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

Reseach Report Number 666
August 2000

Small Grains Updates

Insects

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

Relatively mild weather during the winter encouraged damaging insect populations to develop in small grains. 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 areas in the southern part of the state. A new Hessian fly biotype (biotype L) is established in 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 showing good levels of Hessian fly resistance at Plains and Griffin in 1999/2000 were 'AGS 2000,' 'NK Coker 9835,' 'Croplan SR218,' 'FFR 516,' 'Pioneer 26R24,' 'Pioneer 26R61,' 'Roane,' and 'Roberts.' 'Santee' was resistant at Plains but susceptible at the Griffin site. 'AgriPro Hickory,' 'Pioneer 2684,' and 'Fleming' had moderate or intermediate levels of resistance at both sites. Although rated as resistant in past years, significant infestations occurred in 'Pioneer 2684' in 1999-2000 indicating that this variety has only moderate level of resistance which is not effective under high levels of Hessian fly pressure. Both rye and oats are good Hessian-fly resistant alternatives to wheat for forage production, because rye is highly resistant and oats are immune to the insect.

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.