It’s been a challenging spring in this guy’s garden! Despite getting the normal early start required for successful gardening in Florida, I’ve been affected by Bacterial Leaf Spot stunting my tomatoes, cutworms that reduced my watermelon plantings by half, and an eternal test of my patience in the form of a dog that seems to think my raised beds are merely a shortcut to a destination further out in the yard. My latest adversary is the most potentially destructive yet, an outbreak of Southern Armyworm (Spodoptera eridania).
Unlike some serious garden pests that wait until the heat of summer to emerge, Southern Armyworms begin appearing in spring gardens around the end of April. Adult moths can survive mildly cold weather and venture into the Panhandle as soon as warmer spring weather arrives. Once the adult moths arrive, egg masses are then laid on the undersides of leaves and hatch in a little under a week. Once loosed upon the world, Southern Armyworm larvae (caterpillars) become indiscriminate, voracious feeders and congregate in extremely large numbers, allowing them to destroy small, developing garden vegetable plants in a manner of days. Young larvae feed on the undersides of leaves and leave little but a skeleton. As larvae grow larger, they become solitary and begin to bore into fruit. Once they’ve eaten the good stuff (leaves and fruit), large larvae turn to branches and even plant stems!
The good news for gardeners is that Southern Armyworm, and most other caterpillar pests, are easily controlled if outbreaks are caught early. Scouting is critical for early detection and good control. Armyworm damage generally appears from above as brownish-gray sections of affected leaves with a yellowish ring surrounding these sections, this ring indicates the current feeding zone. Affected areas will appear transparent and “lacy” due to the skeletonizing effects of larval feeding. If you see leaves that look “off” in the manner just described, check underneath for the presence of a horde of tiny greenish worms.
If found in this early stage, an application of Bacillus thuringiensis (Bt), a biological pesticide utilizing a bacterium destructive to caterpillars, is extremely effective. Bt has to be ingested by caterpillars with leaf tissue to work; thorough coverage of leaf surfaces is critical for maximum control. I generally follow up with a sequential application of Bt a day later to ensure that I achieved good coverage of the plant surfaces and, therefore, good control. Unfortunately, Bt is much less effective on older larvae. Infestations not caught early require harsher chemistries like carbamates, pyrethroids and organophosphates for adequate control.
Don’t let armyworms or other caterpillar pests destroy your garden, get out there daily and scout! You have a short window for easy caterpillar control with a harmless to people, natural product, Bt. Don’t waste it!
For more information about Southern Armyworm, other caterpillar pests, Bt, or any other horticultural topic, please consult your local UF/IFAS Extension Agent. Happy Gardening!