PESTS AND DISEASES OF HOT PEPPER

The pests and diseases of hot pepper can be broadly divided into the following four groups: insects, fungi, bacteria and viruses.

Insects

Aphids

These are also commonly called plant lice or green flies, but not all aphid species are green. Although aphids are relatively small they can usually be seen with the naked eye. There are a large number of aphid species which can use crops as their host, some aphids have two or more host species. Aphids suck the plant's sap especially from the under side of young leaves and shoots.

Figure 21 illustrates aphids feeding on the under side of hot pepper leaves. In addition to the direct attack on the plant they are capable of transmitting viruses from an infected plant to a virus free plant, thus spreading the disease. As aphids feed they pass out honeydew attracting ants which feed from it. The ants then build up and can become a pest to field workers and the host plants because the ants tend to deter the aphids' natural enemies which in turn increases the aphid population. A further problem is the growth of the fungus commonly called sooty mould, on the honeyaew. This reduces the efficiency of the leaf surface and if present on fruit will reduce the market value of the crop.

Aphid control: There has been more emphasis on developing and using natural methods of control in recent years. This is partly because many chemical control methods can also reduce populations of the aphid's natural enemies, also because of environmental issues and the consumer's demand for a reduction of chemical residues on market produce. Natural control methods include establishing barrier crops, such as corn (maize) or similar tall annual crops around the perimeter of the plot before the pepper is planted out. Predatory beetles of aphids should also be encouraged. Before using any insecticide check the importing market's regulations and restrictions. There is an increasing use of insecticides such Pyrethrins and similar compounds which breakdown quickly and therefore have a very low persistence. It must also be remembered that many insecticides such as Dimethoate will require a week or more before edible crops can be harvested. A lot of insecticides will also kill pollinating and beneficial insects. Check with the extension service before using any chemicals.

Crickets

The field crickets resemble small grasshoppers except that they are a darker colour with stouter bodies. They live in their holes (or nests) in the soil, usually close to plants, in the nursery and in the field. During the night they emerge and cut off young plants and drag them into their holes.

Severe infestations can make it especially if a cover crop is planned or the present crop is nearing the end of its economic life. In the case of contact weed killers it is important that the chemical being used does not drift onto other crops, gardens and reserves, or splash on the foliage or stems of the pepper plants otherwise they will also be damaged or killed. Residual weed killers are not suitable for ridge and furrow irrigation systems. It is strongly recommended that advice should be obtained from the extension service (see also the end section on 'Organic crops and environmental issues', page 49).

Cricket control: They are best tackled during site preparation by early bush clearance and ploughing. Leaving the site in this partly prepared state will allow their natural enemies, which include birds and lizards, to catch them. Seedbeds can be protected by standing the trays of seedlings on benches or protecting the trays with netting. Where crickets are known to be a problem the field can be drenched with a proprietary preparation of Carbaryl or Diazinon, but seek advice first and carefully follow the manufacturer's instructions.

Cucumber beetle

The cucumber beetle can be a serious problem during the crop's early stages. The adult beetle is almost 1/4 inch (6 mm) long, yellow-green with three black longitudinal stripes on the back. The adult beetles chew small holes in the leaves, resulting in a shot hole effect. Its larvae can seriously damage roots of squashes and related crops. This pest can also be responsible for transmitting bacterial wilt and some mosaic viruses.

Control of cucumber beetle: The borders of pepper plots should be kept free of weeds and volunteer crop plants which are hosts to the beetle. Proprietary preparations of Pirimiphos-methyl have been used as a control, but first seek expert advice.

Pepper hornworm

The so-called pepper hornworm is a green caterpillar of a moth with a wingspan of four inches (approx. 10 cm). The caterpillar quickly grows and reaches approximately 3 1/2 inches (approximately 9 cm) long and about 1/2 inch (12 mm) wide when fully developed. There is a horn like structure on top of the rear end. It is often to be found on the underside of leaves during the day where it is difficult to see. Obvious signs of its night feeding are the fresh green droppings (frass) at the base of plants and shoots and also leaves which have been eaten off.

Control of hornworms: There are several natural enemies of these caterpillars including birds and parasitic wasps. They can also be removed by hand and killed. There are bacterial formulations which can be used as a biological control. Proprietary brands of preparations containing Carbaryl or Pirimiphos-methyl have both been used, but if chemicals have to be resorted to then seek expert advice first.

Mites

These small pests cannot be easily seen with the naked eye. We are more likely to see the accumulative damage that their increasing populations have caused before realising that they are affecting the crop. Mites can cause any of the following symptoms on the plant: distortion, curling, shedding or discolouration of leaves; russeting or bronzing of leaves and stems; in severe cases the plant becomes stunted, the flowers drop and any fruit already formed fails to develop properly (it may be deformed and discoloured). Figure 25 shows typical broad mites damage on hot pepper fruit.

Mite control: Control starts with good nursery and field practice. This includes maintaining a watchful eye for early symptoms during nursery plant production and again while planting out. Any plants seen to be infected by mites must be carefully removed and destroyed, ideally by burning.

Mites are easily transferred from one plant to another by handling, on clothing or by wind. Broad and many other mites have a wide host range so satisfactory isolation is necessary.

Some of the most useful chemical controls are not accepted by countries importing produce, therefore advice must be obtained before using a control product. Wettable sulphur may be able to be used, but check first.

It is important to note that mite has many host crops including sweet potato, Irish potato, tomatoes, cowpeas, beans, mango, citrus, avocado, coffee, papaya and guava.

Where possible peppers should be grown away from these crops, otherwise care should be taken to ensure that mites are not present on these hosts to provide a ready source of infestation.

Nematodes

There are many nematode species, often called eelworms. Some are free living in the soil while others are important plant pests. Root knot eelworm is an economically important member of this group and it can be a serious pest of hot peppers. The microscopic eelworms cause slight to severe swelling and distortion of roots. This in turn limits the plant's ability to take up water and nutrients. Careful digging up of an infected plant will show the root symptoms. The pest is soil borne, the same cultural care as outlined below for Fusarium will assist in reducing its spread.

Other pests of hot pepper

There are many other pests of hot peppers. They include pepper budworm, thrips, corn earworm, pepper weevil, fruit fly, pepper maggot and tropical white mite. Advice should be sought from extension advisors and pest control specialists as to identification and suitable control measures.

Fungi

Fusarium wilt

This is a soil borne fungal disease. Infected plants become weak and show a yellowing of the leaves. On closer examination the cut stem near the base of an infected plant will display a reddish brown, rusty looking discolouration in the interior, also possibly in the interior of where some lower side shoots join the main stem.

Control of Fusarium: The main control methods are by good husbandry and cultural practices. These include:

• Using partially strerilized soil for plant propagation.

• Ensure that all containers for seedlings have been thoroughly cleaned and stored in clean conditions.

• Following a field rotation for planting out.

• Improved drainage.

• Deep ploughing, and as far as possible, allowing soil to be solar sterilized over a period of several months.

FIGURE 28.
Fusarium wilt root damage

• Attend to the soil's liming requirement during field preparations.

• Avoid soil transmission of the disease by cleaning footwear, tools and mobile implements.

• Maintain healthy plants by adequate water and nutrition.

• Carefully remove infected plants and their immediate ball of soil and burn.

• As Fusarium is a high temperature disease mulching helps to insulate the soil and reduce temperatures.

Southern blight (Sclerotium wilt)

This disease may show as a whitish fungal growth on the stems of infected plants, the plants may also display wilting of the lower leaves. The disease is more likely to occur in a short period of time in hot and humid conditions. Affected plants should be removed complete with their root ball and burnt well away from the field. Deep ploughing during site preparation will put the fungus below the root zone.

Anthracnose

This is a common disease of hot peppers. The fungus can be carried over from one season's crop to another or one area to another by diseased plants. Water soaked and dark sunken areas occur on the fruit, these quickly increase in size. Ablack layer later appears on the infected parts; waxy pink patches may also occur on the fruit, these are the disease's spores which will spread the fungus. The affected fruit later rot.

Control of anthracnose: As the fungus can be carried over from one crop to another it is necessary to remove and burn all old plants and fruit material. As far as possible rotations of resistant crops should be practiced. The fungus can also be seed-borne, therefore farmers should obtain their seed supply from approved sources. Seed should not be saved from infected crops. Prompt harvesting of mature fruit reduces the build up of disease.

Bacteria

Bacterial spot

This disease can develop and spread rapidly under hot and moist conditions. The disease can be seed-borne and can be responsible for Seedling blight. The bacterial spots appear as brown spots on the underside of leaves and on the fruit. The bacteria can enter the fruit and cause rotting.

Control of Bacterial spot: Farmers should not save seed from crops showing any signs of the disease. Severely infected crops can be sprayed with proprietary preparations of Mancozeb, but first check that this chemical has been authorized for use and the conditions under which it can be used.

Viruses

There are several important virus diseases of hot pepper. The most important ones in The Bahamas include: Tobacco Etch Virus (TEV) and Potato Virus Y (PVY), both of these cause symptoms of yellowing and mottling of leaves and/or upward leaf roll, infected plants may also be stunted with low fruit yield. Figure 32 shows symptoms of TEV.

Other viruses which can infect hot pepper include Pepper Mottle Virus (PeMV), Pepper Veinal Mottle Virus (PVMV), Tobacco Mosaic Virus (TMV) and Cucumber Mosaic Virus (CMV).

Control of pepper viruses: There is very little that can be directly done as a cure for these plant viruses, the main action is in their prevention.

The following points will assist in avoiding virus infections in the hot pepper crop:

• Use approved seed from a reliable source (some viruses, for example TMV, can be transmitted by seed as well as by insects).

• Produce seedlings under insect proof conditions.

• Take care to avoid aphids and other virus transmitting insects entering the pepper crop. Cultural methods include barrier crops and avoiding unnecessary handling of the plants.

• Ensure that alternative plant hosts, including related volunteer crop plants and related weeds (for example black nightshade), are removed from the pepper crop and its close vicinity.