Rice is a Complex Crop to Produce

Steve Linscombe

LSU AgCenter

H. Rouse Caffey Rice Research Station/Southwest Region

While all agronomic crops require meticulous management, rice is considerably more complex. Much of this complexity is due to the fact that rice is grown under flooded conditions for most of the growing season.

Fifteen years ago, most Louisiana rice was water-seeded as a means of combating red rice. With the advent of Clearfield rice, which allows for herbicidal control of red rice, much of Louisiana’s rice today is dry-seeded, either drilled or broadcast into a dry soil. In dry seeding, rice will either germinate where soil moisture is adequate or fields can be flushed where soil moisture is lacking and rainfall does not occur soon after seeding. After seedlings emerge, they will increase in size until the plants are large enough to tolerate a permanent flood. This is normally when the plants have reached 4-5 inches in height, when they will have developed four to five leaves.

The period from seeding until the permanent flood is established is critical for several management practices. Most herbicide applications are applied during this period and timing of these applications is important. Dr. Eric Webster, LSU AgCenter rice weed scientist, continually stresses that the vast majority of herbicide failures occur when the herbicide is applied too late, and the target weeds are too large for satisfactory control. The most effective weed control is intimately associated with proper timing.

Another important practice where timing is critical is nitrogen fertilization. The bottom line is that the most efficient and effective way to apply nitrogen to rice is to apply the proper rate (at least two-thirds of the growing season requirement) uniformly to a dry soil when the plants are ready for a permanent flood. Then, permanently flood the field as quickly as possible. With this system, most of the applied nitrogen will be moved down into the root zone by the floodwater and be readily available for use by the plants as well as protected from nitrogen loss, which can occur in flooded soil systems.

Again, it is critical to flood the field within five days after the nitrogen has been applied to prevent excessive loss of the nitrogen from volatilization. However, in those cases where fields cannot be flooded that quickly, there are products available that will inhibit nitrogen loss. These products can be applied to the urea nitrogen prior to application. Research conducted by Dr. Dustin Harrell and others at the H. Rouse Caffey Rice Research Station helped make these products available.

Most rice seed used in Louisiana today is treated with a seed treatment insecticide to control the rice water weevil which is the most troublesome insect pest in the state. Major damage in rice from this pest is caused by the larvae, which migrate to the root zone and physically destroy root tissue by feeding on it. If rice seed is not treated, a pyrethroid insecticide can be used to control adults. In this case, the insecticide application must be made when adults are present and prior to their laying eggs, which will later hatch out to larvae. Typically, the adult will not infest a rice field until the flood has been established.

Research conducted by Dr. Mike Stout has shown that shortly after the flood is applied, fields must be scouted to determine if and when a threshold level of adults is present. The treatment must be made shortly after that level is reached. Delay will result not only in a lack of control but also the expense of an ineffective insecticide application.

Fungicide applications for effective disease control also require careful timing. Dr. Don Groth has spent much of his career at the H. Rouse Caffey Rice Research Station fine-tuning timing recommendations for the most effective and economical rice disease control. The three major diseases that fungicides are applied to control are sheath blight, blast and narrow brown leaf spot (Cercospora). However, fungicidal control of rice diseases has become more complex in southwest Louisiana in recent years because of the identification of resistance to certain fungicides used for sheath blight control in an increasing number of fields. Another complication is that the best timing of the applications is typically not identical for all three diseases. Also, typically more than one fungicide will be needed to control the three major diseases.

In spite of these complications, Dr. Groth has been able to demonstrate how to split the difference, make the application at one time and still accomplish acceptable control of all three diseases in most instances. However, for this to work, the timing is critical and centers on when the plants begin to exert the panicles where the grains will form. If you miss this timing by even just a few days, the level of control can be reduced from very good to unacceptable. The single application saves money without sacrificing good disease control and assumes that the proper fungicides are used for specific field conditions.

There are many other examples where timing is critical in rice production. These include 2,4-D herbicide application prior to the panicle initiation stage, midseason nitrogen application, draining fields to prevent straighthead disorder, insecticide treatments to control rice stink bugs and draining fields prior to harvest – just to name a few.

Rice is a difficult crop to produce, and this further illustrates how Louisiana rice farmers need to be excellent at doing what they do.

This project was partially supported by USDA National Institute of Food and Agriculture.

Permission granted March 15, 2017 by B. Leonards (LA Farm & Ranch) to republish article on www.lsuagenter.com.

Rice as the panicle first emerges. This is an appropriate timing for most fungicide applications.