Arkansas Rice: Reasons To Worry About Disease

Sheath blight in rice.

With all the rain from the tropical system known as Barry, sheath blight is picking up speed and we need to stay in front of it. Scout and treat based on threshold and cultivar susceptibility.

We can still outrun a lot of it, but you don’t know unless you look. The weather finally got hot for a few days, but now a cool-down to shockingly low levels is expected. We should be good overall but the low temperatures may actually be close to where problems occur. Low 60s at night in late July!

Warm temperatures and high humidity favor sheath blight. The disease usually starts on the sheath from a compact fungal mass called sclerotium at the water line and then spreads vertically to the height of the crop and later horizontally by plant-to-plant contact. Sheath blight in some cultivars weakens the stature of the plants and can cause lodging.

Most rice fields received a lot of water from Tropical Storm Barry. It is sure humid and temperatures currently are high enough to favor the activity of the fungus.

We have reports of some level of sheath blight on RT XP760 in Arkansas County on row rice and sheath blight reaching up to the panicle in Randolph County on conventional rice.

When sheath blight affects the upper three leaves including the flag leaf before grain fill, the impact on grain quality and yield would be high. With present weather conditions, scout more frequently and suppress the development of the pathogen with one of the recommended fungicides.

Leaf Blast: Stay On Your Toes

Leaf blast has not been severe except in a few isolated cases. To date, leaf blast has been reported from the counties Randolph, Lawrence, Jackson, Woodruff, Poinsett and Monroe. Varieties on which it’s been found include Titan, Jupiter, Diamond, and CL151.

Continue scouting for leaf blast and based on the history of the field, varietal susceptibility, and your management, plan for fungicide applications to protect the crop from devastating neck and panicle blast. Near 100% grain yield loss can happen if your field is left without fungicide management intervention.

Two fungicide applications are recommended:

  • The first from late boot to 10% head spiked out from and boot.
  • The second when the heads are 50% to 75% spiked out from the boot.

In both cases make sure the necks are still in the boot.

Once the panicle necks are out of the boot, it is already too late for fungicide application. Strobilurin fungicides are the available fungicides for use in Arkansas. Except Sercadis and Elegia fungicides in the above table can be used to suppress blast from causing neck and panicle blast.

Smut – Preventive Measures

Remember if your field has a history of kernel smut or false smut, your cultivar is susceptible and received excessive nitrogen fertilization, fungicides containing triazoles (propiconazole or difenconazole) need to be applied as protective between early boot and midboot stages (Fig. 4).

For adequate canopy coverage, a minimum of 10 gallons of water per acre is encouraged to be used to apply the fungicides. Stand-alone fungicides such as Tilt, Bumper, Propimax, or combination fungicides such as Quilt Xcel, Amistar Top, or Stratego can be used.

Remember these points:

  • Well managed fields benefit more from fungicide application.
  • Fungicides applied at recommended timing and rate maximize their benefit.
  • Fungicides mixed and applied using adequate volume of water provide better coverage and benefit.

Rice College Registration Closes July 28

If you would like to attend the 2019 Rice College at the Rice Research and Extension Center on Aug. 1, sign up soon! Space is limited and the deadline is approaching next weekend.

Click here to register.


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