Thursday, June 20, 2024

Better Fungicide Arsenal Available Today

ss-saichukDr. John Saichuck
Extension Rice Specialst

In 2012, we dealt with the worst episode of blast in rice that many of us have seen in our careers. The researchers took advantage of it to eliminate many of the susceptible lines in breeding programs, and farmers took note of the varieties that showed the most injury. This was reflected in the shift of rice acreage from 2012 to 2013.

As can be seen in the pie charts, CL151 was the leading variety in 2012, accounting for 30 percent of Louisiana’s rice acreage, and then dropped down to a tie for sixth place and only four percent of the acreage in 2013. This is a great example of the importance and influence of disease on rice. When farmers weighed the odds of high yields without blast versus low yields with blast, they backed off of CL151. CL111 had demonstrated excellent field tolerance to blast (it is rated moderately susceptible to blast by Dr. Groth) in 2012, thus becoming the leading variety in 2013.

Last summer, I did not find a single blast lesion in any of the fields I checked. Likewise, many growers had little or no blast and felt they could have made even higher yields had they grown CL151. Reports from seed dealers indicate an increase in CL151 this year as some growers are willing to take a chance that the blast epidemic of 2012 was more oddity than a common occurrence. I wish we had some sort of model that would allow us to predict the likelihood of blast, but we do not.

One thing we do have is a much better arsenal of fungicides than we did 20 or so years ago. According to Dr. Groth, the strobilurins – Quadris and Gem – represent one of the most significant breakthroughs in disease management since he started working with rice diseases. For the most part, that is still true, making sheath blight a manageable problem today rather than the disaster it was just a few years ago. Unfortunately, in the past few years Rhizoctonia solani, the pathogen that causes sheath blight, has developed resistance to the strobilurins in some areas of the state. The extent of the spread of this resistant form is not well defined. If an application of the strobilurins does not significantly reduce sheath blight pressure, it is likely that the resistant form is the culprit.

This year, we do have a full label for Sercadis fungicide for use on rice. The active ingredient of this fungicide is fluxapyroxad. In the March issue of Rice Farming, I discussed the grouping system of herbicides to help with resistance management of weeds. A similar system has been implemented with the fungicides. The strobilurins, Quadris and Gem are in Group 11; Sercadis and Convoy are in Group 7; propiconazole (Bumper, Promimax, Tilt and others) are in Group 3. By rotating fungicide groups, it is possible to delay or prevent the development of resistance. If there is some concern about resistance, then switching chemistries would be a good idea. Just make sure the disease in question is on the fungicide label. Convoy is a new name for an old fungicide. If you have been around this game long enough, you may remember Moncut. The active ingredient in both Convoy and Moncut is flutolanil. Pre-mixes of fungicides of different groups will have numbers representing both groups on the label.

Read the labels, pay attention to efficacy and rotate chemistries, if possible. If you have any questions about these materials or management of any rice disease, contact your local county agent.

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ss-hardkeDr. Jarrod T. Hardke
Rice Extension Agronomist
University of Arkansas, Cooperative Extension Service

Plan to avoid disease

The easiest way to deal with disease control is to prevent it in the first place. Starting with clean seed is the first step in the right direction. The next step is to use a fungicide seed treatment. There is no single fungicide active ingredient that will protect you from all seedling diseases. You need a combination of them to give you multiple modes of action to fully protect yourself from the seedling disease complex – made up of seedborne and soilborne diseases. Keep in mind that these fungicide seed treatments don’t last forever. If you’re planting under conditions that may lead to extreme delays in germination and emergence, there’s a good chance you won’t see much bang for your buck.

Hopefully, you also choose to plant a cultivar that is not very susceptible to a disease you know is likely to occur in your field. Case in point – don’t plant a blast susceptible cultivar in a situation that is prone to blast! Those situations would be fields with difficulty maintaining a deep, consistent flood; are surrounded by tree lines; and/or have a general history of blast development. Though we can manage this disease with fungicides, we can save time and money by avoiding the disease to begin with. Consider the same thing with other diseases as well (sheath blight, kernel smut, false smut, etc.).

There are some management practices that make your crop more prone to disease. Excessive nitrogen fertilization can lead to increased disease development. Excessive stand density can also increase the development and spread of disease. Two resources are available to help reduce the incidence of disease associated with excess nitrogen and stand density: the N-STaR program (Nitrogen Soil Test for Rice) for selecting the correct nitrogen rate for your field, and the RICESEED program for selecting the correct seeding rate for your field (

In a later-planted year such as this one where 50 percent of the crop will be planted in May, there are a number of disease concerns. With later planting comes an increased chance of bacterial panicle blight, kernel smut and false smut. If you’re planting a field with a history of bacterial panicle blight, there are no management options other than cultivar selection. Your only option in those situations is to plant a moderately resistant cultivar. For the smuts, prevention is the only option. There is no such thing as “control” of kernel smut or false smut. You can only suppress or prevent them by applying a fungicide prior to panicle emergence. Places to worry about preventing smut include those with high nitrogen rates, high seeding rates and a history of smut problems.

Plan to prevent, avoid and suppress disease in your rice field this year. It’s best to stay ahead of disease than to try to catch up later.

For more information on rice disease management in Arkansas, refer to the MP154 – Arkansas Plant Disease Control Products Guide – 2013 and the Arkansas Rice Production Handbook.

ss-wayDr. M.O. “MO” Way
Rice Research Entomologist

Apply fungicide seed treatments

At the time of writing this article (April 25), the majority of Texas rice acreage is planted except for east of Houston where about 30 percent of rice acreage remains to be planted. Furthermore, the last several days have been warm with no rain, so the Texas rice crop is beginning to look better.

However, I recently inspected a field of hybrid rice in Chambers County. The field was planted in early April during a spell of cold weather. The stand was less than ideal, forcing the grower to replant. Clearly, seedling disease and blackbird problems were evident, but I also observed small white or cream-colored larvae feeding on the germinating rice seed under the soil. These immature insects either are Southern corn rootworm, banded cucumber beetle or Mexican corn rootworm larvae. These larvae are members of the Order Coleoptera (beetles) Family Chrysomelidae (leaf beetles). They are not wireworms, which are somewhat related to them. It goes to show you – when you think you have all the answers, Mother Nature slips you a surprise to keep you humble!

I mentioned seedling diseases in the above paragraph. I think most rice is now treated with fungicides to control seedling diseases. This is good insurance because of trending agronomic practices to reduce seeding rate and plant earlier, which increase seedling disease pressure. Every rice farmer knows the importance of producing a vigorous, uniform stand of rice. Treating your seed with fungicides is a “nobrainer,” particularly if you employ a low seeding rate, conservation tillage and plant early.

Fungi that cause seed rot and seedling blight are Achlya spp., Cochliobolus miyabeanus, Fusarium spp., Pythium spp. Rhizoctonia solani, Sclerotium rolfsii and others. They survive in the soil or on seeds between crops. We have an array of effective fungicides applied to seed to control seedling diseases. Proper fungicide seed treatment can increase stand by 22 to 60 percent and increase yield by five to 22 percent based on the results of field plot tests conducted in Texas.

Scout for foliar diseases in the early season. Brown spot caused by the fungus Cochliobolus miyabeanus and narrow brown leaf spot caused by Cercospora janseana are among the most common foliar diseases in the early season. They survive on seeds and infected crop debris. Rice plants suffering from N, P or K deficiency are especially susceptible to both diseases. Use of resistant varieties and recommended fertilizers are effective to reduce the damage caused by these diseases. Fungicides usually are not recommended for the control of these diseases in the early season except under extremely severe conditions.

In addition, nutrient deficiency, especially P, is frequently present in Texas rice fields. Symptoms caused by P deficiency include small, brown (rust-colored) spots and chlorosis between veins near the tips of old leaves. Potassium-deficient symptoms are easily confused with those of brown spot.

For disease diagnosis assistance, contact Dr. Shane Zhou, plant pathologist, at Texas A&M AgriLife Research and Extension Center at Beaumont via (409)752-2741 or Also, go online to access the 2014 Texas Rice Production Guidelines for more information on disease management at https://beaumont. pdf.

These rice disease management comments for Texas were co-authored by Dr. Mo Way and Dr. Shane Zhou.

chris-greerDr. Chris Greer
UCCE Rice Farming Systems Advisor

Disease and drought water management

The 2014 California rice planting season got off to a delayed start due to a third consecutive dry winter, resulting in the most severe drought in decades. Final surface water allocations were announced in mid- April, and many irrigation districts delayed the start of water deliveries until the first of May. As surface water allocations were reduced in many areas, rice growers will fallow some fields due to lack of surface water or choose to transfer surface water to permanent crops. In addition, some growers will rely more heavily on groundwater for irrigation needs in 2014.

Compressed initial surface water delivery times and the use of groundwater by some growers increases the prospects of slow initial flood-up times. When fields flood slowly, the potential risk of damage to seeds or seedlings from rice seed midge and/or tadpole shrimp may be greater. The damage caused by these pests may predispose rice seeds or seedlings to seed rot and seedling diseases. These diseases are caused by fungi that survive in the soil and produce zoospores when the soil is flooded. Zoospores are attracted to cracks in the seed coat where the endosperm is exposed or to the germinating seedlings. Feeding by rice seed midge or tadpole shrimp may predispose seeds or seedlings to infection by these fungi.

Symptoms of seed rot and seedling disease appear shortly after seeding. The most common sign of the pathogen is whitish fungal hyphae growing over the surface of the seed and young seedling. Algae often colonize the mycelium, turning it green. 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.

Many irrigation districts will be restricting field drainage for contact herbicide applications due to surface water shortages. Draining a field during the season is known to increase the risk of infection and susceptibility of rice plants to rice blast disease. From an irrigation standpoint, maintaining a deep, continuous flood is one of the best management options for minimizing the risks associated with rice blast disease.

As drainage may be restricted, growers may be forced to plan ahead and allow water to slowly subside in order to expose weeds for contact herbicide applications. This may result in prolonged shallow water or drained field conditions that may predispose plants to increased rice blast disease pressure. A flood should be reestablished as soon as practical following contact herbicide applications to minimize this risk. In addition, these fields should be scouted closely for signs of rice blast disease and an appropriate fungicide should be applied to protect emerging panicles if significant levels of disease are present.

Considering all rice diseases that you may encounter throughout the season in California, your best rice disease management tool is a dedicated scouting plan. There is no substitute for field scouting when deciding if timely action needs to be taken in the form of field drainage for seedling diseases or a fungicide application for diseases such as rice blast.

ss-atwellSam Atwell
Agronomy Specialist

Scout early and often

Disease pressure was low last year, but we better not let our guard down in 2014. Rice blast is one of the earliest known foliar diseases, and it was hard to find in 2013. The blast fungus survives in various ways but often is seedborne. To reduce seedborne blast, research suggests Dynasty fungicide (azoxystrobin) at a rate above 0.75 fl oz per cwt seed as adequate. However, note that this seed treatment will not guarantee protection later in the season.

We encourage field scouting, deep flood management and foliar fungicides as needed. In blast-prone fields (lighter soils, tree-lined, low-lying, etc.), plant a hybrid or resistant variety. This takes care of the disease for the most part. Where susceptible varieties are planted in the wrong field, keep a deep flood of four inches on them at all times after initial flood.

Fungicides work best if applied twice for blast. The first application should be made at late boot to beginning panicle tip emergence and the second when panicles are 50-75 percent out of the boot on most of the main tillers. Higher rates are best. If the field is very uniform and disease potential is low to moderate, the best timing would be when panicles are emerging with about 35 percent of the length out of the boot on most of the main tillers. In uneven-maturing fields, it is better to spray based on the earlier maturing parts of the field if disease pressure is substantial. These types of fields would be almost automatic for two applications. Again, proper flood management will really help with blast management and improve performance of the fungicides.

Sheath blight was low in Missouri last year, too. For many years now, strobilurin fungicides have been used to manage sheath blight disease of rice, and they have been the backbone for managing fungal diseases of rice in Southern rice-producing states. Current fungicides are most effective under low or moderate disease pressure. The challenge comes when varieties are highly susceptible and environmental conditions are very favorable for disease development. When we have sheath blight, we recommend our producers use strobilurin+ propiconazole fungicide mixtures to combat sheath blight and the smuts.

Smuts were bad in some fields back in 2011. Fields sprayed properly with propiconazole-containing fungicides worked to minimize these diseases. In some cases, too much nitrogen was applied to affected fields and, in other cases, the fungicide was applied too late in the booting stage for maximum effect. The rice smuts cannot be scouted for, so preventive treatment with propiconazole-containing fungicides is the only chemical control option. Fields with a strong history of the smuts, or those that have been knowingly over-fertilized with nitrogen are most at risk.

Hybrid and medium grains are very unlikely to benefit from fungicide applications. Fungicides should be applied if your effective scouting indicates more than 35 percent positive stops in susceptible varieties and more than 50 percent positive stops in moderately susceptible varieties. Timing and rate of the fungicides to prevent the smuts are critical.

The fungicides need to be applied at early to late boot but before heading begins on any plants in the field. Earlier is usually better in the booting stage, especially for false smut. The minimum rate of 6 fl oz Tilt or Tilt equivalent is now required for most effective results under current conditions, but no application will provide 100 percent control. In the past, we achieved up to 95 percent reduction in kernel smutted kernels using propiconazole with exact timing and rate but only about 65 percent for false smut (at best). Where false smut is moderate, 65 percent reduction is noticeable, but where it is heavy, control is difficult.

Dr. Tom AllenDr. Tom Allen
Mississippi State University Pathologist

Never too early to plan ahead

Even though the majority of the 2014 rice crop has not been planted, planning for a midseason fungicide application should not be far from our minds. Mention of fungicide resistance in row crop production systems such as soybean and rice (Rhizoctonia solani = sheath blight), should remind us to weigh important fungicide application strategies before mid-season.

Preventing fungicide resistance from developing remains an important objective for rice farmers since sheath blight resistant cultivars are not commercially available.

Several factors should be considered when making a fungicide application in rice. Crop coverage, canopy penetration, adjuvant and product choice, as well as fungicide application rate are all important variables. Most fungicide products labeled for rice are preventative. Therefore, applying a fungicide to provide maximum plant coverage is important since fungicides are “locally systemic.” Droplets land on plant tissue, and the activity of the fungicide allows the product to travel short distances beyond the initial droplet; hence, the terminology “locally systemic.” In general, fungicides work by preventing additional spread of the fungus to non-infected plant tissue. To increase the effectiveness of a fungicide application, use a greater water volume; five rather than three gallons/acre.

Canopy penetration can be difficult to achieve. Generally speaking and similar to herbicide applications, fungicide applications should be made when the wind is low. Reducing application volume and applying a fungicide that does not quite reach or penetrate the plant canopy is not effective disease management. In addition, improper application placement or poor canopy penetration can increase the likelihood of fungicide resistance developing.

Adjuvants can increase coverage as well as aid plant canopy penetration. Read and follow label instructions regarding the use, rate and specific type of adjuvant. Choosing a fungicide product is not normally a major decision; however, most rice farmers use the same product annually. In some cases, product choice depends on the particular diseases historically present. In other cases, the product choice may be based on price. Choose a fungicide product that has performed well in university fungicide efficacy trials and keep in mind that for a disease such as sheath blight, a fungicide that contains a strobilurin active ingredient will provide the most effective disease management.

Last, but not least, fungicide application rate is important for several reasons. Fungicide application rates vary widely. However, one thing is certain, resistance management suggests that applying full label rates will help protect against the development of fungicide-resistant fungi in our rice production system. Cutting the labeled rate may be a cheap alternative, but that decision will reduce the amount of chemical that is applied and potentially affect fungicide efficacy.


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