Wheat losses attributed to PM can reach 40% by affecting grain fill, root growth, and reducing test weights 1,2,3. At expected yield losses greater than 10%, fungicides are generally recommended 4,5. Silicon has been shown to be beneficial to plants by suppressing disease and insect herbivory, decreasing lodging of grasses, reducing the effects of abiotic stresses and assisting in growth and mineral nutrition 6,7,8. Silicon plays an active role in host resistance by inducing production of phenolic- like compounds associated with the degradation of PM haustoria and the collapse of conidial chains 9,10. Powdery mildew conidia of infected wheat have increased Si concentrations soon after an induced host response with Si accumulation in halo areas around penetration points 11,12. The effects of Si products on suppression of wheat powdery mildew in field trials on mineral soils in temperate climates, such as northeastern New Jersey, have not been widely investigated. Hypothesis: A calcium silicate slag by-product, when applied as a liming agent, to field grown winter wheat, will affect soil and plant tissue Si levels resulting in suppression of powdery mildew disease and a yield response. Abstract Objectives Results  Some Mid-Atlantic soils can benefit from silicon applications.  Disease suppression can be achieved regardless of fungicide application when a calcium silicate slag by-product is used.  Yield effects may depend upon higher than predicted silicon response levels in mineral soils.  A calcium silicate slag by-product c an adjust pH similar to CaCO 3 when applied at the same CCE rate with an added benefit of fungal lesion suppression, both powdery mildew and Alternaria spp.  Further research is needed to determine the levels of soil silicon needed to affect disease suppression and increase yields in mineral soils. Methods Wheat Yield and Disease Response to Amending Soil with Silicon. Mary C. Provance-Bowley and Joseph R. Heckman Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey Silicon fertilization is known to benefit some crops but there are few soil test guidelines. A soil test critical level of 19 mg kg -1 has been established for rice grown on Histosols in Florida. Previous work in New Jersey (2003) reported that Si fertilization of a Quakertown silt loam was beneficial to pumpkin fruit yield and powdery mildew disease suppression when the acetic acid soil test Si level was 127 mg kg -1. During 3 consecutive years of field trials on a Typic Hapludult soil in NW New Jersey, a calcium silicate slag by-product (CSS) was added as a liming material at a calcium carbonate equivalent (CCE) rate of 4480 kg ha -1 to winter wheat (Triticum aestivum L.) and evaluated for its effects on powdery mildew (PM) disease, causal agent (Blumeria graminis (DC) Speer f. sp. tritici), incidence and grain yield response. Control plots received CaCO 3 at the same CCE liming rate and the site received natural fungal inoculate. Mean soil Si levels of the CaCO 3 controls were 18 mg kg -1 in 2006, 27 mg kg -1 in 2007, and 33 mg kg -1 in 2008, compared with 45 mg kg -1, 62 mg kg -1, and 94 mg kg -1, respectively, in the CSS treated plots, well above expected response levels, in most years. Flag leaf and straw Si concentrations increased with the CSS amendment in all 3 years when compared with the controls. Grain Si concentrations however, were unaffected throughout the trial. In all 3 study years, fungal lesions were lower in the CSS treated plots: 29% in 2006 (PM), 25% in 2007 (Alternaria spp. leaf blotch), and 43% in 2008 (PM). A 10% yield response was also seen in Our findings suggest that crop yield and disease response may be seen with Si additions to some Ultisols in the Mid-Atlantic, even when soil Si is above expected response levels. To evaluate the agronomic response of winter wheat to a calcium silicate slag by-product (CSS) applied as a liming agent to a mineral soil in Northeastern, NJ. 1. Compare powdery mildew disease leaf lesions of CSS treated plants with those receiving CaCO3 and a commercial fungicide. 2. Compare yield response with soil and tissue Si concentration. Summary  Table 1.  Fungal flag leaf lesions were reduced in CSS amended plots in all trial years.  A 10% yield response was seen in 2008 with CSS amendment.  Table 2.  Acetic acid soil silicon levels increased for all treatments during  The highest soil Si levels were found each year with the CSS soil amendment.  The highest soil silicon levels were found in 2008 in CSS treated plots.  Soil pH was adjusted similarly with either CSS or CaCO 3 soil amendment applied at the same calcium carbonate equivalent (CCE).  Table 3.  Grain tissue Si was unaffected by treatment during  Flag leaf and straw Si concentrations were highest with CSS treatment in all years.  Fungicide reduced straw Si concentrations in Introduction  Project Design:  9 Replications of 2 treatments.  20’ X 30’ plots of a Quakertown Silt Loam (Typic Hapludult) soil.  Split plot design for a single fungicide application each year.  Soil Treatments:  Calcium Silicate Slag By-product (CSS).  Calcium Carbonate Control (CaCO 3 ).  Disease Incidence:  Powdery Mildew susceptible winter wheat variety, Seedway  Natural inoculation.  Duration and Location:  3 Consecutive years,  Consistent field site and plot plan each year at Pittstown, NJ.  Data Collection and Analysis:  Plant nutrient analysis of grain, flag leaves and straw.  Whole plant samples for disease diagnostics.  Flag leaf % lesion ratings, 20 random leaves plot -1, 2 person mean.  Mehlich-3 soil analysis and plant tissue acetic acid Si analysis.  Yield Response  Grain harvest weight. References by request: