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Rice planting window opens, new insecticide ready for weevil

In general, fairly early planting of rice is desirable for maximizing yield and quality, as well as increasing the potential for a successful second crop in the southern part of Louisiana. Sometimes, however, planting can be too early.

Here on the Rice Research Station at Crowley, we planted our first rice of 2008 on Feb. 29. This is part of our water-seeded date-of-planting studies we conduct each year to look at the effects of different planting dates on the performance of varieties and experimental lines.

This February planting date is normally considered too early and is about two weeks ahead of the LSU AgCenter’s recommended optimum planting dates for southwest Louisiana, which run from March 15 to April 20.

If everything works to our advantage, and we are successful at establishing good stands at this earliest planting date, we will normally have good yields. Unfortunately, in about 10 of the 20 years we have been conducting these planting studies, we have encountered problems that have led to very poor stands on this early date. This led to poor yields later in the season.

Many of the problems that can plague early-planted rice in the region have also caused us problems in these studies at one time or another through the years. Rice seedling growth and development are certainly temperature dependent. The lower the temperature, the slower the growth and development of rice seedlings.

Here are some rules of thumb for rice:

• At or below 50 degrees, little or no rice seed germination occurs.

• From 50 to 55 degrees, germination increases but not to any great extent until above 60 degrees F.

• Plant survival is not satisfactory until the average daily temperature is above 65 degrees.

Another issue is seedling disease. The two major seedling diseases of water-seeded rice are caused by fungal organisms from the genera Achlya and Pythium. Damage from seedling diseases is directly related to low temperatures and slow seedling growth under these conditions.

Low temperatures, while slowing the growth and development of rice seedlings, do not affect the activity of these disease pathogens. Thus, under low temperatures the disease can overwhelm the seedling, which under higher temperatures might be able to outgrow the effects of the pathogen.

Another major issue with early-planted rice is depredation by blackbirds. Our small date-of-planting research area is normally the first rice planted in Acadia Parish, and if the blackbirds find it, it can be history in a short time.

Blackbird depredation on seeded rice is normally much more severe on early-planted rice for two reasons: (1) typically, the migratory flocks of birds head back north as spring approaches, which lowers the total number of blackbirds in the region at later dates, and (2) the “dilution effect,” meaning as more rice is planted, there is less potential for a huge number of birds congregating in any one particular field.

As mentioned earlier, general recommendations for rice planting dates are March 15 to April 20 in south Louisiana and April 5 to May 10 in north Louisiana. The earlier we can plant and establish a good stand, the better chance we have for maximizing yields and quality as well as increase the potential for a successful second crop in south Louisiana.

Similarly, late-planted rice can also present challenges. In general, our planting date and other research studies have shown trends for lower yields and quality as we plant much later than mid-April in south Louisiana and mid-May in north Louisiana.

Later-planted rice, in general, has a greater chance of being exposed to excessively high temperatures later in the growing season, which can certainly have deleterious effects on both yield and quality.

Also, the potential for damage from most insects and foliar diseases is greater in later-planted rice.

While ideal planting dates will certainly vary from year to year because of specific climatic conditions in any one year, the dates listed above tend to be the best target dates for Louisiana producers to try to get their rice fields planted.

Louisiana rice producers will have a new insecticide available for use for the first time in the 2008 crop. Dermacor X-100 (chemically known as rynaxpyr) has been granted a Section 18 exemption for use as a seed treatment on dry-seeded rice (drill-seeded or dry-broadcast) in Louisiana and Texas for the 2008 growing season for the control of rice water weevil larvae. The seed treatment will be applied by certified seed dealers.

Research conducted by Mike Stout at the Rice Research Station has shown this product to provide excellent control of rice water weevil larvae, which are typically the most damaging insect pests in Louisiana rice production.

Louisiana has also been granted a Section 18 exemption for 2008 for use of Trebon (chemical name etofenprox) for the control of the rice water weevil adults. This product, which also was available for use under a Section 18 in 2007, is applied as a granular formulation when adults are present in the field.


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