Pests & Diseases affecting chilli peppers

So, you've bought (or saved) your seeds, carefully planted them and provided the optimum growing conditions. However danger lurks in every corner of the garden with a whole host of beastly pests and diseases ready to indiscriminately strike down your plants at a moments notice.

In general there are two types of factors which can bring death and destruction to your beloved chile plants - living (biotic) and nonliving (abiotic) agents. Living agents incude insects, bacteria, fungi and viruses. Nonliving agents include extremes of temperature, excess moisture, poor light, insufficient nutrients, poor soil pH and air pollutants.

This chilemans guide aims to provide an overview of some of the more common living agents that can infect your Chile plants to help you identify 'the enemy' and provide you with some ammunition to fight the problem. After all thechileman wants your plants to have a long and healthy life and produce a bountiful harvest of lovely chiles.

Know Your Enemy!

Unfortunately there are a whole host of pests & diseases that can infect Chile pepper plants. Thankfully, only a few are common in the UK with most more of a problem in hotter climates such as the Caribbean and Americas. Although most insects are more of an irritation than a terminal problem causing only localised damage, it is the diseases that they can carry which can do the real damage.

A study by Green, S. K. and Kim, J. S (1991), found that more than half of known viruses are transmitted by aphids (greenfly). Thrips, mites, whiteflies, beetles and nematodes transmit others. Some of the more serious problems such as Bacterial Leaf Rot and Tobacco Mosaic Virus (TMV) are transmitted by direct contact with infected plants, soil or garden tools with others transmitted through mechanisms not yet understood.

Diseased plants can exhibit a variety of symptoms, making diagnosis extremely difficult. Common symptoms include abnormal leaf growth, colour distortion, stunted growth, shrivelled plants and damaged pods. Although pests & diseases can cause considerable yield losses or bring death to your plants, none are believed to directly affect human health.

Prevention is better than the cure

As a general rule, most pests and diseases cannot be completey eradicated, but they can be managed and controlled to minimise the 'collateral' damage. Once a problem has taken hold it is often very difficult to control.

To manage potential problems, early identification, correct diagonsis and the swift implementation of preventitive methods should allow you to get on top of most problems before serious damage if inflicted.

However, for the sake of the environment before automatically reaching for the nearest bottle of poison, there are several much friendlier and easy organic strategies which can be deployed, particularly for controling insects. Unfortunately, the more serious viral & fungal infestations may require Chemical Warfare to be deployed. However, always read the instructions on the bottle carefully and take precautions when using chemical agents.

Organic Strategies for Managing Pests

1. Learn to tolerate some damage: Most healthy Chile plants can tolerate some damage without suffering serious long-term problems or yield reduction. Munched leaves/ damage pods can easily be removed to maintain the attractive appearance of your plant.

2. Introduce the 'Good guys': Aphids feeding in the spring can alarm many Chile growers. Introducing natural predators such as Ladybirds, Parasitic wasps and Lacewings will help clean up most local infestations in a month or so.

3. Hand pick/Hunt down: Hunting down snails and slugs and 'disposing of them' can be a highly satisfying exercise particularly if the little blighters have already struck your prized plants. Night time 'slug hunts' during wet weather can be particularly productive.

4. The Water Hose: A strong water hose will temporarily dislodge flies, aphids and other pests from mature plants. However be careful not to saturate or damage your plants and avoid this using method on young seedlings.

5. Remove diseased plants or plant parts: Simply removing and disposing of badly damaged plants can help reduce the problem and prevent is spreading to adjacent plants.

6. Crop Rotation: This is particularly important strategy for tackling soil borne pathogens such as Verticillium Wilt and root rot.

7. Grow pest resistant & pest tolerant plants: Many hybridised varieties, particularly some of the newer sweet pepper varieties have been developed to give specific resistance to diseases such as Tobacco Mosaic Virus (TMV) and Bacterial Leaf Spot.

8. Innoculate: When growing in pots it is likely that sterilized soil has been used. Sterile soil is ripe for colinisation by many forms of bacteria, fungi, & insects. It is quite likely that the first colinization will not be beneficial. However, just as you can buy yogurts containing beneficial bacteria from the supermarket, you can also buy beneficial bacteria for your soil (though it is a little bit more difficult to get hold of). Beneficial Mycorhizzal fungi is also available, and is starting to become popular in many on-line shops. It may also be useful, depending upon the scope of your growing conditions, to introduce beneficial soil dwelling predatory insects. Introducing your own symbiotic bacteria, fungi, and insects limits the likelihood of colonisation by parasitic forms. In addition to aiding growth of the chile plant, & providing tolerance to environmental stresses, many forms of bacteria and Mycorhizzal fungi are also thought to innoculate the chile plant from diseases and viruses. In addition, they are helpful at reducing the conditions that make these diseases and viruses possible.

What's the Problem? - A Quick Reference Guide

Unless you are an expert taxonomist or have easy access to a laboratory, the correct diagnosis of the problem is probably the most difficult (and critical) factor in your battle with the enemy as a whole host of problems can display similar very symptoms. The following guide will hopeful help you narrow down the problem.

The Leaves:

- see the sections on Aphids, Whitefly, Nematodes and Verticillium Wilt
- could also be caused by a Nitrogen or Magnesium deficiency, mineral deficiency, or excessive watering

- see Bacterial Leaf Spot and Phytopthora blight
- could also be caused by excessive nitrogen.

- see Aphids, Thrips, Spider mites and Viruses

- see slugs & snails and flea beetles

- see sunscald
- could be caused by Chemical or fertiliser burns

- see Bacterial Leaf Spot, Cercospora Leaf Spot Powdery Mildew, Phytopthora blight and viruses
- could also be caused by chemical injury

The Plants:

Browning Stems
- see Bacterial Leaf Spot and Phytopthora blight
- could also be caused by insufficient watering

- see Verticilllium wilt, Bacterial Wilt & Phytopthora blight
- could also be caused by too little/too much watering

Plants Falling Over
- could be caused by waterlogged soil, insufficient plant support or poorly develop roots

Slow growth
- likely to be caused by inadequate light, poor soil, low temperatures. Note some Chile species particularly the Chinese are notoriously slow growing

The Pods:

- see slugs & snails and pepper maggots
- Birds and animals are also partial to the occasional chile pod (animals tend to avoid all but the mildest chile pods - though they might take a test nibble).

- see Anthracnose, Bacterial leaf spot, Blossom End Rot, Phytopthora blight, Grey Mold and thrips
- could also be caused by sunscald or nutrient deficiencies

- see Thrips, Spider mites and viruses. Poor Pollination can also cause this problem

Soft Rot
- see Bacterial Soft Rot and Grey mold

Failure to Ripen
- insufficient ripening time likely to be the problem

Insect Pests

The insects most likely to 'enjoy' your chile plants are slugs & snails, aphids (greenfly/blackfly), pepper maggots,whitefly and nematodes. Flea beetles, cutworms, hornworms, thrips, spider mites and leafminers are less common. To control insect problems, regular inspection is again the key to success.

Slugs & Snails are probably the number 1 enemy of gardeners, these little devils can quite happily turn one of your prize specimens into a swiss cheese practically over night before sliding back to there hideaways, leaving you to wonder what happened. Thankfully, most slugs and snails leave behind one piece of incriminating evidence which helps to both diagnose the problem and track them down, a trail of slime! Slugs are hermaphrodites (they can mate with themselves) and can produce dozens of eggs several times a year. The egg clusters look like little piles of whitish jelly and hatch anywhere from 10 days 28 days. 'Dispose' of any slugs and eggs wherever you find them.

Regular Slug hunts are the best course of action. Container gardening, the use of Copper tape/matting (placed around the plant) and even garlic oil has been used by gardeners with some success.

 Aphids (Greenfly/BlackFly) are one of the commonest and most annoying all garden insects. They are particularly attracted to young tender shoots, sucking your plants dry of sap causing shoots and leaves to become distorted. Plants grown indoors and away from natural garden predators can be particularly prone to infestations. Image © Virtualpepper

Small infestations are relatively easy to control. One method is to introduce natural predators to do the job for you. A second is to attract them away from your like darlings by planting Marigolds (tagetes and calendula) close by. Marigolds are a feeding favourite of the aphids and the theory goes that they will be much more interested in the Marigolds than your Chile plants.

Other friendly ways of controlling aphids include rubbing them off with your fingers or spraying them with a very diluted soap solution, about one teaspoon of fairy Liquid pure soap (as near to 100% fatty acids as you can get - avoid antibacterial, perfumed, & detergent based soaps) to a couple of litres of water. More severe infestations are more troublesome and it may be better to isolate the plants to prevent the problem spreading to your other plants. Unfortunately, spraying severely infested plants will provide only temporary relief and may simply just shift the aphids from one plant to another.

Flea beetles are about 2mm long, shiny in appearance with enlarged hind legs which enable them to jump. Adult flea beetles feed on the undersides of young leaves leaving small pits or irregularly shaped holes. Larvae live primarily in the soil and feed on roots, but cause little damage.

Ensure rapid germination and development of seedlings so that they grow through this vulnerable stage quickly. Flea beetles feed at the height of the day, and they don't like to get wet. Giving them a lunchtime shower can reduce the problem.

Pepper Maggots are whitish yellow, pointed at the head end and 0.5in longwhen fully grown. The maggots feed on the core inside of the pods which causes damaged peppers to turn red prematurely and rot.

Check pods for small puncture holes and destroy and infected pods. Rotting pods will attract other flies if left on the plant.

Root Knot Nematodes are microscopic, eel-like roundworms that live in the soil and feed on roots. Root damage reduces the plants ability to take up water and vital nutrients. Symptoms vary with plant age and the severity of the infestation, but include wilting, nonproductive plants and development of characteristic knots on the plant's roots which can vary in size from smaller than a pinhead to larger than a pea. The problem can be particularly severe in sandy soils.

Crop rotation and adding organic matter to sandy soils can help reduce the impact of nematodes. The best method of control is to plant resistant varieties (often indicated by an N on the seed packet) like California Wonder & Charleston Belle.

Spider Mites can be a serious problem particularly during periods of hot, dry weather. They feed on the underside of leaves and to the naked eye, look like moving dots. When infestation is high, the leaves will have webs on them; if uncontrolled, these mites can kill a plant. Infected leaves often curl downwards and leaves are speckled in appearance, as though covered with hundreds or thousands of pale yellow dots. A simple technique for identifying mites is to tap an infected leaf over a piece of white paper. Wait a few seconds and watch for movement.

Red spider mites breed in hot and dry places. If you can increase the humidity around the plant you decrease the pest's reproduction rate. Dampen down infected areas. For house plants a short holiday somewhere cooler and more humid (the bathroom?) may help get rid of the infestation.

 Thrips are numerous in species and all are extremely small. They are very slender and may be white, yellow, brown or black. Affected leaves are often distorted and curl upward. The lower surface of the leaves can develop a silvery sheen that later turns bronze. Damage on pods appears as brown or silver areas near the calyx.

Thrips do not usually need to be controlled as predatory mites insects will normally do the job for you.

Whiteflies are tiny insects (1.5mm long) with broad wings that fly from the plant when disturbed. They suck plant juices from the leaves, causing them to shrivel, turn yellow and drop. Whiteflies also secrete honeydew which can cause foliage to become sticky and coated with a black sooty mold.

Whitefly control is difficult, since only the last (flying) stage of the whitefly lifecycle is vunerable to spraying. Whitefly control is difficult as they have very fast lifecycles. To eliminate this pest frequent spraying is necessary - at least once a week, and for many weeks/months. Good cultural practices, such as removing infected plants, pruning the top new growth, and/or using a mild diluted (fatty acid based) soap solution are possible controls. Perseverance is neededare the best controls.

Bacterial & Fungal Diseases

 Anthracnose is caused by the fungi Colletotrichum piperatum and C.capsici and is promoted by warm temperatures, high moisture and poor circulation among the plants. Both sweet and hot peppers varieties are susceptible to this disorder. Although the disease does not seriously affect vegetative growth, it can seriously damage pods. Symptoms appear on both ripe and unripe pods and are characterised by sunken, circular spots that can grow up to 1in in diameter. In moist conditions, pink or yellow spore masses may appear.

Crop rotation and the use of disease-free seed. If the disorder is severe, a fungicide may be needed.

 Bacterial Leaf Spot is caused by theseed borne bacterium Xanthomonas campestris pv vesicatoria which also causes bacterial spot in tomatoes and is one of the most serious bacterial disease affecting chiles. The principle sources are infected seed and transplants. Moist conditions encourage disease development.

This disease first appears as small water soaked areas that enlarge upto a quarter inch in diameter. The disease spots have black centres and yellow halos. The spots are depressed on the upper leaf surface, whereas on the lower surface the spots are raised and scab like. Severely spotted leaves will eventually turn yellow and drop off, leaving pods susceptable to sunscald.

Crop rotation and the use of disease-free seed. The use of copper-based fungicides can have some success although excessive use may retard growth and damage plants

 Bacterial Soft Rot is caused by bacterium Erwinia carotovora pv carotovora and affects Chile pods. The internal tissue softens before eventually turning into a watery mass with a foul smell. This problem is worst in wet weather because the bacteria are splashed from the ground and onto the fruit. It can also be started by insect injury.

Keep plants off the ground (on greenhouse staging) and controlling insects can help reduce the threat of this disorder.

Bacterial Wilt is caused by the bacterium Pseudomonas solanacearum. The first symptoms start with the wilting of the leaves. After a few days, a permanent wilt of the entire plant results, with no leaf yellowing. You can test for this bacteria by cutting the roots and lower stems; look for milky streams of bacteria when they are suspended in water.

The best control is to plant clean seed and transplants and to remove diseased plants.

Cercospora Leaf Spot (Frog Eye) is caused by the fungi Cercospora capsici and is worst under extended warm, wet conditions. This disease in characterised by small brown circular leaf lesions that have a watery appearance. Excessive leaf drop may occur in common infestations.

Clean seed and crop rotation are the best preventative measures against this disease. Good airflow around plants in sheltered areas (greenhouse's) will also help minimise this problem. Fungicides are probably the best solution if the problem is extensive.

Damping-off is caused by poor seed quality, improper planting depth, high salt concentrations, a wet seed beds or severe nutrient deficiencies. Several fungi such as Pythium, Rhizoctonia and Fusarium are associated with this problem. Seedlings fail to emerge (pre-emergence damping-off), small seedlings collapse (post-emergence damping-off), or seedlings are stunted (root rot and collar rot).

To control this problem plant only high-quality seed or vigorous transplants and avoid soil that is poorly drained. Good ventilation reduces surface moisture, and therefore the likelihood of damping off. The use of a fungicide, such as a copper based fungicide, or even just watering with chamomile tea (provides a mild fungicide at normal strength), can reduce the likelihood of damping off further.

Grey Mold is a relatively common problem and is caused by the fungus Botrytis cinerea. Symptoms include a sudden collapse of succulent tissues, such as young leaves, stems, and flowers. Grey powdery spore masses occur on the surface of dead plant tissues.

High humidity favours the disease. Ensuring your plants have good air circulation will helps reduce this problem. A fungicide is probably the best bet if the mold is severe.

 Phytophthora Blight (Chile Wilt) is caused by a water borne fugus Phytophthora capsici and is generally observed in wet waterlogged areas. The fungus can invades all plant parts causing at least three separate syndromes: leaf blight, fruit rot, and root rot. It is promoted by warm, wet weather. Plants suffering from this condition often wilt and die, leaving brown stalks and leaves and small, poor-quality fruits. If the fungus enters the roots, the game is unfortunately over as the plants cannot obtain enough water (due to root rot), suddenly wilt, and eventually die. Symptoms of the less serve leaf blight include brown or black spots that may kill a localised portion of the plant. Affected areas are often bordered with a white mold.

Avoid excess watering and poorly drained soil. Fungicides can be used to treat leaf blight and fruit rot. Root rot is usually terminal.

Powdery Mildew is cause by the fungus Leveillula taurica and primarily affects leaves on pepper plants during warm wet conditions. Although the disease commonly occurs on older leaves just before or at fruit set, it can develop at any stage of crop development. Symptoms include patchy, white, powdery growth that can enlarge to cover the entire lower leaf surface Diseased leaves eventually drop off, leaving pods susceptable to sunscald.

Powdery mildew is managed primarily with fungicides. However sprays of sulphur and potassium bicarbonate have been known to have some success.

Verticillium Wilt is caused by soil borne fungus Verticillium dahliae is a soil borne fungi which can infect pepper plants at any growth stage. Cool air and soil temperatures favour it. This problem is particularly hard to pin down, as the symptoms are highly variable. Plants may show a yellowing of leaves and stunted growth. As the disease progresses, the plants can shed leaves and may finally die. If the stem is cut, a brown discoloration may be visible.

Crop rotation is the best control. Neither resistant cultivars nor chemical controls are known.

White Mold is caused by the fungus Sclerotinia sclerotiorum. It causes blighting or rotting of any above or below ground plant parts. At first, the affected area of the plant has a dark green, greasy, or water-soaked appearance. On stems, the lesion may be brown to grey in colour. If the humidity is high, a white, fluffy mold growth may appear.

Controls includes well-drained soil, proper plant spacing, crop rotation, and careful removal of all infected plants as soon as possible. Do not compost or use diseased plants for mulch.

Viral Diseases

Pepper Mosaic & Pepper Mottle Virus (PeMV) is caused when infected aphids and other insects come into direct contact with the plant. Stunted plants, distorted fruit, and yield reduction are all symptoms.

Aphids control and good sanitation practises. Planting resistant varieties is the best way to avoid this problem. Early detection and removal of infected plants helps, but complete control is often difficult.

Tobacco Etch Virus (TEV) is caused when infected aphids and other insects come into direct contact with the plant. Dark green vein bands, leaf distortion and stunted growth are all symptoms. Tabasco Chile plants are particularly susceptible to this disease and often wilt and die.

Aphids control and good sanitation practises. Planting resistant varieties is the best way to avoid this problem. Early detection and removal of infected plants helps, but complete control is often difficult.

Tobacco Mosaic Virus (TMV) is a highly infectious and persistent disease is carried by tobacco in cigarettes and is spread mechanically, by infected hands touching tools or plants. Symptoms can include curling leaves, spotted or mottled fruit, stunted plants and excessive leaf drop.

Smokers should disinfect hands (milk kills TMV) thoroughly before gardening. Growing resistant varieties is the best prevention. Early detection and removal of infected plants helps, but complete control is often difficult. Further Information Sources: The University of Maryland Cooperative extension