Herbicides are often chemical agents used to eradicate or stunt the development of undesirable plants, such as invasive species and weeds in residential or agricultural areas. The simplicity of application, which frequently results in labour cost savings, is a significant benefit of chemical herbicides versus mechanical weed control. Most herbicides are generally safe to animals and people, but they can cause severe death of nontarget plants and the insects that depend on them, especially when sprayed aerially.
1. Spraying
2. Broadcasting
Factors determining the methods of application are:
- Situation of Weed-crop
- Different type of herbicides
- Mode of action and selectivity
- factors in the environment
- Affordability and ease of use
Depending on the target site, the herbicides are classified into
1.Soil applied herbicides
2.Foliage applied or foliar herbicides
The following table lists the various ways that these herbicides are applied:
| Soil application | Foliar application | ||
| 1. | Surface | i. | Blanket spray |
| 2. | Sub surface | ii. | Directed spray |
| 3. | Band | iii. | Protected spray |
| 4. | Fumigation | iv. | Spot treatment |
| 5. | Herbigation |
1. Soil application of herbicides:
(i) Surface application
Different techniques by which these Soil active herbicides are administered equally on the surface of the soil either by spraying or by broadcasting. The sprayed herbicides are either left undisturbed or integrated in to the soil. To stop the herbicides from volatilizing and photo-decomposing, incorporation is used.
eg-
- Fluchoralin, for instance, should be left alone in an irrigation system.
- Incorporated under the condition of rainfed
(ii). Subsurface application
Herbicides are applied in a concentrated band 7 to 10 cm below the soil’s surface in order to suppress perennial weeds. Under the protection of a sweep hood, nozzles of this particular type were first inserted beneath the earth.
e.g.
herbicides that include carbamates Cyperus rotundus
Control of Convolvulus arvensis with nitralin herbicides
(iii). Band application
Application to a confined area along the crop rows leaving an untreated region in the inter-rows. Later inter-rows are farmed to eradicate the weeds. Saving in cost is feasible here. For example when a 30 cm wide band of a pesticide spread across a crop row that were spaced 90 cm apart, then two-third cost is avoided.
(iv). Fumigation
Application of volatile chemicals in to restricted places or in to the soil to generate gas that will destroy weed seeds is termed fumigation. Herbicides used for fumigation are termed as fumigants. These work effectively to get rid of weed seeds as well as perennial weeds. e.g. Metham, methyl bromide
(v). Herbigation
It involves applying herbicides together with irrigation water using sprinkler and surface irrigation systems. While farmers in India use fluchloralin to grow tomatoes and chiles, EPTC use with spray irrigation water is fairly frequent in Lucerne in western nations.
2. Foliar application
(i) Blanket spray
Herbicides are uniformly applied to standing crops without taking the location of the crop into account. Here, only very specific herbicides are used, such as spraying rice with 2,4-Ethyl Ester three weeks after transplanting.
(ii). Directed spray
It involves spraying herbicides on weeds that are growing between rows of crops while avoiding the crops themselves. By using a shield or hood for protection, this would be achieved. For instance, spraying glyphosate with a hood between rows of tapioca to manage Cyperus rotundus
(iii). Protected spray
By covering the crops that are widely spaced with plastic covers, etc., it is possible to administer non-selective herbicides on weeds. This is both costly and time-consuming. However, farmers are employing this kind of glyphosate application to manage weeds in banana, cassava, and jasmine.
(iv). Spot treatment
To kill the weeds and stop their spread, it is often done on limited areas with substantial weed infestations. Here, a rope wick applicator and a herbicide glove are helpful.
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