(1) Rust Marigolds can occur in all reproductive periods, with the onset of more serious in summer. The disease mainly affects the leaves of the plant, and sometimes there are spore mounds on the stem. At the beginning of the disease, only in the back of the leaf blade green loss, after a small amount of black-brown powder, with the aggravation of the disease, the back of the leaf powder into a heap, in the front of the leaf blade also appeared in the same black-brown powder. Prevention and control methods: remove the disease residues in fall and winter, and concentrate on burning; use Bordeaux solution to protect before the onset of the disease, and spray with 50% powder rusting wettable powder 600-800 times liquid, or 15% powder rusting wettable powder 500 times liquid at the early stage of the disease; and harvest in time to reduce the amount of rust spores.

(2) Downy mildew occurs in high temperature and high humidity seasons, and the surface of leaves is gray and white colored with frosty mildew layer at the onset. Prevention and control methods: maintain ventilation and light, soil to maintain low humidity; remove diseased leaves, concentrated burned; in July to August temperatures lower, continuous rainy and foggy weather should be timely protection with Bordeaux liquid, sprayed every 10 to 15 days, 2 to 3 times in a row; the early onset of the disease with 58% mefenamic acid manganese-zinc 500 to 600 times liquid, 75% Chlorothalonil wettable powder 600 to 800 times liquid in water and then sprayed.

(3) root-knot nematode disease infected plant dwarfing, yellowing, infected to a certain extent, the plant in the sunny day at noon began to wilt, to the evening and back to normal, with the aggravation of the disease, the degree of wilting and difficult to recover, and gradually die. There are many root nodules along the roots of the plant, which are bead-like, and the surface of the root nodules is smooth, without short fibrous roots. Generally sporadic occurrence, the incidence rate of 25% to 30%, plant root knot rate of 5% to 45%. Prevention and control methods: available nematode Bik in the sowing or transplanting before doing soil treatment, per 667 meters 2 with 0.5 ~ 1 kg mixed with soil spreading.