fall armyworm

Symptoms

Young caterpillars skeletonise leaves and make "windowpane" patches; older ones chew ragged holes and burrow into the whorl, tassel and cobs of maize, leaving copious moist sawdust-like frass; the caterpillar has a pale inverted "Y" on the head and four dark spots in a square on the second-to-last segment. Populations build explosively and "march" between crops.

Plants affected

• Bermuda grass
• St. Augustine grass
• kikuyu grass
• bell pepper
• Goosegrass
• centipede grass
• seashore paspalum
• Hairy crabgrass
• Cockspur grass
• maize / corn
• Green foxtail
• sorghum

Easily confused with

• false codling moth

  How to tell them apart: Both bore into pepper (Capsicum annuum) fruit, but the larvae and damage pattern differ. Spodoptera frugiperda (fall armyworm) is primarily a leaf and growing-point feeder: look for ragged, window-paned chewing and large irregular holes in leaves, with masses of moist sawdust-like frass in the leaf whorl and on the foliage; the caterpillar is smooth, up to ~40 mm, greenish to brown with a pale inverted Y on the head and four black dots arranged in a square on the second-to-last segment. Thaumatotibia leucotreta (false codling moth) is a dedicated fruit borer: look for a single small (1-2 mm) entry hole on the pepper fruit surrounded by a sunken, often yellow-to-purple discoloured halo, with sticky frass extruded at the hole and internal premature ripening and rot; its larva is short (~15 mm), pinkish-red with a dark head and lives hidden inside the fruit. If damage is mainly on leaves and the whorl, suspect fall armyworm; if the fruit shows a discoloured halo around a frass-plugged hole and a pink larva inside, suspect false codling moth. BOTH are EU-notifiable quarantine pests — report any suspected find to your national plant protection organisation (NPPO) immediately.

• cotton bollworm / pod borer

  How to tell them apart: Fall armyworm (Spodoptera frugiperda): look in the maize whorl for a larva with a pale inverted Y-shaped suture on the dark head capsule and four large black spots arranged in a square on the second-to-last (eighth) abdominal segment; feeding produces ragged, elongated holes and conspicuous moist sawdust-like frass packed deep in the whorl. This is an EU quarantine pest not established in the EU. Cotton bollworm (Helicoverpa armigera): the larva is highly variable in colour (green, pink, brown to almost black) with alternating pale and dark longitudinal stripes and a smooth head lacking the white inverted Y; it has tiny dark microspines giving the skin a rough sandpapery feel and prefers to bore directly into the silks and ear tip rather than shredding whorl leaves. If you find the inverted-Y head and four square-set black spots, treat it as fall armyworm and report it to your national plant protection organisation (NPPO).

• European corn borer

  How to tell them apart: Fall armyworm (Spodoptera frugiperda) larvae sit deep in the maize whorl, are greenish-brown to grey with three thin pale stripes, and show a pale inverted 'Y' on the dark head capsule plus four black dots arranged in a square on the second-to-last segment. Their whorl feeding produces large ragged holes and abundant moist sawdust-like frass packed into the funnel. European corn borer (Ostrinia nubilalis) larvae are dull greyish-pink to cream with a dark brown head and a row of small round dark spots along each side of the body, no inverted-Y and no square of four dots. Older borers tunnel into the stalk and ear shank leaving round bore holes and crumbly dry frass at the entrance, whereas fall armyworm stays a surface whorl feeder for longer. Fall armyworm is a notifiable EU quarantine pest (Reg. 2019/2072) — if you suspect it, do not treat blindly: photograph the larva and report it to your national plant protection organisation (NPPO) immediately.

Common questions

How do I recognise fall armyworm on Bermuda grass?

Young caterpillars skeletonise leaves and make "windowpane" patches; older ones chew ragged holes and burrow into the whorl, tassel and cobs of maize, leaving copious moist sawdust-like frass; the caterpillar has a pale inverted "Y" on the head and four dark spots in a square on the second-to-last segment. Populations build explosively and "march" between crops.

Do I have to report fall armyworm?

Yes. fall armyworm is a regulated quarantine organism in the EU. A suspected finding must be reported to your national plant protection organisation — they will confirm it and tell you what to do next.

How is fall armyworm treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.