The Ri plasmids can be engineered to also contain T-DNA, used for genetic transformation (biotransformation) of the plant cells. The resulting genetically transformed root cultures can produce high levels of secondary metabolites, comparable or even higher than those of intact plants.

Corn gluten meal (CGM) is a natural pre-emergence weed control used in turfgrass, which reduces germination of many broadleaf and grass weed.

Picloram is a pyridine herbicide. It is mainly used to control unwanted trees in pastures and edges of fields in India. It is another synthetic auxin.

Plants growing in  extremely dry soil and arid conditions that are under stress will be more prone to infection. Powdery mildew is a powdery fungus that grows mostly on the upper surface of leaves. It is usually white in colour. It will occasionally spread to the underside of leaves and other parts of the plant, such as stems and sometimes flowers and fruit. Powdery mildew prospers in dry soil conditions.

Aminopyralid is a broad leaf herbicide in the pyridine group, used to control weeds on grassland, such as docks, thistles and nettles. It is notorious for its ability to persist in compost.

ACCase inhibitors compounds kill grasses. Acetyl coenzyme A carboxylase (ACCase) is part of the first step of lipid synthesis. Thus, ACCase inhibitors affect cell membrane production in the meristems of the grass plant. The ACCases of grasses are sensitive to these herbicides, whereas the ACCases of dicot plants are not.

It is a result of Sclerotium rolfsii which is a soil-inhabiting fungus affecting the seed of the plant. This seed-borne disease infects the seed and it turns into blue and black patches.

The fungus Beauveria bassiana is used to prevent potato beetle and codling moth.

Blossom end rot is a common problem of tomatoes, peppers and aubergines grown in a greenhouse caused by erratic watering or dryness at the root. Brown sunken spots develop at the bottom of the fruit opposite stem.

Weeds also vary in their competitive abilities and according to conditions and season. Tall-growing vigorous weeds such as fat hen (Chenopodium album) can have the most pronounced effects on adjacent crops, although seedlings of fat hen that appear in late summer produce only small plants.

In domestic gardens, methods of weed control include covering an area of ground with a material that creates a hostile environment for weed growth, known as a weed mat. Several layers of wet newspaper prevent light from reaching the plants beneath, which kills them.

Citronella oil is popular as a natural insect repellent. Its mosquito repellent qualities are effective in repelling Aedes aegypti (dengue fever mosquito).

This is a fungal disease affecting elms. 

 Ampelomyces quisqualis is an anamorphic fungus that is a hyperparasite of powdery mildews. This parasitism reduces growth and may eventually kill the mildew. L. longisporum is used for management of aphid pests. Insects are infected when they come into contact with the sticky fungal spores which then grow and invade the body. Thus the internal organs are consumed.

Allethrins are synthetic pyrethroids. The compounds have low toxicity for humans and birds and are used in many household insecticides such as RAID and mosquito coils.