By: Jackie Carroll
Bacterial leaf spot on peppers is a devastating disease that can cause disfiguration of the leaves and fruit. In severe cases, the plants may die. There is no cure once the disease takes hold, but there are several things you can do to prevent it and keep it from spreading. Keep reading to learn about treating pepper leaf spots.
What Causes Bacterial Leaf Spot of Pepper?
The bacterium Xanthomonas campestris pv. vesicatoria causes bacterial leaf spot. It thrives in areas with hot summers and frequent rainfall. The bacterium is spread by plant debris in the soil and through infected seeds.
Symptoms of Bacterial Leaf Spot
Bacterial leaf spot causes lesions on the leaves that look as though they are soaked with water. These lesions normally begin on the lower leaves. As the disease progresses, it leaves a dark, purple-brown spot with a light brown center. Bacterial leaf spot on peppers causes spotting and raised cracks in the fruit. The cracks provide an opening for other disease pathogens.
There are no pepper varieties that are reliably resistant to all of types of peppery leaf spot, but planting varieties that are resistant to some of the races may help prevent the disease.
Insecticides containing copper are also useful in preventing the disease. In most cases, however, once the disease appears, copper isn’t effective in treating pepper leaf spots. Use insecticides containing copper early in the season when you’ve had problems with the disease in previous years.
How to Treat Bacterial Leaf Spot
Of course, once the symptoms of bacterial leaf spot begin to appear on your pepper plants, it’s too late to save them. However, if you take precautions before planting next season, you’ll have a better chance of preventing peppery leaf spot problems in the future.
Crop rotation can help prevent bacterial leaf spot. Do not plant peppers or tomatoes in a location where either of these crops has been grown in the past four or five years.
At the end of the season, remove all crop debris from the garden and destroy it. Do not compost plant debris that may contain the disease. Once the area is clean of all visible debris, till the soil or turn it with a shovel to bury any remaining bacteria.
The bacterium is spread by splattering damp soil onto the leaves. Reduce the splatter by using a soaker hose and avoiding overhead watering. Stay out of the garden on wet days to avoid spreading disease on your hands and clothes.
Bacterial leaf spot is also spread through infected seeds. Buy certified disease-free seeds and seedlings. It’s best not to save your own seeds if you’ve ever had a problem with bacterial leaf spot on peppers.
This article was last updated on
Bacterial leaf spot in pepper
Symptoms: brown spots develop on leaves, stems and fruit.
Diagnosis can be confirmed by looking for bacterial streaming in leaf pieces mounted in water. Copious amounts of streaming was observed from the two leaf pieces taken from the leaf in the following photograph plus two pieces from another leaf, and also from the four leaf pieces taken from the three leaves in the next photograph.
Symptoms can develop on seedlings in a greenhouse.
Sources of the pathogen include debris from previous affected crop and contaminated seed. Bacteria might be moved between nearby farms during a windy rainstorm. Tomato is also susceptible, but bacterial spot has not been confirmed on this host on Long Island. This reflects the fact there is host specificity among the multiple species and races of bacteria that cause bacterial spot. Four species in the bacterial genus Xanthomonas (X. euvesicatoria, X. vesicatoria, X. perforans and X. gardneri) have been identified as causing bacterial spot in pepper, tomato, and other solanaceous plants.
Management practices for bacterial spot include selecting resistant varieties when possible. Most resistance genes (e.g. Bs1, Bs2, Bs3, Bs4, and Bs7) are dominant genes that enable the plant to detect specific races of the pathogen and thwart infection. With race specific resistance the variety needs to have resistance to the race(s) present to be effective. The bacterial spot pathogen has proven adept at evolving new races not detected by the resistant variety, necessitating finding another resistance gene. Eleven races of the bacterial spot pathogens had been identified on pepper as of 2012. Two recessive resistance genes (bs5 and bs6) were identified recently. These genes work differently from the other resistance genes. When used together they provide resistance to all currently known races. X10R pepper varieties have a compliment of bacterial spot resistance genes that provide at least intermediate levels of resistance to all currently known races.
Select seed that has been tested and treated for the pathogen.
Treating seed with hot water can be effective for bacteria on and also inside seed when the seed lot is not heavily contaminated. It is best to have seed treated commercially when possible.
Fungicides are most effective applied preventively, similar to other bacterial diseases. Copper plus mancozeb is the standard recommendation, but is not inherently highly effective and resistance to copper, a major concern with bacteria, has been found to be common in pathogen populations examined (not done on Long Island). There are two plant activators: Actigard (only non-bell type pepper) and LifeGard (all pepper types). They need to be applied before disease onset for maximum benefit. Several organic fungicides are labeled that could be better options than copper for managing copper-resistant pathogen strains. They include BacStop, Thyme Guard, and Timorex Gold (botanical oils) Double Nickel and Serifel (Bacillus sp.) Procidic (citric acid) and OxiDate (hydrogen dioxide). These act on the pathogen and thus could be a good complement in a program with a plant activator. Some phosphorous acid fungicides (e.g. K-Phite) are labeled for bacterial diseases including spot. They act both on the plant and pathogen.
Do not apply fungicides when foliage is wet or use an air blast sprayer. Bacteria can be in this water. The force with which the pesticide solution is moved by the sprayer into the canopy can dislodge and move water droplets with bacteria. Force is greater with air blast than standard boom sprayers, and additionally can be of sufficient force to cause small wounds, especially if there are dirt particles, that enable bacteria to enter the plant. Horizontal movement of pesticide solution from air blast sprayers means bacteria can be moved further than with boom sprayers.
Do not work in crops with bacterial diseases when foliage is wet because bacteria can be moved by hands and equipment that touch water that has bacteria.
See Vegetable MD and APSnet articles for more information.
Please Note: The specific directions on pesticide labels must be adhered to — they supersede these recommendations, if there is a conflict. Any reference to commercial products, trade or brand names is for information only no endorsement is intended.
Leaf discoloration and changes in texture often point to issues related to watering, light, or pests. After properly troubleshooting an ailing plant for potential causes of plant stress and determining that it is not due to improper care, leaf spot or fungal infection should be the next area for investigation.
STEP ONE: IDENTIFICATION
LEFT: An example of a fungal infection. RIGHT: An example of a bacterial infection.
How can you tell the difference between leaf discoloration from care related issues and bacterial or fungus spots? Concentric rings or dark margins are often present in both, and are the most apparent sign of an infection. Bacterial leaf spots and blights can occur at the same time as fungal leaf spots and differentiation can sometimes be difficult between the two.
Fungal bodies may appear as black dots in the spots, either in rings or in a central cluster. Over time, the spots may combine or enlarge to form blotches. Keep an eye out for a new leaf or shoot that collapses quickly, often with a "slimy dark appearance". Severely rotted tissue will often have a "rotten smell" because of secondary infection from other common bacteria found in soil and on plant surfaces. If the leaf is held up to a light source, and viewed backlighted, a water soaked area around the dead tissue can sometimes be seen and sometimes leaf spots will have a definite yellow outline or halo.
Symptoms of bacterial infection in plants are much like the symptoms in fungal plant disease. They include leaf spots, wilts, scabs, cankers and rots of roots and fruit the most common symptom being leaf spots. In extreme cases, dark necrotic spots can spread to an entire leaf and kill it.
The best way to treat suspected bacterial infections is to cut out all infected plant parts in order to prevent further spread. You can also use a bactericide in the early stages of the disease. Certain bacterial infections (such as wilts) can be transmitted by insects as they bite and feed on plant tissue. Keeping your plants pest free reduces the risk of infection, as insects can be vectors for both bacterial and fungal infections.
Prevention and early diagnosis are essential to keeping your plants healthy. Healthy plants have stronger immune systems that make them less likely to get sick, so make sure to provide your plants with enough light and water (but not too much!). Practice good plant hygiene by pruning and making cuts with clean, sharp shears and regularly cleaning your tools with rubbing alcohol.
STEP TWO: CAUSES
Bacteria and fungi typically enter through a wound in the plant. Natural openings in the leaves, flowers, and stems can also serve as entry points. Bacteria can be transferred to new plants by wind, water, contaminated soil and insects. Bacteria that cause leaf and flower spots, blights, and rots, are ever-present in the environment! They survive in diseased plant debris, and plants become particularly susceptible during warm weather and prolonged wet periods (overly wet soil or air) frequently encourage bacterial infections.
STEP THREE: PREVENTION/TREATMENT
Contaminated tissue cannot be treated, so prevention is most important and more effective than treatment. Affected foliage should be removed at the first sign of a bacterial or fungal infection. Removing the whole infected leaf is necessary. Then the remainder of the plant can be treated to prevent further damage, using a copper fungicide . Alleviate poor air circulation and crowded conditions as dry air will help prevent further spread. Copper fungicide is not safe for bromeliads or ivy plants, and it should be diluted extra on new growth which is more sensitive.
Jan Byrne, MSU Diagnostic Services, Department of Plant Pathology - April 8, 2011
These practices will help limit the risk of bacterial leaf spot outbreaks in your greenhouse begonias.
Bacterial leaf spot of begonia is caused by Xanthomonas axonopodis pv.begonia (formerly known as X. campestris pv. begonia) Symptoms include water-soaked foliar lesions and wilting. Foliar lesions are especially visible from the underside of the foliage. Severely affected leaves may fall off the plant. This bacterium can also become systemic, meaning it colonizes the vascular tissues of the plant, causing wilting symptoms.
When I mention Xanthomonas many growers automatically think of geraniums. The good news is that this is a different “kind” or pathovar of Xanthomonas. Bacterial leaf spot on begonia is caused by a Xanthomonas that can only infect plants in the genus Begonia. There are many different types of begonias, most of which can be affected, although they vary somewhat in susceptibility.
Disease management begins with healthy plant material, because the disease is frequently spread via contaminated plant material. Inspect incoming begonias for signs of disease. Plants with any suspicious symptoms should be tested at a diagnostic lab before they are put in close proximity to other begonias. Please note that diagnostic test kits for X. axonopodis pv. pelargonii (bacterial wilt of geranium) cannot be used to detect X. axonopodis pv. begoniae.
Within the greenhouse, spread occurs when irrigation water splashes from an infected plant to the foliage of nearby hosts. Overhead irrigation should be carefully timed to minimize the amount of time that the foliage will remain wet. Longer durations of leaf wetness can promote further disease spread.
The bacterium can also be spread mechanically from plant to plant. Greenhouse staff can readily spread the bacterium by handling plants during pruning of blossoms, removing dead leaves, etc. While some handling may be required periodically throughout production, be sure to avoid handling the plant material when the foliage is wet. Frequent hand washing should be encouraged when working with susceptible begonias.
Diseased plant material should be removed and destroyed. It is also important to note that plants adjacent to symptomatic plants may be harboring the bacterium, although they may not yet be showing symptoms. This is especially true if plants are overhead watered. Sanitation is also a critical component of disease control.
Applications of copper-based-fungicides can be used to reduce disease spread. However, note that plants that are systemically infected cannot be successfully treated. Copper-based products vary in their formulations. When choosing a particular copper-based product, note the percent of active ingredient contained in the formulation as well as the REI specified on each product label. These factors may influence your choice of the particular product that you choose to apply.
This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).
Did you find this article useful?
The Signs of Bacterial Leaf Spot
The problem with bacterial leaf spot is that it shows up on plants in many different ways, making identifying this disease harder.
Some symptoms of bacterial leaf spot include:
- Black-edged lesions on the leaves
- Brown spots with yellow halos on the leaves
- Light and dark areas throughout the foliage
- Brownish-yellow edges of the leaf
- Papery, dry leaves that break off easily.
These spots are typically irregular and measure between 3/16 and 1/2 inches wide. It happens on all leaves, no matter if they’re at the top of the bottom of the plant. When clusters of spots happen on the leaves, they kill the tissue of the foliage.
While the disease attacks all leaves, it’s most common on older leaves, especially when it causes leaves to turn papery. It spreads rapidly, so the new leaves are only safe for a short time.
Common Plants for Bacterial Leaf Spot
No plants are safe from this disease. It likes ornamental and edible plants, but some of the most common hosts are:
- Stone fruit trees, such as apricot, peach, plum, and cherry
Bacterial leaf also infects some annual and perennial flowers, but not as often as they infect vegetable plants and fruit trees. Some common flowers that it attacks include:
- Purple Cone Flowers
- Black-Eyed Susan
Identifying Bacterial Spot’s Damage
Among others, tomato and pepper are two of the most common host plants for bacterial spot, especially those that grow in an environment with high dew and warm climate. Aside from these, other hosts include peach, plum, prune, tart cherry, apricot, wild peach, almond, and nectarine.
The symptoms of the disease will depend on a number of factors, such as the specific host. The strain, pathotype, and race of the bacteria will also have a huge impact. Generally, below are some of the most common signs that you have to watch out for:
- The leaves are the ones that will show the first signs of damage, specifically from their underside. There will be irregular and greasy marks. Initially, the color is dark green but after a while, it will turn either gray, purple, white, or yellow. In severe cases, bacterial spot can lead to defoliation of the host plant.
- Damages will also be apparent on the fruit. In the case of pepper, for instance, rough circles will appear. The diameter will be about ¼ inch and it will appear like blisters. Aside from cracks, the surface will also appear rough, which is similar to tomatoes. As the fruit matures, the spots will inevitably grow larger.
Results of Infestation
Like in the case of other bacterial leaf diseases, most of the damages will be cosmetic. The physical appearance of the leaves will be unattractive. The holes in the leaves will inhibit photosynthesis, and hence, will deprive the plants of the nutrients that are essential for survival. They will grow unhealthy. Other parts of the tree will also show signs of infestation. In severe situations, the plant will end up unmarketable. Hence, this will translate to economic losses for commercial growers.
Tomatoes Infected by Bacterial Spots
Treating Pepper Leaf Spots - Signs And Symptoms Of Bacterial Leaf Spot - garden
by Margaret Tuttle McGrath, Department of Plant Pathology, Long Island Horticultural Research and Extension Center, Cornell
and Jude Boucher, Sustainable Agriculture/IPM Educator - Vegetable Crops, University of Connecticut Cooperative Extension System, Vernon, CT
Also see the LIHREC Photo Gallery entry which has information about management as well as more photographs.
Bacterial leaf spot (BLS) is the most common, and one of the two most destructive diseases of peppers in the eastern United States. Leaf spots are water-soaked initially, then turn brown and irregularly shaped ( Figure 1 ). Affected leaves tend to turn yellow ( Figure 2 ) and drop ( Figure 3 ). Yield is reduced because raised, scab-like spots may develop on fruit ( Figure 4 ) and because affected leaves drop off plants, thereby reducing plant productivity and exposing fruit to potential sunscald ( Figure 5 ). Complete crop failure has occurred. Tomato is also susceptible to BLS. The strain of the bacterium that infects tomato causes small spots on pepper.
The first strategy to use for controlling any disease is to eliminate or reduce the amount of the pathogen available to initiate disease. An important source of the bacterium that causes BLS in pepper is infested seed. Therefore, the use of disease-free seed and transplants are some of the most important BLS management practices. Infested crop debris and infected weeds are additional sources of the pathogen and must also be managed in an effective BLS control program.
Seed can be treated with hot water or Clorox® bleach (calcium hypochlorite) to kill the pathogen. Hot-water treatment is more thorough than Clorox because it reaches inside seed however, high temperatures can adversely affect germination if proper precautions are not taken. It is best to have seed custom treated, which some seed companies will do. Furthermore, it you treat the seed, the seed company’s liability and guarantees are null and void. If you decide to do it yourself, treat at 122 o 122oF for 25 minutes. The best way to control temperature while treating seed is to use a precision laboratory water bath. Procedures are described in an article on hot water seed treatment. If great care is taken, hot-water treatment can be done successfully using a large pot on a stovetop and a precision laboratory thermometer ( Figure 6 ).
Click on each photo for Magnification and Description
|Figure 1||Figure 2||Figure 3|
|Figure 5||Figure 6|
With either equipment, expect to spend some time adjusting settings to achieve a constant 122 o F, especially with the stovetop. A very low hot plate or stove setting will probably provide the correct temperature. Wait to begin treatment until the water temperature in the pot is maintained. Have containers of hot and cold water nearby in case the water temperature does not stay at 122 o F. Place seed in a tea infusion ball or in a piece of cotton cloth. Add a metal weight to keep the seed container submerged, but make sure it is not on the pot bottom. Agitate the water continuously. A wooden spoon works well when using a stovetop. Check the temperature constantly. Keep the thermometer off the hot bottom of the pot this can be accomplished by taping it to the inside of the wooden spoon used for stirring (Figure 6). Upon removing, cool the seed under tap water. Spread the seed out on paper towels to air dry at 70-75 o F. It is recommended to conduct a preliminary germination test with a small quantity of treated and untreated seed from each variety and lot number before treating all the seed. Some seed lots produced from stressed plants may not stand up to hot water treatment and germination may be adversely affected (though this is rare with pepper seeds).
Clorox Commercial Solutions® Clorox® Germicidal Bleach (EPA Reg. No 5813-100) and Clorox Commercial Solutions® Ultra Clorox® Germicidal Bleach (EPA Reg. No 67619-8) are labeled for pepper seed treatment. There is less chance of seed being damaged with bleach than hot water however, chemical controls such as Clorox are effective for pathogens on the seed surface only hot-water treatment can kill bacteria inside as well as on the outside of seed. These have 7.85% and 5.84% available chlorine, respectively. To Clorox treat seed, prepare a solution with 10,000 ppm available chlorine. Mix 16.7 or 22.2 fl oz of these products, respectively, with 1 gallon of water to obtain treatment solution. Use 1 gallon of this solution per pound of seed. Put up to 1 pound of seed in a cheesecloth bag, submerge in this solution and provide continuous agitation for 40 minutes, rinse seed under running tap water for 5 minutes, then dry seed thoroughly on paper towel. Put the seed in a new package, not back in the original one. Prepare a fresh batch of the dilute Clorox solution for each 1-pound batch of seed. The soak can stimulate germination, so if the seed is dried and held too long, germination will be reduced. To legally make this treatment, only these formulations can be used and the full label with this use must first be obtained from the Clorox company (800-446-4686) or by going to the following web site.
Enter ‘Clorox Germicidal Bleach’, for ’Name’ in second section on the right side. Click on ‘Search’ below the search section. When the results are displayed, click on the ‘More’ button in the lower right corner of the box for either product. Note that the search results will include other products that do not have use directions for seed treatment.
Either seed treatment should be done within a few weeks of planting. Best is doing right before planting as treatment can prime seed for germination. Afterwards a fungicide can be applied to prevent damping-off and other pathogens from infecting seeds. There are several formulations of Thiram registered for application as a dust or slurry.
Other management techniques which help eliminate or reduce the initial amount of disease pathogen present include greenhouse sanitation, producing your own disease-free transplants, crop rotation, proper weed control and hastening the decomposition of host plant residue. Grow your own transplants under sanitary conditions to avoid importing bacterial leaf spot on seedlings purchased from off-farm sources. Always start with new or disinfected greenhouse supplies and materials when planting peppers. Examine seedlings weekly for symptoms. Reduce favorable conditions for BLS in the greenhouse by keeping it as dry as possible and by minimizing splashing water. In the field, use at least a 3-year rotation because the pathogen can survive in infested crop debris until it completely decomposes. Do not rotate pepper with tomato, eggplant, or potato and do not grow these crops together. Control nightshade, horsenettle, jimsonweed, and all other solanaceous weeds in current and future pepper fields. Disk or plow the field immediately after the final harvest to hasten the breakdown of crop residue.
The second disease control strategy is to reduce the rate at which the disease develops in a planting. This can be accomplished by selecting resistant varieties, applying bactericides if necessary, and/or avoiding conditions that enable the pathogen to spread and multiply rapidly. An integrated management program for BLS is recommended to ensure effective control as bactericides or resistant varieties alone will not be sufficient when conditions are very favorable for BLS (hot and wet) or when less susceptible BLS races are present.
BLS resistant pepper varieties usually provide effective control of BLS and excellent yield. Resistant varieties have performed well in several experiments. For example, susceptible Merlin and North Star were severely infected by BLS and produced only 0.7-1.4 ton/A of marketable fruit while resistant Boynton Bell produced 20.5 ton/A (KY, 1995). All 7 resistant varieties tested on Long Island provided better control of BLS than a weekly preventive spray program of the copper fungicide/bactericide Kocide 2000 + Maneb 75DF (which was applied with a tractor-mounted boom sprayer delivering 100 gpa at 250 psi). These varieties yielded as well as the susceptible standard Camelot treated preventively. Applying Kocide + Maneb to the resistant varieties did not improve disease control or increase yield in these experiments. However, in Florida, where conditions can be very favorable for BLS, growers feel they need to use foliar sprays on resistant peppers.
Effective control of BLS with resistant varieties requires knowing what races of the pathogen are likely to be present. BLS resistant varieties have race-specific resistance. Thus a variety lacking resistance to all of the races present may not perform any better than a susceptible variety. Race 1 occurs throughout the United States. Race 2 is found in Florida and the Caribbean. Race 3 is a common mutant of both race 1 and 2. Races 4 and 5 are uncommon and expected to remain so because they are not fit. Races 1 and 3 have been found in the northern U.S. therefore varieties selected for this area need resistance to both races 1 and 3. The situation could change in the future. A widespread and serious outbreak of BLS caused by races 4 and 6 occurred throughout southern Florida, where most varieties grown have resistance to races 1 - 3, during the unusually wet 19971998 winter vegetable season. Unfortunately, resistance is only available for races 1 - 3 at present. Resistant varieties should be examined routinely for symptoms in order to detect occurrence of new races early enough in disease development to initiate a chemical control program. Results from variety trials also should be considered when selecting resistant varieties as they differ in fruit quality and yield.
A chemical control program is recommended for susceptible varieties that show symptoms, and should begin in the early stages of disease development. Examine the plants every week. It is worthwhile to remove infected plants if they are found early, before there has been the opportunity for spread. If infected plants are found while scouting, apply bactericides (copper fungicides are toxic to bacteria) on a 7 to 10-day schedule use the shorter interval when rain, high humidity and warm temperatures occur. Stretch the interval by one day for each night that temperatures fall below 61 o F. Recent research on Long Island showed that a program where applications began after disease symptoms occurred, was less expensive and worked as well as weekly preventive sprays initiated early in the season before the disease was present. Connecticut growers have used weekly scouting and this "wait-and-see" policy before implementing a spray program with good results for many years. Adding maneb to a copper application has been shown be more effective than using copper alone in some experiments. Efficacy is improved because more copper is dissolved when copper and maneb are agitated together in the spray tank for about 90 minutes before application. However, maneb may not improve efficacy of newer copper formulations that provide more available copper in the spray solution than older products. A high pressure airblast sprayer should not be used because it can disperse the bacteria through a field. Discontinue spraying in late summer when night temperatures are consistently below 61 o F and daytime relative humidity is well below 85%. While chemical control can be effective, it is not foolproof. Failure can occur when conditions are very favorable for disease development and when plants are infected with a bacterial strain that is resistant to copper.
Warm, wet conditions are favorable for diseases caused by bacteria. Therefore, irrigation method is an important consideration in managing BLS in the field. Overhead irrigation provides both a means of spread for the pathogen and favorable conditions for disease development, therefore trickle irrigation is recommended. In addition to movement by splashing water drops, the pathogen can be spread through any mechanical means imaginable when plants are wet, including on workers hands and on machinery such as cultivators. If possible, avoid working fields when the plants are wet and work infested areas last. Disinfect machinery used in infected sections of the field after the job is completed.
Low nitrogen or potassium, and extra high magnesium and calcium levels have been associated with increased crop susceptibility to BLS. Pepper crops that show visible signs of nitrogen deficiency (light colored leaves) have been severely affected by BLS in Connecticut. Researchers have also found that BLS is more severe on pepper plants grown in soils adjusted with dolomitic lime, which is high in magnesium, than plants grown in soils adjusted with Cal limestone (CaCO3). Maintain nutrients at the proper levels (moderate to high) to help plants resist infection.
In summary, some of the most important management practices for BLS in pepper are using hot-water seed treatment, planting disease-free transplants, selecting resistant varieties, and using a 3-year rotation to prevent re-infection. In addition, use trickle irrigation, scout weekly, rogue the first infected plants found, maintain proper nutrient levels, use proper sanitary measures and disk or plow the field immediately after harvest. If necessary, apply copper (or copper plus maneb) after disease detection on a 7 to 10 day schedule with a boom sprayer.
The specific directions on fungicide labels must be adhered to -- they supersede these recommendations, if there is a conflict. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended.