An early but rainy start to the 2024 growing season led to a wide range of small grain planting dates. “Despite weather delays, the small grain stands are very good and the earliest seeded grains are well into tillering,” states Dr. Jochum Wiersma, Extension small grains specialist at the University of Minnesota. However, there are fields where heavy rains closely followed seeding and drowned-out spots may need to be replanted.
With the earliest crops tillering, it’s time to look at weed control programs and start scouting for diseases. While it’s still relatively early in the season, start looking for powdery mildew and tan spot in winter cereals, particularly if a field is wheat on wheat. The risk for Fusarium head blight (FHB) on winter rye is very low due to cool temperatures, so there is no need to treat for it at this time.
English grain and bird-cherry oat aphids – vectors of barley yellow dwarf virus (BYDV) – were reported several weeks ago. Once infected aphids start feeding, they can transmit the virus to the plant, which eventually appears stunted and yellowed. Management is through aphid control and depending on thresholds, treatment might coincide with a herbicide program. Keep in mind that tank mixes of an insecticide with contact herbicides and/or fungicides can increase leaf burning.
Early-season small grain yellowing can have other causes. Cool temperatures, wet soils and small root systems can lead to early season nitrogen (N) stress. Unless N deficiencies are severe, the crop should recover quickly once temperatures warm and soils dry.
Sulfur (S) deficiency also causes yellow leaves, but symptoms occur in new growth rather than old growth like an N deficiency. If ammonium sulfate (AMS) wasn’t included in the starter blend and S deficiency symptoms are present, an AMS application may be in order.
Asters yellow is another insect-vectored disease, but carried by aster leafhoppers instead. Crop consultants in central portions of the Red River Valley are reporting large infestations. At this time, an economic threshold for leafhoppers in cereals hasn’t been determined.
Finally, crop injury and yellowing may be caused by herbicide carryover after a dry year, even when rotation restrictions have been followed. Herbicide degradation depends on active soil microbia, which in turn require moisture. Watch for carryover issues from residual soybean herbicides this year.
Most of our corn and soybean seed has very high germination rates and can remain viable in the soil for a long time. “However, this season’s wet conditions could bring on seedling disease issues that we normally don’t see on a wide scale,” states Dean Malvick, University of Minnesota Extension plant pathologist. “There are two timeframes to consider,” he adds.
The first is immediate and focuses on seed and seedling diseases caused by the ‘big 4’ pathogens: Pythium, Phytopthora, Rhizoctonia and Fusarium. Three or some variation of these can cross between corn and soybeans. The exception is Phytopthora sogae which only appears to infect soybean.
Now is a good time to scout for seedling disease. Look for plants with differing heights, discoloration or missing or dying plants. These pathogens can kill seedlings when they’re emerging or soon after, so scout to distinguish between disease and other causes. If seedlings have been infected but are surviving, there’s a good chance that many will pull through.
“One of the more widely used Phytopthora resistance genes in soybean varieties, Rps1K, has been breaking. We’d like to know how widespread the pathogen is that can overcome this trait,” says Malvick. “So if you suspect Phytopthora root and stem rot, we’re requesting soil samples from problem fields (dmalvick@umn.edu).”
The second timeframe deals with early-season infection that doesn’t become apparent until later in the season. It’s widely thought that soybeans can be infected with the fungus that causes sudden death syndrome (SDS) in very early stages of seedling growth. Whether or not SDS develops will depend on conditions during June and July that promote the disease. Scouting will be key.
For more information from University of Minnesota Extension, visit extension.umn.edu/crop-production.
Thanks to the Soybean Research and Promotion Council and the Corn Research and Promotion Council for their generous support of this program.
