Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu and Victor Green; vmgreen@udel.edu
We are well into corn and soybean season, but those considering planting wheat in 2016 should already be thinking about variety selection. Variety selection is the most important part of wheat production, and selection of varieties with resistance to commonly occurring diseases is paramount. The University of Delaware conducts small grain variety trials to assess relative performance of varieties under Delaware growing conditions. This year, the site at Middletown experienced significant pressure from regional populations of powdery mildew as well as pressure from stripe rust, which entered the site and could be detected on susceptible varieties in mid-April, around flag leaf emergence.
Varieties were rated on May 25, 2016 at approximately the soft dough stage prior to the onset of senescence by using a relative, whole plot rating system, where 0 indicates a clean canopy and 5 indicates near complete disease presence on the flag leaves. Thus, 0-1 =excellent resistance; 1-2 very good resistance 2-3 = marginal resistance, 3-4 = susceptible, and 4-5 = very susceptible.
Powdery Mildew and Stripe Rust Ratings for Wheat Variety Trial at Middletown, DE — 2016
| Variety | Stripe Rust |
Powdery Mildew |
| VAW11-106 VaTech/VCIA | 0.0 | 1.7 |
| Hilliard VaTech/VCIA | 0.0 | 1.2 |
| MBX 14-K-297 Mercer | 0.0 | 3.5 |
| MBX 14-S-210 Mercer | 2.5 | 1.0 |
| MBX11-V-258 Mercer | 5.0 | 1.5 |
| MBX 15-E-229 Mercer | 3.2 | 0.7 |
| MBX 16-A-206 ****** Mercer | 1.2 | 3.2 |
| MBX16-B-203 Mercer | 2.5 | 3.7 |
| USG 3523 USG | 0.7 | 3.0 |
| USG 3404 USG | 0.0 | 1.6 |
| USG 3316 USG | 3.5 | 4.0 |
| USG 3895 USG | 0.0 | 2.2 |
| USG 3197 USG | 1.5 | 2.6 |
| USG 3201 USG | 0.0 | 2.3 |
| 9223 Dyna -Gro | 0.0 | 3.7 |
| 9552 Dyna -Gro | 0.0 | 3.5 |
| 9522 Dyna -Gro | 0.0 | 2.2 |
| Shirley Dyna -Gro | 4.9 | 0.9 |
| 9692 Dyna -Gro | 3.0 | 4.0 |
| WX15742 Dyna -Gro | 2.5 | 2.0 |
| FS 860 Grow Mark | 2.0 | 2.2 |
| FS 865 Grow Mark | 2.2 | 4.8 |
| FSX 870 Grow Mark | 3.5 | 1.5 |
| FSX 871 Grow Mark | 0.7 | 3.0 |
| FSX 872 Grow Mark | 0.0 | 1.7 |
| 415 Agri-Maxx | 0.7 | 2.5 |
| 444 Agri-Maxx | 0.0 | 2.5 |
| 446 Agri-Maxx | 0.2 | 3.2 |
| 454 Agri-Maxx | 2.7 | 4.5 |
| 462 Agri-Maxx | 4.7 | 2.5 |
| Exp 1674 Agri-Maxx | 0.0 | 1.7 |
| 15MW315 University of MD EXP | 0.2 | 4.0 |
| FS 850 Grow Mark | 0.7 | 2.5 |
| FS854 Grow Mark | 0.0 | 2.2 |
| SS-8360 Southern States | 0.0 | 3.0 |
| SS-8340 Southern States | 0.0 | 2.7 |
| SS-8513 Southern States | 0.5 | 1.7 |
| SS-8415 Southern States | 0.5 | 1.5 |
| SS-8530 Southern States | 3.0 | 1.0 |
Keep in mind that these trials test against regional populations of pathogens. Due to issues with our powdery mildew populations defeating a commonly used resistance gene, you may see some varieties that are labeled as very good or excellent for powdery mildew not performing well in this trial. This regional disease data is critical in ensuring productive crops and assisting you with variety selection. We did not rate for leaf blotch complex (Tan spot, Stagonospora leaf and glume blotch) because stripe rust susceptible varieties (3 or greater on the rating scale) did not have flag leaf tissue present at rating and therefore we could not accurately rate the varieties for this disease. Other sites did not have sufficient disease to rate by the soft dough stage.
Varieties were planted into a clean bed on 10/20/15 at 1.5 million seeds/A. The first application of nitrogen (N-sul at 15 gal/a= 45 lbs.N) was applied on 3/3/16. The second application of nitrogen (50:50 mixture, 19 gallon N-sul , 11 gallon water (2.9 lbs N/gal) = 55 lbs total N) was applied on 3/17/16. At this time Powerflex herbicide was also applied at 2 oz/A. Warrior insecticide was applied to manage cereal leaf beetle on 5/5/16.
Yield and lodging data for this site and others will be made available soon. However, at the Middletown site we did see that increasing levels of rated diseases resulted in lower yields overall. For example, the average yield difference between a variety with a powdery mildew rating less than 1 and a variety with a rating greater than 4 was approximately 12%.