R2103 June ‘18
a) State ONE situation where EACH of the following types of herbicide could be used.
State an active ingredient for each situation, by completing the table below.
i) selective; 2 marks
ii) contact. 2 marks
b) Name TWO distinct weeds that could be controlled by a selective weed killer. 2 marks
c) State TWO benefits and TWO disadvantages of using chemicals to control weeds. 4 marks
This question relates to the following part of the syllabus:
2.2 Describe the biology of ephemeral, annual and perennial weeds.
State what is meant by EACH of the following types of weed and give the botanical names of TWO examples:
- ephemeral to include Cardamine hirsuta (hairy bitter cress) and Capsella bursapastoris (Shepherds purse).
- annual to include Veronica persica (Speedwell) and Poa annua (Meadow grass).
- perennial to include Ranunculus repens (Creeping buttercup) and Aegopodium podagraria (Ground elder).
Describe how these types of weeds relate to horticultural situations, to include:
- recently cultivated soil - herbaceous perennial borders - woody perennial plantings - lawns
State the botanical names of TWO weeds associated with EACH of these situations.
2.3 Describe how weeds can be controlled.
State what is meant by contact, translocated and selective herbicides
Describe ONE situation where EACH type of herbicide can be used appropriately.
State the active ingredient of ONE example of EACH type of herbicide.
For part a) there is quite a lot to read for the question, but the table makes it clear what is wanted as well, and quicker to fill in the answers.
You need to be able to understand what ‘selective’ and ‘contact’ herbicides are. Examples of situations are given in the syllabus which can be used when appropriate, or you can give a suitable one of your own.
The examiner’s comments suggest suitable situations as a playing field or lawn for a selective herbicide, and paths or gravel for a contact herbicide.
It is important to realise that it is the active ingredient which is asked for rather than the trade name. Suitable herbicides are suggested as 2, 4-D, MCPA or Dicamba for the selective herbicide and Acetic acid, Fatty acids or Diquat for the contact herbicides.
It is also important to make sure you give up to date examples for this as products are often withdrawn from use. You can check with the lists the RHS produce:
or on the HSE site:
For part b) you need to use the botanical names for the weeds. The examiner’s comments suggest Taraxacum officinale and Ranunculus repens as examples that would gain full marks. You are asked for distinct examples, so make sure you choose ones from different genera.
For part c) make it clear in your answer which points are the benefits and which the disadvantages. Headings are useful for these followed by bullet points or numbers to show the two points for each.
Some of the suitable answers suggested by the examiner’s comments are:
· Translocated chemicals can kill the whole plant which prevents regrowth from the root.
· Chemicals can be residual which prevents germination of further weeds.
· Risk of spray drift onto other plants.
· Chemicals can contaminate the soil if used inappropriately.