Preparation of Herbicidal Sprays at Appropriate Concentrations
In order to achieve good results, it is not only necessary to use adequate quantities of recommended herbicides but the herbicidal sprays should be correctly prepared and properly applied. Some important considerations in the regard are as follows:
1.Time of Application:
It should be applied at right stage to get maximum efficiency. The time of application of different herbicides varies with the crop. The right time for spraying 2,4-D in wheat is at fully tillered stage. It is sprayed earlier, the ears will be abnormal and if sprayed later, weeds may not be killed. There are three times of application viz. Pre-planning, pre-emergence and post-emergence application.
2. Concentration of Weedicides:
It should be just as per the recommendations and if necessary repeated sprays may be given.
3. Formulation of Herbicides:
The herbicides are formulated in different ways to affect is solubility, volatility and toxicity to plats. The herbicides are formulated to be applied as solutions of water or oils, emulsions, wettable powders, granules and dusts.
4. Method of Application:
Different methods of application of herbicides are possible e.g. broad cast or blanket application, band application, placement, direct sprays by adjusting the height of the nozzle and spot treatment for small specified area.
5. Application Used their Care and Maintences:
Equipments used for application of herbicides may be sprayers power Knapsac of foot paddle for spraying liquids. Adusters for dispersing solids, fumigators and injectors for distributing material on the soil surface or in the soil. In order to use all these equipments properly proper lubrication, cleaning, checking of nuts, filters and hoses, calibration, using clean, nozzles proper cleaning and washing after use and proper storage in go down are necessary.
6. Calculating Proper Quantities of Herbicides:
The herbicides are available either in solid or liquid form. The laber of the containers will read a.e = Acid equivalent or a.e. active ingredient for solids and gm/lit a.e. or a.e. for liquids.
It refers to that part of a formulation that theoretically can be converted into acid. In this case the acid equivalent is given as the active ingredient or acid equivalent is given on label.
It is that part of a chemical formulation which is directly responsible for herbicidal effect.
Thus the commercial herbicide production is made up of two parts i.e. the effective part and the inert part. Since all the recommendations are made on the basis of a.e. or a.i. certain amount of calculations becomes necessary to find out the quantity of commercial product to be required for a given area.
To calculate the weight of the commercial produce required the formula used is:
Weight of chemical to be applied a.i.
Weight of commercial material required = ————————————————————-
% of a.e. expressed as decimal
Example No. 1
If you buy a herbicide with 80% (0.80 a.i.) as diuron. You want to apply one kg a.i. of Diuron per ha. Find out the quantity of commercial produce required per ha.
——– x ———- 1250 gm of the commercial product is need to apply her ha.
80 1 1.250 kg a.i. of Diuron.
In this case 1250 gm of commercial product is required to add to the amount of water required to cover a hectare.
Example No. 2
Suppose Na salt of 2.4-D contains 80% a.i. and if 1 ½ kg of a.i. per ha is to be sprayed. The quantity of Na salt required will be
———————- x —————— = 1875 gm/ha = 1.875 kg/ha
Example No. 3
The Na salt of 2,4-D with 80% a.i. is to be sprayed on 1/10 of ha @ 0.75 kg a.i. /ha.
The quantity of Na salt required will be:
100 3 1 1000
——————– x —————– x ————– x ————— = 93.75 gm
80 4 10 1
Example No. 4
If in area of 0.5 ha is to be sprayed with Simazine (50 p.c. wettable powder) @ 2 kg a.i. / ha the quantity of commercial herbicide required will be.
5 2 100
————- x ————- X —————– = 2 kg for 0.5 ha
10 1 50
Parts Per Million (PPM):
It refers to the number of parts by weight or volume of a constituent in 1, 00,000 parts of final mixture by weight on volume. The stated conc. should tell whether PPM is measured by weight or volume. For herbicidal purposes, it usually refers to a given weight of a chemical in a given volume of spray.
It is similar to ppm except that it is expressed as percentages, 1000 ppm is equivalent to 0.1 % and 5000 pm to 0.5% 1% solution (10000) ppm contains one gm of 2,4-D (acid equivalent in 100 cm3 of spray). The conversion of percent to ppm and vice versa can be done by equation.
Percent = ——————— = PPM = Percent x 10000
1% = ——————– = 1, 10,000 = 1 x 10,000