Hello everyone! I just received urgent information about this year’s wheat crop. Please take a few moments to observe comments from University Specialist about recent findings throughout the state.
Sincerely,
Rick Morris
Harvey’s Agronomist
STRIPE RUST
Low to medium levels of wheat stripe rust have been observed over the past week in a handful of fields in Raleigh, Plymouth, and near Goldsboro in the central Coastal Plain. In the Goldsboro area, the infection had clearly been present for some time.
Current weather in North Carolina is ideal for stripe rust development. This disease can spread very fast.
Unfortunately, we do not have good comprehensive stripe rust ratings for North Carolina commercial varieties because this disease is fairly rare here. Varieties that are widely planted and susceptible to stripe rust include DG Shirley and SS 8404, but many other varieties are susceptible too.
LEAF RUST
Unusually early and heavy levels of leaf rust have been observed broadly across the Coastal Plain. The early severity is due to the warm winter. We have leaf rust ratings for many, but not all, wheat varieties grown in North Carolina (http://www.smallgrains.ncsu.edu/_Misc/No38VarietySelection2015.pdf).
RECOMMENDATION
Please see the attached photos to distinguish leaf and stripe rust. Scout fields for rust. If significant infection is found and, *if* the field has good yield potential, treat immediately with fungicide. It is more important to catch stripe rust early than to catch leaf rust early. As you can see from the attached fungicide table, numerous products are highly effective on stripe and/or leaf rust.
The closer the crop is getting to flag leaf or beyond, the more you should avoid a strobilurin or strobi-containing product due to the risk of increasing DON if there is a scab epidemic at flowering.
WHEAT ROOT ROT
This week, we received several samples of stunted wheat from Robeson, Lenoir, and Beaufort. There are more reports of wheat “going backward” in the Tidewater area. Contrary to my earlier message, we have NOT found downy mildew. The problem we have confirmed is a root rot caused by a related soilborne pathogen. This is Pythium root rot. Pythium is a fungus-like organism called an oomycete, and it is widespread in soil and plant debris. What has brought on the root rot problems is frequent excessive rain and prolonged standing water.
The wheat in this March 29 photo was badly damaged by Pythium root rot at the Lenoir County OVT. Root systems rotted over the winter, and were unable to take up nitrogen at top-dress. A few plants had intact roots so they could absorb the nitrogen and start jointing. This is why we started noticing the stunting after top-dress. The level of damage depended on position in the field, with lower areas hardest hit.
We have tested and ruled out wheat soilborne mosaic virus and wheat spindle-streak mosaic virus in all of these samples.
Should growers abandon fields with widespread stunting of this type? It depends on how widespread and severe the damage is. No chemical remedy is available, and additional nutrients will not help a crop with severe stunting of roots and aboveground parts.
For the future:
Pythium root rot:
Main symptoms are severe stunting, with missing or poorly tillered plants, and brown rotten areas at the bases of the most stunted tillers. The first true leaf is often noticeably shorter than a normal, healthy first leaf. There is no known variety resistance. The pathogen remains in and on crop residues and can persist for years. Straw on the soil surface or only slightly incorporated will favor Pythium root rot. Waterlogged soil is the chief reason for a severe outbreak. Thus, good drainage is a key control measure. High-quality seed should be used in fields where drainage is problematic, and seed treatments containing metalaxyl or mefanoxam may be advisable. Seed age can significantly impact a seed’s sensitivity to Pythium root rot. Older seeds or seeds that have been coated with seed treatment for an extended period of time are more prone to infection, because pesticides tend to degrade the integrity of the seed coat and cause the seeds to ‘leak’ more exudates when they are germinating. The longer the seeds have been treated, the more susceptible they become. In general, seeds coated for 1 year or more could be more prone to Pythium root rot.
NCERA 184 Wheat fungicide table 2015_V3
