Before choosing the best insecticide for aphids: inspect the colony
Identify the insects on the crop before choosing an aphid insecticide. Aphids have soft bodies and a characteristic pear-shaped outline. Many species have cornicles, the paired tubelike structures near the rear of the abdomen. Individuals may be winged or wingless, and colour alone is unreliable for separating species. White cast skins can remain around a colony after aphids moult.
Inspect fresh growth and leaf undersides with a hand lens. Open curled leaves to distinguish living insects from cast skins. Photograph the colony on its host plant.
Honeydew is a sticky excretion associated with aphid feeding. Sooty mould can grow on that material and blacken the surface beneath a colony. Sticky foliage, dark deposits and ants are useful clues, but the inspection still needs to locate the responsible insect. Several other sucking pests also produce honeydew.
Some aphids distort developing foliage. Curled leaves shelter colonies from contact treatments and natural enemies.
Heavy aphid populations can yellow leaves and stunt shoots. Some species distort growth and transmit plant viruses. Susceptible vegetables can become infected even when aphid numbers are low. Killing a visible colony after transmission does not reverse an infection.
Parasitic wasps, lady beetles, lacewings and syrphid fly larvae attack aphids. Parasitised aphids become swollen, hardened mummies. Compare living colonies with these mummies when inspecting a shoot.
Broad-spectrum insecticides can destroy aphid predators and parasitoids. Check which beneficial organisms are active in the crop before selecting a treatment.
Ants tend aphids for honeydew and defend them from predators and parasitoids. Follow ant trails to colonies when investigating poor biological control.
Inspect transplants for aphids before planting. Avoid excess nitrogen, which favours aphid reproduction. Check nearby host plants and protect vulnerable seedlings.
Soaps and oils kill aphids they contact, with little persistent control of later arrivals. Coverage of the colony matters.
Greenfly are aphids, and aphids can be yellow, brown, red or black. Some species feed on roots or woody tissue. Many reproduce through live-bearing females under favourable conditions.
Inspect potato aphids with the host in view
In potatoes, examine green peach aphid, Myzus persicae, and potato aphid, Macrosiphum euphorbiae. The former has an oval body; potato aphids have a more elongated pear-shaped outline. Colour varies, and adult females can be winged or wingless. Keep the host and the insect's body shape together in a diagnostic photograph.
Before choosing the best insecticide for whiteflies: inspect leaf undersides
Before comparing products, identify the host plant, the attached nymphs and the mobile adults.
Whiteflies excrete sugary honeydew on which black sooty mould grows. Heavy populations can cause leaf yellowing, drying and loss. Record the live insects as well as the deposits beneath them.
Rounded emergence holes in whitefly cases indicate parasitoid activity. Some immature whiteflies are naturally dark, so examine the case before counting it as parasitised. Broad-spectrum treatments can disrupt natural enemies.
Whiteflies have four nymphal instars. The newly hatched crawler moves before settling to feed. Later instars are flattened and immobile, with greatly reduced legs and antennae. Winged adults can leave the leaf you are looking at, so record the stage and whether it moves.
Adults have yellowish bodies beneath whitish wax. Wing markings differ between species; the last nymphal stage often provides the most useful identification characters. Examine body shape and other features alongside colour.
Whiteflies belong to Hemiptera, alongside aphids, scales and mealybugs. True flies belong to Diptera. Wax covers adult wings and bodies. Some whitefly species have broad host ranges; others, particularly on woody plants, are more restricted. Include the host name with any specimen.
Before choosing the best insecticide for scale insects: check living stages
Armoured scales have a covering that lifts away while the insect remains on the plant. Soft scales have a different body structure. Identify the family and species before assessing whether a colony needs control.
Keep your spray records in one place. Free to start.
Armoured scales do not excrete honeydew. Soft scales and certain other scale groups do. Honeydew supports sooty mould and attracts ants. Inspect the insects responsible for sticky foliage.
Old scale covers remain on plants after insects die. Examine a portion of the population for living scales, parasitoid emergence holes and other signs of parasitism.
Crawlers are the mobile early stage of scales. They disperse over plant surfaces and settle at feeding sites. Many become relatively immobile once established. Distinguish moving crawlers from settled insects during inspection.
Use transparent double-sided tape around infested twigs to detect scale crawlers. Examine yellow or orange specks under a hand lens and distinguish them from pollen, dust and trapped mites.
Scales feed on leaves, twigs, branches and other plant parts. Damaging populations cause yellowing, leaf loss, reduced growth and dieback. Many plants tolerate low populations. Assess living insects alongside fresh crop injury.
Small parasitic wasps, lady beetles, lacewings and predatory mites attack scales. Persistent broad-spectrum insecticides, dust and honeydew-tending ants disrupt this natural control.
For contact treatments, time applications to the susceptible crawler stage and reach the infested surfaces. Systemic options act differently and depend on the scale species and host.
Scale damage depends on the species, host cultivar, environment and natural enemies. Note fresh dieback, growth condition, fruit marking and honeydew alongside what you see of living insects.
Photograph the covering from above and from the side on the affected twig, cane or leaf, and show living scales beneath lifted covers. Preserve removed crawler tapes between white paper and clear plastic for comparison.
Before choosing the best insecticide for mealybugs: locate hidden colonies
Whether you want a mealy bug pesticide, a mealy bugs pesticide, a mealybugs pesticide or the best systemic insecticide for mealybugs, locate the living colony and its feeding site first. Compare a contact product by coverage, crop use and formulation. In a greenhouse, note which biological-control organisms are already in use.
The waxy coating of adult mealybugs and their habit of hiding make a contact mealybug insecticide less effective. Insecticidal soaps, horticultural oils and neem oil applied directly to young nymphs can reduce numbers. A systemic insecticide such as dinotefuran may reduce mealybug numbers on some landscape plants, but neonicotinoids are less reliable on mealybugs than on other piercing-sucking insects, and their use should be avoided where possible because of the harm to natural enemies and pollinators. Check any product in the Malta authorisation guide before use.
Mealybugs are soft, oval, wax-covered insects. Colonies produce honeydew and black sooty mould. Woolly aphids, cottony cushion scale, some soft scales and whiteflies also have waxy coatings. Examine the organism beneath the coating to distinguish them.
Newly hatched mealybug crawlers move before developing their protective wax. Older stages move less rapidly. Compare the stages present when judging whether a contact treatment can reach them.
Look for mealybugs in concealed plant crevices, and after treatment inspect hidden colonies as well as exposed leaves. Check pots, stakes and other materials for insects or egg sacs.
Mealybugs suck plant sap and contaminate foliage or fruit with honeydew and wax. Heavy populations reduce vigour, slow growth and cause leaf drop. Count living insects separately from old surface contamination.
Excess nitrogen and regular irrigation encourage tender growth and mealybug egg production. Protected conditions favour persistent populations. Review nutrition and growing conditions alongside the pesticide history.
Many mealybugs lay eggs in cottony sacs. Longtailed mealybug eggs hatch within the female, so colonies can reproduce without visible egg sacs. Compare wax filaments and body features to identify the species.
Mealybug-destroyer lady beetles prey on mealybugs. Their larvae have a waxy covering; examine the insect beneath it before classifying it as a pest.
Next step
Enter colony counts and beneficial-insect observations in the IPM monitoring sheet. Check the exact product and crop use through the Malta authorisation guide.