Amaranth leaf webber

young leaves and growing tips folded over and tied together with fine silk webbing, like a little tent or parcel. Open one and the leaf inside is eaten down to a thin, see-through skin — "windowed" and skeletonised (only the veins left) — and packed with green-black droppings (frass). Under heavy attack whole plants look stripped, ragged and dirty with webbing.

hiding inside the webbed fold — a slender, translucent green caterpillar up to about 1.5–2 cm long (shorter than your little finger), with a faint darker line down its back, a dark head, and rows of tiny dark dots along its body. When you open the shelter it wriggles backward violently and drops on a silk thread — a sure give-away.

a small dark-brown moth about the size of your thumbnail (~2 cm across the wings) with a clear wavy white band across each wing and a little tuft at the tail. It hides under leaves by day and flutters up in a quick zig-zag at dusk when you brush through the crop.

with flea beetles (which chew clean round shot-holes but leave no silk), leaf miners (which make pale squiggly tunnels inside the leaf), or cutworms (which cut seedlings off at the base at night). The sure sign of the leaf webber is leaves silked together with a green caterpillar living inside.

check twice a week from the seedling stage right through leafy growth and cutting — this crop is at risk from its first true leaves all the way through the leafy growing and harvest season. Scout in the cool of early morning or late afternoon, when the caterpillars are active near the surface and the moths flutter up.

The pest breeds fastest in warm, humid spells (around 22–32°C with damp air) and several generations can pile up quickly — so step up scouting after a run of hot, sticky days.

across the bed or field so you check all four corners and the middle, not just the edge by the path. Stop at about 5 to 10 spots and look at 10 plants at each stop.

the growing tips and youngest leaves first (the caterpillars prefer tender foliage). Turn leaves over to spot pale eggs and tiny caterpillars underneath, and gently open any folded or webbed leaves to find the green caterpillar and its droppings inside.

treat when you find webbing and caterpillars on about 2 in every 10 plants (1 in 5). If you are growing a young crop to sell whole, act even earlier — at the first webbed leaves — because buyers reject any leaf with silk, holes or droppings on it.

don't plant amaranth back-to-back on the same ground. The caterpillars need a constant supply of tender leaves, so rotate your leafy plots and leave a gap in time that starves each new generation. After every harvest, pull out and destroy old crop residues and weeds — wild amaranth and pigweed shelter the pest between crops.

inspect young plants from the day they come up and handpick and crush the webbed shelters with the caterpillar inside — pinch them or drop them into a tin of soapy water. Because they cluster in the folded leaves, pulling off and burning the worst-webbed tips clears many at once and stops them spreading to clean plants.

Bacillus thuringiensis (Bt) is a natural soil bacterium sold as a powder or liquid that only sickens caterpillars that eat it and is harmless to you, to bees and to helpful insects. Spray it onto the growing tips and the undersides of leaves while the caterpillars are still small and out in the open — before they web up — because once they seal themselves inside the fold, no spray can reach them. Spray in the cool of the day and wet the plants well.

if webbing keeps spreading past the threshold, spray spinosad, an approved leafy-vegetable insecticide. Because you eat and sell the leaves, you MUST respect the pre-harvest interval (PHI) — the set number of days you must wait after spraying before you may pick or sell — printed on the label. Safety: cover your skin, eyes, nose and mouth; spray in the cool of the day with the wind at your back; keep it off food, drinking water, children and bees; and wash yourself and your clothes afterwards.

don't spray the same product every time, or the pest gets used to it and it stops working. Rotate to a different chemical group between sprays, and lean on Bt, handpicking and field sanitation first so you spray as little as possible.

harvest the good, clean leaves early before more are ruined, then cut down and burn or bury the badly webbed, skeletonised plants so the caterpillars have nothing to crawl onto. Afterwards clear every residue and rest the ground from amaranth — plant a non-leafy crop next — to starve out the next generation before you grow leafy greens there again.