Growers across Ontario have been able to seed winter wheat this fall into almost perfect conditions, and there may be a record acreage seeded. A significant portion of winter wheat acres were seeded in September but with persistent summer like conditions, growers continued seeding well into late October. Early planted fields are well tillered with 3-4 tillers/plant and late October planted fields are at the 1 to 2 leaf stage. Winter triticale and winter barley fields are also tillering significantly with winter triticale fields planted in early September having 7+ tillers. While almost every acre was seeded into ideal conditions, there are reports of yellowing fields across Ontario and Quebec (Figure 1). This has stimulated questions regarding fall fungicide and nutrient applications to correct this yellowing.
Why is my field turning yellow?
With above normal temperatures, winter wheat growth above ground is rapid; however, under these warmer temperatures, wheat root growth is slower. Photosynthate partitioned to the roots is reduced, and the number, length and diameter of roots is particularly affected1. Slower root growth coupled with prolonged dry periods results in reduced nutrient uptake and signs of temporary nutrient deficiencies.
Should I make a fall nutrient application?
In some fields, manganese deficiency may be the culprit and can be confirmed with a tissue test. If manganese deficiency has been confirmed, a foliar application at 2 lbs of Mn per acre using manganese sulphate powder will correct the deficiency. Sulphur deficiency may be another cause of some of the yellowing in these fields. Previous Ontario research has shown no benefit to fall applied sulphur compared to spring applied. However, recent work out of Michigan State by Dr. Kurt Steinke indicates that fall applied sulphur at planting may provide benefit. This needs to be further explored, but if tissue samples indicate sulphur deficiency, a fall application may be of benefit. Temporary nitrogen deficiency may also be the cause of yellowing in some of these fields. Previous Ontario research has shown that fall applied nitrogen has no significant impact on yield, moisture, test weight, 1000 kernel weight or protein2. Fall applied N is not recommended in Ontario. It can have significant negative environmental impacts and has no economic benefit to the grower. Areas with recent rainfall have reported improvements in affected crops. With more rain and typical fall temperatures forecasted, growers are urged to hold off on any unnecessary fall nutrient applications.
Should I apply a fall fungicide to my winter wheat?
While leaf rust, also known as brown rust, is being found in winter wheat, levels remain low and are not of significant concern. Leaf rust is most damaging when the upper leaves of the canopy are infected just prior to flowering. Leaf rust infection occurs when temperatures are between 15 and 20C and there is six hours of no moisture on the leaves making the conditions this fall ideal for infection. However, leaf rust thrives and continues through its disease cycle only in humid conditions and when temperatures are between 18 – 25 C3. It is anticipated that with cooler nighttime temperatures and forecasted cooler daytime temperatures, the disease cycle will be disrupted negating any need for a fungicide application. Furthermore, the fungus (mycelium) causing leaf rust requires living tissue to survive; therefore, does not normally overwinter to any degree in northern areas such as Ontario and Quebec. Factors that typically influence overwintering potential include the severity of winter temperatures (colder winters = lower risk), the length of snow cover (insulating fungus from freezing temps), and infected volunteer wheat plants that survive the winter.
Previous research has not shown an economic response to fall applied foliar fungicide applications. Research conducted by Dr. Kelly Turkington, AAFC Lacombe, concluded that a fall applied fungicide in mid-October, in fields with high levels of stripe rust, resulted in a 0.8 bu/ac yield response but decreased net returns by $10/ac4.
Barley yellow dwarf virus (BYDV) has also been top of mind for many as field symptoms resemble BYDV. However, some of these symptoms are likely caused by wind injury (Figure 2) as fall infections of BYDV are not typically evident until the spring. Visible symptoms of BYDV do not usually appear until aphids are gone, but can lead to underdeveloped root systems, decreased tillering, delayed maturity and symptoms of nutrient deficiencies. BYDV is usually found in patches 1–2 m (3–7 ft) in diameter but can occur uniformly throughout the field if aphid populations are also uniform throughout the field. BYDV is transmitted by aphids that have picked up the virus from other infected plants and transmit the disease when feeding on host crops. These aphid species include the corn leaf aphid, the English grain aphid and the bird cherry-oat aphid. Foliar fungicide and insecticide applications at this late date will not help manage or reduce BYVD. Foliar fungicides are used to manage diseases caused by fungal pathogens; they do not affect viruses such as BYDV.
Most winter wheat is going into winter in excellent shape. Growers are encouraged to be diligent with their field scouting this fall and make note of any fields of concern. Walk those fields first in the spring. As for any further applications this fall? Almost none are required.
Sources:
1Batts G. R., Ellis R. H., Morison J. I. L., Nkemka P. N., Gregory P. J., Hadley P. (1998). Yield and partitioning in crops of contrasting cultivars of winter wheat in response to CO2 and temperature in field studies using temperature gradient tunnels. J. Agric. Sci. 130 17–27. Yield and partitioning in crops of contrasting cultivars of winter wheat in response to CO2 and temperature in field studies using temperature gradient tunnels | The Journal of Agricultural Science | Cambridge Core
2Winter Wheat Nitrogen Response: https://www.ontariosoilcrop.org/wp-content/uploads/2023/02/v10crpadv_cer2_2013_winter_wheat_nitroen_response.pdf
3Leaf Rust of Wheat: https://cropprotectionnetwork.org/encyclopedia/leaf-rust-of-wheat
4Fall Fungicide And Seed Treatment Application On Winter Wheat: https://mbcropalliance.ca/directory/production-resources/fall-fungicide-and-seed-treatment-application-on-winter-wheat/