Rainfall at the correct time and amount affects yield per acre significantly for all types of pyrethrum plant clones. The rainfall or watering requirements range from 30 inches (762mm) spread over the growing season to as much as 50 inches (1270mm). Pyrethrum is intolerant of excessively wet conditions. Excessive rains will likely cause root rot and other diseases caused by fungus. On the other hand, pyrethrum is somewhat drought resistant, and a short dry spell (45 days or less) at the right time can be good for flowering. A longer dry spell or drought can be disastrous for a given years yield. Rains or watering, just prior to significant flowering can results in more flowers and increased pyrethrum content.