Red rice control

Aggressive, difficult to identify and holder of genetic, morphological and biochemical characteristics very similar to those of the cultivated grain, red rice challenges producers and researchers. The use integrated management tools, which does not privilege the isolated use of one Only technology is the way to prevent and minimize losses.

O harmful rice popularly known as red rice belongs to the same species of cultivated rice (Oryza sativa L.), both originating from Asia. From this region, probably as seed contaminant from cultivated rice, spread to all other who grow rice around the world. Worldwide, harmful rice is the species responsible due to the greatest losses in areas cultivated with rice. In Brazil, this species is widespread in the main producing areas, with a reported reduction in productivity of up to 100%, when the occurrence is high.

 Red rice or black rice initially received This name is due to the color of the pericarp. As the years passed and the I continue to live with cultivated rice, its color and shape have changed. It is currently possible to find grains with different colors, even white. and with a similar shape to that cultivated. The process of phenotypic approximation and genotypic pattern observed in weedy rice occurs due to gene flow between these genotypes, where the cultivated rice acts by donating characters via pollen to the harmful rice. This, in turn, behaves as a good acceptor during the flourishing. However, it is important to highlight that the crossing rate is low, not exceeding 5%, but enough to provide this approximation of characters between cultivated and weedy rice.

A joint presence in the field of harmful and cultivated rice easily generates confusion in identification. In general, harmful rice presents itself with greater initial vigor, larger stature and reduced cycle. In the presence of natural threshing and seed dormancy are the characteristics that provide natural reseeding and future reinfestations of this weed. In this context, in areas with the presence of harmful rice, every year they are added to the soil new seeds of this species, which can remain dormant and viable in the soil for up to 30 years. Allied to this, uneven germination and emergence throughout of the years has the potential to increase the variability and adaptability of rice harmful to the cultivation system. 

A presence of harmful rice in rice growing areas causes losses direct and indirect to culture. Directly, the losses are caused as a result of its high adaptability to the production system and thus high competitiveness for essential resources such as water, light and nutrients, resulting in less development and crop productivity. Indirectly, the presence of harmful rice during Harvesting depreciates the harvested product, generating discounts on the amount paid to the producer. In industry, contamination with harmful grains harms processing of rice, reduce the yield of whole grains and the final quality of the product, in addition to limiting the price received for the product. It is important to highlight that the grains of harmful rice are edible, but do not have the palatability and cooking required by the consumer. Consequently, the presence of grains of harmful rice next to the cultivated one significantly reduces the value added to the product.

O efficient management of this weed is required in order to reduce impacts on culture and the final quality of the product. However, for belong to the same species as cultivated rice, and have practically the same genetic, morphological and biochemical characteristics, the control of this plant weed is difficult. The management of harmful rice in the irrigated and pre-germinated is based on the continuous presence of water in the area, avoiding germination and establishment of the invader. This management tool has been used for many years, however it does not control plants already established in the area. Therefore, a chemical control was developed using of selective herbicides to crops.

O advent of technology Clearfield (CL), allowed control of the harmful rice after its establishment, without harming the crop. That production system is based on the use of cultivars tolerant to herbicides. chemical group of imidazolinones. The herbicides used were specially developed for the soil and climate conditions of Brazil and allow for a selective control of this invader. CL rice cultivars are not transgenic and rather, resulting from induced mutations that gave rise to plants resistant to these herbicides. This system provides the receipt of certified seeds free from harmful rice by producers and, furthermore, makes it possible to reclaim abandoned areas as a result of high infestation. A adoption of this technology by producers was broad and, currently, the rice cultivation CL occupies 74,4% of the area sown in Rio Grande do Sul, the main national producer.

A maintaining technology efficiency CL was linked to the non-continuous cultivation of these cultivars in the same area for more two years. With subsequent conventional rice cultivation or crop rotation crops or even livestock. In many cases this recommendation has not been respected, aggravated by late controls and use of low doses of recommended herbicides. In this scenario, the escape of harmful rice was observed and, its presence in the area allowed crossbreeding with cultivated rice. In this way, the resistance to herbicides was transferred to harmful rice, making them tolerant, reducing the efficiency of the technology. The evolution of resistance to imidazolinones in harmful rice, is also associated with contamination of seeds kept under the producer's control and used in the following harvest.

The use of cultivars CL cannot be the only tool used in the management of harmful rice, requiring additional management practices management, implemented even before sowing. The use of seeds certified must be recommended, avoiding the introduction of plant seeds weeds at the time of sowing. The practice of using saved seeds by the producers themselves in the following harvest must be extinguished, in order to avoid this contamination at the time of sowing. Therefore, when thinking about the management of harmful rice, the seed is the most important input and the Certification origin becomes essential.

Pre-sowing management of rice based on the use of glyphosate and paraquat has resulted in benefits significant effects on weed control, mainly in reducing the weed bank. seeds. Both reduce the infestation of harmful rice due to desiccation in advance, leaving the area clean for longer. Initially, you must stimulate the germination of existing seeds in the bank, for later desiccation or mechanical control. This action facilitates prior control, enhancing the establishment of rice cultivated in an area free from the invader, increasing the effectiveness of water depth management and chemical control in the period post-sowing. Together, these actions facilitate control and slow down evolution. of weedy rice resistant to herbicides, especially imidazolinones.

In the irrigated cropping system, the presence of the water layer must be permanent, with entry after establishment of the crop and removal at harvest. Weed control is most effective when water entry is anticipated, with rice at a stage of 3 leaves to 4 leaves. Additionally, the efficiency of herbicides is directly related to water input, or In other words, the sooner the better, as delay favors the establishment and development of weeds.

 Observation of harmful rice escapes, given the management actions used, it is not uncommon, requiring control of these escapes in order to prevent plants from producing seeds and its deposition in the seed bank. It is worth noting that a single weedy rice has the capacity to produce more than 2000 seeds, considering that 50% of them will be viable in the first year, there will be 1000 new plants in next harvest. In this sense, strategies that involve the rouging must be considered, promoting the removal of plants undesirables before they form grains. At the rouging chemical, glove and chemical bar are used, associated with the application of a systemic herbicide. The use of chemical bars is only possible in the control of harmful rice of high height compared to the cultivated one.

They should soon hit the market national new technologies aimed at controlling harmful rice. The system Provisia will provide cultivars resistant to herbicides from the aryloxyphenoxypropionate chemical group (FOPs) and Full Page to ACCase inhibitor herbicides. To date, they are in the testing phase. Taking into account the current scenario, the incorporation of technologies and available knowledge still promotes control of harmful rice in a satisfactory. However, success in this task will not be achieved with isolated use of a technology but rather through the integrated use of management tools.

Article published in issue 218 of Cultivar Grandes Culturas, July 2017.