Diseases and pests of bulbous plants
Yellow dwarfism – the most common viral disease is caused by Allium virus. It strikes an onion, causing the appearance of light yellow streaks on the seed shoots and on the chives. Growth is stunted, and bulbs of infected plants have thick necks and are not suitable for storage. Viruses are transmitted primarily through aphids, by rash bulbs, and through a speech bubble. Infested chives collapse and hang down to the ground. In addition to onions, this virus infects shallots and ornamental plants, narcissus and sapphires. It is dangerous mainly for seed crops. Infested plants should be removed. You also need to fight aphids.
The jaundice of asters on onions is caused by a germ – Mycoplazma, carried by insects. It hibernates in stored bulbs and perennial plants. Diseased bulbs release early leaves during storage. This disease can take its toll in seed crops. Infested plants should be removed. Symptoms vary: leaves show yellow streaks at first, then they undergo chlorosis, they become narrow and die at the top.
Downy mildew of onion is the most dangerous disease of this plant, caused by a pathogen – Downy mildew destructor. Apart from onions, it can also attack other onion species. Defeats the chives (leaves), with light green or yellowish patches, later covered with gray-violet coating, darkening over time. Infected leaves wilt, wrinkle, they put them on the ground and dry up. The mycelium hibernates in infected bulbs. Willing to avoid this disease, watering plants in the evening should be avoided, because it favors the spread of the disease. This disease is controlled by spraying, after noticing the first symptoms of paralysis, with Ridol plus 45 WP – 0,6% with the addition of a humidifier. It should be sprayed several times every 7-10 days.
Onion blade. It is a fungal disease, which attacks onion seedlings. Infected seedlings die within several days. Lead streaks appear on pinches of diseased seedlings, which break after a while, and from them black spores spill out. Infested plants appear covered with soot. These are the spores of the fungus Urocystis cepulae.
Green onions and seedlings should be grown in places of high prevalence of this disease, because older plants are not susceptible to this disease. This disease also affects freshly planted cloves of garlic. Its prevention consists in collecting and destroying diseased seedlings, using longer breaks in the cultivation of onions, seed dressing with seed dressing T. (on 10 g nasion 1 g of mortar). You can also sow Sadoplon for disinfecting purposes 75 in an amount 10 g/m2.
Onion cream, the most dangerous of pests of onions, is a fly-like, but smaller than a housefly. She lays her eggs on the ground near the onion. Whitish, legless larvae, length 8 Mm, bite inside the plant. Wanting to find out, if the onion is overrun by the cream, pull on the tip of the middle leaf. If easily pulled out and rotten at the root, meaning, that the garbage larva is feeding inside.
The first generation does the most damage, occurring at the end of May or in June. Second generation, August, it is less harmful. This pest is prevented by treating the seeds with Primicid 20 and scattering directly before sowing on Basudin soil 10 G (10 g na 1 m2 or 1 g na 1 m in a row).
Onions and garlic are also attacked by nematodes invisible to the naked eye – niszczyka and other nematodes. They attack seedlings, causing stunted growth, thickening of the base and twisting of the leaves. The larvae of these pests hibernate in the soil in plant debris. In spring they move to the soil, and then penetrate into the underground parts of plants. From here they travel upwards, to the stems, leaves and inflorescence shoots (they also attack parsley, celery, corn, leave, carrot, potato, narcissus bulbs, tulips and hyacinths). Leaves of infested young plants twist, they brighten and often die. In old plants, the leaves are shortened, yellow and rot at the root. Onion tissues soften and often break apart. The inside of the onion turns floury, and the heels break.
Control is not to grow the plants under attack on the spot, where this pest has occurred by 3-4 summer and decontamination of soil in autumn with chemical preparations recommended for this purpose.
Onions, Garlic, leek and celery is struck by a butterfly called chives bite. It is dark brown, about wingspan 13 Mm. The caterpillar is green or yellowish white; grows up to 5 mm in length. After wintering in spring, female moths lay their eggs on the leaves or the root neck of plants. Young caterpillars initially forage on the surface, and then bite inside. The first generation of this pest feeds in May – june, the second in August – September. The caterpillars are sprayed with Sadofos liquid 30 and Insectophos liquid 50.