Ganesh S Rao, Herbicide Expert, Srijana Consultancy. The author has 38 years of experience in herbicide sales, marketing, and new product development. Responsible for 100 plus global patents.
19 October 2023, New Delhi: The article address the gaps in the usage of herbicides at all stakeholder level, internal and external, and it is an effort to deliver the basics of herbicide till the advanced module depending upon the situation and requirements. The article mentions a few keywords used in the herbicides segment and also recommendations for herbicides for key row crops that include Rice, Soybean, Wheat, and Corn. This would help in keeping a check on the indiscriminate use of herbicides and tackle issues of resistance.
The above chart indicates the percentage of yield loss for the crops mentioned on the X axis, if proper weed management is not considered at the appropriate time, nonetheless, it is very important to control the weeds during the period of maximum crop weed competition.
Keywords Used In This Article
Weeds – A plant considered undesirable in a particular situation, growing where it conflicts with the interest of the grower economically as well as aesthetically.
Herbicides – Chemical actives used to control/kill undesirable vegetation. If they are organic, then are called Bio herbicides.
Window of application – If applied before the emergence of weeds then it is called pre-emergent, if applied after the emergence then called post-emergent.
Contact Herbicides – If herbicides kill weeds by contact action, then called contact herbicides. It doesn’t go inside the plant, at best is translaminar, for example – Glufosinate.
Systemic Herbicides – When herbicide is absorbed and transported through the plant. Example – Glyphosate.
Residual Herbicides – These are soil herbicides, they have long-lasting activity in the soil thus preventing new germinations. Example – Pendimethalin.
Choice of Herbicides to effectively control key weeds in Row crops
India grows around 44 million hectares of Rice every year. Transplanted rice occupies around 85 to 90 % of the total acreage and the balance is direct seeded rice.
For effective weed control in Rice for both cultures (TPR and DSR) the good practice is to start with Pre-emergent applications. We can use Pretilachlor, and Butachlor which can be tank mixed with Pyraxosulfuron, this would enable very effective control of broad-spectrum weed including sedges.
Whenever the field suffers water shortage, the efficacy of PE herbicides goes down significantly, and new weeds start emerging especially the grassy ones. The rice needs a minimum of 45 days of free growth without competition from the weeds. In this case, farmers may have to go for a second round sequential application of early post-emergent herbicides like Bispyribac sodium along with some other broad-leaf herbicides like Chlorimuron. If you see only narrow-leaf weeds then your choice would be fops like Cyhalopfop or Fenoxaprop as rescue applications.
Soybean is a very important oil seed crop grown in India. The weed system in the Soybean crop has evolved more in recent times. Many weeds are showing tolerance to frequently used herbicides like Imazethapyr. Under these circumstances farmers have to make a wise choice of application, the recommendation is to go for two applications, one pre-emergence followed by post-emergence, we call it a sequential application or programmed application.
We have many good herbicides available. My recommendations would be a mixture of Metolachlor + Dichlosulam or Metolachlor + Sulfentrazone, this application would provide effective control of Grasses, BLWs, and sedges. This can be followed with a sequential over-the-top application of ant Fops/Dims. Clomazone could be another active which can be used as a PE application.
Another important cereal crop of the country is grown in around 33 million hectares. There are two key segments, that is core resistant areas and emerging resistant areas, here I am referring to a super weed by the name of Phalaris Minor. This is a very noxious weed, if left uncontrolled can reduce the yield by 90%.
Here again, my recommendation is to follow the sequential application of pre-emergent herbicides followed by post. Pyroxasulfone along with Pendimethalin or Pyroxasulfone along with Metribuzin would provide very satisfactory control of most of the weeds including resistance Phalaris. In non-resistance geographies, farmers can use Pinoxaden or Clodinafop tank mixed with BLW herbicides.
This is an emerging crop for the country, the weed control concepts are picking up, however in general the overall knowledge on proper weed control is lacking among internal, external, and end customers.
Again it will be like other row crops like Wheat and Beans. Go with a basal application of S-Metolachlor/Metolachlor + Mesotrione and sequence with a post-emergent herbicide like Topramezone/Tembotrione tank mix with Atrazine if required. I highly recommend going with Pre-emergent to protect the crop from critical crop weed competition from day one. This would also help in resistance management. If the field has a significant population of sedges, then you may have to investigate the increased rate of S-Metolachlor.
In the years to come, the game of weed control is going to get tougher and tougher. It is because of many factors like indiscriminate use, and wrong dosage mainly to control the tolerant or resistant weeds, especially the ones with non-target site resistance. Emerging markets will see increased use of herbicides due to labor shortages and resistance, big markets will see increased resistance and more and more herbicides will become ineffective.
We cannot stop the resistance but surely delay the consequences of it with the right use.
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