A look at some of the problems encountered when growing coriander are pests and diseases;
- Singular, or closely grouped circular to irregularly shaped holes in foliage;
- Heavy feeding by young larvae leads to skeletonized leaves;
- Shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance;
- Young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside
Organic methods of controlling army worms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.
Aphids (Willow-carrot aphid)
- Small soft bodied insects on underside of leaves and/or stems of plant, usually green or yellow in color. If aphid infestation is heavy it may cause leaves to yellow and/or distort.
- Aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants
- If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control,
- Check transplants for aphids before planting, use tolerant varieties if available, reflective mulches such as silver colored plastic can deter aphids from feeding on plants.
- Sprayed Sturdy plants with a strong jet of water to knock aphids from leaves. Insecticides are generally only required to treat aphids if the infestation is very high. Plants generally tolerate low and medium level infestation, insecticidal soaps or oils such as neem or canola oil are usually the best method of control, always check the labels of the products for specific usage guidelines prior to use.
- Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits;
- Larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed
- Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants
- Hand-pick larvae after dark
- Spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it)
- Apply appropriate insecticides to infested areas of garden or field if not growing organically.
Symptoms: Small water-soaked lesions near base of petioles which become soft, sunken and brown
Management: Control relies on the avoidance of conditions conducive to bacterial infection: plant coriander in well-draining soils; allow plants to dry before irrigating again; avoid wounding plants during harvest to prevent pst harvest development of disease; disinfect all equipment regularly
2. Bacterial leaf spot
Symptoms: Very small water-soaked spots between leaf veins which enlarge and turn dark brown to black; stems may have elongated dark streaks; inflorescences yellowing and turning brown and blighted; water-soaked lesions on fruit
Management: Bacterial leaf spot is difficult to control; plant pathogen-free seed; avoid overhead irrigation; do not work with plants when they are wet.
Symptoms: Soft, rotting seeds which fail to germinate; rapid death of seedling prior to emergence from soil; collpase of seedlings after they have emerged from the soil caused by water-soaked reddish lesions girdling the stem at the soil line
Management: Avoid planting in poorly draining, cool, wet soil; planting in raised beds will help with soil drainage; plant high quality seed that germinates quickly; treat seeds with fungicide prior to planting to eliminate fungal pathogens.