Lichen Control Challenge Quiz

Explore key facts about common diseases affecting apple plants, with a special focus on understanding and controlling lichen and similar issues. This quiz tests knowledge of symptoms, control measures, and misconceptions in apple horticulture.

1. Identifying Apple Tree Lichens

   You notice gray-green patches growing on the branches and trunks of your apple trees. Which of the following best describes this growth?

   1. Cedar Rust
   2. Powdery Mildew
   3. Lichen
   4. Apple Scab

   Explanation: Lichen appears as gray-green patches on wood surfaces but is not a disease; it is a symbiosis of algae and fungi. Powdery mildew causes white powder on leaves and fruit. Apple scab leads to dark, sunken spots on leaves and fruit. Cedar rust creates orange spots, particularly on leaves.

2. Impact of Lichens on Apple Trees

   What effect do lichens typically have on the health and yield of apple trees?

   1. Reduce flower formation
   2. Cause severe leaf drop
   3. Lead to fruit rot
   4. Generally harmless

   Explanation: Lichens are generally harmless to apple trees and do not harm tree health or productivity; they simply grow on surfaces. In contrast, severe leaf drop, fruit rot, and reduced flower formation are symptoms of infectious diseases, not lichen growth.

3. Best Approach to Lichen Control

   What is the most recommended method for controlling lichens on apple tree bark?

   1. Improve air circulation
   2. Cover bark with plastic
   3. Apply heavy fungicide
   4. Water tree daily

   Explanation: Improving air circulation by pruning lets more sunlight and wind reach the branches, discouraging lichen growth. Heavy fungicide application targets pathogens, not lichens. Overwatering can worsen other problems, and covering bark with plastic can lead to moisture buildup and rot.

4. Distinguishing Lichens from Other Diseases

   If an apple tree's leaves show black, velvety spots after rain, which disease is most likely responsible?

   1. Apple Scab
   2. Fire Blight
   3. Lichen
   4. Black Knot

   Explanation: Apple scab causes black, velvety spots on leaves and fruit, especially after wet conditions. Lichens do not appear on leaves or cause spots. Black knot forms swelling on twigs, and fire blight causes wilt and blackening but not velvety spots.

5. Lichen Spread and Conditions

   Which environmental condition is most likely to encourage lichen growth on apple trees?

   1. High humidity with poor airflow
   2. Constant direct sun with wind
   3. Excessive salt in irrigation
   4. Sandy drought-prone soil

   Explanation: Lichens thrive in humid, shaded areas with little airflow, which favors their growth on bark. Sandy, drought-prone soils and high salt levels are more likely to affect rooting or nutrient uptake. Constant direct sun and wind typically discourage lichen establishment.