Dr. Jarrod Hardke
Rice Research Entomologist,
University of Arkansas, Cooperative Extension Service
Later planting increases disease risk
A wet spring leading to delayed planting results in plenty of issues in rice. Beyond the concerns of potential yield reductions and a late harvest, later planting typically increases the chances of running into increased disease problems.
Late planting increases the risk of problems with bacterial panicle blight (BPB), which can be devastating in years it develops at high levels. There are no options for managing this disease other than host plant resistance. Currently, the only dependable recommended options are RiceTec hybrids or Jupiter. Two other cultivars – Taggart and Mermentau – have shown promise in artificial field situations and greenhouse testing, but haven’t been verified under natural BPB conditions. I would use caution with those two cultivars until we learn more, but they do appear to be better than other cultivars except the hybrids and Jupiter.
Last year, many were reminded that blast isn’t gone and shouldn’t be forgotten. Blast pressure increases as the season progresses, so later plantings will be at greater risk when planting susceptible cultivars. Management of blast is achieved through host plant resistance, water management and fungicide applications. If a field does not have the water capacity to maintain a deep, adequate flood throughout the growing season, it is increasingly important to choose a cultivar with increased tolerance to blast. If a field is surrounded by tree lines that will prolong dew periods, again cultivar selection is critical. Keep in mind that fungicides do not provide 100 percent prevention of panicle and/or neck blast. There are fields in Arkansas where blast cannot be managed with fungicide applications alone, but only with cultivar selection (plant resistance). If you have a field with questionable water availability, surrounded by tree lines and a history of blast issues, then properly selecting a more blast-resistant cultivar is extremely important.
In situations where we can successfully manage blast on susceptible cultivars, it is recommended that two fungicide applications be made – the first application at boot-split to 10 percent heading, and the second application approximately seven days later (~75 percent heading) but before the panicles completely emerge from the boot. Successful fungicide applications must be preventative. Once the panicle and/or neck is infected, there’s nothing we can do.
A threshold exists for initiating treatment with a fungicide to manage sheath blight. Begin scouting at mid-season and continue through 50 percent heading. For cultivars rated very susceptible (VS) and susceptible (S), treat when 35 percent of stops are positive for sheath blight and the upper two to three leaves are threatened. For moderately susceptible (MS) cultivars, treat when 50 percent of stops are positive for sheath blight and the upper two to three leaves are threatened. For kernel smut and false smut, there is no treatment threshold. For susceptible cultivars, a single fungicide application is recommended between boot and boot-split, but before heading. Applications made after panicles begin to emerge from the boot are too late. Treat based on knowledge of cultivar susceptibility and field history. With most rice diseases, risk increases as we increase production inputs such as seeding rate and nitrogen rate. This is especially true of sheath blight and the smuts. Manage inputs for optimum production, but avoid overages that will increase issues with disease. It’s much easier to manage slight disease pressure than intense disease pressure. Even cultivars with some tolerance to a disease may be overcome if conditions are optimal for their development. Disease management should involve sound agronomic management practices including cultivar selection, seeding rate, fertility, scouting and appropriately timed fungicide applications only when needed. For more information on rice disease management in Arkansas, please refer to the MP154 – Arkansas Plant Disease Control Products Guide – 2015 and the Arkansas Rice Production Handbook.
Dr. M.O. “MO” Way
Rice Research Entomologist
Well, it continues to rain here in Beaumont – Groundhog Day over and over… From March 1, 2015, to April 28, the Beaumont Center has received 17.8 inches of rain! In addition, cooler than normal temperatures prevail. Nevertheless, I have not received any calls concerning poor stands. It’s too late now for most farmers to treat seed with a fungicide(s), but environmental conditions this year vividly demonstrate the importance of protecting your seed from seedling diseases.
We all know weather can have a huge impact on disease and other pest problems, which in some cases can be enhanced by wet, cool weather. So, because of the atypical weather we are experiencing now, we need to scout our fields extra carefully! We may experience new pest problems or certain old pest problems may become more severe. Be on the lookout for any atypical pest problems this year and be sure to notify your local rice scientists about your observations.
Seems like I get more questions about narrow brown leaf spot (NBLS) than any other rice disease, so I will try to say a few words about this disease. NBLS has been reported to cause yield losses up to 40 percent as well as premature ripening and milling quality reductions. This disease is caused by the fungus, Cercospora janseana, which overwinters in the soil on plant debris. Thus, conservation tillage/no tillage can exacerbate NBLS severity. A bad infestation in Louisiana occurred in 2007 when Dr. Don Groth surmised the disease got its start overwintering on rice debris in crayfish ponds.
Spores are airborne with infections becoming more severe and noticeable as rice matures. The fungus attacks foliage, sheaths, internodes, panicle branches and hulls of rice. You all are familiar with the symptoms that are very diagnostic – short, linear (parallel with leaf veins), narrow, brown lesions on the foliage. I commonly observe symptoms on the internodes of ratoon rice. These lesions are reddish- brown and extend up and down the internode. I know when you control insect pests, like rice water weevil and stalk borers, in the main crop, you get a yield boost in both main and ratoon crops.
I suspect the same may hold true for NBLS – control it in the main crop and you may get a benefit in the ratoon crop. In addition, low N levels are associated with more severe NBLS infestations. There are reports that NBLS can be more severe in potassium-deficient soils, but I do not know the reason(s). However, potassium concentration in soil is greatest during early growth of rice and gradually declines to low concentrations coinciding with NBLS symptom expression during boot and heading.
Probably the best management practice for NBLS is to plant resistant varieties, but be aware that disease resistance can be short-lived, which is why our rice pathologists routinely evaluate new and old varieties for resistance to various diseases. Dr. Shane Zhou’s recent evaluations rate Antonio, CL111, CL151, Chenier, Cocodrie, Colorado and Presidio as susceptible to NBLS. Resistant varieties include CLXL729, CLXL730, CLXL745, Jasmine 85, XL723 and XL744. For a complete listing go to the following link: https://beaumont.tamu.edu/eLibrary/ Bulletins/2014_Rice_Production_Guidelines.pdf, pages 46- 48 of the 2014 Texas Rice Production Guidelines.
Another good management tactic is to reduce cutting height of your main crop which Shane found reduces severity of NBLS in the ratoon crop. This can also help control stalk borer damage in the ratoon crop. As far as chemical control, fungicides with the active ingredient propiconizole should be applied mid to late boot. But, be sure to follow label instructions!
One last comment: Texas is hosting the 2016 Rice Technical Working Group meeting in Galveston at Moody Gardens from Feb. 29 through March 4, 2016. We invite and encourage you to attend – bring your family and enjoy the Texas Gulf Coast!
These rice disease management comments for Texas were coauthored by Dr. Mo Way and Dr. Shane Zhou.
Late-planted rice and disease pressure
I hope we get enough rice planted this year to have potential disease problems. It’s April 25, and we are less than five percent planted. We have a few hundred acres of our clay soils that have been water-seeded. So, we will have to scout as usual and see how all this late-planted rice responds to disease pressure during the season.
Diseases reduce yield and quality and increase production cost. Although disease pressure has been relatively low in Missouri for the past few years, we did have a couple of blast hot spots found on CL151 last year. Increasing inputs and adapting new high-yielding varieties may make us more vulnerable. Don’t let your guard down. High-yielding conventional varieties need to be scouted closely for early disease detection, then quick foliar fungicide applications can be made in a preventive manner. Hybrid varieties generally have a better disease package, but don’t forget them.
We need to pay special attention to blast again this year due to the late planting. Rice development will be pushed back further into hot weather where some farmers have problems with pumping enough water. Hot weather and lack of water induce blast. This will be a compounding problem for farmers that intend to plant more rowrice or furrow-irrigated rice.
Along with blast, we recommend scouting weekly for sheath blight, straighthead, bacterial panicle blight, narrow brown spot, leaf spot, stem rot, black sheath rot and kernel and false smut. Descriptions of all rice diseases and their control can be found in the new UAR Rice Production Hand Book and MP 154 Arkansas Plant Disease Control Products Guide.
The Missouri rice growers and I want to thank the University of Arkansas and other universities for sharing their rice information and recommendations.
Dr. Jason Bond
Weed Science Specialist
Be aware of blast
The 2014 Mississippi rice growing season was highlighted by several odd occurrences (mostly related to environmental conditions). One of those was widespread leaf blast throughout the Delta. Generally speaking, blast is a rare occurrence in Mississippi. However, with the increase in cultivated acres on silt loam textured soils, several challenges increased the incidence of blast. Lighter soil classes, where maintaining a flood can become problematic, can increase the likelihood of blast occurrence. Other states in the Mid-South, namely Arkansas and Louisiana, observe more blast on an annual basis because their acreage is predominantly cultivated on silt loam soils. General guidelines for blast management indicate that fungicide applications to prevent yield loss as a result of the leaf blast phase may not be economically beneficial, especially when miss-timed. More importantly, reducing the occurrence of the neck blast phase can be achieved by utilizing “field” resistant techniques.
For 2015, rice farmers should be aware that the majority of conventional rice varieties cultivated throughout the Mississippi Delta are likely at least rated as susceptible to the rice blast pathogen and should be scouted frequently. Best management practices to increase field resistance include reducing dense canopies by proper N fertilization and reducing seeding rates to help minimize the occurrence of long durations of leaf wetness. Monitoring and maintaining the flood by reducing areas in a field where flood levels may become low (< 4 inches) has been observed to reduce the risk of blast development.
Dr. Tom Allen contributed to this article.
Scouting for disease is fundamental
In order to effectively manage diseases in rice, you have to remember that rice disease development is a function of the variety or hybrid you have chosen to plant, presence of the disease pathogen and the current environment for that pathogen to develop. The most common diseases in rice that we can use a fungicide to manage include blast, sheath blight, cerscospora (narrow brown leaf spot; NBLS) and the smuts (kernel smut and false smut). Scouting is an important in-season tool to determine the presence and severity of rice diseases, particularly for sheath blight and blast.
One of the best methods of scouting for sheath blight was taught to me by Dr. Saichuk several years ago when I first began working in rice. First, scouting for sheath blight should begin in earnest at green ring for very susceptible (VS) rice varieties, panicle differentiation (PD; approximately 1/2-inch internode) for susceptible varieties (S) and approximately seven days later for moderately susceptible (MS) varieties.
When scouting a field, we want to make sure our disease evaluation is based on the whole field not just a localized area of a field. An easy way to do this is by taking a minimum of 50 evaluation stops with a minimum of 50 steps between stops. The “50 stops and 50 steps” rule can change if more than one person is helping scout a field. In the verification program, if we have five people scouting, we will usually start at different locations of the field and do a 10-stop transect each. If you are strapped for time and are scouting alone, it is acceptable to reduce the 50 stops to a minimum of 10 stops. It just won’t be as thorough as a 50-stop evaluation. At each stop, you will want to evaluate if the disease is present on approximately a three-foot section by opening up the canopy. You can use a homemade push pole to do this. The push pole can be inexpensively made out of 1/4-inch PVC pipe. If you record a positive stop, you may also want to subjectively rate the severity of the disease from one to 10. A one rating would indicate that only one or two lesions were present and a 10 rating would be a complete infestation. Also, look around to see if the typical sheath blight “bird-nest” damage is present. If so, count the stop as a positive one and move on. Once you are out of the field, compile the positive stops and determine if spraying is justified.
Typically, if you are growing a variety that is rated as VS (CL111, CL161 and Cypress) or S (Catahoula, Cheniere, CL151, CL152, CL261, CL271, Cocodrie, Jazzman-2, LaKast and Mermentau) for sheath blight, consider spraying if you have three out of 10 positive stops. If you are growing a variety that is rated MS (Antonio, Caffey, CLXL729, Colorado, Jazzman, Jupiter, XL723 and Taggart) for sheath blight, consider spraying when five out of 10 stops are positive. Typically, if a moderately resistant (MR) variety is grown, we would not spray unless five out of 10 stops were positive and the severity was rated five or greater. Research by Dr. Groth has shown that sheath blight is best controlled when applied between early boot and heading. If sheath blight is found early and is severe (five or greater rating), a PD+7 application followed by the boot-to-heading application may be necessary.
Once a decision to spray for sheath blight has been made, determine which fungicide to use and the appropriate rate. A strobilurin fungicide like Quadris, Equation or Gem is recommended for sheath blight. Also, strobilurin and propiconazole premixes like Quilt, Quilt Xcel and Stratego can be used if you also want protection from blast, NBLS and smuts. However, if strobilurin-resistant sheath blight is known to be on your farm or has been located on a nearby farm, you will need to use a carboxamide fungicide like Convoy or Sercadis. Please refer to the labels for appropriate rates.
Dr. Luis Espino
Rice Farming Systems Advisor
Diseases are a continuous threat in California rice production. Early on, seed rot and seedling disease can kill seeds and seedlings and reduce stand. Bakanae can also kill young seedlings, although its symptoms might not appear until after tillering, blanking panicles of infected plants. During tillering, stem rot and aggregate sheath spot can infect plants and, under favorable disease conditions, kill tillers. Blast can infect foliage and panicles, killing plants or blanking infected panicles.
Cultural practices like variety selection, seeding rate, fertility and rice straw management can influence disease incidence and severity. Fungicides are only recommended for control of aggregate sheath spot, stem rot or blast. Use of certified seed with good vigor will ensure fast seed germination, reducing the likelihood of seed rot and seedling disease. The use of sodium hypochlorite during seed soaking has reduced bakanae infections tremendously, to the point where it is rare to find bakanae infected plants in fields planted with treated seed.
Plant density can have an effect on the incidence and severity of stem rot and aggregate sheath spot. To avoid dense stands, the recommended seeding rate in most cases is 150 pounds per acre. Blast and stem rot are favored by excess nitrogen fertilization. Growers can experiment by varying their typical nitrogen rate by five percent in a portion of a field and in that way arrive at a nitrogen rate that maximizes yields without causing disease outbreaks or excess lodging. The application of a mid-season topdress should be assessed using the color chart or a chlorophyll meter.
Besides nitrogen, water management also affects the incidence and severity of blast. Water seeding reduces blast transmission from seed to seedling, and therefore is recommended over dry or drill seeding. Fortunately, in California most of the rice acreage is water-seeded. Also, continuous flood limits blast development. Generally, fields that are drained for a herbicide application, stand establishment or fields that have lost their water during early crop development tend to have more severe blast infections.
Variety selection also plays an important role in blast infection and development. Rice varieties M-104 and M-205 have the least tolerance to blast. If these varieties are planted in areas where blast is endemic, a fungicide treatment may be necessary to prevent disease development. M-208 is the only rice variety resistant to blast in California. Rice straw management also plays a significant role in the cycle of most diseases. Rice straw can serve as inoculum for bakanae, stem rot, aggregate sheath spot and blast. Elimination of straw by burning, incorporation, winter flooding or removal can reduce the amount of inoculum present in the field before planting. However, straw elimination is not a guarantee of a blast-free field because the blast fungus produces spores that can travel from infected to uninfected fields during the season.