RX for Healthy House Plants - Part 4

Insects and Diseases

Read part 1 | 2 | 3 in this 4 part series

Insects

The materials listed below for the control of insects and diseases are basic ingredients and not trade names. Check contents and recommended use on manufacturers’ labels before making purchases. Combination sprays containing a good insecticide such as malathion with a good fungicide are very useful.

APHID: Mostly greenish (black on chrysanthemum), about 1/16 inch long, soft somewhat pear-shaped body, mostly wingless. Aphids suck plant juices making foliage appear shiny and sticky. Usually found on terminal growth. Control: spray with malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control.

CATERPILLAR AND EARWIG: Caterpillars have soft, cylindrical and segmented bodies and are readily seen. Earwigs resemble beetles. Both these insects chew holes in leaves, flowers or stems. Control: malathion or neem oil.

CYCLAMEN MITE: Tiny whitish mites visible only with a strong lens. Easily spread from plant to plant on hands and clothing. Leaves appear distorted, curled and often brittle. Buds may be deformed and black. Plant usually stunted. Control: avoid splashing water, and isolate plant. Spray at ten day intervals with malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control.

LACEBUG: About 1/2 inch long. Clear lace-like wings lie flat over back. Black specks often seen on under leaf surface are insect excrement. Foliage appears mottled and stippled and later turns brown and crisp. Control: spray with neem oil or malathion.

MEALY BUG: White cottony appearing insect usually on under-leaf, surface; appears to be motionless. Effect on plant not striking but gradual weakening results. Control: spray with ma-lathion.

MIDGE OR GALL FLY: Small yellowish gnat-like fly. Eggs layed near shoot tips and emerging young maggots penetrate succulent tissue. Galls on stem and leaf indicate presence of maggots. Small buds turn brown and are deformed. Control: spray with malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control.

NEMATODE, LEAF: Microscopic eel-like worms. Mostly troublesome on chrysanthemums producing bronze to gray wedgeshaped areas in the leaf. Eventually entire leaf turns brown and hangs on the stem. Control: preventive means consist of taking cuttings from terminal growth, never from divisions. Avoid splashing water, and plant in sterilized soil and containers.

NEMATODES, ROOT: Microscopic eel-like worms which penetrate root tissue forming small knots or galls which are easily visible. Injured roots eventually cause poor top growth. Control: discard infected stock. Cuttings from the infected stock may be used when absolutely necessary, but avoid portions which have been in contact with the soil. Use sterilized soil and equipment.

RED SPIDER MITE: Tiny mite, tan to reddish, is small but may be seen with the naked eye. Moves rapidly. Usually seen on underside of leaf and often produces a fine webbing. Most often seen during hot dry weather. Control: spray with malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control.

SCALE: Small insect which inserts sucking mouth part in plant tissue and then develops a hard scale over its body and remains permanently attached to the leaf in one position. Scales may be picked or rubbed off and are readily seen. (The reproductive bodies a ferns, known as spores, resemble scale and are often confused with them.) Found on underside of leaf or on stem. Foliage pales and plant loses vigor. Control: spray with malathion.

SLUG AND SNAIL: A slug is a soft, slimy, legless creature found under stones, flats and around clay pot rims; feeds at night chewing ragged holes in foliage; may leave a typical slimy track behind them as they move from place to place. Control: hand picking effective, or a commercial bait containing metaldehyde may be scattered on the soil or on pieces of wood so it won’t get wet (moisture reduces effectiveness).

SPRINGTAIL: Small white jumping insect which appears at soil surface; does no real harm but considered annoying. Control: a malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control solution watered into the soil.

THRIP: Difficult but not impossible to see with the naked eye. Movement very rapid. Yellowish brown in color and very thin, with narrow (but almost invisible) wings. Sucks plant juices, making leaves appear silvery. Buds and flowers may be deformed and petals appear streaked. Control: malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control.

WHITE FLY: Adult flies white and very active. Usually fly off when plant disturbed. Easy to detect. Suck juices from lower leaf surface. Leaf appears pale and stippled. (A sticky excrement with a sooty mold often seen on upper leaf surface.) Control: malathion, neem oil or Bayer 3-in-1 insect Disease and Mite control.

Diseases

BLACKLEG: Caused by a fungus. Results in a blackening and rotting at the base of cuttings. Control: sterilize soil and equipment before taking cut-tings.

BOTRYTIS: Fungus disease which produces a brownish gray mold. May cause spotting and eventual rot of leaves, flowers and stems. Control: provide better ventilation and air circulation; avoid drafts and rapid temperature changes. Keep foliage dry, and destroy infected foliage or flowers. Control: spray with captan or Daconil.

CHLOROSIS: Term applied to a general yellowing of normally green foliage. Not a disease but so listed for convenience. May be due to low nitrogen, or, where plants which require an acid soil are concerned, a lack of iron. Control: if feeding doesn’t restore normal green color suspect soil acidity. Either repot in a soil high in humus (and therefore acid) or treat soil with ferrous sulphate. Note: Light foliage may be caused by too much or not enough light, soggy soil or injured roots.

CRINKLES AND MOSAIC: Caused by an invisible virus. Irregular yellow spots are produced on leaf which may become ruffled and dwarfed. Control: destroy plants immediately by burning.

DAMPING-OFF: Caused by a fungus in the soil. Usually attacks seedlings and cuttings, causing rot at soil surface. Control: use sterilized rooting media and equipment as well as planting in sterile soil. A soil drench of zineb or captan may stop an infection which has already started.

MILDEW: Caused by a fungus. Produces a white powdery growth on leaves, stems and sometimes flowers. Control: avoid splashing water and drafts which spread the fungus. Spray with Captan spray or use sulphur dust or spray.

STEM ROT: Fungus causes decay of stem at soil surface. Control: prevention is best means of control. Use sterilized soil and equipment. Plants may often be saved after infection by drenching soil with zineb or captan, and then spraying plant repeatedly with the same solution.

by Charles H. Potter

Related Articles

• 4-Point Summary of Plant Disorders - Environmental factors should be carefully checked with plant requirements. These include light, temperature, presence of harmful gas, humidity, soil composition, water and fertilizer. Improper environment is responsible for more plant troubles than insects and diseases combined. Premature leaf and flower drop, spindly growth and failure to flower can usually be traced to an improper balance
• RX for Healthy House Plants - Part 3 - Greenhouse Plants Part 1 | 2 in this 4 part series AZALEA Soil: pure acid peat or soil mixture with a high peat or leafmold content. Temp: 55′ to 60°. Light: full sun. Bloom Requirements: failure to bloom due to too high a temperature; plants brought in from outdoors in the fall should be kept in