Most frequent and destructive disease for peppers in eastern US is bacterial leaf spot caused by Xanthomonas campestris pv. vesicatoria. One season it can live in seeds and plant waste, and the other it is a rod-shaped gram-negative bacterium (Frank et al. 2005). Different strains or races of the bacteria are cultivar-specific, generating disease symptoms in specific types because of their strict host specificity. Early defoliation of infected leaves and disfigured fruits can be devastating to a pepper crop caused by bacterial leaf spot. As the condition progresses, it becomes increasingly difficult to discover a cure. As a result, farmers have a number of ways for preventing it from spreading.
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Common pepper disease
Small, water-soaked spots that emerge on the lower surface of older leaves are a sign of bacterial spot on the upper surface of the leaf. In Maryland, this is a significant pestilential illness. Tomatoes are also a target on occasion. The dots eventually become gray to tan in color with deeper outlines. When it’s hot and humid outside, lesions grow larger. Foliage may then go from green to yellow to brown before dropping. Stems may also become infected. Small, raised rough spots appear on fruits, but they have no effect on the taste or texture of the fruit. The sunscald of peppers will occur if the leaves of the plant are severely diseased. Working with plants that have been infected with bacteria spreads bacterial leaf spot. When the weather is rainy, this disease has the potential to defoliate plants. The disease’s transmission is slowed by dry, hot weather. Seed or transplants can carry the disease, and it can survive in crop leftovers and soil over the winter.
Bacterial spot can be minimized by following these tips:
- Opt for hardy plants.
- You should buy seeds and plants that are free of disease.
- Soak the seeds for two minutes in a 10% chlorine bleach solution to disinfect them (1 part bleach; 9 parts water). Before planting, make sure seeds have been thoroughly cleaned and dried.
- Apply a thick organic mulch, like newspaper wrapped in straw or grass clippings, to the roots of your plants.
- The use of water sprayed from above is should be avoided.
- At the end of the growing season, remove and dispose of any plant portions that have been contaminated with disease or pests.
- To inhibit the spread of infection, use fixed copper (an organic fungicide) every 10-14 days.
- If the infection is serious, move the peppers to a new area and cover the soil with black mulch or garden fabric before planting.
Leaf spot, fruit spot, and stem canker are all examples of disease signs that may emerge on the plant’s above-ground section. Early signs, on the other hand, are water-soaked lesions on leaves (Figure 1) that can quickly turn dark brown and grow into patches up to 1/4 inch in diameter with slightly elevated borders (see Figure 1). In less humid conditions, these patches might dry out and the injured tissues can fall off, giving the affected leaves a torn appearance (Figure 2).
Variable in size, the lesions have angular or uneven borders. Larger lesions (greater than 1/2 centimeter) may be apparent on some cultivars, whilst on others, multiple minor lesions (more than 1/4 centimeter) may cover more than 80 percent of the leaf’s surface area. The leaves of some plants may have a mix of minor and big lesions. Affected leaves become yellow and die prematurely, limiting plant output and exposing fruit to possible sunscald. This can dramatically diminish yield. In addition, fruits with raised, scab-like patches are unsellable. Although bacterial infections may not cause fruit to rot directly, lesions can allow other fruit-rotting pathogens to enter, resulting in fruit deterioration….
Disease Cycle & Epidemiology
Time periods characterized by high humidity combined with warm temperatures favor the growth of bacterial spots. It is possible for the pathogen to persist in seeds and plant detritus (McGrath & Boucher, 2012). Although the permanence of debris and the pathogen depends on environmental conditions, it is fairly typical for the disease to survive at least a year in debris. Even if the organism survives the decomposition process, it will perish in the soil after a few weeks. An inoculum source can also be found in weeds and volunteer host plants.
Relative humidity over 85 percent, long durations of leaf wetness, and heat waves are all favorable conditions for disease growth. More than three days of relative humidity below 40% can lower illness severity and delay its onset by up to two weeks. Even if favorable conditions return, prolonged periods of low humidity have an irreversible impact on disease propagation and progression.
Seed contamination is the primary source of bacterial leaf spot infection in cooler climes (Agrios, 2005). Plants with bacterial spot symptoms can even be grown from infected dried seeds that have been stored in the cold for a decade. This is why seeds are critical to the propagation and survival of the disease. Wind-driven rain, irrigation droplets, aerosols, and the handling of wet plants can spread bacteria over fields. If the plants remain moist for an extended period of time, the risk of infection increases.
Using resistant varieties
- The pathogen has up to 11 known variants, thus resistant types must be able to withstand all the strains that are widespread in a given area. There are sweet pepper types that are resistant to all strains or several strains. Autry, Green Flash, Labelle and Ninja are just a few of the F1s that make up this collection. The Green Machine, Antebellum with X10R, and 4288a with bs5+bs6 genes can also be used. Please visit http://vegetablemdonline.ppath.cornell-edu/Tables to see the entire set of tables: TableList.htm
- In order to avoid the spread of the pathogen, the most effective management technique is to employ pathogen-free seeds and disease-free transplants. To prevent the spread of bacterial leaf spot on seedlings obtained from outside the farm, it is best to cultivate your own transplants under sanitary conditions. Infected transplants, including your own, should be discarded after thorough inspection. Seeds can either be purchased from an established seed supplier, or you can treat your own seeds by following the instructions below.
- To reduce the bacterial population on a seed’s surface, dilute two parts Clorox with eight parts water for 40 minutes. However, this treatment has minimal effect on germs found within the seeds themselves.
- To reduce bacterial populations on the surface and inside the seeds, soak the seeds for 30 minutes in water pre-heated to 125 F/51 C. Heat treatment, on the other hand, has the potential to interfere with seed germination if it is not carried out correctly, but the danger associated with bleach treatment is minimal.
- The prevention of the leaf spot bacteria spreading in the field begins with the control of bacterial spot on greenhouse transplants. Symptomatic seedlings might be spotted by inspecting transplants on a regular basis. If a diseased transplant is found at an early stage, it can be removed and destroyed or treated with streptomycin. Multiple administrations of streptomycin may lead to the emergence of strains of leaf spot bacteria that are resistant to the antibiotic.
- Copper sprays can be used to control bacterial leaf spot, but they are not as effective when used alone on a continuous basis. If combined with plant resistance-inducing agents, such as Regalia or Actigard, this combination can provide a strong defense against the disease. Depending on the plant’s growth stage, fixed copper and Actigard are applied at varying rates. In the early season, 1 ounce per 100 gallons of Actigard is applied at transplant; 1/2 ounce is used two weeks later; and 1/3 ounce is advised for future sprays. Penncozeb and Quintec, two other medications, were also found to be beneficial in some tests. However, organic growers should use copper and Regalia combination instead of copper and Actigard. When it’s raining, humid, or warm outside, utilize a seven- to ten-day interval; if it’s dry, go with a longer one.
- Leaf spots caused by bacteria can be controlled by using copper sprays, however they are not as effective when applied on a regular basis. A plant resistance inducer, such as Regalia or Actigard can be used in conjunction with these sprays to help defend against the disease. Different rates of Actigard and fixed copper are used based on the growth stage of the plants. In the early season, 1 ounce per 100 gallons of Actigard is used at transplant; 1/2 ounce is used two weeks later, and 1/3 ounce is advised for future sprays. It has been demonstrated to be effective in some tests using Penncozeb and Quintec. Instead of copper and Actigard, organic farmers should use copper and Regalia. Utilize a seven- to ten-day cycle; in times of rain, high humidity, and warm temperatures, go with the shorter cycle, and in times of drought, go with the longer cycle.
- For an effective BLS management program, weeds and infected crop debris are additional sources of the disease. Nightshade, horsenettle, jimsonweed, and all other solanaceous weeds must be eliminated from pepper crops now and in the future. To speed up crop residue breakdown, disking or plowing the field right after harvest might be used.
- To prevent the spread of pathogens through volunteers and crop residue, crop rotation should be implemented. The presence of bacterial spot should be avoided in fields that have recently been planted with peppers or tomatoes. As a general rule, rotate crops every three years in the field to prevent the pathogen from reactivating. Don’t grow peppers with other vegetables like tomatoes, eggplants, or potatoes.
- To prevent the spread of disease in the greenhouse, destroy trays close to the outbreak site. Always use new or cleaned greenhouse supplies and materials while planting peppers. Between seedling crops, trays, benches, equipment, and greenhouse structures should be cleaned and sanitized.
- Avoiding conditions that allow the disease to spread and multiply quickly is an important part of good cultural practices. Splashing water spreads bacteria. When plants are moist, the field should not be entered, so an alternative means of irrigation should be used.
- One intervention, such as seed treatment, has been demonstrated to be insufficient for controlling bacterial leaf spot in peppers, hence an integrated strategy is the optimum approach (Stall et al., 2009). In addition to the preceding techniques, this integrated strategy comprises inspecting the field, removing affected plants, and timing mechanical and labor operations to occur at periods when the risk of spreading leaf spot bacteria is low.
What are the Symptoms of Bacterial Leaf Spots?
A bacterial leaf spot might show up as little water-soaked areas under pepper leaves. Eventually, the leaves will become brown and have a raised appearance. The spots on the upper side of the leaves have beige centers and dark brown margins, as can be seen in the image below.
The speckled leaves will begin to fall when they turn yellow. Sunscald can occur if your peppers lose their leaves and are exposed to direct sunlight. In addition, if your pepper plants don’t have enough leaves, they won’t be able to grow and produce excellent fruit.
It is possible that bacterial leaf spot will infect your peppers as well. Because infected peppers are smaller and sometimes exhibit abnormalities, the remaining fruits may not be harvestable. When peppers have lesions on them, they are more vulnerable to various pathogens that can cause decay and other ailments, such as bacteria.
How to Prevent Bacterial Leaf Spots
There is no known remedy for bacterial leaf spot. If the symptoms begin to spread, it will be too late to halt them. Bacterial leaf spots can be prevented in numerous ways, as previously indicated.
Crop rotation can help limit the spread of bacterial leaf spot. It’s best to avoid the same spot for peppers for at least four to five years.
After a full growing season, remove any crop residue from your garden beds and dispose of it properly. Make sure that you don’t put them in the compost because they may have infectious diseases that could harm your new plants after you’ve cleared everything out.
Bacterial leaf spot is commonly brought on by watering from above, which brings soil moisture to the leaves. Use a soaker hose or an appropriate irrigation system to irrigate your pepper plants to avoid excessive splattering. As a rule of thumb, avoid watering your plants from above.
Seeds tainted with the illness might also transmit it. Local garden shops are the best place to get seeds and seedlings that are disease-free. If you’ve ever experienced bacterial leaf spot, don’t utilize your pepper seeds.
Other Ways to Prevent Bacterial Lead Spots
To avoid bacterial leaf spot, there are various options. As an example, you may try planting resistant types or cultivating your peppers with organic mulch; switching to drip irrigation; inspecting your plants for weeds more frequently; or sterilizing your seed starting solution for two minutes with bleach.
Mix one part bleach with nine parts water to produce your own chlorine solution if you’re not sure how. Before you plant your seeds, ensure sure they’ve been well rinsed and dried.
Why It Pays to Grow Your Peppers in a Greenhouse
Growing peppers in a greenhouse has various advantages. Among the many advantages of growing plants in a tiny greenhouse are the following:
Protect your plants from pests and diseases
There are a variety of insects that might cause harm to your peppers. These include flea beetles, aphids, cutworms, corn borer, and whiteflies. Many other diseases, such as powdery mildew and mosaic virus, can harm your plants in addition to leaf spot. Placing them in an enclosed greenhouse lowers the risk of attracting pests and other infectious diseases.
Keep your plants safe from unpredictable climates
Many insects can hurt your pepper plants. Some of the most common ones are flea beetles, cutworms, aphids, corn borer, and whiteflies. There are several more diseases that might harm your plants, such as southern blight, powdery mildew, and the mosaic virus. An covered greenhouse reduces the risk of attracting bugs and other infectious illnesses by keeping them out of direct sunlight.
Start planting early
Did you know that you may start your plants out on the right foot by using mini-greenhouses? As soon as the cold season begins in your location, you can begin planting seeds and seedlings in your garden. Your vegetables can be transplanted into your garden as soon as the weather clears and warms up.
Perfect for people with limited garden space
For those who enjoy gardening but lack a garden space, a small greenhouse is an excellent alternative. Almost anything may be grown in them, and they’re small and portable. Mini-greenhouses provide the same advantages as larger ones, despite their size.
Final Thoughts on How to Cure Bacterial Leaf Spots on Peppers
The first thing you need to know about bacterial leaf spots on peppers is that they can’t be cured if the symptoms begin to spread. However, this can be avoided. Make sure you plant pepper kinds that are resistant to illness and that the seeds are clean and disease-free. Before you plant your transplants in your garden, isolate them and look for any signs of disease.