Hoya plants are generally hardy and easy to care for, but they can still be susceptible to diseases and pests. Here is a detailed guide on some of the most common Hoya diseases and pests to look out for:

1. Mealybugs: Mealybugs are small, white, fuzzy insects that can infest Hoya plants. They can be found on the leaves, stems, and flowers of the plant. Mealybugs suck the sap from the plant, which can cause it to weaken and die. To treat mealybugs, isolate the plant and spray it with a mixture of water and rubbing alcohol. You can also use insecticidal soap or a horticultural oil to treat the plant.

2. Spider mites: Spider mites are tiny, spider-like insects that can infest Hoya plants. They feed on the plant's sap and can cause the leaves to turn yellow and drop off. To treat spider mites, isolate the plant and spray it with a mixture of water and neem oil or insecticidal soap.

3. Scale insects: Scale insects are small, oval-shaped insects that can be found on the leaves and stems of Hoya plants. They suck the sap from the plant, which can cause the leaves to turn yellow and drop off. To treat scale insects, isolate the plant and spray it with a mixture of water and rubbing alcohol.

4. Leaf spot: Leaf spot is a fungal disease that can affect Hoya plants. It appears as brown or black spots on the leaves and can cause them to drop off. To prevent leaf spot, avoid overwatering and make sure that the plant has good air circulation. If leaf spot occurs, remove the affected leaves and treat the plant with a fungicide.

5. Root rot: Root rot is a fungal disease that can affect Hoya plants. It occurs when the soil is too moist and can cause the roots to rot. To prevent root rot, make sure that the soil has good drainage and that the plant is not overwatered. If root rot occurs, remove the affected roots and repot the plant in fresh soil.

In summary, Hoya plants can be susceptible to diseases and pests such as mealybugs, spider mites, scale insects, leaf spot, and root rot. To prevent these problems, it's important to provide proper care for your Hoya plant, including good watering practices, proper lighting, and fertilizer. If you do notice any signs of disease or pests, it's important to take action right away to prevent the problem from spreading. With proper care, your Hoya plant can continue to thrive and add beauty to your indoor space.