- Specialists Speaking -
When to recommend a fungicide
Dr. John Saichuk
Because we are in the process of revising our rice production handbook, and I am required to edit or at least review all chapters, I just finished reading the chapter submitted by Drs. Groth, Hollier and Rush on rice disease management. It reminded me of when I was a student in Dr. Rush’s class and he said 80 percent of our exams would come from material he had time to cover in class. The remaining 20 percent we had to get on our own from the text book. I thought he was bluffing. He was not. It was the only text book I read cover to cover in my entire college career, and he was one of the best teachers I had in the three universities I attended.
The disease management chapter was excellent. They listed nine major and about 15 minor diseases of rice in Louisiana. The fact that we normally deal with about three or four of these diseases in any given year is testimony to the success of plant breeders in developing varieties resistant or tolerant to many of these pathogens. Most of the diseases are caused by fungi or bacteria (the pathogens), which are living organisms, so these diseases are biotic in origin. Some scientists argue that conditions like straighthead should be separated from the classic diseases and treated as physiological disorders.
Management in recent years has become a matter of determining if the disease is present and then choosing a fungicide. For the most part that has been successful. In northeast Louisiana, the likelihood of kernel or false smut developing prompted the use of fungicides without the documented presence of disease because the symptoms of these diseases are not manifested until it is too late to use a fungicide. A couple of years ago, the net blotch phase of narrow brown leaf spot hit the southeastern part of the state very hard. Now farmers, field men and consultants find themselves in the position of making fungicide recommendations in the absence of disease, too.
When sheath blight or blast is discovered when scouting, the decision is easier to make. If the fungicide does its job well – whether it was worth its expense or not – can’t be determined because it may also have been a situation where there was no disease development. Sometimes it is better to just make the decision and not think about it.
What will we do in our verification fields? I do not know yet. A field full of weeds or a poor stand does not have the yield potential to justify a fungicide in some years. High prices this year could have some farmers thinking protection of whatever yield potential exists is important. It is always easier to justify the use of a fungicide on susceptible varieties than on resistant or tolerant ones. Sometimes we get lucky. If it is a year of low rainfall and dry conditions at the time of disease onset (usually between internode elongation [green ring] and heading), we can skip the fungicide. Fields in which a ratoon crop is planned make it easier to justify a fungicide. Where rice is being grown for seed, it is almost foolish not to use a fungicide as insurance.
When straighthead, hydrogen sulfide toxicity (Calcasieu disease) and localized decline are present, the field should be drained about 10 days to two weeks prior to internode elongation. So far, all we have is field history to provide a good guide. Straighthead and hydrogen sulfide have no other remedies. Dr. Gary Breitenbeck is still studying the relationship between silica and localized decline. Given the time and resources, I believe he will figure it out.
Dr. Nathan Buehring
Rice diseases can be very costly for you, the producer. Fungicides can be costly if you apply them when they are not needed, and foliar rice diseases can be costly if they are left untreated. When looking at using a fungicide for sheath blight control, consider the susceptibility of the rice variety you are growing.
Here is how I rank the most popular varieties we grow in Mississippi in susceptibility to sheath blight from very susceptible to least susceptible: CL 161 (VS), CL 171-AR (VS), Cocodrie (S), Sabine (S), Wells (MS) and XL 723 (MS). CL 161 and CL 171-AR are rated very susceptible to sheath blight, and it can move up the plant very rapidly on these varieties.
I would begin scouting these varieties shortly after mid-season. Some of the previous research would suggest that two fungicide applications may be necessary for adequate control of sheath blight. If sheath blight is a problem shortly after mid-season, I generally recommend applying six to nine fl oz/A of Quadris and make another application (either Quilt or Stratego) at the late boot timing.
Cocodrie is rated susceptible to sheath blight. In most cases, this variety is not as susceptible as CL 161. Therefore, a fungicide application can possibly be delayed until the boot stage. Closely monitoring disease progression will help in making the best decision on applying a fungicide at the appropriate time.
Wells and XL 723 varieties are rated moderately susceptible to sheath blight, and, traditionally, it has not been as big of an issue in these cultivars. However, in some on-farm trials, we have seen an economic benefit in making a fungicide application to these cultivars. Once again, scouting and monitoring disease presence and pressure will help you make sound decisions on whether or not to make a fungicide application.
Fungicide rates for sheath blight control will depend on how long you need to protect the crop. If you are applying a fungicide in the preboot timing, a higher fungicide rate will be needed to protect the crop through heading. As you get closer to heading, a lower rate may be used since the length of residual control needed will be less.
Last year I had several questions on how early to spray a fungicide that contains propiconazole (Quilt and Stratego) and get protection from kernel smut. To get protection from kernel smut, the application needs to be made in the boot stage. If applying in the early to mid-boot stage, an equivalent rate of Tilt at six to eight fl oz/A will be necessary. If applying in the mid- to late boot stage, an equivalent rate of Tilt at four to six fl oz/A will be necessary.
Tankmix option can save money
DR. M.O. “Mo” WAY
This month’s topic is disease management, which is key to producing a profitable crop. Varietal selection, planting date, seeding rate, method of irrigation, soil type, weather, crop rotation and the decision to ratoon crop all impact disease management. Many of the above cultural practices cannot be manipulated at this time, because in Texas, we are relatively far along in the growing season. However, you still have time to adjust your fertility program to discourage disease. In other words, do not over fertilize your crop, which can lead to increased sheath blight severity.
Also, I strongly recommend scouting your fields and only applying fungicides if disease levels exceed threshold values. The 2008 Texas Rice Production Guidelines (http://beaumont.tamu.edu) describe sampling methods (using a “T-tool”) to estimate sheath blight severity. Use these guidelines on which to base your treatment decisions; just because you plant a sheath blight susceptible cultivar does not mean automatic fungicide applications. We all know the price of rice is at an all time high, but input costs are too, so wise management decisions based on scouting are imperative.
If sheath blight threshold levels are exceeded, you may want to consider tankmixing a fungicide with a pyrethroid insecticide in stalk borer-prone areas (e.g., Jackson, Matagorda, Colorado and Wharton Counties). This can save you an aerial application charge.
We in Texas realize the importance of our ratoon rice crop. In general, any stresses on your main crop will have a negative impact on your ratoon crop. So, not controlling sheath blight in your main crop not only will result in a loss of main crop yield but also of ratoon crop yield.
Last year, I observed many fields with Cercospora (narrow brown leaf spot) and brown spot. Research by Dr. Don Groth at LSU has shown that Cereospora is more problematic than once thought. Tilt, Stratego and Quilt fungicides applied mid- to late boot have been effective in suppressing this disease. Again, consult the 2008 Texas Rice Production Guidelines for more information. Be on the lookout for panicle blight this season. Research in Central America suggests the panicle rice mite may be associated with this disorder. Contact me at (409) 658-7394 if you suspect your rice has panicle blight.
We have a new Extension rice pathologist. Dr. Young-Ki Jo is working cooperatively with Dr. Don Groth and me to evaluate novel fungicides for sheath blight control. Please welcome Dr. Jo, who is a key addition to our Texas rice faculty.
For all you Razorbacks: Last weekend we were camping on the Quachita River near Pencil Bluff – full moon over the river, fireflies blinking in the trees and a whippoorwill singing in the night. My old buddies, Glenn, Mark, Mike and “Mr. Ron Rico,” spent an enjoyable weekend in this beautiful region of Arkansas. Thanks for the good times, Arkansas!
Dr. CHRIS GREER
What a difference it makes when we have a dry spring in which to prepare rice seedbeds. No rain delays, time to spend with your family on the weekends and, hopefully, fewer frustrations. Usually we view this as a luxury. However, too much of a good thing can sometimes get us into trouble. Sometimes we plant rice because we can rather than planting it on a date that will minimize risks and optimize the chance for a successful crop.
This urge to plant early is widespread and contagious in California this season. As of April 22, there has been a significant amount of rice planted, and preparation of other fields seems to be proceeding rapidly. UC Cooperative Extension recommends a preferred seeding date of April 20 to May 25 and an optimum seeding date of May 1 to May 10 for most California rice varieties. Very early planted rice may be subject to environmental conditions that are unfavorable for rice growth and development and possibly predispose the plants to disease.
Early planted rice is often in jeopardy of struggling through cool temperatures, which slow germination and seedling emergence. Under these conditions, plants are predisposed to seedling diseases, which may be caused by several organisms and produce symptoms of seedling rot or seedling blight under water-seeded conditions. The best way to avoid these diseases is to outrun them by planting when temperatures have risen to a point that favors rapid seed germination and stand establishment.
Laser leveling and maintaining a flood of four inches promote rapid germination and stand establishment without the loss of weed control often associated with draining for stand establishment. Planting high quality seed with 85 percent germination or more when water temperatures are favorable for seed germination and growth (> 70°F) is an important cultural management practice for these diseases. In recent years, higher seeding rates have been used to compensate for seed rot and seedling disease.
Keep an eye open for signs of seedling disease by inspecting poor germinating seeds or slow growing seedlings by pinching the seed to determine if it has been rotted and looking for fungal growth on the seed or seedling. Seed that are infected shortly after seeding often don’t germinate because the endosperm or embryo is rapidly destroyed. Growth of seedlings may be greatly impeded when seeds are infected following germination. Symptoms of seedling disease may include stunting, yellowing or rotting of the seedlings.
There is no substitute for field scouting when deciding if a fungicide application for diseases, such as aggregate sheath spot and rice blast, is needed. Inspect your crop weekly for disease symptoms, even if you think it is too early. As rice approaches the boot stage, increase scouting intensity for the presence of rice blast and aggregate sheath spot diseases to determine your risk based upon disease incidence, disease severity, weather forecasts and consultation with your pest control adviser prior to ordering a fungicide application.
Flood management impacts diseases
Ideally, farmers need to be able to establish the flood in two to three days in dry-seeded rice. Realistically, the time required may range from two days to 15 days. When the time is delayed to more than two days, nitrogen is lost by ammonia volatilization. Using Agrotain-treated urea has proven to substantially increase nitrogen fertilizer efficiency on many of the fields in Arkansas.
Flood management is a critical step in managing rice blast disease. Dr. Fleet Lee demonstrated that a deep flood after mid-season can greatly reduce the incidence and severity of rice blast, even in blast-susceptible varieties. The inability to maintain a constant flood when growing a blast-susceptible variety increases the risk of blast enormously. We have seen this across Arkansas as we have planted predominantly blast-susceptible varieties over the past seven to eight years and have managed to escape a widespread blast epidemic.
When growing blast-susceptible varieties, a shallow, but steady, flood should be maintained until mid-season. After mid-season, bring the flood depth to four to six inches and maintain until maturity. Fields that must be drained for straighthead often are the most severely effected. Blast becomes established while the field has been drained. If weather and water capacity limit the ability to re-establish the flood, blast can spread throughout the field and become severe.
While the majority of the rice produced in the Mid-South is flood- irrigated, there has been increased interest in Arkansas in furrow-irrigated rice (or “row-watered rice”). The biggest issues with furrow-irrigated rice are disease risks and unknowns concerning other management. In research trials, yields have been reduced compared to flood-irrigated rice. A blast-resistant variety is needed to reduce the risk from this disease. Hybrid rice has been an effective choice to plant in these situations.
Residual herbicides have certainly made weeds easier to manage in this system but are still not fool-proof. Weeds not commonly a problem in rice become a serious problem due to the lack of a flood for control. For example, palmer amaranth (pigweed) is normally controlled by the flood but in furrow-irrigated rice can be a challenge. Current residual herbicides labeled for rice do not provide effective residual control of pigweeds. Propanil and Aim burn the vegetation but normally do not give a complete kill. Repeat applications may be needed in fields with heavy pigweed pressure.
DR. JOE HENGGELER
What the cost for irrigation pumping will be for 2008 is probably on the mind of many Missouri rice growers. Every week it seems that the price for a barrel of oil has reached a new record. Currently, the cost for fuel in southeast Missouri and the subsequent cost per acre-inch of water can be seen in Table 1.
1. The obvious way to manage cost is to use electricity. If service is not at your field, look into bringing in a three-phase line. Assuming that 80 acres are to be irrigated and 20 inches will be applied, one can spend about $15,000 to bring in power lines and still be ahead based on a seven-year cost recovery. Also, neighbors may be willing to share the costs of new power lines, and/or the utility may add an incentive like decreasing future KWH costs as a rebate. If just single-phase service is available, look into using it. The phase converter that will be required costs about $3,500 for a 40-horsepower unit.
2. Natural gas may be an option if electricity is not available, but electricity seems to be the most steady, as it is based on coal and nuclear power. Local rice grower groups may want to visit with the managers of natural gas companies since the summertime useage that irrigators use would come at the companies’ lowest use season.
3. Use multiple-inlet irrigation using poly-pipe. Researchers feel that energy use can be decreased by 20 percent, mostly from capturing and using more rainfall. Along the same line, 0-level basins can provide the same benefit, as reported by an Arkansas rice farmer at a recent irrigation meeting. However, 0-level has other issues to consider.
4. Keep your well from clogging up from iron bacteria. Assume that when new, your clean well screens allowed 300 GPM for one foot of drawdown. This means that a 3,000 GPM flow rate lowered the water table 10 feet. If the screen is 40 percent clogged, the specific capacity may now be only 180 GPM/ft; the draw-down is now 17 feet. The additional seven feet will raise costs by about $500 per year to the diesel user based on the same acres and inches as before.
5. Locate any paddies that may leak more than others. One way to do this is to put out some yardsticks in paddies, and once pumping is cut off, time how long it takes to drop the water level an inch. As long as water is not cascading into another paddy, and the water surface still covers the entire paddy, this will work even on paddies with slope. Next year, one can try to manage around the leaky areas.