Ginger Blast (Known as Bacterial Wilt in Other Countries)
Ginger blast is a fatal disease that occurs universally in all ginger-growing areas. The yield may decrease by 10 to 20 percent on an average or over 50 percent in heavily infected plots. It is a serious threat to ginger production. Ginger blast is a bacterial disease caused by Pseudomonas solanacearum (now known as Ralstonia solanacearum). Besides ginger, this bacterium also infects tomato, eggplant, hot pepper, potato, and other solanaceous crops.
Following infection, the leaves droop, loosing their glossiness, then become yellow and whither from the bottom to top, leaf edges crimp and die at last. If stem is infected the base would show watersoaking, leaves turn yellow and then break at the base. Infected rhizome shows watersoaking, then turns brown and rots (for details see chapter 9-ed.).
Pathogenic bacteria mainly live through the winter in rhizomes and soil. The organisms can survive more than two years in soil and enter through wound and natural orifices of stems. The disease is spread in the following ways.
Seed: Contaminated seed rhizome is the primary infecting source and the main way of spreading the disease.
Soil: If diseased plants are left in the field, bacteria remain in the soil. If ginger is continuously planted in the same field, infection occurs as soon as the rhizome sprouts. So contaminated soil is another important source of ginger blast, especially in the traditional ginger-growing regions. Contaminated soil bacteria accumulate year by year, so the disease will become more and more widespread year after year.
Fertilizer: Some farmers use plant residues or topsoil to make manure and supply the same into the ginger field as base fertilizer. This practice adds R. solanacearum to the ginger field and may aggravate the disease.
Water: Irrigating water and rain are also a medium for spreading the disease. If water is polluted, R. solanacearum will flow into the field with water and cause the disease to occur.
In the north of China, ginger blast usually starts in July, reaches a peak in August to September, and declines by October. The time and degree of the disease are related to the temperature and rainfall. The optimum temperature for disease development is 26 to 31°C. In general, the higher the temperature is, the shorter the incubation time and course of the disease, and the quicker the disease spreads. In high-temperature and rainy weather, pathogen bacteria reproduce rapidly and spread through water and cause infection in a short time.
Prevention and Cure: The crop is susceptible to ginger blast at all stages of development and there is more than one way of disease spread. So it is difficult to prevent and control. At present, there is a lack of ideal bactericides and resistant cultivars. Therefore, only phytosanitation can prevent and keep the disease under control.
Rotation: Rotation of crops is an important way to reduce the bacterial population in soil and their spread, especially in diseased plots. In such plots, ginger should be planted only once in three years. Tomato, eggplant, hot pepper, potato, or other solanaceous crops should not be rotated, and land under the cultivation of these crops should not be used for growing ginger.
Rhizome Selection: Before ginger is harvested, select healthy and strong plants in the field, harvest them separately, and then store such rhizomes separately after fungicidal treatment. Before next year's planting season, be selective in choosing rhizomes with a view to eliminating the hidden bacterial source of ginger blast, which may be carried in the rhizome.
Field Selection and Soil Preparation: Select a sandy or loam plot—either a slopey land, or slightly elevated area that is well drained. Level it up and make suitable trenches that are about 15 to 20 m long. Drains need to be set out in fields to drain off rainwater. Supply clean fertilizer, and irrigate with germ-free water.
Control Disease Spreading: If a diseased plant is found in field, it should be rooted out together with the soil. Spread bleaching powder in the infected hole and all around, and irrigate. For every hole, use 0.125 kg of bleaching powder. Then cover it with germfree soil.
Use of Bactericides: Dip seed rhizomes for 20 minutes in 1:1:100 Bordeaux mixture before they are broken off for planting. Dip the cut ends in fresh and clean plant ash to seal off wounds. Or soak rhizomes for 10 minutes in 1:100 formalin and seal them in plastic film for 6 hours before planting. If diseased plants are found, pull them out and treat the area in the way mentioned above and pour 50 percent carbendazim solution. This has the effect of preventing the disease from spreading continuously.
Symptom: This disease affects leaves, occurring in the form of spots that are yellow to white, spindleshaped or long and round and 2 to 5 cm long. The middle of the spots turns thin and papery. In badly affected cases, the white spots spread over the whole leaf. Acicular conidiophores can be seen in diseased leaf.
Pathogen Spread: Ginger leaf spot is caused by the fungus Phyllosticta zingiberi Hori. This fungus survives in contaminated rhizomes or in the field in the debris left after harvesting. It perennates the winter in the form of mycelia and conidiospores in the soil. Conidiospores are the primary infecting source, which are spread through rainwater. The disease is promoted by warm and moist conditions, so it is severe in the warm rainy season, especially when plants are close, the soil is sticky, and the humidity is higher.
Prevention and Control:
1. Rotate crops for 2 to 3 years or more.
2. Plant in a higher elevated field that is conveniently irrigated and drained.
3. Do not supply too much nitrogenous fertilizer, and pay attention to application of N, P, and K fertilizer in stages in small split doses.
4. Spray 70 percent thiophenate—methyl liquefiable powder and 75 percent chlo-rothalonil liquefiable powder (1 g/1 l) in the early disease stage. Spray two to three times once every 7 to 10 days.
Symptoms: This disease mainly affects leaves. Infected leaves show brown spots on the top and edges that spread inward and become ellipsoid or spindle-shaped speckles. Most of the spots have halos. Many spots coalesce and cause the leaves to turn brown and gradually dry rot.
Pathogeny: This disease is caused by Colletotrichum capsici (Syd.). Bullet at Bibsy and C. gloeosporioides (Penz.) Sacc. These pathogens mainly do harm to Zingiberaceae and Solanaceae plants.
Disease Spread: The pathogens live through winter in the form of mycelia and spores in diseased plants or in the soil. Conidiospores are the main infecting source, transmitting the disease through rainwater or small insects activity. Continous cultivation in the same area, higher humidity, and too much nitrogenous fertilizer favor the disease occurrence.
Prevention and Control:
1. Pay attention to rotation of crops (avoid solanaceous and zingiberaceous crops).
2. Eliminate the diseased plants thoroughly by burning them to keep field clean.
3. Pay attention to application of N, P, and K fertilizers in small split doses.
4. Prevent the movement of people or animals in the field.
5. Spray 70 percent thiophenate—methyl liquefiable powder 1g/1 l, solution, or, 30 percent suspension in the primary infection stage. Spray two to three times continuously once every 10 to 15 days.
Stem Borer (Ostrinia nubilalis Hiibner)
The stem borer is a serious insect pest. Besides ginger, it also damages corn, Chinese sorghum, and other crops.
Damage Symptom: The larvae of the borer enter through cracks or wounds in the leaf sheath and stem or heart leaf. They bore into the central portion and eat out the tissue. Stems and leaves turn yellow and wither. If seedlings were attacked, stems are easily broken off.
Form and Characteristics: The stem borer is a grayish yellow and brown moth. The body is 10 to 15 mm long. The forewings are grayish and yellow, and have seven little black points on the edges. The underwings are white. The male moth is smaller than the female; the color of its body and alae is slightly deeper. The antennae are flagelliform. The female moth's antennae are filar, and the black points on the forewing are not very evident. The eggs are 1.28 mm long, 0.78 mm thick, straw yellow in color, and flat elliptical in shape. The surfaces of the eggs have tortoiseshell-like marks. Eggs are deposited on the underside of leaves and arrayed in two rows. The larvae are 28 mm long; milk white when just hatched and straw yellow when mature, and having prominently purple lines at two sides. Pupae are 12 to 16 mm long, and red brown to dark brown in color, with white annular lines in the joints of every section.
Prevention and Control: Clean broken branches, withered leaves, and weeds and burn them. Spray 50 percent fenitrothion emulsion (2 ml/1 l water) or dichlorvos (1.5 ml/1l) or trichlorfon (1.5 ml/l). Spray 2—3 times a month from the beginning of June.
Damage Symptoms: The black cutworm is a widespread insect pest infesting many kinds of seedlings of many vegetables and field crops. It is a serious pest at the seedling stage. It usually harms the base of ginger plants by eating away the tissue and causing heart leaves to wither (dead heart), turn yellow, and then the plants collapse suddenly.
Form and Characteristics: The body of adult black cutworms is 16 to 23 mm long. The wingspread is 42 to 53 mm, and its color is dark brown. The forewing has two horizontal lines that separate the whole alae into three sections, and it has an obvious kidney-shaped spot with two black xiphoid stripes. The underwing is solid gray. The eggs are 5 mm long and shaped like a half ball, and they have an apophysis on the length and breadth of their surfaces. The primiparous eggs are milk white, then later some red spots and stripes appear on them and before incubation they become grayish black. The larvae are 37 to 47 mm long, grayish black except for the stern, which is tan and has two deep brown vertical stripes. Pupae are 18 to 23 mm long, red brown, and have a glossy appearance.
The black cutworm goes through several generations in a year. It lives through winter in the form of an old and a mature larva and pupa. It is the first-generation larvae that mainly damage ginger seedlings. They copulate and oviposit at night; every female moth can oviposit 800 to 1,000 eggs on an average. The larvae have strong tropism to a black light lamp and wine with sugar and vinegar. Larvae hide in soil during the daytime and come out at night. Black cutworms are found in warm and moist environments; the suitable temperature is 13 to 25°C.
Prevention and Control:
2. Mix sugar, vinegar, distilled spirit, water, and 90 percent trichlorfon evenly in the proportion of 6:3:1:10:1, spread it in field to trap and kill flies.
3. Use 5 kg sautés chaff, wheat bran, or bean cake, add 200 g trichlorfon and suitable water, mix them well and spread in the field to trap and kill larvae.
4. Spray 2.5 percent deltamethrin (1 ml/3 l water), 90 percent trichlorfon (1 ml/800 ml water), or phoxim (1 ml/800 ml water) solution to the leaves to kill larvae.
Thrips are insect pests. Besides ginger, they also damage other liliaceous plants, cucurbits, solanaceous plants, and many other vegetables. It can also do harm to plants such as tobacco, cotton and other crops.
Damage and Symptoms: Both adult thrips and their nymphs suck plant juice, damaging leaves. Such leaves usually have many fine and off-white spots. Under serious infestation, the leaves become scorched, twisted, and even dry up.
The insect body is 1 to 1.3 mm long and straw yellow to puce in color, but mostly hazel. Their plural eyes are amaranth in color, coarse grainshaped, and protrude slightly. Each antenna has seven sections. The male insect has no wings, whereas females have light filemot wings. The eggs are kidney shaped and kelly green in color. The young nymphs are white and transparent, and the older ones straw yellow to deep yellow and 0.9 mm long. The shape of the pupa is similar to that of an older nymph; the little wings have developed and the pupa can move but cannot eat.
Thrips undergo about 10 generations in a year in the north of China. They mainly live through the winter in the form of imagos (adult) or nymphs in the sheath of garlic or Chinese onion. Pupae live through the winter in soil, garlic, or Chinese onion field. Adults are very active; they can jump and fly. Thrips are photophobic and usually hide in a leaf axil or leaf shade during daytime. The best-fitting temperature for thrips is 23 to 28°C with a relative humidity of 40 to 70 percent. Therefore, the damage is most serious in the last 10 days of May to the first 10 days of June every year. After July, once the rainfall increases, gradually the insect population goes down to a certain degree.
Prevention and Control:
1. Eliminate weeds, stumps, and plant debris in early spring, and burn or bury them to kill adults and nymphs.
2. Spray 50 percent dichlorvos 1 ml in one l or 40 percent dimethoate (1 ml/1 l), or 2.5 percent deltamethrin 1 ml in 3 l to leaves. One can also use 3 percent malathion powder and 1.5 percent dimethoate powder together in the proportion of 1:1 and dust on leaves directly in early morning before dew has disappeared.
3. Thrips are attracted to the blue color, so blue sticky boards can be fixed in fields to trap them.
The ginger maggot is the main pest of ginger in storage. It also sometimes damages seed and plants in the field.
Damage Characteristics: Ginger maggots aggregate in moist dark places, and their larvae bore through rhizome skin and enter rhizomes and eat the inner tissue. Frass is extruded through the borehole, and the rhizome becomes rotten. There is still doubt whether this is a primary pest or a secondary pest attacking rotten rhizomes.
The adult moth is grayish brown. The male is 1.3 to 1.6 mm long and has a pair of forewings; the female is 1.7 to 2.1 mm long and has no wings. Eggs are ellipsoid and 0.025 to 0.03 mm long. Larvae are 4 to 5 mm long with a black head and pale white body. Pupae are milk white at first, then become yellow brown, and finally become grayish brown before eclosion.
Ginger maggots can exist at 4 to 35°C and are fond of moist conditions, but the damage gets aggravated after the "Tomb-sweeping Day" (a Chinese festival) when the temperature goes up. Ginger maggots go through many generations in a year.
The following methods are mostly adopted in the ginger storage cellar.
1. Clear and clean the ginger cellar thoroughly before ginger is stored. Spray 80 percent dichlorvos (1 ml/ 1 l) solution in the cellar.
2. Put several small vials filled with dichlorvos (original liquid) in the cellar after ginger is put inside.
3. Sprinkle dichlorvos (original liquid) over firewood or sawdust and burn to sterilize the cellar.
4. Prevention in the field: Management method includes selection of seed carefully, elimination of affected ginger, and dipping seed ginger in 80 percent dichlorvos (1 ml/ 1 l) solution for 5 to 10 minutes.
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