter wheat volunteers in several locations across the state. Growers who have any volunteer patches or fields should get those areas destroyed, as they are only serving as disease sources for adjacent crops.
BYDV attacks wheat, barley and oats. The symptoms in wheat and barley generally include a golden yellow discoloration from the leaf tip downward.
BYDV in Barley
BYDV in Wheat
In oats, the virus causes a reddish bronzing of the leaves. Cereal aphids, such as oat bird cherry aphid and English grain aphid, transmit yellow dwarf. Dan Waldstein, Area Specialist at the North Central Research Extension Center, detected a few aphids and symptoms similar to BYDV in wheat, near Minot, and Suanne Kallis, NDSU IPM field scout in the southeast, also detected grain aphids, so aphids are here. Grain aphids that transmit BYDV can be controlled with insecticides, if detected in fields and as their population starts to increase.
WINTER WHEAT AND HEAD SCAB RISK
The Fusarium head blight (scab) forecasting model indicates moderate risk of infection to any moderately susceptible to susceptible winter wheat varieties in the northeast corner of ND, if those varieties are in the flowering stages of development. Abundant rains in those areas, with associated long dew periods, are contributing to weather that could favor scab development in any vulnerable crop.
NDSU IPM SURVEY RESULTS, JUNE 6
The NDSU IPM field scouts looked at 87 wheat fields and 6 barley fields during their first full week of scouting around the state. The field scouts did not observe any stripe or leaf rust in wheat. The dominant disease in wheat was tan spot, with almost 90% of fields showing symptoms, although the range of severity was wide, from 1% to 22%. The NDSU small grain disease forecasting system is showing favorable conditions for tan spot infection across much of the state. In barley, a few fields showed some fungal leaf spots, as well.
Extension Plant Pathologist
LOOKOUT FOR APHANOMYCES ROOT ROT OF SUGARBEET
During wet and warm conditions, sugarbeet may be affected by Aphanomyces root rot caused by the pathogen Aphanomyces cochlioides. The disease is most damaging in wet soils at temperatures of 68 to 86 F. Aphanomyces can be deadly in the seedling stage, and can also cause serious root rot later in the season. Infected seedlings typically have roots and hypocotyls that become black and shrink to a dark, slender thread. Infected plants have light green leaves with older leaves becoming yellow. Plants tend to wilt in the afternoons of hot, dry, and sunny days. Assessment of fields should therefore be done in the afternoons of hot sunny days. Fields of surviving plants with severe root infections have reduced root yield, lower sucrose content, and higher impurities. During defoliation, many of the infected roots are knocked out of the soil and are not harvested. Diseased roots have much higher respiration rates compared to healthy roots. Consequently, the quality of storage piles can be reduced when diseased roots are stored with healthy roots.
Fields with a history of Aphanomyces should be planted with tolerant varieties approved for the grower’s factory district. Many high yielding Aphanomyces tolerant varieties are available. For additional protection for fields with a history of the disease, seeds should be treated with Tachigaren, especially since sugarbeet growing areas in North Dakota and Minnesota are in a wet cycle, with conditions favorable for Aphanomyces occurring annually. Planting should be done as early as possible to facilitate early and vigorous growth in conditions unfavorable to the pathogen. Field drainage should be improved since the pathogen needs adequate free moisture to germinate and cause infections. Fields with a history of severe Aphanomyces should be treated with about 10 tons of factory spent lime per acre. Research shows that plots treated with spent lime results in a significant reduction in Aphanomyces root rot, and high recoverable sucrose yields. Effective control of weeds such as lambsquarters, pigweed and kochia which serve as host to A. cochlioides, helps to reduce the pathogen’s population.
Extension Sugarbeet Specialist
SCLEROTINIA STEM ROT RISK MAP FOR CANOLA TO BE DEPLOYED JUNE 16
NDSU Canola Pathologist, Dr. Luis del Rio, will be deploying the Sclerotinia stem rot (SSR) Risk Map for Canola for the 2010-season beginning June 16. The risk map uses weather variables to predict the threat of sclerotinia throughout the northern growing region. The risk map is designed to help producers determine if a fungicide application may be warranted for management of the disease.
The sclerotinia life-cycle begins when the overwintering structure, sclerotia, germinates and forms small mushroom-like structures called apothecia. Apothecia release ascospores, which can utilize canola petals as a food source. From those colonized petals, infection then progresses into branches and stems and can result in yield losses and lodging. Because the infection begins on flower petals, canola is only at risk for SSR during flowering. In general, 1-2 inches of rain within a week or two of flowering will provide a favorable environment for sclerotia germination and subsequent spore formation. Moderate temperatures and long dew periods (or rain) during bloom will favor infection and disease development.
The risk map is generated by analyzing weather variables from NDAWN weather stations throughout the state. When favorable environments exist for disease development, a ‘risk’ will be reported on the risk map. Two words of caution: First, disease development is driven by a combination of environmental conditions and availability of apothecia in the field, that means the risk could be higher/lower than estimated depending on prior history of Sclerotinia problems and crop rotations used in the previous three years; thus, the map should be viewed only as a guide to aid in the decision making process. Secondly, canola is only at risk in flowering so the risk map is only applicable to your field during (or possibly immediately prior) to bloom.
The risk map can be found at www.ag.ndsu.edu/sclerotinia. A risk calculator, included as a link at the risk map web site, provides an interactive program that adjusts the estimation of risk using field-specific information provided by the grower. A link to the risk map can be found at the North Canola Growers Association web site, www.northerncanola.com, or by searching for ‘canola sclerotinia risk map’ using an internet search engine. Dr. Luis del Rio can be contacted directly at email@example.com.
Extension Plant Pathologist