Disease Management

Cucumber Bacterial Wilt

BACTERIAL WILT OF CUCURBITS

The Plant Disease Diagnostic Clinic

Prepared by M. Bess Dicklow, UMass Extension, 107 Fernald Hall, University of Massachusetts, Amherst, MA 01003-9320. Tel. 413-577-1827 Fax. 43-545-2115. mbdicklo@umext.umass.edu

Bacterial wilt caused by Erwinia tracheiphila is a serious threat to commercial cucumber and melon production and is rapidly becoming more important in pumpkin and squash cultivation.

E. tracheiphila is dispersed within and among fields by the cucumber beetle vector. The bacterium is transmitted mechanically by contact with contaminated mouthparts and does not reproduce within the beetle. The beetles feed on leaves and stems, E. tracheiphila multiplies in the wound, enters the xylem vessels (water conducting tissues), and moves through the petioles to the stems. Masses of bacteria, gums, and resin plug the vascular system, resulting in wilt. Bacteria spread throughout the plant through adjacent xylem vessels. Infected plants serve as a reservoir of bacteria for subsequent infections.

The expression of symptoms varies with the different crop species. Cucumber and melon plants are severely affected; individual runners or whole plants wilt and die rapidly. Often affected plant parts will appear dark green before irreversible wilt. Wilt is most severe early in the season when the plants are rapidly growing. Summer squash and pumpkin may wilt dramatically during the heat of the day and partially recover by morning. Foliage appears yellow before the entire plant collapses and dies. Young pumpkin plants lose vigor and die within two weeks of initial symptom expression. Weather has little effect on the incidence of wilt, but may influence the rate of symptom expression.

Management of Bacterial Wilt

• Because this bacterium is transmitted systemically, copper sprays are of no value. Cucumber beetles must be controlled by appropriate insecticide programs.
• Scout twice weekly at seedling stage for cucumber beetles. Treat when beetle numbers reach the threshold of 1 beetle per 100 feet of row.
• Use crop rotation to reduce beetle numbers.
• Rogue infected plants.
• Spunbonded row covers will exclude beetles.
• Plant a sprayed perimeter trap crop of Blue Hubbard squash to protect more susceptible crops.
• Resistant cultivars of cucumber are being developed. No resistance has been identified in melon.
• Bait formulations consisting of attractants, feeding stimulants, and insecticide are being developed and tested.

Chemical recommendations:

bifenthrin (Capture 2 EC): 2.6 to 3.4 oz/A (3 dh, REI 12 h).

carbaryl (Sevin XLR PLUS): 1 qt/a (3 dh, REI 12 h). Very toxic to bees and aphid natural enemies. Apply at night. Do not apply when foliage is wet.

endosulfan (Thionex 50 W): 1 to 2 lb/A (2 dh, REI 24 h). Toxic to bees; apply in the evening.

imidacloprid (Admire 2F): 1-1½ pt/A (21 dh, REI 12 h). Systemic insecticide applied in-furrow, banded, drench, or drip irrigation to seedling root zone. Do not apply as foliar spray.

kaolin (Surrond WP): 12 ½ to 25 lb/A (0 dh, REI 4 h). Suppression and repellence only. Use prior to flowering to avoid residue.

methomyl (Lannate SP): ½ to 1 lb/A (1 dh for ½ lb, 3 dh for > ½; REI 48 h).

permethrin (Ambush): 6.4 to 12.8 oz/A (0 dh, REI 12 h).

pyrethrin (PyGanic EC 5.0): 4.5 to 18 oz/A (0 dh, REI 12 h).