Rice Disease Status In 2026
FELIPE DALLA LANA
RAYNE, LOUISIANA
The first crop of the 2026 rice season is moving quickly toward harvest, with a few fields already harvested in Southwest Louisiana and many more expected to be cut in the coming weeks. Although we still have a long road ahead in North Louisiana and with the second crop in South Louisiana, we can already begin to take notes on how this season may be remembered. There are many things to discuss this year, but production economics, weather, and disease are likely to be at the top of the list for most growers. Before discussing disease status this season, let’s briefly review why diseases occur and what drives their intensity.
The good, the bad, and the ugly
You may have heard plant pathologists refer to the “disease triangle.” This core concept states that plant disease occurrence and intensity depend on the interaction among the host variety, the pathogen, and the environment. Some varieties have a type of genetic resistance that can help prevent disease infection. Others may still become infected, but the disease intensity and its impact on yield and grain quality are lower than in more susceptible varieties. These two types of resistance are often referred to as vertical or qualitative resistance and horizontal or quantitative resistance, respectively. Examples of quantitative resistance include what we see with sheath blight or bacterial panicle blight, where some varieties are more prone to severe epidemics than others. In these cases, the disease and its impact are still present in the field, just at a smaller scale. In contrast, varieties with qualitative resistance are expected to have little to no problem with the disease for which they are resistant. This happens because the genetic resistance, often governed by a single gene, makes the interaction between the pathogen and the plant incompatible, preventing disease development. However, there is a catch. Qualitative resistance is specific to a pathogen race. In other words, changes in the pathogen population can break this resistance, and a variety that once appeared immune may develop severe symptoms. Unfortunately, during the 2026 season, we observed severe blast symptoms in some inbred and hybrid varieties that had not previously shown blast problems in Louisiana, suggesting that genetic resistance may no longer be effective for controlling the disease in parts of the region.
The pathogen component of the disease triangle is often one of the most complex parts of this interaction. Genetic changes in the overall pathogen population are not easily noticed until they occur on a larger scale. For example, two blast spores may look identical under the microscope and produce the same symptoms on a susceptible variety. However, their genetics may be very different, with one spore able to infect a particular variety while the other cannot, or one may be resistant to a fungicide while the other remains sensitive. Many factors can contribute to changes in pathogen populations, but everything starts with mutation. A mutation is an unexpected change in the genetic code of an organism. Mutations happen all the time, but usually at a very low rate, roughly one per billion spores produced, and most of them do not cause noticeable changes in pathogen biology or performance. However, when we consider that each lesion can produce thousands of spores, multiplied by the number of lesions per plant, plants per field, and fields in a region, it is reasonable to expect that changes in pathogen populations can occur relatively quickly. Another important aspect of the pathogen is how much inoculum is available and when it is present relative to crop development. For example, sheath blight inoculum survives in the soil, and rotations with soybeans can increase inoculum levels, raising the risk of disease outbreaks. For rotten-neck blast, infection occurs after panicle emergence from the boot. If airborne spores arrive only after grain filling, we should not expect a major impact.
Finally, the environment is arguably the component that gives direction to how much disease we see in any given year. Each disease has a different set of conditions needed for development. These conditions include several factors, such as fertility, plant density, and others, but weather is probably the most important component. Overall, most fungal diseases observed in Louisiana rice thrive under warm temperatures, high relative humidity, and cloudy conditions. These conditions protect spores and other pathogen structures, allowing them to infect healthy tissue and expand lesions in both size and number. Some diseases infect the plant at a particular growth stage, such as rotten-neck blast after panicle emergence, so weather during that growth stage is especially important. Other diseases, such as sheath blight, take advantage of the protection provided by the lower canopy, where the microclimate is often very conducive to disease once the rows close. This is less common in second-crop fields and fields with very low plant density, where the lower canopy is more exposed.
Rice disease status in 2026
The 2026 rice season is already remarkable for its disease intensity. The season started strong, as favorable early- season conditions allowed many fields to be planted on time. Historically, fields planted earlier often experience less disease pressure than those planted later. However, the weather changed in May and part of June. Continuous rainy and cloudy days brought textbook conditions for disease infection and development.
At the Rice Pathology Program, we received an unprecedented number of samples, calls, and messages requesting disease diagnosis. Most samples were related to blast. The disease started unusually early compared with what we typically expect. For reference, most of our research field plots intended for blast research are planted in May because we often only see significant disease levels later in the season. In addition to the early disease onset, some inbred and hybrid varieties that were considered resistant to blast began to show symptoms. This is an indication that pathogen populations have changed, but we will confirm this with appropriate tests after the season ends. Correct disease identification is crucial for management because blast can develop quickly and has the potential to cause substantial yield and grain quality losses, which can economically justify chemical control. However, other diseases that can be misdiagnosed as blast, such as stackburn, do not usually have an important impact on yield or grain quality and may not justify a fungicide application.
In addition to problems with blast, weather conditions were also very favorable for sheath blight. Unlike blast, however, we can anticipate, at least to some extent, how much sheath blight pressure to expect in a field based on the field history. This is because sheath blight is caused by a soilborne fungus. Fields with a history of sheath blight or fields under rice-soybean rotation are expected to have a higher risk of disease outbreaks. The disease is particularly difficult to control because varieties have limited resistance and fungicide coverage can be challenging, especially because the disease starts in the lower canopy. As the crop progresses, especially during grain filling, the plant becomes weaker and the disease often reaches the upper canopy, where it becomes more visible. At that point, there is little that can be done for the current crop, but it is a good opportunity to assess how much inoculum may be present for next season.
Other diseases, such as Cercospora, kernel smut, false smut, and bacterial panicle blight, are expected to become more visible as fields move into the final stages of development. We have observed all of these diseases in the field this season, except false smut, but it is still too early to determine whether they will also become major problems during this busy disease season. Weather over the next few weeks will play a crucial role. For now, the best thing growers can do to prevent further disease-related impact is to harvest fields as early as possible. Significant Cercospora damage has been observed in fields where harvest was delayed due to weather conditions. Finally, we are still monitoring the “new disease” in the country, hoja blanca disease. The disease was first reported in Texas in 2024 and has already been reported there again this year. The virus is transmitted by infected rice delphacids. Our efforts, in collaboration with Dr. Musgrove and Dr. Madison Flasco, are focused on monitoring for its presence in Louisiana. As I write this article, the disease has not been reported in our state. ∆
FELIPE DALLA LANA
LSU AGCENTER
Figure 1. Rotten neck blast impacting rice.
Figure 2. Sheath blight impacting rice.
