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 included 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.

Wheat variety response to Sencor (metribuzin) herbicide, Griffin, GA 1998-99.

  Yield Sensitivity Classification1
 
Cultivar
Wheat
Injury
Untreated
Weed-free
Treated
Weed-free
Yield
Difference2
UGA
Tests
Sencor
Label

  % bu/acre bu/acre  
 
AgriPro D93*7163 10 56 56 NS T NOL
AgriPro Hickory 5 57 51 NS T MT
AgriPro Mason 2.5 66 60 NS T T
AgriPro Patton 0 65 60 NS T T
AgriPro Shelby 0 61 60 NS T T
 
Delta King 1551W 5 52 48 NS T NOL
Jackson 2.5 60 57 NS T T
Terral LA 422 5 65 62 NS T NOL
NK Coker 9134 5 71 63 NS T T
NK Coker 9704 5 54 51 NS T3 S3
 
NK Coker 9803 5 57 48 NS T M T
Pioneer 2684 2.5 58 55 NS T T
Pioneer 26R46 2.5 66 66 NS T NOL
Pioneer 26R61 2.5 69 68 NS T NOL
Pocahontas 5 59 50 NS T T
 
UGA88622E51 10 59 54 NS T NOL
UGA89482E7 2.5 74 70 NS T NOL
Fleming 12.5 63 52 NS MT S
Pioneer 2643 15 65 45 S MT3 NOL
Roberts 12.5 66 57 NS MT NOL
 
UGA881178E53 12.5 66 56 NS MT NOL
Clemson 201 57.5 62 36 S S NOL
FL8868 32.5 66 47 S S NOL
GA-Dozier 68.5 51 24 S S S
GA-Gore 27.5 66 52 S S S
 
GA-Stuckey 80 55 26 S S S
Jaypee 55 60 26 S S S
Morey 70 63 18 S S S
NK BL931167 32.5 52 32 S S NOL
NK Coker 9663 50 74 43 S S NOL
 
NK Coker 9835 30 63 44 S S S
Pioneer 2691 22.5 61 44 S S NOL
Roane 20 52 44 NS S NOL
UGA881428LE2 50 67 43 S S NOL
UGA901146E15 72.5 67 23 S S NOL
 
UGA90524E35 42.5 70 43 S S NOL
USG 3209 55 50 21 S S NOL

1.  Sensitivity Classification: T = Tolerant (UGA studies indicated 10% or less visual injury and no stand loss); MT = Moderately Tolerant (UGA studies indicated visual injury from 11 to 20% with no stand loss); S = Sensitive (UGA studies indicated greater than 20% visual injury and/or stand loss); and NOL = not on label.
2.  Where yield differences are marked with "S", differences between Sencor-treated plots and untreated plots were significantly different at the 10% probability level. For varieties marked "NS", yields were not significantly different.
3.  NK Coker 9704 scored a rating of "Tolerant" in UGA tests. However, it is rated as "Sensitive" on the Sencor label, which indicates that in at least one trial severe injury and/or stand loss was observed with the cultivar. Therefore, NK Coker 9704 should be regarded as "Sensitive". Pioneer 2643 was initially rated as "Moderately Tolerant" based on early-season visual injury, but based on yields it should be regarded as "Sensitive".


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.



Hessian fly infestations in entries of the State Wheat Variety Trial at Plains, GA in 1999.

 
Brand-Variety
% infested
stems
HF immatures
per stem

Jaypee 86.7 * 3.17 *
NK-Coker 9663 80.0 * 3.06 *
Jackson 78.9 * 4.30 *
UGA 911316E46 78.9 * 3.71 *
FFR 502R 73.3 * 3.14 *
 
UGA 90277AE22 72.2 * 3.09 *
AgriPro Marion 71.1 * 3.86 *
LA 87167D8-10-2-5 68.9 * 3.74 *
NK Coker 9803 68.9 * 3.53 *
AgriPro Shelby 68.9 * 3.27 *
 
UGA 901146E15 67.8 * 2.64 *
UGA 90552AE33 67.8 * 2.41 *
FFR 518R 66.7 * 3.40 *
Pioneer 2691 66.7 * 3.18 *
Delta King 9051 64.4 * 2.23 *
 
FFR 502B 62.0 * 3.10 *
FFR 518B 60.0 * 3.32 *
AgriPro Patton 56.7 * 2.32 *
NK Coker 9704 54.4 * 2.63 *
LA 90145G16-2-1-2 54.4 * 2.60 *
 
Pioneer 2643 51.1 * 2.16 *
Clemson 201 48.9 * 2.18 *
Terral 422 47.8 * 1.46 *
Delta King 1551W 40.0 * 1.70 *
AgriPro Mason 40.0 * 1.64 *
 
USG 3209 33.3 * 0.88
Fleming 25.6 * 0.70
AgriPro Hickory 23.3 * 0.57
UGA 88622E51 15.6 0.34
Roane 14.4 0.24
 
Pioneer 26R46 13.3 0.42
Pioneer 2684 13.3 0.22
Morey 13.3 0.20
UGA 881178E53 10.0 0.29
Pocahontas 7.8 0.09
 
UGA 93059LE6 5.6 0.09
UGA 91436E29 4.4 0.14
NK Coker 9134 4.4 0.10
UGA 89482E7 4.4 0.10
Delta King 9027 3.3 0.09
 
UGA 881428LE2 3.3 0.07
Pioneer 26R61 2.2 0.10
NK BL931167 2.2 0.07
UGA 90524E35 2.2 0.02
UGA 91426E39 1.1 0.01
 
GA-Dozier 1.1 0.01
FL 8868 1.1 0.01
NK Coker 9835 0 0
Delta King 9121 0 0
GA-Gore 0 0
 
LA 85411D4-6-3-1 0 0
GA-Stuckey 0 0
92485-E15 0 0
Roberts 0 0
 
LSD (0.05) 18.4 1.15
LSD (0.1) 15.4 0.96

* Indicates mean is significantly greater than zero (P < 0.05; LSD test).
Entry Means average of 3 replicates, RCBD.