Crop failure can occur due to various factors such as adverse weather conditions, pest attacks, poor quality seeds, and inadequate irrigation. Among the given options, the reason for crop failure that does not fit is "Manure are of good quality" (option C).

I. Importance of Manure
Manure plays a crucial role in agriculture as it provides essential nutrients to the soil, improves soil structure, enhances water-holding capacity, and promotes microbial activity. It replenishes the soil with organic matter and nutrients, ensuring the healthy growth of crops. However, the quality of manure alone cannot determine the success or failure of crops. Other factors need to be considered as well.

II. Factors Contributing to Crop Failure
a) Insufficient Monsoon:
Monsoon is a vital source of water for agriculture in many regions. Inadequate rainfall during the monsoon season can lead to drought-like conditions, resulting in crop failure. This can happen due to climate change, unpredictable weather patterns, or natural variations in rainfall.

b) Pest Attacks:
Pests can cause significant damage to crops, leading to reduced yields or complete crop failure. Insect pests, diseases, and weeds compete with crops for nutrients and water, affecting their growth and productivity. Factors such as changes in pest populations, lack of effective pest management strategies, or the emergence of new pest species can contribute to crop failure.

c) Poor Quality Seeds:
The quality of seeds is crucial for successful crop cultivation. Poor quality seeds may lack vigor, have low germination rates, or be susceptible to diseases. Such seeds can result in stunted growth, low yields, or complete crop failure. Factors such as improper storage, genetic deterioration, or the use of uncertified or adulterated seeds can contribute to poor seed quality.

III. Conclusion
While manure of good quality is important for maintaining soil fertility and crop productivity, it alone cannot prevent crop failure. Adverse weather conditions, pest attacks, and poor quality seeds are equally significant factors that can lead to crop failure. Therefore, option C, "Manure are of good quality," is the correct answer as it does not align with the other factors commonly associated with crop failure.