It is that time of year to start up the biweekly small grains disease and pest updates to help guide your input decisions between now and the beginning of grainfill. I should have started up two weeks ago when the first winter rye fields reached anthesis, but I was distracted by fieldwork and finishing seeding. I'm using the fact that the three crop scouts funded by grants from the Minnesota Wheat Research & Promotion Council and the Minnesota Soybean Research & Promotion Council started their work last week as an excuse to start this yearly cycle.
Bruce Potter found English grain and bird cherry-oat aphids in Lamberton in early May. Aphids since have made it north; I found both a few aphids and plants that are symptomatic for the Barley Yellow Dwarf virus (BYDV) in my winter wheat trials and the scouts reported one lonely aphid in one of the ten fields they scouted last week in the southern parts of the Red River Valley. NDSU has updated its thresholds for the control of aphids in wheat and barley; the new threshold is 4 aphids per stem before the crop is fully headed. The scout also found grasshoppers in 6 out of the 10 fields this past week. One of the upsides of the wet spring is that entomopathogenic fungi can hopefully reduce the number of grasshoppers.
The wet weather and the current temperatures are near ideal for both tan spot and stripe rust. I wrote a short article last week about stripe rust and why it is a concern this year. You can find that article here. Until last week I had a hard time finding tan spot. That has since changed. The winter wheat nursery at the NWROC in Crookston has now ample tan spot in the lower and middle portion of the canopy. As in any year, applying a fungicide to control this and other leaf diseases in winter wheat at Feekes 10.51 or anthesis almost always makes economic sense even if the risk models for Fusarium Head Blight indicate low risk (which is currently the case). Make absolutely sure you scout your late-seeded spring wheat if it is following wheat and consider adding half a labeled rate of a labeled fungicide to your herbicide program to control this early-season tan spot.
While we did not find stripe rust in the winter wheat nursery, we did find a few pustules of leaf rust and the first signs of bacterial leaf streak. Both those diseases are a bit of an unexpected find, largely because temperatures have been a bit cooler than either disease really likes. It is too early to tell whether both those diseases will become a serious problem.
Finally, the saturated soil conditions in many parts of the Red River Valley combined with the high numbers of aster leaf hoppers that were around in parts of the region a couple of weeks ago may give rise to another uncommon disease. Aster yellows of wheat symptoms look a lot like those of BYDV. Saturated soil conditions worsen the disease and change the symptomatology to bronzing/purpling of not just the leaf blade but also the leaf sheath in susceptible varieties. Unfortunately, there is no economic threshold for aster leaf hoppers nor is there a cure for aster yellows in wheat.
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