In most developing countries including Uganda the use of modern synthetic pesticides is limited and sometimes non-existent.

This is so not only because they are expensive but also because of the small fields cultivated by subsistence farmers making the use of such pesticides uneconomical.

Yet, most of these countries lie in tropical and subtropical areas where pests and diseases are abundant throughout the year.

The battle against pests is a difficult one even with the advanced technology that exists today.

The implication to this is that in these areas, pests and diseases pose a major problem in agricultural production.

According to a 2004 publication by Food and Agriculture Organisation, pests contribute 30-40% of crop loss worldwide while the loss in the tropics is reported to be even higher than 40%.

However experts are advising farmers to battle the challenge of insects in particular using certain repellent plants to reduce the insect infestation in their farms

In the publication scientists outline insect repellent plants which can work in farmer fields in Uganda and in other developing countries faced with the same challenge

Farmers in Uganda can effectively deter insects and bugs by strategically planting and utilizing certain repellent plants around their farms and crops. 

These plants, often with strong odors or containing insecticidal properties, can act as natural barriers or pest control agents. 

Specific plants and their uses

Marigold

Planting marigolds also known with its scientific name Tagetes spp. around crops can help repel nematodes and other soil-borne pests. Their strong scent also deters various insects. 

Chill pepper

Chili peppers (Capsicum spp.) contain capsaicin, a compound that can repel many insects. Farmers can make chili-based sprays or use crushed chili pods with ash to deter storage pests. This works well at storage level.

Mexican marigold

Known for its strong, pungent odor, Mexican marigold is effective in repelling various pests at field level, including those that attack stored grains. 

Tithonia and Leucaena

Both Tithonia and Leucaena can be classified as shrubs, though their growth habits can vary. 

Tithonia diversifolia, also known as Mexican sunflower, is typically described as a shrubby, herbaceous plant that can grow from 2 to 3 meters tall. Leucaena leucocephala, on the other hand, is a shrub or small tree, sometimes reaching heights of 18 meters if not managed

These plants can be planted in and around fields to deter pests and also provide additional benefits like soil improvement. 

Pyrethrum

Pyrethrum, derived from chrysanthemum flowers, contains natural insecticides. It can be used to make sprays or mixed with stored grains to deter pests. 

Lantana camara

The dried and crushed leaves of this plant can be mixed with stored grains to repel pests. 

Onions and garlic

These can be planted near crops to deter insects due to their strong odors. 

Coriander

Coriander can be used in a similar way to onions and garlic, as a natural insect repellent.

Desmodium 

Desmodium helps in pest control through a push-pull strategy, where it repels certain pests while attracting beneficial insects that prey on them. 

It also disrupts the life cycle of parasitic weeds like Striga. Specifically, Desmodium emits volatile chemicals that deter stemborer moths from laying eggs on nearby crops. 

It also attracts parasitoid wasps that attack stemborer larvae. 

Additionally, Desmodium's roots release chemicals that can either stimulate the germination of Striga seeds or inhibit their growth, leading to suicidal germination and reducing the weed's presence in the soil.

Methods of application

Intercropping

Planting pest-repellent plants alongside crops can create a natural barrier.

Repellent sprays

Farmers can create organic pesticides by boiling leaves of certain plants like Mexican marigold or chives and using the resulting liquid as a spray.

Mixtures for storage:

Dried and crushed repellent plants can be mixed with stored grains and ash to deter storage pests. 

Additional tips for effective pest management:

Cultural practices

Clearing fields of weeds and infected plant parts, proper soil management, and crop rotation are important aspects of pest control. 

Resistant varieties

Farmers can also choose crop varieties that are naturally resistant to certain pests. 

Integrated pest management

A holistic approach that combines different control methods (including the use of repellent plants) to minimize pest damage

Types of Insects

There are various types of insects that infest farmer fields across the country causing destruction to various crops mainly vegetables, legumes and cereals and they are explained as below.

Field Crickets

Their host plants include tomatoes, eggplants, green pepper, water melon and cereals such as rice among others.

It feeds on plants at the root level and cuts the plants off from its growing roots

Variegated grasshopper

The host plants include cassava, citrus, cotton, maize, cocoa, coffee, sweet potato and yams among others and it mainly feeds on leaves.

Thrips

Thrips are known to feed on a wide range of host plants, including various vegetables, fruits, ornamentals, and field crops. 

Thrips parvispinus has a host range of plant species which include eggplant, pepper, potato, and green bean for vegetables; avocado for fruit; and azalea, begonia, and cyclamen for ornamentals.

They also commonly infest crops like maize, onion, cotton and various legumes.

Aphids

Aphids are known to infest a wide variety of plants, including both cultivated crops and wild plants. Common host plants include various vegetables, fruits, ornamentals, and greenhouse plants. 

Specific examples include legumes such as Pea, bean, lentil, chickpea, alfalfa, lupin, soybean, plus a number of cereals and wild plants and the suck sap from plants.

Spider mites and rust mites

Spider mites are known to infest a wide range of plants, including fruit trees, vegetables, berries, vines, houseplants, and ornamentals. Some specific examples of host plants include beans, cassava, cotton, citrus, okra, tomato, papaya, potato, tobacco, strawberry, and various cucurbits and legumes

Rust mites mainly infest vegetables causing rust on its leaves

Ladybird beetles and Blister beetles

Lady bird beetles are known to feed on crops such as wheat, apple, mustard and watermelon among others while blister beetles feed mainly on vegetables and flowers

Leaf minors 

These insects are known to be feeding on vegetables and legumes such as cabbage, other brassicas, okra, onion, pigeon pea, bell pepper, cucumber, pumpkin, cowpea, potato, passion fruit, tomato and common bean

The maggots suck sap from plant leaves causing severe damage leading to limited growth to maturity.

Ball worms

Bollworms, primarily known as helicoverpa armigera Helicoverpa armigera and pink bollworm, have a wide range of host plants. 

Armigera is known to feed on over 180 plant species, including important crops like cotton, maize, soybean, pepper, and hibiscus species and okra

The feed on young plants and fruits and mature level.

Fall Armyworms

Fall Army worm feeds on a wide variety of plants. It is known to attack over 350 plant species, causing significant damage to important crops.

Some of its most common host plants include maize, sorghum, rice, sugarcane and wheat. 

It also attacks other crops like cotton, soybean and various vegetables. 

In Africa, it has been confirmed to feed on maize, sorghum, sugarcane, rice, millet, wild sorghum, cotton, napier grass, capsicum and rhodes grass. 

Nematodes and Root knot

Root-knot nematodes have a very wide host range, affecting a vast array of plants including many common vegetables, fruits and ornamentals. 

Examples include tomato, papaya, banana, sweet potato, taro, carrots, beans, peas, and many others. Even some crops in the grass family like rice, maize, and sugarcane can be hosts

They also feed on ornamental crops, as well as trees, grasses and even some weeds.