Article in English: There are different kinds of fungi that can kill your radish or make it taste really bad. Usually there are obvious signs of a fungus problem that you can watch out for and subsequently deal with.  If pale yellow and grey spots appear on the radish leaves, your radish might have leaf spot, also known as Septoria leaf spot, a fungal disease. If you do have this, make sure that your planting bed is well-drained (the water doesn't just sit there) and add organic matter (like compost). Remove the infected radishes. To avoid this problem, rotate your crops so that you don't plant your radishes in the same bed each time. Also, keep your garden free of plant debris (dead plants, weeds you've picked, etc.). If pale green spots start appearing on the upper side of the leaves, with a purple downy growth on the undersides, you might be dealing with downy mildew, a type of fungus. Get rid of infected plants and make sure that you aren't over-watering. Avoiding radish over-crowding by thinning the herd. To avoid downy mildew, make sure that you rotate your crops, and keep the garden free of plant debris. If the radish leaves turn yellow between their veins, if the leaf margins turn brown and curl upward, if the stem base turns dark brown, black, and becomes slimy, you might have blackleg, a fungal disease. Add organic matter, like compost, to the plant bed, and make sure that your soil is well drained (not holding too much water and that you aren't over-watering). To avoid getting this, make sure that you rotate your crops. Fungi aren't the only things that can cause problems with your radishes. Certain bugs can get into your plants and feed on them so that they begin to die. Many times you can avoid these bugs by keeping your garden clear of plant debris and weeds. If they do show up there are some ways you can deal with them.  If your leaves are looking faded and you find that there are tunnels and grooves in the roots, you might have root maggots. These tiny critters are small, gray/white, legless worms. Flies lay...

Summary in Vietnamese:
Xử lý nấm. Loại bỏ sâu bọ gây hại. Kiểm tra đất.