On the basis of your reading, answer the following questions briefly.
a. What are weeds? What do they do?
b. Why do crops die if there are weeds in a field?
c. What harm can be caused if herbicides are misused?
d. Name two herbicides that chemical industries have introduced in the recent past.
e. Which species of plants are spared by the most effective chemical herbicides?
f. What are the scientists engaged in, all over the world these days?
g. What advantages do biological agents have over chemical herbicides?
h. How do biological agents differ from chemical herbicides with regard to their application?
Answers
Answer:
Herbicides (US: /ˈɜːrbɪsaɪdz/, UK: /ˈhɜːr-/), also commonly known as weedkillers, are substances used to control unwanted plants.[1] Selective herbicides control specific weed species, while leaving the desired crop relatively unharmed, while non-selective herbicides (sometimes called total weedkillers in commercial products) can be used to clear waste ground, industrial and construction sites, railways and railway embankments as they kill all plant material with which they come into contact. Apart from selective/non-selective, other important distinctions include persistence (also known as residual action: how long the product stays in place and remains active), means of uptake (whether it is absorbed by above-ground foliage only, through the roots, or by other means), and mechanism of action (how it works). Historically, products such as common salt and other metal salts were used as herbicides, however these have gradually fallen out of favor and in some countries a number of these are banned due to their persistence in soil, and toxicity and groundwater contamination concerns. Herbicides have also been used in warfare and conflict.