Effect of seeding rate and insecticide seed treatment on aphid infestation, barley yellow dwarf disease incidence and yield of winter wheat

Studies in Georgia have found that full wheat yield could be achieved with modern adapted winter wheat cultivars while reducing seeding rates by 30% or more.  Insecticide seed treatments such as imidacloprid (Gaucho) can reduce aphid infestations and barley yellow dwarf incidence but this treatment generally is not cost effective at higher seeding rate.  We conducted a study to evaluate the effect of Gaucho seed treatment at reduced seeding rates on aphid infestation, BYD incidence, wheat tillering and yield.  Trials were conducted at Plains and Tifton GA over two seasons.  Two cultivars 'AGS 2000' and 'Roberts' were planted at four seed rates, 10, 20, 30 and 40 seeds per ft² (108, 215, 323, and 430 seeds per m²) with and without Gaucho 480 at 1.5 fl oz per 100 lbs seed (47 g ai/100 kg).  These first-year results suggest that wheat seeding rates can be reduced without adversely affecting yield.  Aphid infestations and presumably number of viruliferous aphids were not different among seeding rates but aphids per plant declined as seeding rate increased. Imidacloprid effectively controlled aphids at 30 days after planting. Conversely, BYD incidence as measured by symptomatic stems declined with increased seeding rate.  Consequently, reduced seeding rates may not reduce yield potential but reduced plant populations may increase the risk of aphid infestation and BYD infection thereby making aphid control more critical.