a) The photograph shows a leatherjacket, a pest of many cereal and root crops - Leaving Cert Agricultural Science - Question 8 - 2006

1. Pesticides: Applying chemical pesticides can effectively reduce leatherjacket populations, ensuring they do not damage crops.
2. Cultural Practices: Practices such as crop rotation or rolling of soil can help disrupt the life cycle of leatherjackets, making it less likely for them to infest crops.

Biological control refers to the use of natural predators, parasites, or pathogens to manage pest populations. This method aims to reduce reliance on chemical pesticides and promote a more balanced ecosystem.

An example of biological control is the use of ladybugs to control aphid populations in agricultural fields. Ladybugs feed on aphids, significantly reducing their numbers without the need for chemical interventions.

The spread of blight in potato crops is facilitated by damp, humid, and warm conditions, typically above 10 degrees Celsius. Such environments promote the growth and dissemination of the disease-causing organism.

The disease is caused by a fungus known as Phytophthora infestans, which is a water mold notorious for its rapid spread and destructive nature.

1. Visual Symptoms: Infected potato plants exhibit dark brown or black lesions on the leaves, which can lead to wilting and significant leaf drop.
2. Yield Impact: The disease causes potatoes to develop patches that turn brown or discolored beneath the skin, thereby reducing the quality and yield of the crop.

1. Selection of Seed: Using disease-resistant seed varieties can help reduce the incidence of blight.
2. Fungicide Application: Spraying with fungicides at intervals during the growing season can help manage the disease, though great care must be taken to prevent harm to beneficial organisms.