0—No infection.
1—Slight infection which is about 25% of full scale. One or two leaves became yellow.
2—Moderate infection. Two or three leaves became yellow, 50% of leaves became wilting.
3—Extensive infection. The all plant leaves became yellow, 75% of leaves became wilting, and growth was inhibited.
4—Complete infection. The whole plant leaves became yellow, 100% of leaves became wilting, and the plant was died.