Louisiana Rice: Updates And Fungicide Considerations

Sheath blight in rice.

The bulk of northeast Louisiana’s rice crop is ready for the permanent flood. However, wet soils have limited opportunities to apply our preflood nitrogen fertilizers on dry soil. Applications of early season N into standing floods are very inefficient and require additional applications of N to make up for this loss of efficiency.

If possible, it is always best to wait for the ground to dry before applying the preflood nitrogen and stick to the standard two-way split nitrogen fertilizer application recommendation.

Here in southwest Louisiana we continue to see stress symptoms on rice associated with flooding and high water in early May. Bronzing-like symptoms as well as brown spot can be seen on many fields. Brown spot is caused by the fungus Cochliobolus miyabeanus. Brown spot is generally brought on by some kind of external stress.

The most common stress where the fungus appears is when rice is deficient in nitrogen. Both the flooding-induced bronzing and brown spot symptoms will go away with a little nitrogen fertilizer, warm weather and sunshine. Unfortunately, the weather has been overcast and rainy for several days and looks to be the same in the coming days. These conditions have delayed the recovery of the rice, and it is worrisome to keep looking at sick rice that does not seem to want to recover. I hope the sun comes out soon.

Some heading has started in the southwest part of the state on a limited basis. Another concern with the recent rains is that heavy mid-day rains when the florets are open can cause grain sterility and reduce yield potential.

Really, the only thing these conditions are good for is disease. Disease incidence has really picked up in the last week, especially sheath blight. Be sure to start scouting your field. Dr. Don Groth has put together his fungicide rate recommendations below and he also addresses the reported limited supply of the Sercadis fungicide.

Once the rice is headed, it is also time to start scouting for stink bugs. Dr. Blake Wilson has also contributed an article on best management practices for stink bug management in rice. 

Sercadis vs Elegia Fungicide

We have heard several reports of Sercadis shortages in South Louisiana for rice sheath blight control. Sercadis, in the Fungicide Resistance Action Committee (FRAC) Group 7 mode of action, has good activity against sheath blight and the strobilurin (FRAC Group 11) resistant sheath blight fungus.

Elegia, also in the FRAC Group 7, is another fungicide with similar activity against both the wild and resistant sheath blight fungi. Both fungicides are good choices for control of the strobilurin resistant sheath blight fungus and as a rotation option for strobilurin fungicides resistance management to delay resistance development.

Sercadis is applied as a single 6.8 oz/A application at mid-boot, or as two 4.5 oz/A applications at early boot and late boot. Elegia is applied at early to mid-boot at 32 oz/A. Propiconazole (Tilt, Bumper, PropiMax etc.) can be tank mixed with either product to expand and increase activity against Cercospora, grain smuts and other rice diseases. Propiconazole has some activity against sheath blight and is in FRAC Group 3.

There are reports of resistance to the FRAC Group 7 fungicides in the sheath blight pathogen population. At this point, results are contradictory and confusing.  The probability is that Rhizoctonia solani, the sheath blight pathogen, has become tolerant to the Group 7 fungicides due to extensive use on rice and soybeans. Other products with different modes of action will be needed in the future. However, at this time it this resistance does not appear to be wide spread nor prevalent in most rice fields. Studies are under way to confirm resistance and determine its distribution.

Suggested Fungicide Rates and Timings for Louisiana

Here are some of the fungicide suggestion I have made the last couple of years. Adding Propiconazole (Tilt or other products) adds Cercospora and kernel smut activity. If you have the strobilurin resistant sheath blight fungus you have to use Sercadis or Elegia.

If you have blast you have to use a strobilurin fungicide (Quadris, Stratego, Quilt, Quilt Xcel). Rotation of fungicide activity is always a good idea. Remember to scout so you know which diseases are present and the rice’s growth stage.

Fungicides:

Stratego: 19 oz/A (you can add 3 oz/A Tilt).

Apply at boot to 35 days preharvest

Quilt Xcel: 21 oz/A (you can add 3 oz/A Tilt)

Boot, no heading

Quilt: 28 oz/A (you can add 2 oz/A Tilt)

Boot, no heading

Quadris: 12 oz/A boot to heading (you can add up to 10 oz/A Tilt but no heading then)

Sercadis: 6.8 oz/A (you can add up to 10 oz/A Tilt)

Boot

or 4.5 oz/A followed by 4.5 oz/A 7-14 days later

Elegia:  32 oz/A (you can add up to 10 oz/A Tilt)

Boot

Tilt/PropiMax/Bumper/etc.

Boot no heading

8-10 oz/A or 6 oz/A followed by 6 oz/A 7-14 days later

Timing:

  • Boot (2-4 inch panicle) for SB, Cercospora and Kernel smut
  • Heading (50-70% heads emerging or boot split) for SB, Cercospora, Blast

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