Strategic Weed Control in Hybrid Rice
“Weed” is a harsh and very condemning term that we can coin for a plant whose economic importance and value is yet to be discovered. Weed is a plant that is unwanted at a particular space and time. Such unwantedness can be traced by generalizing that it can do more harm than good under such particular condition.
These are some of the possible damages weeds can do in ricefields.
1. It reduces yield due to competition with crops for light, water, and nutrients.
2. It reduces quality of produce through adulteration.
3. It blocks irrigation and drainage-canals.
4. It interferes with cultural practices.
5. It makes harvesting difficult.
6. It harbors insect pest and pathogens that attack the rice.
In comparison with other pests, weeds do not show visible damage to rice and because of this farmers do not recognize the yield reducing effect of weeds. Some farmers often neglect their presence, and will only remove when weeds have already grown vigorously and have already produced seeds. On the other hand, some farmers are so meticulously concerned to achieve a weed-free field in the whole cropping season. Both situations are an example of improper weed management. Removal of weeds after completing their life cycle is already too late because the weeds have already established themselves in the ricefield. Maintaining absolutely weed-free fields is too costly and time and labor consuming. Both approaches will reduce – farmer’s productivity either by reduced yields or by unnecessary channeling of resources to weed control. Weeds should only be controlled only when they pose significant yield reduction.
To avoid significant yield losses, we must observe a timely weed management. Providing a good head start for the rice will pose less competition, thus weed management should be done early in the cropping season within the first 40 days. The said 40 days corresponds to the critical period of crop-weed competition.
WEED MANAGEMENT STRATEGIES
Over the years, weed management strategies have evolved from manual to mechanical to the use of herbicides. Mechanical control includes some cultural practices, including the seedbed preparation, crop rotation, land leveling; levee construction, seed selection and water management.
Moisture availability, financial capability of the farmer, and cultural practices significantly contribute to the reduction of weed problems, control, and cost. These are some of the strategies that farmers can employ.
1. Use hybrid varieties with high percentage of productive tillers. The use of hybrid seeds from reputable sources such as Pioneer Hi-Bred will ensure farmers that the seeds have high germination percentage, minimal or no weed seed mixtures. The use of hybrid seeds also assures an increase in yield. Planting of hybrid rice follows a planting scheme, one seedling per hill with given dimensions, thus population density and spacing is properly observed. Weed management is easier because planting is more organized. Correct choice of hybrid variety should also be considered.
Remember that a weed is any plant that competes for basic necessities of your crop. Therefore, non-productive tillers can be considered as weeds! Choose hybrid varieties that have high percentage of productive tillers such as Pioneer’s PHB71. Be wary of varieties that have recommended spacing of less than 15 cm between hills as these varieties tend to produce non-productive tillers if planted in more than 15-centimeter spacing.
2. Good land preparation. The farmers’ first line of defense against weeds is good land preparation. It is one of the standard cultural management practices for good seedling establishment. A field that is properly prepared will have good water management and reduced weed population. Good land preparation involves one round of plowing, followed by a weekly interval of 2-3 harrowing and leveling. Puddling uproots weeds that grow after plowing and buries them under the layers of mud. The process also allows for weeds to flush and then removed by the Subsequent harrowing. Research shows that cultivation stimulates first weed flush by 50 percent to 79 percent (Baki and Jeremiah Jr., 2001 and Paller. 2002). Leveling, on the other hand, become very important by eliminating the areas that were inadequately flooded and hence, ideal for the growth of weeds.
Good land preparation will prevent the re-establishment of the previously existing weed population.
3. Good water management. Flooding is commonly practiced to control weeds, especially in transplanted irrigated rice. The flooded condition will inhibit the germination of most weed species associated with rice because of reduced oxygen supply and accumulation of carbon dioxide and other gaseous products o: anaerobic respiration.
Research shows that it is desirable that the field is flooded 2-3 days after transplanting at a 5 cm water depth. In direct seeded rice, flooding is done at 7-10 days, accompanied with pre-emergence and early post emergence herbicides that take its full effect when the field is in the saturated condition. Late emerging weeds can be further controlled if the water is maintained at 3 cm-5 cm deep throughout the season.
Intermittent irrigation enhances growth; however minimal application of herbicides can control weeds.
4. Weed Control Action Indicator. The Weed Control Action Indicator (WCAI is a tool used to determine if there is need for a subsequent weed control after implementing an initial weed management strategy. WCAI was developed at UPLB and has been tested in different agronomic crops, especially in rice. The parameters being used as basis for the decision making were percentage weed cover (WC) and relative weed height (RWH) of the crop over the weeds.
At 15 DAS, if RWH > 20% and %,WC >5%, there is a need for a subsequent weed control.
At 30 and 45 DAS, if RWH > 30% and %WC > 5%, there a need for a subsequent weed control.
By using WCAI, farmers are able to implement different weed control options such as spot weeding or use oi post-emergence herbicides application Research shows that WCAI can reduce weed control cost by 6 percent to 79 percent.
5. Use of herbicides from reputable suppliers. Herbicides are agrochemicals that either kill or suppress the growth of weeds, thus farmers who will employ this control should be properly equipped with the required skills and knowledge on how to apply them. It is a must that farmers should have a basic identification and knowledge about weeds and the intensity of the infestation. Proper timing and method of application should also be observed.
Make sure that you are using herbicides from a reputable company with excel after sales support such as DuPont. An excellent pre- and early post-emergence herbicide is DuPont’s Londax. Almix is a recommended post-emergence herbicide for rice. Consult your local DuPont technical support if you have questions regarding these herbicides.
By Mar Nas and Steve Ching