Small Grains Disease Update 06/01/2020
This is the first small grains disease update of the 2020 growing season. The Covid-19 pandemic forced some changes in how we gather information about the situation on the ground. This year there are no scouts trekking across the state to determine the presence of disease and pest problems in fields. Instead, I’ll rely on colleagues, cooperators, crop consultants, and you to share observations. Sharing what you see in combination with the weather-based risk assessment models will give me a pretty good idea of the state of affairs and the best way to manage any emerging problems.
In my travels last week to the southwest corner of the state and comments I received from the St. Paul campus and the Lamberton ROC tell me that tan spot is starting to develop in winter wheat. Tan spot is wheat’s ‘canary in the coal mine’. Most winter wheat varieties aren’t particularly resistant to this foliar pathogen and it important to halt the progression of the disease into the upper canopy. It will depend on how much and where you find the tan spot in the lower canopy and the crop stage whether you will want to apply a full labeled rate of a labeled product at Feekes 9 (flag leaf fully extended) or if you can wait to combine the control of leaf diseases with the suppression of FHB at Feekes 10.51 (beginning of anthesis).
If you have spring wheat following spring wheat, I advise you to also scout for the presence of tan spot and consider adding half a labeled rate of a fungicide when you are making your herbicide application. The weather risk models are indicating that the risk of tan spot is greatest in the eastern half of the state
So far there are no reports of leaf or stripe rust in either winter wheat or spring wheat. The risk models also show a low risk for either disease to develop even if spores should arrive on southerly winds.
I have received a report of powdery mildew in rye. The rye crop is rapidly approaching flowering with the earliest seeded hybrid rye fields already heading in southern MN and the earliest maturing open-pollinated varieties heading at the NWROC in Crookston. The warmer weather that is forecasted for this week should slow down the development of powdery mildew into the upper canopy. A telltale sign that powdery mildew is staling is a change of color of the mycelium in the lower canopy from white/light grey to a tan color.
However, I consider controlling the powdery mildew in your rye if you are in an area of the state where the overnight temperatures remain in the lower fifties and you do not see this change in color of the powdery mildew mycelium.
Finally, Bruce Potter has found both English grain and bird cherry-oat aphids in wheat and rye in SE Minnesota. Judging from what Bruce has reported and I saw, these flights were large enough that I suspect that there may be individual fields of winter wheat and rye that will be at the threshold of 80% of the stems across the field having one or more aphids to warrant an insecticide application prior to heading.
Source: Jochum Wiersma, U of MN Extension