AGR 3102PRINCIPLES OF WEED SCIENCE
Calibration
Objective: To determine the rate and volume of spray for a given area
Introduction
Calibration is simply the accurate determination of the spray volume delivered by the sprayer and verification that the spray pattern is correct. A sprayer that is not properly calibrated may result in wasteful and harmful over-application of the herbicide, or reduced effectiveness due to under-application. Herbicide sprayers should be calibrated at least once per season, more often if the sprayer is used frequently.
Principles of Calibration
Often the carrier is water. Calibration is usually done to estimate the volume of water required for an area, e.g. 300 L/ha
Methods of calibration
Usually it depends on the sprayer’s walking speed. There are several ways of calibrating; this section discusses one of those methods:
- Measure and mark the length of the area/distance to be sprayed (e.g. 10 m long).
- Fill the spray tank up with clean water to a define mark. Spray the water on a dry surface and measure the spray width from the nozzle (e.g. 0.5 m).
- Walk pace and spray the marked area at a constant pressure. Record the time taken to finish the pace (e.g. 20 s).
- Using the same pressure, measure the nozzle output in litres over one minute in a measuring jug (e.g. 500 mL/min).
- Repeat steps 2 – 4 at least twice. Record all data.
From step 1 – 5:
Size of the sprayed area = 10 m (spray distance) x 0.5 m (spray width) : 5 m2
Time needed to complete spray = 20 seconds
Average volume of water used = 20 s x 500 mL : 166.67 mL
60 s
* 5 m2 required 166.67 mL (0.167 L) of water
How much water is needed for 1 ha area?
= 10000 m2 x 0.167 L : 334 L
5 m2
* 1 ha area required 334 L of water for spray application
Practical Work
- Conduct the calibration work and collect the following data: distance of an area to be sprayed, spray width, spray walking speed, and spray volume.
- Calculate the rate and volume of spray required for 1 ha.
AGR 3102PRINCIPLES OF WEED SCIENCE
Weed Composition and Growth
Objective: To study weed composition and growth in a specific area
Introduction
Weeds are plants which grow where they are not wanted. They differ from other plants in being more aggressive, having peculiar characteristics that make them more competitive. Weeds decrease the crop yield by competing for water, nutrients, space and light. Some weeds are also allelopathic and adversely affect crops. Losses in crop yield and production caused by weedsare well documented in many studies. Therefore, there is an urgent need for effective weed management programs. For such programs to be visible, accurate information on the weed flora and the distribution, abundance and phenology (life cycle responding to climatic condition) of weed species and weedcommunities are pre-requisite. Such kind of data may also be valuable for understanding weedcommunities and for creating a higher biodiversity in arable land. Weed communities are affected by many factors as farm management practices, crop type, season, and soil characteristics.The many factors involved in the formation of the weed community make it difficult to evaluate the relative importance of each individual factor.
Weed Sampling
Weed biomass and number of weed plants will be assessed in the specified areas. The samplings will be done at random in each plot using the list or census count quadrat method. Each group will be provided with 2 quadrat sizes: 20 cm x 20 cm; and 50 cm x 50 cm for the evaluation. A minimum of 8 quadrats must be sampled in each specified plot using both small and large quadrats*.
*The recommended quadrat sizes are for the herbaceous plants. For big woody tress, techniques such as recording the number of the trees met along the crop rows, or using bigger quadrat can be applied.
Data Analysis
Weed species collected in each quadrat must be identified, listed and counted. Collected weeds must be harvested aboveground (using scissors/shears provided), sorted by species, and weighed.
Data will be recorded for:
1.Weed species
2.Number of weed according to species
3.Weed growth (weed biomass) according to species
Analyse weed number and biomass from both small and large quadrat individually, and get the average. Count the density (no. of plants/m2), as well as biomass (fresh weight of plants/m2) of each species from both quadrats. Draw a graph/table for each data and compare the results for each data between small and large quadrats.
Using all the data above, calculate the summed dominance ratio (SDR) of the weed species using the following equations:
SDR = relative density (RD) + relative dry weight (RDW)
2
where,
RD = Number of a single species x 100
Total number of all species
RDW = Dry weight of a single species x 100
Total dry weight of all species
Draw a graph/table discussing the SDR values for all weed species analysed in both small and large quadrats, and compare results between these two quadrats. Report the conclusion.
Question to Answer
Is there any difference obtained in weed density, weed biomass, and SDR between small and large quadrats for each recorded weed species? Why?
AGR 3102PRINCIPLES OF WEED SCIENCE
Herbicides
Objective: To identify and study the characteristic of several herbicides available in the market
Introduction
A herbicide is a type of pesticide used to kill or inhibit growth of unwanted plants. Herbicides can be classified based on different activity, chemical family, mode of action, or type of vegetation controlled (selectivity). The classification by mode-of-action indicates the first plant enzyme or site-of-action targeted/inhibited by the herbicide. Worldwide, expenditure on herbicides accounts for approximately 40% of all pesticide expenditures. In the agricultural market, herbicides are sold in several formulations and names.
Formulation:mixture of pure chemical with inert material for specific purposes.
Among the types of formulation are wettable powders, emulsion, and dust.
Names:the name used for each type of herbicides based on its pure chemical
(chemical structure) or trade names.
Activity:the form of its action/effectiveness on plants. Can be either:
Contact herbicides destroy only the plant tissue in contact with the
Chemical, thus require even coverage in their application. Generally,
these are the fastest acting herbicides. They are less effective on
perennial plants, which are able to regrow from rhizomes, roots or
tubers.
Systemic herbicides are translocated through the plant via
circulation system, either from foliar application down to the roots,
or from soil application up to the leaves. They are capable of
controlling perennial plants and may be slower acting but ultimately
more effective than contact herbicides. Residual herbicides remain
active in the ground for certain length of time, and can control
germinating seedlings via shoot or root uptake.
Selectivity:there are selective and non-selective herbicides:
Selective herbicides
target only a specific type of plant, often broadleaved plants or grasses,
making them safe and effective for targeted weed control. A herbicide that destroys only broadleaved plants generally won't harm grass crops.
Non-selective (broad-spectrum) herbicides kill all plant life, regardless of type. Non-selectives are used to establish areas free of all plants, such as construction areas, although some non-selective herbicides are also used in agriculture such as paraquat, diquat, and glyphosate.
Application:within this classification are post-emergence and pre-emergence
herbicides. Post-emergence herbicides work best after the plant has
emerged and is visible. This type of herbicide is most effective when sprayed on the plant's leaves. Pre-emergence herbicides are effective on plants before they germinate and start to grow. Pre-emergence herbicides are applied to the soil and watered in thoroughly one to three weeks before the weed seeds germinate.
Practical Works
Observe and record the main information about each displayed herbicide. Among the information are names, formulation, type of activity, active ingredients, toxicity, its application/use rate, and safety measures. Record all these information and submit the report.
AGR 3102PRINCIPLES OF WEED SCIENCE
Spraying Equipment (Knapsack Sprayer)
Objective: To study:a) The components of herbicides knapsack sprayer
b) The operation and care of spraying equipments
c) The safety procedures during spraying
Introduction
Knapsack sprayers are widely use in many countries, and considered as the world’s most used type of sprayer.Knapsack sprayers come in many different forms but the basic components and requirements for use are the same for all. Knapsack sprayers have a tank of up to 20 L capacity and are carried on the back and pumped manually; or have a motor that pressurises the spray liquid and may also force air to carry the spray. Basically, knapsack or other small size portable sprayers come in handy when:
- Cost of larger equipment restricting purchase
- Convenience and simplicity of use is taken into account
- Size of farm not demanding larger sprayer
Components of Knapsack Sprayer
Knapsack sprayers are available in many different configurations they all comprise of the same basic components. These components are:
Shoulder strap, tank cap, strainer, tank, pressure vacuum tank, inlet valve, outlet valve, diaphragm, operation lever, hose, spray lance, and nozzle.
The lanceor wand usually has a simple on-off valve.Nozzles are comprised of a spray tip, a filter/strainer, and a nozzle body and cap. The nozzle tip is the most important nozzle component. It determines the flow and distribution of the spray. There are many different types of tips, each designed for a certain type of spray application. To prevent spray drift when spraying in windy conditions a protector hood is included, that fixes to the front of the spray lance.
Operation and Care
Efficient and effective spraying depend on the type and condition of the equipment used. Often there are three things which need high concern when spraying:
Flow of solution by hydraulic pressure
Flow of solution by air pressure
Dispersion of spraying droplets by spinning of the disc
Problems that may happen are the reduction of pressure that can affect the flow of the solution, which caused by operational system blockage or damage/worn parts. Maintain our spraying equipment to a high standard, following recommendations in the sprayer manual such as:
- Always wash all equipment after use.
- Repair any leaks immediately.
- Replace worn parts.
- Keep spraying equipment safe, away from children, food stuff and animals.
- Regularly calibrate sprayer output and keep all spraying records
- Use clean water for mixing.
Safety
Among the safety procedures are:
- For non-selective herbicides, direct the spray to the targeted weeds only & use low pressure.
- Ensure that spraying equipment is clean from herbicide from previous spray.
- Safety for workers and environment: follow directions on the manual.
Practical Works
Several spraying equipments are displayed for observation on parts and components. Record any information provided.