MINI WHITE PAPER ON SWEET POTATOES

8) Main diseases and insect pests affecting sweetpotatoes

Fusarium wilt or Stem rot

After planting, leaves turn yellow (and eventually die) while stems stop growing and begin to crack. Cracking occurs frequently in sandy soil and during high-temperature years. In fields affected by this disease, avoid continuous cropping and completely sterilize all seed sweetpotatoes and sprouts.

Black rot

After planting, lower leaves turn yellow and fall off. Black rot is transmitted by seed sweetpotatoes and sprouts; once in the fields, it is difficult to control.

Black spot

This disease occurs in August and September. Leaves first develop round brown spots about 1-3 mm across, then turn light brown to grayish brown before dying and falling off. Copper preparations are an effective response. Also, be sure to completely dispose of damaged leaves and sterilize all seed sweetpotatoes.

Sweetpotato leaf worm

Frequently seen in temperate regions in western Japan. As adults, these pests can consume all of a plant's leaves, causing great damage. Three to four generations appear annually, with the greatest damage occurring in autumn. Treatment should commence as soon as these pests initially appear; use DDVP emulsifier or diptelex emulsifier.

Sweetpotato leaf folder

Sweetpotato leaf folder larvae eat leaves from the time sweetpotatoes are in their nursery beds until they are harvested. They wrap leaves with silk strands, and hide themselves inside. In temperate districts, 6-7 generations appear; in moderate-temperature districts, 4-5 generations are more common. To control sweetpotato leaf folder, use the same chemicals used for sweetpotato leaf worm infestations.

Common Cutworm or cluster caterpillor

Common Cutworm larvae only eat the back sides of leaves, leaving the leaf surface alone. Since the leaves affected turn white, they can be easily identified. Four generations appear. To fight this pest, use the same chemicals used for sweetpotato leaf worm infestations.

Gold beetles

These larvae appear in the greatest numbers in mid-August. Accordingly, apply diazinon granules, fine granules or baijit granules in early July when they first begin to appear. Otherwise, sterilize the soil to control nematodes.

Root-knot and root-lesion nematodes

These nematodes deter the initial growth of sweetpotatoes, damage their nutrition levels, cause storage root deformation, and produce brown to blackish-brown spots on the potato's surface. To avoid nematode infestations, avoid continuous cropping, cultivate pest resistant crops such as peanuts, and sterilize tubers with chlorpicrin or DD when growing for fresh consumption.

Fusarium wilt or Stem rot	After planting, leaves turn yellow (and eventually die) while stems stop growing and begin to crack. Cracking occurs frequently in sandy soil and during high-temperature years. In fields affected by this disease, avoid continuous cropping and completely sterilize all seed sweetpotatoes and sprouts.
Black rot	After planting, lower leaves turn yellow and fall off. Black rot is transmitted by seed sweetpotatoes and sprouts; once in the fields, it is difficult to control.
Black spot	This disease occurs in August and September. Leaves first develop round brown spots about 1-3 mm across, then turn light brown to grayish brown before dying and falling off. Copper preparations are an effective response. Also, be sure to completely dispose of damaged leaves and sterilize all seed sweetpotatoes.
Sweetpotato leaf worm	Frequently seen in temperate regions in western Japan. As adults, these pests can consume all of a plant's leaves, causing great damage. Three to four generations appear annually, with the greatest damage occurring in autumn. Treatment should commence as soon as these pests initially appear; use DDVP emulsifier or diptelex emulsifier.
Sweetpotato leaf folder	Sweetpotato leaf folder larvae eat leaves from the time sweetpotatoes are in their nursery beds until they are harvested. They wrap leaves with silk strands, and hide themselves inside. In temperate districts, 6-7 generations appear; in moderate-temperature districts, 4-5 generations are more common. To control sweetpotato leaf folder, use the same chemicals used for sweetpotato leaf worm infestations.
Common Cutworm or cluster caterpillor	Common Cutworm larvae only eat the back sides of leaves, leaving the leaf surface alone. Since the leaves affected turn white, they can be easily identified. Four generations appear. To fight this pest, use the same chemicals used for sweetpotato leaf worm infestations.
Gold beetles	These larvae appear in the greatest numbers in mid-August. Accordingly, apply diazinon granules, fine granules or baijit granules in early July when they first begin to appear. Otherwise, sterilize the soil to control nematodes.
Root-knot and root-lesion nematodes	These nematodes deter the initial growth of sweetpotatoes, damage their nutrition levels, cause storage root deformation, and produce brown to blackish-brown spots on the potato's surface. To avoid nematode infestations, avoid continuous cropping, cultivate pest resistant crops such as peanuts, and sterilize tubers with chlorpicrin or DD when growing for fresh consumption.