Louisiana Rice: Early Season Challenges for 2021

    Zinc deficiency in rice. Photo: University of Arkansas

    Every year is unique when it comes to the challenges that we face in a rice growing season and 2021 is no exception. The first few weeks of March were somewhat normal, and we were able to plant a significant amount of rice in southwest Louisiana in a short amount of time.

    The last week of March and the whole month of April were much more challenging. The weather across the state during that time was either wet, overcast with little sunshine, cold, or a combination of the above.

    These conditions have caused a plethora of problems with the rice crop, and I would like to cover the most commonly asked questions we received and their respective recommendations.

    The most common problem with the poor growing conditions this year is stressed rice that is not growing and looks sick. This can be caused by many things. One common cause is stress from a recent herbicide application.

    While many herbicides are labeled and safe to apply in a rice crop, they can still cause a significant amount of stress to the rice until the it can metabolize the herbicide. This can happen very quickly in good growing conditions but can be very slow in wet, overcast, and cold weather.

    The remedy for this is simply warm weather and sunshine. If there is water on the field, this can sometimes make the herbicides hotter, and draining will help the rice recover.

    A second condition this year is cold-induced zinc deficiency. This often occurs early in the season when the rice plant does not have a developed root system and is unable to take up zinc in the soil. This can often be difficult to identify on very young rice, but as it gets older, it can be identified by the reddish splotches on the leaf often referred to as bronzing. In this case, many growers elect to apply a foliar zinc herbicide to the crop.

    Zinc soil applications are also beneficial; however, until the rice plant is actively growing again, and the root system is larger, the rice plant will have some difficulty getting the zinc needed. If water is standing on the field, it will need to be drained to help the rice recover.

    During the less-than-ideal growing conditions that we have had thus far, there has been a lot of rice that has reached tillering and needs to be fertilized with nitrogen. The most common question regarding this is if nitrogen should be applied or delayed until better growing conditions? The answer depends on each individual situation.

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    In the case of drill-seeded rice, if the application of urea can be applied on dry ground and flooded quickly, it is ok to apply the nitrogen. In this scenario, the nitrogen will be safely stabilized in the anerobic (no oxygen) flooded soil conditions and the rice can take it up at its leisure when it begins growing again.

    In water-seeded rice where nitrogen will have to be applied into standing water, it may be best to wait for better growing conditions. In this scenario, nitrogen can be lost very quickly due to various loss mechanisms. When nitrogen fertilizer must be dropped into standing water, you will want to wait until better growing conditions (warmer weather and sunshine) so that more of the applied nitrogen can be taken up by the rice plant before it is lost.

    In a situation where water-seeded rice is well into tillering or has signs of nitrogen deficiency, it is probably best to go ahead and apply that nitrogen knowing that you will most likely have to apply more nitrogen later to make up for the lost nitrogen.

    Nitrogen deficient rice can be identified by the chlorosis (yellowing) of the older leaves first. Nitrogen deficiency symptoms are often accompanied by small circular reddish-brown spots (brownspot disease).

    Brownspot, caused by the fungus Cochiobolus miyabeanus, can be triggered by several plant stresses, but nitrogen deficiency is the most common stress associated with the disease. This is also the most common fungus that causes seedling blight. We have seen a tremendous amount of seedling blight early on this season.

    Another field issue we have seen this year is the early appearance of the South American rice miner. This pest feeds on new leaves in the whorl of the plant. As new leaves emerge you can see where the pest has fed, and this causes the field to have a ragged look.

    Unfortunately, an insecticide is ineffective for the pest since it is protected in the whorl. Like most of our other issues we have seen thus far this year, the rice will eventually outgrow the damage once we have better growing conditions.




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