Sulfur and Potassium Deficiency in Rice

During the past few days, we have received a few calls about suspected sulfur and potassium deficiency in rice. The deficiency symptoms can be confusing and hopefully we can provide some assistance in distinguishing these problems from other stem and leaf diseases.


Sulfur deficiency of rice: The following images show leaf symptoms of sulfur deficiency. We rarely see this in Arkansas and it is usually in patches or areas of fields, often associated with sandy regions but may be reported on “cut” spots as well. In the latter, it may be associated with other deficiencies from what we have observed.

Sulfur deficiency shows up in the upper leaves, from a distance appearing dull or bright yellow, at least at first.

Closer examination may show shortened leaves with tip discoloration (yellowing) following by the formation of rows of brown spots between the veins proceeding from the tips downward.

Another view of the tip discoloration and the spotting between veins.

Potassium Deficiency: Many silt loam rice soils in Arkansas are low in available potassium. Rice grown on these soils is subject to potassium deficiency, which often gets noticed during the early to mid booting stages, and to more severe stem rot and brown spot.

As shown above, potassium deficiency may show up as a later season tip discoloration. From a distance, patches in the field may turn reddish or brown and seem to spread across the field over time as the plants become deficient over larger areas. Wells rice shows this symptom as reddish tip discoloration, and the affected length of leaves may be several inches from tip downwards.

If you examine rice plants in suspected potassium deficiency areas, you may find increased disease symptoms of stem rot as above, in severe cases killing the stems resulting in partially blanked discolored panicles.

You may also notice severe brown spot as above. This often occurs on deficient Bengal and other rice varieties.

Sometimes, rice developing deficiency earlier in the season will be stunted, with more yellowing of the tips of the lower leaves and tip discoloration.

An unexplained tip discoloration symptom that shows up during booting is the so-called “high yield disease”. Sometimes lush, rapidly growing rice fields will exhibit widespread tip discoloration of the field usually on the 3rd leaf down. This is the leaf that is sticking up the tallest for a while at early boot, until the flag and flag minus one leaves are fully developed. The discoloration is usually yellowish to a light brown and the leaf tips may have some spots, etc on them, however tip discoloration is very mild and remains so compared to true deficiencies which continue to move down the leaf tips pretty quickly. The above phenomenon has been associated with lush, high yield potential fields in the past, thus the nickname.

If caught in time, nutrient deficiencies may be stopped by the application of “rescue” fertilizer applications but these attempts are too late to prevent yield losses. They may stop progression of the symptoms or help slow diseases a bit. Greater success for salvaging these situations is achieved with early detection.

One of the biggest challenges with potassium deficiency is what is known as “hidden hunger”. This occurs when the plants are slightly deficient in potassium but no visable deficiency symptoms are displayed by the plant. Because of this situation, we strongly recommend adequate soil sampling and application of preplant potassium as recommended. We have observed significant yield increases from potassium from plots exhibiting only mild or no deficiency symptoms until it is too late.

June 23 Rice Crop Condition and Progress

As of June 20, all of the rice in Arkansas has emerged. Early rice should be heading within the next 2 weeks. This means that the optimum timing for sheath blight and kernel smut fungicides is approaching. As of June 20, 20% of the crop is reported to be in excellent condition, 50% good, 26% fair, and 4% poor.

Average temperatures were above normal ranging from 4 degrees above normal at Texarkana to 8 degrees above normal at several locations for the week ending June 20. The temperatures ranged from a low of 64 degrees at Calico Rock to a high of 101 degrees at El Dorado and Eudora. This completes 4 straight weeks and 5 of the last 6 weeks with temperatures significantly above normal. Rainfall for the week ending June 20 ranged from none at several locations to a high of 1.53 inches at Harrison. Overall, soil moisture supplies were 13% very short, 47% short, 38% adequate, and 2% surplus. The extended heat and dry weather have caused a significant strain on the irrigation capacity across the Delta. Rice fields have spots (some large, some small) that are burning because the well is unable to keep up with the dry weather. The impact of this heat will be significant if the weather pattern continues after the rice begins heading.

The National Weather Service publishes a national drought monitor weekly on the web. To view this site, go to: http://drought.unl.edu/dm/monitor.html.  This site provides a map that illustrates the level of drought in the various regions of the US.

Very early estimates suggest that CL 151 is the most widely planted variety so far (about 23% of the acreage). The next most widely planted varieties are Rice Tec CL XL 745 (18%), Wells (16%), and Jupiter (12%). These numbers are preliminary and may change as we get more information available.

June 15 Rice Crop Condition and Progress

The weather this spring has allowed rice to be planted across most of the state at record pace. As of June 13, all of the rice has emerged. This compares to 99% last week and 95% this time last year. Our planting progress has proceeded about 2-3 weeks ahead of the 5-year average and a month ahead of last year. As of June 13, 19% of the crop is reported to be in excellent condition, 51% good, 26% fair, and 4% poor.

Average temperatures were above normal ranging from 3 degrees above normal at Conway and Hot Springs to 7 degrees above normal at several locations for the week ending June 13. The temperatures ranged from a low of 56 degrees at Calico Rock to a high of 99 degrees at Stuttgart and Keiser. This completes three straight weeks and 4 of the last five weeks with temperatures significantly above normal. In addition to early planting, the warm temperatures have allowed the crop to progress much quicker. Rainfall for the week ending June 13 ranged from none at several locations to a high of 3.23 inches at Dardanelle. Overall, soil moisture supplies were 2% very short, 28% short, 60% adequate, and 10% surplus.

While some rice is just emerging, the early rice is at early boot stage. Keep a close watch for rice blast and do the best you can to keep susceptible varieties flooded. Leaf blast has been reported in rice counties from North to South.

Very early estimates suggest that CL 151 is the most widely planted variety so far (about 23% of the acreage). The next most widely planted varieties are Rice Tec CL XL 745 (18%), Wells (16%), and Jupiter (12%). These numbers are preliminary and may change as we get more information available.

Don't Forget to Enroll Late Fields in DD50 Program

Early fields should be scouted carefully as midseason approaches. The warmer temperatures have caused the crop to progress quicker than predicted by the Rice DD50 Program in some cases. As the later rice emerges, be sure to enroll those fields in the Arkansas Rice DD50 Program. Five new varieties have been added to the program for 2010. The program can be accessed through the county Extension office or online at: http://dd50.uaex.edu/dd50Logon.asp. In order to enroll, you need the variety name, the emergence date, and the number of acres. The program will predict the timing of approximately 27 different production practices. This allows growers and consultants to be more efficient in scouting the crop and more timely with treatments. On-time decisions can often be the difference between success and failure. It is also important to the industry to enroll these fields. The data helps the mills prepare for harvest while it also serves to estimate the important varieties across the state.

Herbicide Injury Appears Again

I have looked at a couple of fields that have experienced Permit injury similar to what we have seen in the past.  The common symptoms include bright, distinctive yellowing about 7 days after flooding similar to what would be expected with sulfur deficiency, some stunted growth but not always severe, typically occurs on silt loam soils with high soil pH, and normally recovers within about 2 weeks. The yellowing is similar to what is observed with clorimuron (Classic, Canopy XL) carry-over into rice. The yellow color also resembles Newpath injury. All of the compounds are similar and have similar modes of action. Plant tissue analysis normally suggests that the plant nutrient status is normal (i.e. nothing is deficient). A few years ago, we were able to observe the injury in sprayed and unsprayed areas of a field. This allowed us to verify our suspicions.

The green rice in the above photo is an area that was not sprayed and obviously resulted in no rice injury but also no nutsedge control. While the rice seems to be severely affected, little or no yield loss has been observed in the fields where this has occurred.

While this may explain the yellowing in some fields, there are other problems that may be occurring. I am aware of a couple of fields in the past that have similar symptoms and Permit was not applied to the fields.

Draining the fields has been a common practice to get the field to recover. Various fertilizers have also been used with ammonium sulfate being most common. While the fertilizer is only going to correct nutrient deficiencies that may result from the rice being stressed, the nitrogen may help encourage the crop to recover more quickly.

Managing Rice Blast and Straighthead

The following questions have arisen repeatedly the last few days:

Question:

We have found blast lesions on CL 151 and CL 142 recently. How concerned should we be about each one and how should we manage to minimize neck blast later on each?

Answer:

You should be more concerned about CL 151 than CL 142. CL 151 is very susceptible to neck blast and under favorable conditions, can be difficult to manage with respect to this disease. If leaf blast is found, or the field has a history of blast or has blast potential (erratic flood history, tree lines, river bottoms, sandy or other water percolating soil type) then you should pump up the field to a minimum 4 inch flood depth in the shallowest part of the field and try to maintain the rest of the season. If you find areas that are burning down from leaf blast, you should consider treating these regions (usually along edges or tree lines) with an application of Quadris, Quilt Xcel, Quilt, Gem or Stratego to minimize blast spore production for the field. If you are spraying the field for sheath blight anyway, the sheath blight application should suffice, depending on timing. If the field does not have hotspots, but only scattered leaf blast, this is not a step I would consider. CL 151 fields with any evidence of leaf blast should be sprayed twice to minimize neck blast, once at boot split and the second about a week later when the earliest heads are about 3/4 out of the boot. You should not cut rates either on this variety. Fields should be scouted extensively in June to mid July to determine leaf blast as lesions tend to disappear during boot to early heading for most observers.

CL 142 is less susceptible to blast in our limited experience than CL 151. It reacts more like Wells, so far. Again, pump up the field if leaf blast is found or in fields with a strong history or potential for blast. Fields like this should probably be sprayed at boot split for blast. Since this variety seems to behave like Wells, the second application and rates are subject to field judgment. If conditions are hot and dry, you can probably get by with less fungicide and perhaps one application. If this is the decision, make sure the fungicide application made is the boot split one, as it is more important. For both CL 151 and CL 142, this application is also appropriate for sheath blight control, if this disease has not been that aggressive earlier.

Question:

Is Taggart resistant to straighthead and how should it be treated to prevent this disease?

Answer:

Based on two straighthead nurseries observed in 2009, we rated Taggart as resistant when compared to susceptible checks like Cocodrie and CL 131 (very susceptible). On typical fields, Taggart will likely not need to be drained or drained "dry to cracking", based on this experience. On fields with a very strong history of straighthead, it may be beneficial to drain most varieties, but resistant ones will not require as much drying as susceptible varieties, and the benefit will not be as great, obviously. On these fields, if it is raining to the degree that draining cannot be done, a variety like Taggart will still perform, whereas Cocodrie and the like will be devastated.

LATE PLANTED RICE VARIETIES

There are still a few folks trying to plant some rice. The most common question is what variety is the best to plant in June. In general, the best varieties are the best varieties planted late. Later maturing varieties do better than earlier maturing varieties. The hybrids are good selections because of the yield potential and disease resistance. My experience with the Clearfield varieties is that tend to lose more yield potential when planted in June that many of the conventional varieties. Be cautious about the increased risk for rice blast. Francis does well planted late, as long as you can manage the flood effectively to control rice blast.

Ultimately, all varieties are going to yield less than they would have if they had been planted in April. Decisions should be made with the assumption that my yield is going to be no more than about 120 bushels/acre. I know that higher yields can be obtained with June planted rice. It is better, however, to expect less than what you get than to get less than enough to make ends meet.

RICE DISEASE UPDATE

It seems the worst disease affect rice of late is self-inflicted. Newpath drift has been widespread. When the wind gets high, the farmers start getting nervous about getting their fields sprayed, we don’t always use good judgment. I know that the longer we wait, the bigger the grass gets. But if we can’t keep it in the field, the big grass is going to seem like a rather small problem. The general misconception is that Newpath does not drift. However, we have tracked cases for more than a mile. The earliest fields are reaching midseason and the impact of Newpath drift onto conventional rice is now even greater. Significant yield losses will be observed if the drift occurs after the rice reaches midseason. We need to be especially cautious around conventional rice.

In regard to true disease problems, rice blast month (June) has officially started with the first reports of leaf blast. Leaf blast has been found on fields of CL 151 and CL 142 in central Arkansas and in southeast Arkansas. Finding leaf blast in June is normal and it allows you to prepare for managing the disease early. A deep flood is the most effective control measure to prevent or reduced neck blast or panicle blast later in the season. Fields should be flooded as deep as possible (4-6 inches on the shallow side) until maturity. Scouting now is critical to be able to manage for the disease later.

WHAT ABOUT FOLIAR FERTILIZERS FOR RICE?

It seems the salesmen are active convincing growers to invest in foliar fertilizers for rice. They seem like a good deal, but are they? It greens the crop so it must be “doing some good”, right? Well, maybe for some micronutrients, but probably not for most nutrients.

For rice, zinc is the only fertilizer that the University of Arkansas recommends a foliar application. Even then, applying liquid zinc is not the preferred method. I have received questions about applications of boron, managanese, and other micronutrients to rice. We have no data to support these recommendations. Even in fields where soybeans do respond to boron, application of boron to rice has not been beneficial.


The major nutrients, such as nitrogen, potassium, phosphorus, and sulfur are needed by the plant in large quantities. The amounts taken up by the plant range from as little as 25 lbs/acre for sulfur to as much as 200 lbs/acre for nitrogen. Liquid fertilizer (almost all kinds) typically weighs about 10 lbs for each gallon. The amount of nitrogen in the fertilizer is about 3.2 lbs for each gallon (32%). To get 100 lbs of nitrogen, you need to apply over 30 gallons per acre. A pound is a pound is a pound. Regardless of the form, if the plant requires 90 lbs of potassium, the plant requires 90 lbs regardless of whether it is applied as a granule or in a liquid. When adequate amounts of liquid fertilizer are applied to rice, foliar burn is often a problem. Because of these problems, granular fertilizer is for the major nutrients are much more effective.

The only micronutrient that is recommended by foliar application for rice is zinc. The preferred method of applying zinc is to apply zinc sulfate (36% zinc) prior to planting. Zinc seed treatments are effective if the soil test levels are only moderately low. However, if the rice has emerged, foliar application of zinc is effective when applied prior to flooding. At least 1 lb/acre of zinc should be applied when using liquid zinc products. For most products, this will require a minimum application rate of 1 gallon of liquid zinc per acre. This is true for any product that is 10% zinc or less. While some products have been marketed at 1 quart or 1 pint per acre rates, these rates are not sufficient to prevent zinc deficiency on soils with low soil test zinc levels.

JUNE 8 RICE CROP CONDITION AND PROGRESS

The weather this spring has allowed rice to be planted across most of the state at record pace. As of June 6, rice planting is finally complete. This compares to 99% last week and 97% this time last year. Rice planting is typically complete during the second week of June, although a few acres may actually still be planted later. The USDA estimates that 99% of the rice acreage has emerged. This compares to 89% last year at this time and 96% for the 5-year average. Our planting progress has proceeded about 2-3 weeks ahead of the 5-year average and a month ahead of last year. As of June 6, 18% of the crop is reported to be in excellent condition, 53% good, 25% fair, and 4% poor.

Average temperatures were above normal ranging from 4 degrees above normal at several locations to 8 degrees above normal at Keiser and Brinkley for the week ending June 6. The temperatures ranged from a low of 61 degrees at several locations to a high of 98 degrees at El Dorado. Rainfall for the week ending May 30 ranged from none at several locations to a high of 1.9 inches at Mena. Overall, soil moisture supplies were 2% very short, 29% short, 64% adequate, and 5% surplus.

Much of the rice is reaching the stage for flood establishment and several thousand acres have already been flooded. Remember to wait until the soil dries to apply preflood nitrogen fertilizer and then apply a shallow flood as quickly as possible. Some rice has reached midseason. Remember that a there is a window for applying midseason N between green ring and ½” internode elongation.

Very early estimates suggest that CL 151 is the most widely planted variety so far (about 23% of the acreage). The next most widely planted varieties are Wells (16%), Rice Tec CL XL 745 (16%) and Jupiter (12%). These numbers are preliminary and may change as we get more information available.