Wednesday, June 2, 2010

Pest control and micro - element deficiency management

PRSV induces vein - banding mottling and yellowing spot or distortion of leafs, water soaking streaks on and petioles, and ring spots appear on fruits or even on leaves. It stunts the plants and drastically reduces the size of fruits, sugar content, and taste. Some infected plants will bear fruit or production would decline. It spreads very fast and has become the limiting factor in papaya production in many areas of the world.

PLDMV induces characteristics rosettes of leaves with slender stems on the crown top. The fruit has the same markings as PRSV, but there are bumpy swellings around the ring spots.
Both viruses are transmitted by sap (via mechanical means) or aphids. No evidence has been found that they are seed transmitted.
1. Select to grow the tolerant varieties such as Known You No. 1 and Red Lady.
2. Grow the seedlings and trees under the net house or screen house.
3. Transplant at a time when there are relatively few winged aphids around and protect the seedling with transplant cylindrical plastic film and supports.
4. Inter- crop papaya with barrier crop such as corn, but never host crops such as cucurbit.
(May sow the corn seed one month after transplanting)
5. Mulch silver and black plastic film to deter winged aphids from visiting young seedling.
6. Immediately eradicate and burry the whole infected plant once found
7. Do not touch the healthy plants if hand or foot is contaminated with infected plant
8. Control the aphids
9. Practice cross protection with specific mild strain, but it often breaks down after a few months, losing its affectiveness.
10. Papaya tree may be treated as an annual crop and requires replanting every year in order to cut down on virus infection in the area where virus occurs seriously

B. Damping-off (Pythium aphanidermatum, P. ultimum, Phytophthora palmivora and Rhizoctonia sp.) The fungi live in the soil. The disease is favored by high temperature and wet weather, wet soil, poor drainage, deep sowing, thick sowing (crowded), poor soil aeration, high nitrogen in the soil and sunshine shortage. Infected seedlings will wilt, fall and then die.
1. Use virgin soil or sterlize the soil with steam at 180°F (82.3°C) for 30 minutes or fumigate with methyl bromide (see manufactures recommendations)
2. Improve above mentioned enviormental conditions to be favorable to the seedlings.
3. Protect with plastic film from rain water.
4. Drench the slution of 35% Etridiazole (Terrazole)

C. Phytophthora Fruit Rot (Phytophthora palmivaro)

Occurs in the hot and humid season, especially after typhoon attacks. It induces root rot on young and adult plants, and finally wilts or dies. Also it may cause large lesions and white mold appears on the fruit and then fruit drops.
1. Rotate with other crops.
2. Select well drained soil.
3. Avoid harming the roots.
4. Control the snails and ants.
5. Rogue and deply bury the diseased fruits.
6. Spray 80% Mancozeb (Dithane M - 45) W.P. at 1:400 weekly.

D. PowderyMildew (Oidium caricae)
White and gray powder-like mold appears on the leaves, petioles, stem and young fruits in early spring season (around 18-22° C). It stunts the plant, induces leaf dropping, or does not set fruit.
Control: Spray one of the following fungicides with the sticker at 10-14 intervals.
1. 50% benomyl (benlate) W.P. 1:3000
2. 70% wettable sulfur at 1:400
3. 10.5% Penconzaole E.C.1: 2000 phytotoxic to seedling.
4. 50% Binapacryl W.P 1:2000 phytotoxic to seedling.
5. 18.6% Triforine E.C. 1:1000 phytotoxic to seedling.
6. 19.5% Dinocap W.P.1:1500 phytotoxic to seedling.
Caution should be taken that the above mentioned chemicals may injure papaya at high temperature or/and at high high concentration.

E. Anthracnose ( Colletotrichum gloeaporides,, Glomerella cingulata)
It attacks the petioles and fruits. Symptoms mainly appear on the mature fruit and thus shorthen its shelf life. The symptoms are usually round, water soaked lesions which if enlarged, will be slightly sunken. The fungus frequently produces light-orange masses of spores in the central lesion.
1. Weekly spray 80% Mancozeb (Dithane M -45) W.P. 1:400 with spreader/sticker. 2.Treat the harvested fruits with hot water at 49°C for 20 minutes, then dip in the cool water for 20 minutes and then dry it.

F. Black Spot (Asperisporium caricae, Caercospora papayae)
The leaf spots are grayish-white, roughly circular to irregular in shape. Heavily infected leaves turn yellow and dry up. The spots on fruit are tiny water-soaked, turning black and corky. Wet and cool place at hill side is more serious.

G. Root Rot (Rhizoctonia solani, Fusarium sp.)
It causes root decay, eaf yellowing, and failing plant after raining. It also kill young seedlings in the nursery.
1. Rotation
2. Good drainage
3. Staking
4. Sterilization of the nursery bed with formaldehyde two weeks before sowing or treating the seeds with thiram (TMTD) or captan.

H. Collar Rot, Foot Rot (Pythium aphanidermatum)
Symptoms include swellig, cracking and rotting of the stem, when it comes in contact with water during the rainy season.
Control: Please refer to “ Damping-off” control.

I. Stem-end Rot (Ascochyta sp. And other fungi)
A dry, firm, dark rot usually occurs after picking. It starts at the stem-end and extends into the fruit.
Control: Pick the fruits with part of peduncle.

J. Rhizopus Fruit Rot (Rhizipus stolonifer)
The fungus invades injured mature fruit only It causes soft rot and produces masses of visible black sporangia; leakage of cell fluids from the rotting fruit will also occur.
1. Be careful when picking, transporting and packing to avoid bruising or injuring the fruit.
2. Heat treatment to kill the pathogen.
3. Remove and destroy the rotting fruit in the packing sheds.

K. Black Rot (Erwinia cypripedii)
The symptom mainly appears on the top of the stem. It primarily causes water-soak, then turns to black and leaves fall. New shoots may be infected and finally the plant dies.
Occasionally the symptom of water-soaked lesions are found on the leaves and petioles and will turn to brown angular and necrotic spots. Bacteria also invade the flesh, induce brown spots and decay, producing poor odor.
1. Eradicate the severely infected plant.
2. Cut the infected portion of the stem under sunny day, then paste with sulfur to develop the new shoot.
3. The seriously infected plantation should be destroyed.

L. Boron Deficiency.
This physiological problem is common in the sandy or gravel soil during dry cool season.
The latex could be found on the surface of immature fruits. Gall-like malformation of the fruit is also found in the severe plantation. The fruits are hard and not easy to get ripe,tasteless and having no commercial value.
1. Use more organic manure
2. Dissolve the Borax in hot water, then spray 0.25% Borax or Boric acid solution on the
leaves at the beginning of dry season at 2-3 weeks intervals.
3. Apply 2.5-5g Borax per plant (5-10kg/ha) along with other fertilizers bby side dressing at
the beginning of dry season.

M. Nematode Diseases
2. Reniform Nematode (Rotylenchulus Reniformis)
The young female nematode penetrates the root, causing stunting of the trees which are stressed and wilt more readily than the healthy ones. Fruits are smaller and may become tasteless as well.
3. Root-knot Nematode (Meloidogyne sp.)
It causes swelling or retardation of the root and stunting of the plants.
1. Rotate after rice crop.
2. Control with nematocide.

N. Mites
1. Spider Mites:Carmine Mite (Tetranychus cinnabarinus): It infests widely on many kinds of plants and more seriously on papaya. The leaves become matted with webbing.Citrus Red Mite ( Panonychus citri) & Texas Citrus Mite ( Eutetranychus banksi): The outbreaks of both mites occur only periodically, usually during the fall, causing matted but not prominent webbing, and inducing bleached punctures on leaves. The premature leaves drop and the plants become weak. The damage may widely spread rapidly.
2. False Spider Mites: Red and black flat mite (Brevipalpus phoenicis): It causes corky scarring of papaya fruit and reduces its market value. The mite is found onto the stem and advances onto the petioles and fruits.
3. Tuckerellid Mites: Twelve -tailes Tuckerellid (Tuckerella pavoniformis): It is minor pest. Injurious symptom is similar to that caused by red and black flat mite.
1. Fungicide such as Binapacryl, Trifornine, Dinocap used for powdery mildew control is also effective on spider or false spider mites. Spray 25% Morestan W.P. at 1:1000~1500 or 50% plictran W.P. at 1:2500~3000 at 10-15 days intervals.
Notice that too high concentration or/and high temperature may cause plant injury. Also,do not use the same chemical continuously because in this way, the mites may become tolerant to pesticide.
3. Tarsonemid Mite
Broad mite (Hemitarsonemus latus): It damages the seedlings and young plant greatly,causing stunted and distorted leaves. In a serious situation, the rosette leaves will appear,and the growing tips may be aborted.
Control: Spray 75% wettable sulfur at 1:300 on the top of stem at 10-15 days intervals until normal new leaves occur.

O. Aphids (Myzus persicae, Aphis spp….etc.)
Aphids suck young leaves whish become curled and crinkled, and even defoliate, especially at seedling stage. Some aphids also transmit the virus diseases

P. Red Scale (Aonideilla inornata)
It mainly infests stem after flowering and then spreads to the fruits.
Control: Spray one of the following pesticides at 7-10 days intervals.
1. 33% Formothion E.C. at 1:660
2. 50% Malathion E.C. at 1:500-1000
3. 44% Methidation E.C. at 1:1000
4. 40% Methidation E.C. at 1:800
The above pesticides are also effective to control aphids and some other insects of Papaya.

Q. Other Insects:
Scales, thrips, beetles, stink bug, leaf hopper, moths., mealy bug, and white fly are minor insects, but may occasionally cause certain damage to papaya.
1. Keeping the plantation relatively free of weeds can control aphids, leaf hopper and thrips outbreaks to a large extent.
2. Harvest all the fruits at the mature-green stage, and then pick dispose of all soft ripen and infested fruits promptly to prevent fruit fly infestation and reproduction within the plantation.
3. Select the proper insecticide to control the outbreaks of certain insects.

Biological Control: Apply the eggs of Mallad basalis walker (20-60 eggs/ plant or 100,000 eggs/hectare) to control mites, aphids, white flies if the papaya is grown in the screen house.

R. Snail and Slug: It feeds on young plants, shoots, or flower buds in humid place. Also, it can transmit the pathogen of phytophthora fruit rot.
1. Grow the seedlings at a safe place.
2. Collect the snails in the evening and at dawn and properly dispose them of.
3. Protect with big plastic cylinder film after transplanting. (This may also protect from virus infection)
4. Apply “Arttitox” 10-15 granules each square meter.

Compiled by Harsh Saxena

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