SMALL GRAINS UPDATES
Dr. J. W. Johnson, Department of Crop and Soil Sciences, Georgia Station, Griffin, GA 30223-1797.
The Small Grains Program announces the release of 'Roberts' wheat. This variety was developed jointly by the Georgia and Florida Agricultural Experiment Stations with support from State and Hatch funds. The name of 'Roberts' was selected to honor Dr. J. R. Roberts, a retired breeder and pathologist with the USDA-ARS. He was located at the Georgia Experiment Station for 15 years. His research areas were insects and rusts of small grains.
'Roberts' wheat was tested under the experimental number GA 871339-E18. It is a late maturing, medium height variety with medium straw strength and high yield potential when grown in the piedmont and mountain regions of the Southeastern U.S. 'Roberts' has good resistance to powdery mildew and Hessian fly and is moderately resistant to leaf rust.
Breeder's seed of 'Roberts' will be maintained by the Georgia Agricultural Experiment Station. The Foundation class of seed of this variety will be made available to seed growers in Georgia by the Georgia Seed Development Commission in the fall of 1998.
Barry M. Cunfer, Department of Plant Pathology, Georgia Station, Griffin, GA 30223
Cultivars which are susceptible to foliar diseases but have other favorable agronomic traits such as high yield potential are placed on the recommended list of cultivars. Many cultivars are not placed on the list because of disease susceptibility or are removed from the list after several years because they become highly susceptible. The frequent rains during the late winter and spring of 1998 favored foliar diseases. Leaf and glume blotch was more severe than it had been in the past five years. Leaf rust was heavy on susceptible cultivars. In tests conducted at Plains, application of Tilt increased yields of three recommended susceptible cultivars 7-13 bu/acre, which was an economic return. When nonrecommended disease-susceptible cultivars are grown, the likelihood that they will respond to fungicide treatment is very low during years such as 1998 when conditions are highly favorable for disease. Even in seasons when disease pressure is moderate, recommended cultivars which are susceptible will respond better to fungicide application than nonrecommended susceptible cultivars. Therefore, growing cultivars on the recommended list offers the best opportunity to control diseases and maintain profitability.
Problems have been reported with low seed germination in rye seed stocks. Growers planting seed early for grazing should consider a seed treatment containing metalaxyl which controls soilborne Pythium fungi. This may be especially important in the lower coastal plain because soil temperatures are likely to be higher than normal in late summer and early fall. Species of Pythium can rot rye seed before it germinates when soil is 75 F or higher. As soil temperature declines, Pythium is less likely to cause damping off. However, metalaxyl seed treatment may also be beneficial this year for rye planted for grain. Seed treatment fungicides which control seedborne fungi which cause seedling blight should be considered for all small grains.
The smut of ryegrass confused with Karnal bunt in 1996 has been identified by USDA scientists as a new species of the smut fungi. During the past two years I have found that this smut occurs on ryegrass in wheat fields throughout the state. Spores from ryegrass contaminate wheat seed during harvesting. APHIS found no Karnal bunt in Georgia as part of their national survey in 1998. However, USDA quarantine regulations remain in effect if the disease is found anywhere in the U.S.
G. David Buntin, Department of Entomology, Griffin, Georgia 30223
Relatively mild weather during the winter encouraged damaging insect populations to develop in small grains in 1997/1998. 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. However, Hessian fly infestations reached damaging levels in some fields in the southern part of the state. A new Hessian fly biotype (biotype L) was discovered near Griffin several years ago and is well established throughout northern Georgia and seems to be present in the upper coastal plain region of the state. Biotype L potentially can overcome virtually all the Hessian fly resistant varieties currently grown in the state. However, Hessian fly infestations in entries of the wheat variety trial at Plains shows that some varieties are resistant (see table). 'NK Coker 9835', 'GA-Stuckey', 'Fleming', 'GA-Gore', 'Roberts', 'AgriPro Hickory', 'Morey', 'Pioneer 2580', 'Pioneer 2628', and 'Pioneer 2684 still have good resistance at this location. 'NK Coker 9663' and 'Pioneer 2691' are partially resistant. Fly infestations were low in the Griffin trial and are not shown. If susceptible varieties are planted, growers especially in the southern part of the state should use an at-planting insecticide such as DiSyston or phorate to control Hessian fly in the fall and early winter. Rye is resistant and oats are immune to the insect. Both rye and oats are good Hessian-fly resistant alternatives to wheat for forage production.
Aphid populations were generally low in the fall and early winter. The mild winter encouraged large populations of aphids to develop in February and March in some areas of 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 mostly low throughout the state with only some fields showing symptoms and damage. At-planting insecticides can control aphids in the fall, and fields in some areas were treated specifically for aphid control and BYDV reduction using foliar insecticide applications.
The cereal leaf beetle now is established throughout northern Georgia and is present throughout most of the upper 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 well below the treatment threshold of 0.5 larva or adult per stalk. However, damage was very evident in the northwestern region of the state and in some areas of the lower piedmont region with some fields in these areas needing treatment with insecticide. Cereal leaf beetle can be effectively controlled with a number of insecticides applied when larvae are active. 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.
Hessian infestations in entries of the State Wheat
Variety Trial at Plains, GA in spring of 1998.
|~||NK Coker 9704||62.2*||1.74*|
|~||NK Coker 9803||58.9*||1.94*|
|Delta King 1551W||44.4*||0.86*|
|#/~||NK Coker 9134||18.9*||0.37|
|#||NK Coker 9663||15.6||0.40|
|#||NK Coker 9835||1.1||0.02|
|*||Indicates mean is significantly greater than zero (P < 0.1; LSD test).|
|~||Susceptible in previous tests.|
|#||Resistant in previous tests.|