Thomas A. ZitterProfessor, Department of Plant PathologyCornell University, Ithaca, NY 14853
Plant diseases can be a limiting factor in pepper production wherever the crop is grown. Moisture in the form of wind blown rain, saturated soils and high humidity plays a major role in the occurrence of both bacterial and fungal diseases. Insects that attack pepper serve to create wounds favorable for bacterial soft rot and spread several virus diseases. Clean seed, greenhouse sanitation, crop rotation, and cultural measures in the field are all key components for disease control, but it all starts with the seed! This is especially true for the first disease discussed, bacterial leaf spot. All major seed companies are incorporating disease resistance into most released varieties with emphasis placed on bacterial leaf spot, Phytophthora blight, and assorted virus diseases.
Bacterial Leaf Spot (BLS)
Bacterial leaf spot is caused by two major groups of bacteria, Xanthomonas campestris pv. vesicatoria and Xanthomonas vesicatoria (some literature will also mention Xanthomonas axonopodis pv. vesicatoria). A number of races occur for each of these pathogens, with some occurring more commonly on pepper and others on tomato. Both bacteria are gram-negative rods, have a single polar flagellum used for mobility, and are found only in association with plants or plant materials. The BLS pathogens are seedborne, both within the seed and on the seed surface. BLS may also survive on plant debris in the soil for 1-2 years, therefore a 2-year rotation out of pepper and tomato is essential.
Seed can be treated with hot water (122°F for 25 minutes) or with Clorox® (EPA Reg. No. 5813-1; label available from Clorox at 800-446-4686). Hot water is more effective for controlling bacteria on and within seed, but hot water can adversely affect germination if not properly performed (see ref. 3). Treating the seed yourself nullifies the seed company's liability and voids their guarantees. Mix 1 quart of Clorox® bleach (calcium hypochlorite) with 4 quarts of water to treat up to 1 pound of seed in a cheesecloth bag, add ½ tsp. of surfactant (dishwashing detergent), and submerge in the solution with agitation for 40 minutes, rinse under running tap water for 5 min, and dry seed thoroughly. Treated seed should be dusted with Thiram 75W [dithiocarbamate] (1 tsp. per pound of seed), and planted soon after treatment.
Some varieties currently have resistance to all three races of BLS (BLSR1, 2, 3) that commonly occur in our area. These include Boynton Bell, Aristotle, Commandant, Enterprise, Revolution, X3R Camelot, and X3R Wizard. King Arthur is resistant to race 2 and Admiral is resistant to races 1 and 2. Resistance to races 1 and 3 are most important for the Northeast.
Use of disease-free seed and a 2-year rotation in the field should solve most of the BLS problems, but some persistent cases may require chemical treatments. Streptomycin (Agri-Mycin 17, Agri-Strep) sprays (1 lb per 100 gallons or 1 ¼ tsp per gallon) may be applied to transplants prior to transplanting. In the field, applying fixed copper (1 lb active ingredient per acre) plus maneb (1 ½ lb 80WP per acre) has been shown to reduce the spread of BLS.
Bacterial Soft Rot (BSR)
Bacterial soft rot is caused primarily by Erwinia carotovora subsp. carotovora. The bacterium is commonly associated with plants, soils and surface water, and thus is a common contaminant. BSR is primarily a post-harvest problem except when fruit are injured in the field by insect feeding. The European corn borer larvae tunnel under the calyx (cap), and their entry holes are marked by sawdust-like frass. Insecticide treatments should coincide with peaks in adult activity as determined by pheromone or light traps. Registered insecticides include cyfluthrin (Baythroid 2), esfenvalerate (Asana XL), permethrin (Ambush), and spinosad (SpinTor 2SC). Hot pepper varieties are most resistant to larval feeding, while green bell peppers are most susceptible.
Pythium Damping Off (also caused by Phytophthora spp., and Rhizoctonia solani)
Pythium Root Rot
Phytophthora Crown Rot and Aerial Blight
Cucumber Mosaic Virus (cucumovirus, aphid transmitted, not seed transmitted in pepper, many weed hosts)
TMV is worldwide in distribution and can readily be transmitted by physical contact. No insect vectors are known. TMV is one of the most stable plant viruses, capable of surviving on dried plant debris and roots of tomato and probably pepper for many years. It is known to be seedborne in pepper and tomato. Although the natural host range of TMV is wide, it is primarily a problem for solanaceous crops (pepper and tomato).
Tomato spotted wilt virus (TSWV) causes brown spotting or dark ringspots on foliage and fruit, and stunting and distortion of the young growth of pepper plants. TSWV is transmitted by at least 8 species of thrips, with the tobacco thrips (Frankliniella fusca) and western flower thrips (F. occidentalis) considered to be the most important vectors. Thrips acquire TSWV by feeding on infected plants only as larvae. After a latent period of 3-7 days, they are then able to transmit the virus to uninfected plants for the remainder of their lives. TSWV has a host range in excess of 600 plant species, but many of these plants do not support thrips reproduction and are considered 'dead ends' for virus spread.
1. Compendium of Pepper Diseases. 2003. Ed. K. Pernezny, P. D. Roberts, J. F. Murphy, and N. P. Goldberg. APS Press, St. Paul, MN. 63pp.
2. Northeast Pepper Integrated Pest Management (IPM) Manual. 2001. Ed. T. Jude Boucher and Richard A. Ashley. University of Connecticut, Cooperative Extension System.136pp.
3. Vegetable MD online web site: http://vegetablemdonline.ppath.cornell.edu/ for selected fact sheets, news articles (ie. Managing Bacterial Leaf Spot in Pepper), and images.
4. Fungicide Resistance Action Committee site for Fungicide Groups: http://www.frac.info/publications/FRACCODE_sept2002.pdf