2005 Pest Management Guide:

Sheath Blight
Sheath blight, caused by the fungus Rhizoctonia solani AG-1-IA, is the most important and widespread disease in Midsouth and Delta rice. Environmental conditions favoring development are hot, damp weather (80 to 90 degrees Fahrenheit), nighttime temperatures of 74 to 82 degrees F and high humidity (95 percent).

Symptoms usually appear on the sheath of the first leaf above the waterline about the time of internode elongation. An oblong, water-soaked lesion on the leaf sheath first appears at or near the waterline. The chlorophyll (green color) fades, and with time, the lesion becomes about 1 inch long and develops a grayish-white center surrounded by a dark purplish or reddish-brown margin.

Panicle Blight
The disease, caused by Pseudomonas glumae bacterium, is characterized by brown or straw-colored discoloration of florets on a panicle branch.

Lesions are not apparent below the grain, and panicle branches remain green. In some cases, there is some browning of the sheath, which may be confused with sheath rot. The grain stops developing and the florets turn gray. It is more severe in late-planted rice where the rice is maturing and late night temperatures are high.

Straighthead
A physiological disorder, straighthead is associated with sandy, sandy loam and some silt loam soils; fields with arsenic residues; fields with high organic matter such as those recently cleared of timber, those with a long history of fish production or pasture; or fields with large amounts of plant residue incorporated into the soil before flooding.

Under certain conditions, arsenic levels can increase in these soils where cotton has been grown and MSMA or other arsenical pesticides used. Panicles are upright at maturity because the grain does not fill or panicles do not emerge from the flag leaf sheath. Especially in long-grain varieties, the rice hulls may be distorted or “parrot beaked,” which is diagnostic for straighthead. But the symptoms may be uncommon on certain varieties.

Kernel Smut
Kernel smut, caused by the fungus Neovossia horrida (Tilletia barclayana), causes the endosperm of the rice grain to be replaced partially or completely by a black mass of smut spores. Usually only one to five grains per panicle are infected, but up to 15 percent of the kernels may be infected on highly susceptible varieties.

Disease symptoms typically occur when rice approaches maturity as black spore masses form in place of all the kernel or a portion of it. The disease is easily observed in the morning when the smut spores absorb water. Once expanded by the absorption of water, the spore masses push out of the hull to become visible. As the day progresses, the spore masses dry down to a powder and can easily be rubbed off on fingers. The black spores survive in the soil between crops.