The thing about foliar diseases is that you can't do anything about them once you have them. That crop needs to be harvested as soon as possible in order to help prevent damage to the new seedlings, he noted. Seedling diseases, such as phytophthora, pithium, fusarium crown rot and aphanelmytese can cause problems as well. Carlton advised choosing varieties with good resistance to these seedling diseases and to cut alfalfa at the early bloom stage. To manage crown rot, he also suggested selecting resistant varieties and also to make sure the soil has good drainage and avoid mechanical damage to the plant.
Insects also can damage alfalfa.
The first insect to worry about in the spring is the alfalfa weevil. Carlton said the weevil overwinters. In the spring, the adults will lay eggs, which will hatch into larvae, which do the most damage to the plant. The larval worm will be seen at the top of the stem. It is green with white stripes and a black head.