What to Do When Garlic Gets Viral Disease? All the Control Methods Are Here
Dai Hongming of Baimi Town, Jiangyan City called on December 1 and said that his 2 mu of garlic was at the 5-6 leaf stage, and recently 50% of the plants in the field had whole leaves turning yellow and deformed and twisted, with white root systems, and no herbicide had been used earlier. He asked what disease the garlic had and how to control it.
On December 3, the Agricultural Technology 001 Studio received the diseased garlic seedlings he sent by express mail. Upon careful examination of the diseased seedlings, they were roughly at the 3-5 leaf stage, with intermittent short yellow-green striped spots on the basal 1-2 leaves, some leaf tips already withered, and the upper leaves showing long yellow-green striped spots, with some plants having yellowed central leaves; every leaf was twisted and deformed, and the upper part of some central leaves was wrapped by adjacent leaves and could not extend normally. The pseudostems of the diseased plants were relatively thin, the growth was weak, and root growth was basically normal. Researcher Zhou Yijun of the Plant Virus Disease Group, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, after carefully examining the submitted diseased garlic plants, diagnosed that the garlic had viral disease.
It is understood that garlic viral disease is caused by complex infection by multiple viruses. In the early stage of the disease, intermittent yellow dots appear along the leaf veins, which later connect into yellow-green stripes; the plants become stunted, and the central leaves of individual plants are wrapped by adjacent leaves, showing curled deformities and being unable to fully extend for a long time, causing the leaves to twist. The bulbs of diseased plants become smaller, and the number of cloves and fibrous roots decreases; in severe cases the cloves become hard, especially during storage. Once the virus invades the plant body, it not only affects the current generation, but after the mother bulb carries the virus it can be passed to offspring through vertical transmission, leading to degeneration of seed characteristics.
A high-temperature and dry environment favors the occurrence of garlic viral disease, and the optimum temperature for disease development is 20-30°C, with relative humidity of about 70%. The main peak periods of garlic viral disease in the middle and lower reaches of the Yangtze River are autumn from September to November and spring from April to June. Garlic is susceptible to infection from the seedling stage to the adult plant stage. When virus-carrying bulbs are sown, the plants develop the disease after emergence, and in the field the virus is transmitted non-persistently by aphids. The disease is more severe when aphid populations are large, under high temperature and drought, with extensive management, and under continuous cropping with other Allium plants.
According to a telephone follow-up, the garlic in the above field was harmed by many aphids at the 2-3 leaf stage, and no timely pesticide control was applied when the aphids occurred, resulting in a large outbreak of aphids. In the early growth period of garlic this year, temperatures were relatively high and there was not much rain, which favored the occurrence of aphids. The large outbreak of aphids was the main reason for the viral disease in the garlic in the above field. In addition, the garlic plants grew weakly and had poor disease resistance, and combined with the failure to apply timely pesticide control of aphids, the viral disease spread and worsened.
After garlic develops viral disease, there is no effective pesticide for control; the disease is mainly controlled by managing the virus-transmitting vector, aphids. For aphid control, pesticides such as acetamiprid, pymetrozine, nitenpyram, carbosulfan, thiamethoxam, thiacloprid, deltamethrin, and pirimicarb can be used. In addition, to prevent garlic viral disease, seed selection should also be strict, using virus-free garlic seed; a 3-4 year rotation should be implemented, avoiding continuous cropping with garlic and other Allium crops; and fertilizer and water management should be strengthened to avoid premature aging and improve plant disease resistance.