Part I - Disease control

Question 1

Plant pathogens can be used to our advantage in the biological control of weeds. Describe the two main approaches to biological control of weeds and provide examples.

Answer 1

Classical control:
Pathogen has to be host-specific, self-sustainable & continue to infect weeds without human interaction, for example, rust, Puccinia, on skeleton weed.

Innundative control:
Periodic application of pathogen to weeds. Is applied similarly to a herbicide. BCA (Biological control agent) may survive at low levels. Example: Acremonium diospyri to control persimmon trees in the US.

Question 2

How does fungicide resistance occur in plant pathogen populations and what strategies can be used to prevent it happening?

Answer 2

It occurs when plant pathogens develop the ability to survive and reproduce in the presence of a fungicide. This may be due to mutation, gene xfer or selection.

To prevent it from happening the following strategies could be used:
Rotating fungicides, pathogens are less likely to develop resistance to multiple fungicides.
Using fungicides at the correct rate and times, it will reduce the selection pressure for resistant individuals.
Following a pest management control strategy, which uses a combination of methods, including cultural practices, biological control, and chemical control, to manage pests.

Question 3

Which of the following insects are not known to transmit plant viruses?
1. Thrips
2. Aphids
3. Mosquitoes
4. Whitefies

Answer 3

Mosqueeftoes

Question 4

How does a protectant fungicide differ from a systemic fungicide?

Answer 4

Protectant fungicides form a protective barrier on the surface of the plant, preventing fungi from attaching and infecting the plant. (Contact fungicide)

Systemic fungicides are absorbed into the plant’s tissues, where they move throughout the plant and protect it from fungal infection. Useful to fight infection that has already started.

Question 5

What is disease forecasting and how is it used in plant protection?

Answer 5

Process of predicting the occurrence or change in severity of plant diseases.
Disease forecasting systems are used by growers to make economic decisions about disease treatments for control.
It is used for:
Prevention
Early detection
Yield estimation
Economic analysis

Question 6

Provide the name of an insect vector of a bacterial pathogen and name the disease it causes.

Answer 6

Aphids
They can transmit Xylella fastidiosa, which causes Pierce’s disease in grapes.