By Pierce A. Paul
Among the questions that we have had to answer thus far this season as we get ready to plant wheat are:
1- What are the real dangers of planting wheat after wheat?
2- Now that we have an excellent group of fungicides, can we get away with planting wheat after wheat?
Response: We never recommend planting wheat after wheat or ever wheat after corn simply because these are very bad disease management practices. Several important diseases of wheat (powdery mildew, Septoria, Stagonospora, head scab, and root diseases) survive in wheat stubble and some of the same pathogens that affect wheat also affect corn, therefore, planting wheat after wheat or wheat after corn drastically increases the risk of losses due to diseases. How big of a problem you have will depend on the growing conditions, as well as your disease management program. For mildew, Septoria and Stagonospora, planting a resistant variety and applying a good fungicide should prevent major problems. For head scab, planting the best resistant variety and applying Prosaro or Caramba will help, but will not give you the best results if you plant wheat after wheat or corn and the weather becomes very wet and humid at flowering time. However, the biggest problems with wheat-on-wheat, with fewer solutions, are root diseases such as take-all. Fungicides will not help, and although varieties are known to vary in their susceptibility to take-all, this type of information is not readily available. Old-fashion deep tillage with a moldboard plow will help to control all of the aforementioned diseases, including take-all, but we all know of the detriment of this type of tillage.
Recommendation:
Just avoid planting wheat after wheat or after corn, soybean should be off early, just wait;
If you absolutely have to or want to plant wheat after wheat, make sure you plant a resistant variety, but remember, no variety is resistant to all of the diseases you are likely to see in a wheat-on-wheat system;
Be prepared to apply a fungicide, but this will not help with root diseases;
If you can, plow under crop residue to remove them from the surface and speed up decomposition.
3- Do we have good, high-yielding scab resistant varieties?
Response: When selecting varieties give priority to head scab resistance. We now have several moderate-to-high-yielding varieties with very good resistance to scab, so you no longer need to choose between yield and scab resistance. In the table below (modified from the wheat performance trial http://www.oardc.ohio-state.edu/wheattrials/), any variety with a scab score similar to or lower than that of Truman, one of the most scab resistant varieties, is considered “resistant (R)” to scab. But remember, “R” for scab is not the same as R for Septoria or powdery mildew. In other words “R” for scab does not mean you will not get scab or have problems with vomitoxin if the weather becomes wet and humid at flowering, it simply means that if you plant a R or MR variety you will get less scab and less vomitoxin than if you plant an S or MS variety, but you will still need to apply Prosaro or Caramba at anthesis (at flowering) if conditions become favorable for scab.
Recommendation: User the table below to identify R and MR varieties and then go to the performance trial results (http://www.oardc.ohio-state.edu/wheattrials/) to check yield and other agronomic traits. Select high-yielding varieties with high test weight, good straw strength, and adequate disease resistance.
R = resistance equal to or better than Truman
MR = not as resistant as Truman but similar to Freedom
S = just as susceptible as Pioneer2545
MS = better than Pioneer2545, but not as resistant as Freedom or Truman.
Other Management Recommendations:
Optimum seeding rates are between 1.2 and 1.6 million seeds per acre. For drills with 7.5-inch row spacing this is about 18 to 24 seeds per foot of row with normal sized seed. When wheat is planted on time, actual seeding rate has little effect on yield, but high seeding rates (above 30 seeds per foot of row) increase lodging and the risk of severe powdery mildew development next spring. During the 2014-2015 with funding from the Ohio Small Grains Marketing Program, we conducted a wheat seeding rate study at three locations in Ohio (Crawford, Pickaway, and Wood Counties). We seeded wheat at 0.25, 0.50, 1.0, 1.5, and 2.0 million seeds/acre. On average, there was a 9 bu/acre yield reduction when seeding rate was reduced from 2.0 to 0.25 million seeds/acre. Economic return tended to be greatest when wheat was seeded between 1.0 to 1.5 million seeds/acre. There is no evidence that more seed is better, it only costs more money.
Plant after the Hessian Fly Safe Date for your county. This date varies depending on state location – starting as early as September 22 for northern counties and as late as October 5 for southern counties. Planting before the Fly Safe Date increases the risk of insect and diseases problems including Hessian fly and aphids carrying Barley Yellow Dwarf Virus. The best time to plant is within 10 days after the Fly Safe Date. Delayed planting may result in reduced winter hardiness from inadequate fall growth. The Hessian Fly Safe Date for each county can be found at:
Plant seed 1.5 inches deep and make sure planting depth is uniform across the field. Planting depth is critical for tiller development and winter survival. No-till wheat into soybean stubble is ideal, but make sure the soybean residue is uniformly spread over the surface of the ground. Shallow planting is the main cause of low tiller numbers and poor over-winter survival caused by heaving and freezing injury. Remember, you cannot compensate for a poor planting job by planting more seeds; it just costs more money.
Apply 20 to 30 lb of actual nitrogen per acre at planting to promote fall tiller development. A soil test should be completed to determine phosphorus and potassium needs. Wheat requires more phosphorus than corn or soybean, and soil test levels should be maintained between 25-40 ppm for optimum production. If the soil test indicates less than 25 ppm, then apply 80 to 100 pounds of P2O5 at planting, depending on yield potential. Do not add any phosphorus if soil test levels are higher than 50 ppm. Soil potassium should be maintained at levels of 100, 120, and 140 ppm for soils with cation exchange capacities of 10, 20, or 30 meq, respectively. If potassium levels are low, apply 100-200 pounds of K2O at planting, depending on soil CEC and yield potential. In Ohio, limed soils usually have adequate calcium and magnesium. Soil pH should be between 6.3 and 7.0. Wheat generally does not respond to sulfur on most Ohio soils unless fields are sandy, low organic matter, low CEC, and/or have a history of sulfur response. Sulfur should be applied on responsive soils in the spring unless applying elemental sulfur. The key to a successful wheat crop is adequate and timely management.