Fungicide timing critical for smut management

Dustin Harrell, L:Su AgCenter rice specialist

DR. DUSTIN HARRELL
LOUISIANA
Extension Rice Specialist
dharrell@agcenter.lsu.edu

Kernel smut in rice seemed to be more prevalent in southwest Louisiana last year than it has been historically. Typically, kernel smut pressure in southwest Louisiana is much lower than in the northeastern Louisiana rice-production area.

Because of this, management for the disease in the southwestern part of the state has not been a focal point by some producers and consultants. Due to the increased prevalence of kernel smut in 2016, I thought it would be good to hit the basics about the disease and its management to reduce its occurrence in the 2017 crop.

Kernel smut can be identified by a black mass of fungal spores found inside the rice hull, oozing out of the hull seams and attaching to the outside of the hull when the grain is at or near maturity. The spores will even attach and stain your pants when walking through an infected field.

kernel smut

The best way to control kernel smut is with a propiconazole fungicide application when the rice has a 2- to 4-inch panicle around the mid-boot stage of development—photo courtesy LSU AgCenter

When a heavily infested field is harvested, large clouds of the spores can form. This further spreads the spores, which seem to attach to everything they come in contact with. Kernel smut is caused by the fungus Tilletia barclayana, and its occurrence results in reduced rice grain yield and quality.

The disease can be spread by the spores overwintering in the soil or from planting seed that has the spores. Later-planted rice and higher nitrogen fertilizer rates favor the development of the disease.

The best way to control kernel smut is with a propiconazole fungicide application when the rice has a 2- to 4-inch panicle around the mid-boot stage of development. Applications of a propiconazole fungicide made once the boot has split and the first floret has begun to emerge are too late and will not effectively manage the disease.

This is unfortunate, since heading is the most effective fungicide timing for blast, sheath blight and cercospora when targeting a “single shot” fungicide management strategy. Therefore, if you have a history of smut pressure and you want to reduce the disease potential, a mid-boot propiconazole application will have to be added to your disease management strategy this season.

Managing rice in a late-planted year

Bruce Linquist

BRUCE LINQUIST
CALIFORNIA
UCCE Rice Specialist
balinquist@ucdavis.edu

This year is looking like it is going to be a late-planted year. We know from our research that planting later tends to reduce yields. It is encouraging to remember that our top yield contest winner who got 127 hundredweight per acre had a planting date of May 21. Late planting dates, along with already low rice prices, necessitate careful management and extra thought to inputs.

Here are some suggestions to reduce input costs, maintain yields and avoid delayed harvests. First, earlier duration varieties need to be considered. Good candidates included M-105 and M-206.

Second, apply your starter blend of NPK 20 to 30 days after planting. This has several benefits: It eliminates a pass before planting, allowing for earlier planting; it reduces scum build up; and it can replace the post-herbicide N application that many growers have been doing.

Third, only apply P and K if necessary. If your soil P values are above 15 ppm (bicarbonate P) or if your soil K values are above 120 ppm, applications of these nutrients may not be necessary.

Fourth, apply a top-dress of N at panicle initiation only if needed (the Leaf Color Chart can be used to determine need). If a top dress is applied when it is not needed, yields can be reduced and harvest delayed. This can be a particular problem if harvest is already going to be delayed due to late planting.

In early March, I traveled to Australia to attend the International Temperate Rice Conference. Australia is the only country to have higher average yields than California. They have a very similar growing climate to what we have in the state, so it was a good place to learn.

One thing I came away with was that, like California, Australia has a problem with cold temperatures during booting (between PI and heading) that reduce yields. Australian growers are very diligent in raising their flood water during this time to about 8 to 10 inches deep to protect the developing panicle from cold stress.

In a study we recently conducted, cold stress during booting was the No. 1 temperature-related factor that reduced California rice yields. Interestingly, even in the northern part of the rice-growing area, which is warmer, the number of nights with cold stress (less than 57 degrees Fahrenheit) during this critical three-week period ranged from zero to 13 nights and averaged close to four nights per year (we used the Durham CIMIS weather station).

Furthermore, late plantings shift the booting period later into the season, putting them at greater risk for cold nighttime temperatures. Therefore, in all areas of the state, growers need to be diligent in raising their water height during this critical period.

Use cultural management to reduce disease pressure

DR. JARROD HARDKE
ARKANSAS
Asst. Professor/Rice Extension
Agronomist
University of Arkansas Cooperative
Extension Service
jhardke@uaex.edu

Disease management starts at planting. Selecting the right cultivar for the right field provides the best chance to minimize disease pressure for the season.

In fields with a history of severe blast disease pressure, it is best to plant a hybrid or a variety with improved blast resistance. Remember to keep a flood more than 4 inches deep after midseason to suppress blast development. In certain fields in Arkansas, blast cannot be managed by fungicide applications alone and planting a susceptible cultivar could lead to severe losses. When fungicides are needed, use two applications to achieve the best blast management.

Once we have selected our cultivar, we then need to give it the best chance to succeed. Earlier planting dates have shown to reduce disease pressure.

Generally speaking, rice planted before early May has the best chance to escape severe disease problems. Avoidance can be a great tool to minimize the need for fungicide applications and potential yield losses associated with disease pressure.

Selecting appropriate seeding rates also can help to reduce disease pressure. When rice stands are too thick, it promotes and increases the sheath blight severity.

Luckily some cultivars have improved resistance to sheath blight for fields with a severe history of the disease. If sheath blight is prevented from reaching upper canopy leaves and causing direct yield loss, it can still have a negative impact.

A high frequency of sheath blight throughout the middle to lower rice canopy can still weaken stems and increase the risk of lodging should harvest be delayed for any reason.

The use of proper nitrogen rates also can help limit disease problems. Sheath blight, kernel smut and false smut incidence can all be increased with excessive nitrogen rates. The use of the Nitrogen Soil Test for Rice (N-STaR) can help determine field-specific nitrogen rates to maximize yield and avoid over-fertilization.

In addition, Greenseeker technology is now recommended for determining midseason nitrogen needs, which which may help to prevent over-application of nitrogen when it is not needed. (See page 10 for related article.)

Few cultivars have resistance to the smuts and fungicides may be needed for management. Remember that if making a fungicide application for smut prevention, you must spray before boot split. If the application hasn’t been made by then, you’ve missed your window and you should save your money.

Proper cultural management is our best tool to minimize disease issues. Cultivar selection, seeding rates, nitrogen rates and fungicide application timing (when needed) can help ensure a successful season with minimal losses from disease.

For more information, consult the “MP154—Arkansas Plant Disease Control Products Guide—2017” and the “Arkansas Rice Production Handbook.”

Scouting doesn’t cost; it pays with early detection

Dr. Mo Way

DR. M.O. “MO” WAY
TEXAS
Rice Research Entomologist
moway@aesrg.tamu.edu

For this month’s Rice Farming article, I want to talk about the value of scouting your fields. I have been in many rice fields where farmers finally observe a problem that should have been addressed earlier. Of course, by the time the unsuspecting farmers notice the problem, frequently it is too late to do anything about it.

For example, chinch bugs can attack rice as soon as rice emerges from the soil. If NipsIt Inside or CruiserMaxx Rice has not been applied to the seed, these pests with piercing-sucking mouthparts can reduce a stand.

In Texas, the treatment threshold for chinch bugs is about one adult per two seedlings. If you have not planted treated seed, then pyrethroids applied in higher-than-normal final spray volumes usually do the trick.

chinch bugs

Adult and nymph chinch bugs feed on rice seedling culm—photo courtesy LSU AgCenter

You can also flush your fields to drown them or make them sick. But to get the most bang out of your spray dollar, early detection is essential.

Don’t just check your fields from your pick-up—walk into the field at least 100 feet and check along this transect. Carry a pocket knife, a magnifying glass and your smartphone camera.

Observe in a number of spots in your fields—you may only have an isolated affected area, which you may be able to treat without having to spray your entire field.

chinch bug feeding on levee rice

Chinch bugs can quickly destroy levee rice if not caught early by scouting—photo by Dr. M.O. Way

When you are looking for chinch bugs, scout during the cooler parts of the day. During the heat of the afternoon, they move down into the cracks in the soil where they are harder to detect. Get on your hands and knees and wiggle seedlings from side to side to observe any chinch bugs below ground level on the plant.

Often times, you can find them in the whorls of seedling sedges. Young nymphs are orange. If you see these critters along with adults, you know they are reproducing on your rice—this is bad.

Another early season rice pest is fall armyworm. Again, farmers often detect larval populations after economic damage has been done.

Scout your fields looking for the larvae and ragged defoliated rice—treatment threshold is about 20 percent defoliation in the presence of larvae. Frequently, farmers are alerted to a fall armyworm problem when they see cattle egrets in their fields.

By this time, the birds are feeding on larvae and economic damage has been done. Dermacor X-100-treated seed does a good job as do pyrethroids applied when larvae are young.

Other insects you should scout for while looking for the above pests are aphids, South American rice miner and rice delphacid, which did not invade Texas rice fields last year but was very problematic on our ratoon crop in 2015.

Basically, look for anything out of the ordinary, including insects, diseases, nutrient disorders, etc. Immediately report any problems you are not sure of to your local Cooperative Extension agent or rice scientist.

My Entomology Project’s “2016 Entomology Research Report” can be downloaded from http://bit.ly/2qbP0BT.

Study your situation and be timely with all inputs

Sam Atwell

SAM ATWELL
MISSOURI
Agronomy Specialist
atwells@missouri.edu

Due to a very dry fall, Missouri growers had regraded and prepared their fields for 2017 and were ready to plant in early April. Recent rains saturated our soils, so very early planting has been delayed, which is OK because we have plenty of time.

How do we make a profit growing rice with current prices in 2017? I believe most farmers grow rice as economically as possible already. So I have no advice except study your situation with your consultant and be timely with every input. Cutting inputs and making big changes may not be advisable in most cases.

Early insects and diseases reduce yield and quality and increase production cost, which lowers profit. I follow University of Arkansas recommendations to always plant treated seed. Integrated pest management and consultants are a great investment, and we should never let our guard down checking fields.

High-yielding hybrid and conventional varieties need to be scouted closely for early insect and disease detection, then foliar applications can be made in a preventive manner.

Hybrid varieties generally have a better disease package, but don’t ignore scouting them. Although disease and insect pressure has been relatively low in Missouri the past few years, we were hit hard in isolated areas with sheath blight, blast and insects in 2016. We hope for better results in 2017.