Common diseases and insect pests of African violets and their control

I. Diseases

1. Ring spot disease This is a disease caused by virus, which is generally transmitted by thrips. After infection with virus, leaves will produce ring spots. Prevention of virus disease by controlling thrips is the main measure to prevent ring spot disease. Virus-infected plants, generally no medicine can be cured, only uprooted and destroyed.

2. Leaf spot disease This is a leaf disease caused by fungi, which occurs first on the lower leaves of plants, especially on leaves damaged or in contact with substrates. At the beginning of the disease, small necrotic spots appeared on the leaves, and then the disease spots expanded rapidly. The diameter of the disease spots could reach 5 cm or even larger under suitable conditions. Suitable fungicides are carbendazim, chlorothalonil, thiophanate-methyl, benomyl, etc., sprayed in the early stage of the disease, 7~10 days once, continuous spray 2~3 times.

3. Powdery mildew is easy to occur in rainy season or high temperature and humidity, with more leaves and flowers. Chlorotic macula appeared in the early stage of the disease, gradually enlarged, and then a layer of white powder was born. In severe cases, the whole leaf was covered with white powder. Suitable fungicides are sulfur mixture, triadimefon, polysulfide, thiophane methyl, chlorothalonil, benomyl and so on.

4. Phytophthora is also a fungal disease, which can occur from seedling stage to adult plant. From the leaves began to be damaged, brown spots, water-stained, with obvious ring patterns. When wet, the edge is not obvious, the expansion is very fast, there are sparse white mold on the lesion, when dry, the lesion stops expanding, and the diseased tissue dries up. Suitable fungicides are metalaxyl, metalaxyl manganese zinc, ethyl phosphorus aluminum, anti-virus alum, can kill and so on.

5. White silk disease mainly damages stem base and root. At the beginning, there are water-stained yellow brown spots near the base of the soil, and quickly spread into the roots, seriously damaged parts rot, the whole plant dies. The disease often grows white silk thallus, radiates and spreads on the surface of the substrate. At the later stage, the mycelium interweaves to form sclerotia which is white at first, yellow gradually and brown at last. To prevent and control white silk disease, fungicides such as triadimefon, carbendazim, lichen, bordeaux mixture and baumestone sulfur mixture can be sprayed on the stem base and substrate.

II. Pests

1. Stenotarsus albus is a kind of mite, light brown, extremely small, not easy to observe with the naked eye. Female mites are about 0.23 mm long and male mites about 0.2 mm. It can harm leaves and flowers, but it is mostly hidden in the young leaves and buds that have not been unfolded. It lives by sucking juice after pricking and grinding the epidermis of leaves. The injured parts appear chlorotic spots, deformity, curl, shrinkage, etc. In severe cases, the young leaves are difficult to develop, and the petals are deformed, resulting in shedding.

Insecticides can be selected in addition to dimethoate, omethoate, dichlorvos, marathon, etc., there are many specialized acaricides, such as dicofol, acarb, bromofen, mite) competition, benmite, sweep mite treasure, etc.

2. Scale insects are about 1~3 mm in length and have round or oval eggs. Scale insects suck leaf sap by piercing, so that leaves produce chlorotic spots, serious when the whole leaf chlorotic yellow.

When the eggs hatch, the nymph can move around to find a place to eat leaves, secreting a protective wax and staying put. Before the eggs are hatched to be fixed, the shell has not thickened at this time, and the control effect of spraying is the best. General organophosphorus insecticides such as dichlorvos, malathion and fenitrothion can be used for control. When the scale insect fixed down, because it has a layer of waxy cover protection, can only be used to control systemic pesticides, common dimethoate, omethoate, acephate and so on. You can also use special drugs such as Sujieke.

For a small number of scale insects, artificial methods can also be used to remove. For example, gently scrape off the worm with a small bamboo chip, or carefully brush it off with a soft brush, or gently wipe it off with a cotton ball dipped in vinegar or medical alcohol.

3. Thrips are very small individuals, which can harm flowers and leaves. They use their mouthparts to scrape the epidermis and absorb juice, so that green spots or stripes appear at the injured places. In serious cases, the petals turn brown and deformed. Suitable pesticides are Qixingbao, dimethoate, omethoate, marathon, acephate, dichlorvos, carbaryl and so on.

4. Aphids are also small individuals, which can harm leaves and flowers. When the number is large, they can cover a layer on the surface. Aphids suck sap through needle-like mouthparts, causing deformity or curling of the injured parts. There are many suitable pesticides, such as dimethoate, omethoate, acephate, fenitrothion, phoxim, aphid, rotenin, pyrethrins, fenvalerate and so on.

When cultivating African violets, the potted substrate should be clean and sterile, drained and ventilated, and the water should not be poured too much. When the temperature is high and humidity is high, ventilation should be paid attention to, which can greatly reduce the occurrence of diseases and insect pests. Because some pesticides will cause yellow spots on leaves, thus reducing the ornamental value of plants, pesticides should not be used to control pests as much as possible.