Above is a photograph sent to me by B. D. Fontenot. I forwarded it to Dr. Groth who identified the disease as Black Kernel. It is a fairly common fungal disease generally regarded as a minor problem. For some reason this year there is quite a bit showing up and the rainy weather will probably make it worse. I noticed some in our field in Cameron parish but it was scattered and much lighter than shown in these panicles.
It should not be confused with Kernel Smut which also causes black kernels. The smut fungus actually invades the grain and replaces it becoming visible when it begins to ooze out between the hulls. Black Kernel attacks from the outside and covers the grain completely.
Dr. Groth said he has seen False Smut too. This one causes the development of very conspicuous greenish masses in the panicle. They change from greenish to bright orange with maturity.
The following was put together by Dr. Don Groth to make everyone aware we are seeing lots of blast this year. I have had several calls today and some last week too.
Leaf blast found in several rice fields earlier than normal this year
Rice Research Station, LSU Agricultural Center
Leaf blast has been found in several rice fields in southern Louisiana on several varieties earlier than normal this year. In experimental plots significant leaf blast has been found on Bengal, Caffey, CL151, CL152, CL162, CL181, CL261, Cypress, Jupiter, Rex, and Wells. In several commercial fields a fungicide application at vegetative growth stages has been necessary to protect the rice from severe leaf blast. Remember, blast is one of the most explosive and damaging rice diseases and must be managed effectively and aggressively.
Blast can be found from the seedling stage to maturity. The leaf blast phase occurs between the seedling and late tillering stages. Leaf spots start as small white, gray or blue-tinged spots. They enlarge quickly under moist conditions to either oval or diamond-shaped spots or linear lesions with pointed ends with gray or white centers and narrow brown borders. Rotten neck symptoms appear at the base of the panicle, starting at the node. The tissue turns brown and shrivels, causing the stem to snap and lodge. Panicle branches and stems of florets also have gray-brown lesions at the branch joints. The pathogen can also infect stem nodes and leaf collars. If temperature exceeds 95 degrees blast development tends to slow down significantly.
Losses due to blast are escalating with current practices that require draining fields for insect control, correction of herbicide damage, or to prevent straighthead. Under upland conditions, rice plants can be killed by leaf blast. Head damage can range from a few sterile seeds to complete sterility. Milling losses can be significant due to poor grain filling. Lodging can occur with node blast.
The most important management practice is to maintain the flood. This year flood early and flood fast to help protect the crop especially susceptible varieties. Dense stands and excessive nitrogen fertilizer both also tend to increase disease damage. Blast is worse in late planted fields, fields with light and sandy soils, and in tree-lined fields. Fungicides are available for reducing blast but fungicide timing is critical. Leaf blast present in the field isthe indicator to spray for blast. Remember when scouting for disease also scout for rice growth stages so fungicides can be applied in a timely manner. If a single application is going to be used it should be applied when 50 to 70 percent of the heads have just begun to emerge, because fungicide application before or after that growth stage will not provide good control of this disease. Under severe disease pressure, which we seem to have this year, two applications may be necessary the first at the boot growth stage (2- to 4-inch panicle) followed by an application at heading as described above. The first application controls the leaf blast present in the field reducing spore production which allows the heading application a better chance of controlling the head infections. Fungicides containing the active ingredient trifloxystrobin (Gem and Stratego) have the best blast activity but azoxystrobin containing fungicides (Quadris, Quilt, and Quilt Excel) also have good blast activity. Gem fungicide is not readily available but the Stratego fungicide is priced less and has propiconazole already in it for broader disease control including Cercospora. The rate of Stratego is 16-19 oz/A, Quadris 12-15 oz/A, Quilt 28-34 oz/A, and Quadris Xcel 21-28 oz/A. In the areas where there strobilurin resistant sheath blight pathogen Rhizoctonia solani is present, it is recommended that the Section 18 fungicide Sercadis, which has no blast activity, is applied at boot and a blast active fungicide is applied at heading.
Below are two photographs taken in Vermilion parish. Dr. Groth had earlier examined leaves collected from the same field and suspects the disease is brown spot. Interestingly, the spots were mainly on the lower leaves indicating the environmental conditions favorable for the development of this weak pathogen were no longer present.