What is the outlook for wheat diseases for this spring?

Sandra Wick, Crop Production Agent 

Stripe Rust

The moisture around the district was a much welcomed event!!! We received some significant rainfall amounts around the district that ranged from 2 inches to over 3 ½ inches!!! However with that can also set up some conditions for diseases in your wheat this spring.

Rust diseases, (Leaf and Stripe Rust), are some of the most important concerns in the state and annually cause more yield loss than most other diseases of wheat and often become established in Texas and Oklahoma before spreading north to Kansas. We can use outbreaks in these southern areas as early indicators of problems that may arise in Kansas according to Dr. Erick DeWolf, K-State Research and Extension plant pathologist. This year, the early reports from Texas indicate that stripe rust levels are low in most areas and Oklahoma has yet to report stripe rust in 2017. So the good news is……..this suggests that the risk of stripe rust in Kansas is much lower than in 2015 or 2016! The recent moist weather has been favorable to fungal diseases, such as tan spot, and can also bring rust spores from Texas and Oklahoma into Kansas, so producers should be actively scouting for these diseases from now on.

NEWS BREAK……. But Stripe rust was found this week in Kansas, down in the southeast and southcentral part of the state, but is pretty much contained in the lower canopy. So be prepared to scout your wheat in the next week or two. 

Leaf Rust

An early fungicide application might be beneficial in situations where a susceptible variety is experiencing significant tan spot incidence early in the season. For most fields, however, growers should focus on evaluating the need for a fungicide application between flag leaf emergence and flowering.

Leaf rust, however, has been more of a problem in Texas, with reports of severe leaf rust in mid-canopy prior to heading. Oklahoma reported some active leaf rust earlier this season, but the dry conditions in March appeared to hold the disease in check. According to the K-State Research and Extension plant pathology lab, there are no reports of leaf rust to date in Kansas for the 2017 season. We have a lot of acres planted to varieties that are susceptible to leaf rust (T158, LCS Mint, WB4458 or Winterhawk). We will need to watch for signs of leaf rust as we approach flag leaf emergence in Kansas during April. 

Tan Spot

Tan spot, may be starting to show up, especially in fields with continuous wheat which allows the fungus to buildup on the wheat residue over the winter. The initial symptoms of tan spot are small dark brown spots that expand to become tan elliptical or diamond-shaped lesions with a yellow halo. Average statewide yield losses from tan spot have been estimated at almost 2 percent per year, but can be as much as 25 percent in highly susceptible varieties. Tan spot can be managed by selecting resistant varieties or with a fungicide spray. A fungicide application made between flag leaf emergence and flowering should provide effective disease control and a yield increase.

Wheat Streak Mosaic

The viral disease, Wheat Streak Mosaic (WSM), has emerged as a serious problem in parts of western Kansas again in 2017. Wheat steak mosaic causes a yellow discoloration of leaves and severe stunting in infected plants. The KSU diagnostic lab was receiving samples of wheat with wheat streak mosaic already in the fall, which is an early indication that this may be an above-average year for this disease. DeWolf reported that the KSU lab continues to receive samples with symptoms of wheat streak mosaic this spring and reports of above-normal levels of the disease in some areas of west central Kansas. I have received several calls on yellowing wheat wondering if WSM could be the reason. The wheat that I have examined at this time appears to be a combination of drought stress with some nitrogen deficiency in the lower leaves. Because of the dry conditions prior to the recent rain, root development of the wheat plants was fairly small and may not be down in the soil profile where the nitrogen is located. The precipitation may reduce the drought stress that was hastening the decline of fields infected with wheat streak mosaic in western Kansas. Symptoms of wheat streak mosaic and barley yellow dwarf are likely to intensify as temperatures warm at the end of the week.

Common Root Rot

Several samples, from the KSU plant pathology lab, of wheat from western Kansas have also been infected with common root rot. This fungal disease causes dark-colored lesions on the sub-crown internode and other roots. DeWolf explained that the damaged roots often break off when plants are removed from the soil. Common root rot is present at low levels almost every year in Kansas and survives between seasons on crop residues and organic matter in the soil. In most years, the plants have enough healthy roots to compensate for the damage caused by the disease. When soil conditions are dry, however, the damage caused by common root rot can cause more problems. Under dry soil conditions, the plants are not growing as vigorously and often have poorly developed root systems. Any damage to the root system by common root rot aggravates the drought stress and is likely contributing to the decline of some wheat fields this season.

Fortunately, parts of north central Kansas did receive some moisture which will certainly help with our dry conditions. Let’s hope we continue to receive some moisture.

K-State Research and Extension has an excellent publication, “Wheat Disease ID Book” that is available either online or at one of our Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center.

For further information on disease management in your wheat, contact me at any Post Rock Extension District Office in Beloit, Lincoln, Mankato, Osborne or Smith Center. If you have further questions with wheat production, contact me at any Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center.