IDENTIFYING BACTERIAL PANICLE BLIGHT AND NECK BLAST OF RICE

(by Whitney Ginn and Rick Cartwright)
We are currently observing widespread neck blast of rice in Arkansas for the third year in a row, largely on the rice varieties CL 151, CL 261, Francis, Jupiter and at lower levels on Wells and CL 142. The blast problem was likely increased by frequent May rains that resulted in a lot of leaf blast in the state, followed by erratic drought patterns that made keeping a deep, consistent flood on rice fields difficult.

Recently, we also began noticing symptoms of bacterial panicle blight developing in fields of CL 261 and CL 181, and at low levels in CL 151, CL 142, CL 111 and Francis. Weather patterns in recent weeks have included very warm nights with high humidity, conditions that favor this disease. We are hopeful that bacterial panicle blight will stay at low levels, but early observations concern us that this may be a panicle blight year like we saw in 1995, 1998, and 2001 on Bengal and a few other varieties.

Distinguishing between bacterial panicle blight and early neck blast symptoms is not difficult, with some practice. The following photos illustrate the diagnostic differences.

Bacterial Panicle Blight: Note the cluster pattern of early infected heads (A), with a mixture of tan, green, brownish or gray kernels – but a green rachis (panicle branches)(B). At least some kernels will have a distinctly brown base (C) and inside the small kernel will be aborted and rotted at the base.

Neck blast of rice: Note the “white heads” in affected field (D) and the dark lesion on the node below the infected panicle (E); dark lesions may also appear in the rachis, resulting in blighted spikelets or kernels; earlier lesions of blast can be found on leaves, collars and lower stem nodes (G); spores can be easily observed at 100X if a microscope is available (F).

July 20 Rice Crop Condition and Progress

As of July 19, the USDA reports that 37% of the crop is heading. This compares to 16% last week, 9% this time last year, and a 5-year average of 9% for this week. Arkansas rice does not normally begin heading in June but we saw that happen in 2010. The crop was seeded earlier and we had 8 straight weeks with temperatures above normal. Thus, the crop has developed much sooner than normal. As of July 19, 21% of the crop is reported to be in excellent condition, 44% good, 30% fair, and 5% poor.

Average temperatures for the week ending July 19 were near to slightly above normal. The temperatures ranged from 1 degrees below normal at Newport to 4 degrees above normal at several locations. The temperatures ranged from a low of 68 degrees at several locations to a high of 100 degrees in Little Rock and El Dorado. Rainfall for the week ending July 12 ranged from none at Hope and El Dorado to a high of 7.0 inches at Fayetteville. Overall, soil moisture supplies were 5% very short, 29% short, 59% adequate, and 7% 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. Officially, most of Eastern and Southern Arkansas is “abnormally dry”, which is effectively a mild drought. These data are collected as of Friday and do not reflect the rainfall that has occurred in much of Eastern Arkansas.

TIMING FOR BLAST FUNGICIDES

To minimize neck blast with current fungicides, the products MUST be applied preventatively – before the panicles have emerged fully from the boot. The photos below illustrate growth stages for application of the fungicides registered for neck blast prevention, based on the most severe disease pressure situation =[ highly susceptible variety (example = CL 151, Francis, CL 261) + erratic flood depth or shallow flood depth + field with a history of blast disease, etc.].

The photo first photo below is equivalent to late (fully swollen) boot to boot split (5% heading) and is appropriate for the first application. The second photo is equivalent to 50-90% heading and is appropriate for the secondapplication. Note that the bases of all panicles are still in the boot. We believe that when the base comes out, the neck of the panicle often gets infected at that point, and once the fungus is inside, fungicides cannot do much to prevent subsequent damage.

For one-shot applications to a field, the best timing is between these two growth stages, when about 1/3 of the panicle is emerging from the boot (30-50% heading), as seen in the first photo, far right tiller. It is always better to err on the early side of these stages, than later. In most cases, a late boot to boot split application can be followed by the second application in 5 days and things should work out.

While 19 oz of Stratego at full boot to boot split, followed by 12 oz of Quadris at the second timing is a good program to minimize neck blast in fields with severe disease pressure in Arkansas, 12 oz of Quadris followed by 12 oz Quadris and 21 oz Quilt Xcel followed by 12 oz Quadris are also effective choices. Please keep in mind that Stratego and Quilt Xcel have 35 day PHI restrictions while Quadris has a 28 day PHI, and fully read these labels for other guidelines and restrictions.

July 12 Rice Crop Condition and Progress

As of July 12, the USDA reports that 16% of the crop is heading. This compares to 8% last week, 5% this time last year, and a 5-year average of 3% for this week. Arkansas rice does not normally begin heading in June but we saw that happen in 2010. The crop was seeded earlier and we had 8 straight weeks with temperatures above normal. Thus, the crop has developed much sooner than normal. As of July 12, 21% of the crop is reported to be in excellent condition, 43% good, 30% fair, and 5% poor and 1% very poor.


Average temperatures for the week ending July 12 were near normal for the first time in several weeks. The temperatures ranged from 2 degrees below normal at Hot Springs to 3 degrees above normal at Keiser. The temperatures ranged from a low of 58 degrees at Batesville to a high of 97 degrees at Camden. Rainfall for the week ending July 12 ranged from a trace at Stuttgart and DeQueen to a high of 6.1 inches at Mountain Home. Overall, soil moisture supplies were 14% very short, 36% short, 50% adequate, and 2% surplus. These data are collected as of Friday and do not reflect the rainfall that has occurred in much of Eastern Arkansas. 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. Officially, most of Eastern and Southern Arkansas is “abnormally dry”, which is effectively a mild drought. These data are collected as of Friday and do not reflect the rainfall that has occurred in much of Eastern Arkansas.

The USDA acreage report indicates that we have planted record rice acreage in Arkansas in 2010. The planted acreage is estimated at 1.681 million acres, up 13% from last year’s planted acreage of 1.486 million. The 1.681 million acres is also 38,000 over the previous record acres of 1.643 million planted in 2005. If the forecasts for good yields are realized, record production is likely. However, the heat and drought coupled with the amount of rice planted on marginal soils are not likely to allow us to harvest a record yield. 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 (17%), and Jupiter (12%). These numbers are preliminary and may change as we get more information available.