HPIPM:Bacterial Spot

Author: Howard F. Schwartz and David H. Gent

Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Gammaproteobacteria
Order	Xanthomonadales
Family	Xanthomonadaceae
Genus	Xanthomonas

Scientific Name

Xanthomonas vesicatoria

Scientific Name Synonyms

Xanthomonas campestris pv. vesicatoria

Xanthomonas vesicatoria pv. vesicatoria

Xanthomonas axonopodis pv. vesicatoria

Phytomonas vesicatoria

Common Name

bacterial spot

Identification and Life Cycle

Bacterial spot is caused by two species of bacteria, Xanthomonas axonopodis pv. vesicatoria and X. vesicatoria. Bacterial spot can be damaging to both pepper and tomato in the High Plains during warm (75 to 86ºF), humid, rainy weather. Bacterial spot does not affect eggplant. Bacteria are introduced onto plants by planting contaminated seed and transplants, splashing rain or irrigation water, aerosols, or on contaminated equipment. The bacteria multiply on leaves to form large populations before penetrating through natural openings or wounds created by wind-blown sand, insect feeding, or mechanical injury. The bacterial spot pathogens survive between susceptible crops in and on weed, volunteer plants, infested crop debris, culls, and contaminated seed and transplants.

Plant Response and Damage

The bacterial spot pathogens can infect all aboveground plant parts. Disease symptoms begin as small, brown, water-soaked lesions, which turn brown with necrotic centers. Leaf lesions are generally sunken on the upper surface, but are raised on lower surfaces. Lesions are rarely larger than 0.12 inch, but when conditions are favorable for disease, lesions coalesce and from large blighted areas. Infected leaves turn yellow and drop prematurely. Fruit lesions begin as small (0.04 inch) circular green spots, but turn brown and become cracked and roughened with age. Bacterial spot reduces both yield and fruit quality. Infected fruit is generally unmarketable.

Biological Control

Bacteriophage, viruses that attacked bacteria, control bacterial spot but must be applied at dusk at least twice weekly to be effective. Nonpathogenic Xanthomonas spp. provide some control of bacterial spot.

Cultural Control

Plant only high quality seed and transplants free from the bacterial spot pathogens. Hot water treatments can reduce seed contamination, but may reduce germination. Practice a three-year or longer crop rotation between susceptible crops; do not plant tomato and pepper consecutively in a field. Eliminate weeds, volunteers, crop debris, and cull piles that can serve as inoculum sources. Avoid reuse of irrigation tail water and overhead irrigation if possible. Resistant varieties are available, but should be chosen carefully to match the most prevalent pathogenic races of the pathogen present. Eleven pathogenic races are known to occur; no single resistance gene will provide resistance to all pathogenic races.

Chemical Control

Resistance to copper bactericides and streptomycin are widespread in the bacterial spot pathogens. Tank-mixing copper bactericides with EBDC fungicides such as maneb can provide some suppression of copper-tolerant strains of X. axonopodis pv. vesicatoria. The plant activator Actigard can provide effective control of both copper sensitive and tolerant strains of the pathogen, but can reduce yields in the absence of disease. Chemical controls are most effective when combined with as many cultural and biological controls as possible.

Product List for Bacterial Spot:

Pesticide	Product per acre	Application Frequency (days)	Remarks
Acibenzolar
Actigard 50 WG	0.33-0.75 oz	7-14 days	Do not apply to stressed plants; Start applications at a low rate and slowly increase; Maximum of 4 ounces per season; 14 day PHI
Copper Fungicides
Champ Dry Prill	1.33 lb	5-7 days
Champ Formula 2	1.33 pt	5-7 days
Copper-Count-N	4-6 pt	7 days
Cuprofix MZ Disperss	1.75-4.75 lb	7-10 days
Kocide 101	1.5-3 lbs	5-7 days
Kocide DF	1.5-3 lb	5-7 days
Kocide 4.5LF	1-2 pts	5-7 days
Kocide 3000	0.75-1.75 lb	5-10 days	Maximum of 21 lb product/A
Nordox	1.5-2.0 lb	7-10 days
Tri Basic Copper	2-4 pt	7-10 days	1 day PHI
Copper/EBDC/Zoxamide Mixtures
Cuprofix Disperss MZ	1.75-4.75 lb	3-10 days	Maximum of 21 pounds per season; 5 day PHI
Gavel	1.5-2.0 lb	7-10 days	Maximum of 4 (west of Rockies) to 8 (east of Rockies) applications, 5 day PHI
ManKocide	2.5-5.0 lb	3-10 days	Maximum of 42.7 pounds per season; 5 day PHI
Famoxadone/Cymoxanil
Tanos	8-10 oz	5-7 days	Suppression; Rotate with other fungicides; 3 day PHI
Streptomycin
Agri-Strep	1 lb/100 gal	4-5 days	Registered for tomato only; Apply once after transplanting

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.