The Georgia Agricultural Experiment Station
College of Agricultural and Environmental Sciences
The University of Georgia

Research Report Number 659
August 1999

SMALL GRAINS UPDATES

VARIETY RELEASES

Dr. J. W. Johnson, Department of Crop and Soil Sciences, Georgia Station, Griffin, GA 30223-1797.

   The Small Grains Breeding Program announces the release of '89482E7' wheat. This variety was developed jointly by the Georgia and Florida Agricultural Experiment Stations with support from State and Hatch funds. '89482E7' is a high yielding, medium maturing, medium height variety with excellent test weight and straw strength.

   Breeder's seed of '89482E7' will be maintained by the Georgia Agricultural Experiment Station. The Foundation class of seed of this variety will be made available by the Georgia Seed Development Commission in the fall of 1999.

METRIBUZIN SENSITIVITY

D. C. Bridges, J. L. Day, J.W. Johnson, and P.L. Raymer, Department of Crop and Soil Sciences, Georgia Station, Griffin, GA 30223-1797.

   In recent years Georgia wheat farmers have increasingly experienced difficulties controlling Italian (annual) ryegrass in wheat with Hoelon (diclofop). An option is to use Sencor (metribuzin) as a postemergence treatment for control of annual ryegrass, wild radish, and other broadleaf species. Approximately 10 years ago metribuzin use among Georgia wheat growers was fairly common, but use had declined over the intervening years. However, the current difficulties in controlling ryegrass with Hoelon have spurred interest in once again using Sencor.

   Some wheat cultivars are sensitive to Sencor (metribuzin). If Sencor is applied to sensitive cultivars severe injury and/or stand loss may occur. The Sencor label contains a list of known tolerant and sensitive wheat and barley cultivars. However, the label does not contain all varieties that are currently grown in Georgia. Until about 10 years ago field experiments were routinely conducted to determine cultivar sensitivity to metribuzin. Due to the increased interest in using metribuzin for winter wheat weed control we resumed cultivar evaluations using metribuzin during the 1997-98 wheat season and conducted trials again during the 1998-99 season.

   The following table summarizes data collected in a field trial at Griffin, Georgia during the 1998/99 growing season. Wheat was seeded 13 November 1998 at a seeding rate of 2 bu/acre. Paired treated and untreated plots were inlcuded in each of four replicates. Metribuzin (Sencor) was applied postemergence at a rate of 0.375 lb ai/acre to wheat in the 2-3 leaf stage on 4 December 1998. Wheat injury was visually estimated on 14 January 1999 and yields were determined in June.

DISEASES

Barry M. Cunfer, Department of Plant Pathology, Griffin Campus, Griffin, GA 30223

    Weather patterns this spring were conducive for powdery mildew on wheat. This disease is favored by rainy conditions but also is able to develop under relatively dry conditions as occurred this spring. Powdery mildew was severe in our breeding nurseries on susceptible lines. Growers should continue to select powdery mildew resistant cultivars. Dry weather slowed the progress of leaf rust. However, rust caused some damage on susceptible cultivars. Some growers used center pivot overhead irrigation to compensate for moisture stress during grain filling. Some fields with a rust susceptible cultivar had a significant increase in leaf rust as a result. Irrigated fields should be monitored for diseases. Growers should consider use of a foliar fungicide prior to irrigation if irrigation is applied after heading. Stagonospora leaf and glume blotch was relatively low because of dry conditions. Barley yellow dwarf on wheat appeared late in the season and caused some yield reductions, especially in the Piedmont and Mountain areas.

   Fusarium foot rot was found in several fields in Laurens County. Plants were severely stunted and killed before maturity with only a few shriveled seeds per plant. The dead plants were often in circular to oval areas in the field. These dead plants looked similar to groupings of "whiteheads" caused by take-all root rot. However, unlike take-all, the base of the stem was not black and although the root system was damaged, the stems did not release easily from the roots when plants were pulled. When the dried leaf sheaths at the base of the plants were carefully removed, often the inner sheaths had a diffuse violet color and rotting of the crown was evident. In the Pacific Northwest, this disease is often called "dryland root rot". When rainfall is below normal in areas which typically have low seasonal rainfall, root rot can be severe. Fusarium spores are present in the soil all the time. They cause seedling damping off and may cause minor damage to roots of adult plants in most years. This is because Fusarium is held in check by soil bacteria and other antagonistic fungi. However, when soil moisture declines the antagonists cease to be active, but Fusarium is still able grow and invade stressed plants. This is the situation we had this spring due to drought. As a result, a disease rarely encountered in the Southeast became significant because of environmental conditions.

   The fungicide azoxystrobin (brand name Quadris) received a label for use on wheat. This is a new type of fungicide chemistry and has been very effective in tests I have conducted for the past several years. It has a wide range of effectiveness against powdery mildew, leaf rust, and stagonospora leaf and glume blotch. Currently the cost is higher than Tilt or other fungicides. Growers should compare the options for disease control.

   Karnal bunt continues to be quarantined in the U.S. The number of samples collected in Georgia as part of the national monitoring program has been reduced to seven for 1999.

INSECTS

G. David Buntin, Department of Entomology, Griffin, Georgia

   Relatively mild weather during the winter encouraged damaging insect populations to develop in small grains in 1998/1999. The Hessian fly, Mayetiola destructor, can cause extensive damage to winter wheat, triticale and barley. Most wheat fields were planted with a resistant variety, and some fields were treated with an at-planting application of insecticide. Hessian fly infestations reached damaging levels in some fields in the southern part of the state. A new Hessian fly biotype (biotype L) is well established throughout northern Georgia and is present in low numbers in southern Georgia. Biotype L can overcome virtually all the Hessian fly resistant varieties currently grown in the state. Varieties still showing good levels of Hessian fly resistance at Plains in 1998/1999 were 'NK Coker 9835', 'NK Coker 9134', 'GA-Stuckey', 'GA-Gore ', ' AgriPro Hickory', 'Delta King 9121', 'Delta King 9027', 'Morey', 'Pioneer 26R46', 'Pioneer 26R61', 'Pioneer 2684', and 'Roberts'. Rye is highly resistant, and oats are immune to the insect. Both rye and oats are good Hessian-fly resistant alternatives to wheat for forage production.

   The mild winter and dry spring encouraged large populations of aphids to develop throughout the state. Aphids caused direct feeding injury to small grains during head emergence and grain fill. Aphids also transmit barley yellow dwarf virus (BYDV) which can cause large yield reductions in wheat, oats, barley and triticale. BYDV symptoms were present in low to moderate levels throughout the state and the disease caused considerable damage to wheat in some areas this season. Although the level of expression of symptoms varies between varieties, no varieties are truly resistant or tolerant of BYDV infection. Systemic insecticide seed treatments and properly timed foliar applications of insecticides can greatly reduce aphid numbers and minimize BYDV incidence.

   The cereal leaf beetle now is established throughout northern and most of southern Georgia. Populations continue to increase and caused noticeable damage this year in the coastal plain region. Larvae and adults are present in the spring during grain filling where they remove the upper leaf surface and chew elongated holes in leaves. Populations in most areas still are below the treatment threshold of 0.5 larva or adult per stalk. However, damage was very evident in the northwestern and central Piedmont regions of the state with some fields needing treatment with an insecticide. Cereal leaf beetle can be effectively controlled by a number of insecticides when applied to active larvae. Consult your local county extension agent for a list of recommended insecticides for this insect and for management practices for other insect pests of small grains.