Tri-State Neighbor: South Dakota Farm Newspaper

The 2008 wheat crop is nearly all in the bin and appears to be another record-setting yield for South Dakota.

For much of the state, the cool, moist spring was a boon to wheat production, raising one of the highest yielding wheat crops ever. Despite the high yields, producers battled an array of wheat diseases in 2008, including tan spot, bacterial blight, wheat streak mosaic and others. High market prices throughout the growing season kept farmers on their toes trying to manage threats. For many producers that meant applying fungicides.

Here are four planting-time decisions that can mean the difference between a healthy, highly productive wheat crop come springtime, or a crop whose yield potential is limited by root rots, rust and other production problems.

Resistant varieties

The word “varieties” is very interesting as it is applied to seeds. It implies a range of choices, a plethora of cultivars from which to select, kind of like at the ice cream store with its 31 flavors. And though growers can select from dozens of winter wheat varieties, most tend to plant as few as one variety, and often it is the same “flavor” they have become accustomed to over years of experience.

The trouble with this vanilla planting scheme is that not only have they exposed themselves to significant risk due to lack of diversity, but often, they have chosen to use a variety that is inferior in either agronomics or disease resistance (or both) when compared to some available alternatives.

Leaf rust poses one of the greatest disease risks to winter wheat in South Dakota. Rust management is achieved in two ways: through planting a resistant variety which is at very low risk to the disease in the coming season or by chemically managing rust on susceptible varieties.

The first option when combined with varieties that have strong agronomic qualities will cost essentially nothing. The potential upside is great considering rust losses can range from 5-30 percent in a season. For a 50 bushel-per-acre crop, and $8 wheat, that amounts to savings of $20 to $120 in protected yield per acre.

All may not be lost for a susceptible line, however. If rust does come into the picture, a foliar fungicide, at $25 to $30 per acre will prevent much of that yield loss, if used at the proper time.

Certified seed

Once a grower has settled on the varieties, his or her next step in a sound plant disease management strategy is to plant healthy seed. One of the easiest and most effective ways of achieving this strategy is to use seeds certified to be disease-free and with a known germination rate.

Seed-borne diseases pose a major threat to winter wheat yields and quality. Fungal diseases such as smut and bunt as well as viruses and other potential disease problems are often introduced to a field through contaminated seed.

Certified seed is wheat that has been inspected and declared to be free of diseases and weed contamination, has had germination tests to prove quality and is of genetically pure identity. The alternative to certified seed is often bin-run seeds from the farmers' own stores.

Certified seed often costs more than bin-run seed, however, the extra cost can pay off in many ways. Often, less seed will be required when planting certified seed as growers may tend to overcompensate for an unknown germ rate by planting more bin-run seed per acre. Furthermore, any seed-borne diseases present in bin-run will result in reduced vigor and greater stand losses over the winter.

Seed treatment

While it ought to be the goal of every producer to minimize unnecessary inputs such as “insurance” fungicide applications, there are some things that make good sense in many, if not most, situations.

Fungicide seed treatments are one input that offers an efficient way to get the crop started on the right root. Soil and seed-borne pathogens can make life difficult for a young wheat plant. Seed treatments allow young plants to build strong root systems, increasing the yield potential and overall health.

Also, soils in South Dakota are often cold at planting time. They might also be dry in the fall, or damp in the springtime. In any of these situations, seedling emergence may be delayed or early growth slowed, allowing pathogens an advantage. But with seed treatment, many of the pathogens trying to gain entry are suppressed or eliminated. Several products are available, and not all are created equal. Some work better against root rotters, while others are better for smuts and bunts.

Proper planting timing

While not strictly a matter of disease management, planting timing can have a strong influence on several important small grains diseases. Wheat streak mosaic virus affects wheat that emerges while the vector (the wheat curl mite) is still alive and feeding on nearby weeds or volunteer wheat. The mite (carrying the virus) moves as the older plants die.

The main key to managing WSMV is in maintaining at least a two-week period free of green tissue in the field. We call it “breaking the green-bridge.”

Proper planting timing can help delay wheat emergence past the time when there is actively growing or green tissues in the vicinity. Also, planting too late can be a problem if winter injury or chronic root rots, smut or common bunt are present in the field. These late planted crops tend to be more susceptible to infection.