Updated: Nov 6, 2018
By Karen Miller, Master Gardener Entomology Specialist
Our “Ask a Master Gardener” program has received several inquiries about a pale green to brown or black worm, striped with white to yellowish lines from head to toe and munching on our warm season turf grasses. These “worms” are actually the larvae stage or caterpillar of nocturnal moths known as Armyworm moths. It seems this insect common name, “the armyworm” describes the caterpillar’s eating habits, they eat until nothing is left, then the entire group will “march in line” to the next available food source. Four common species found in Texas are the fall Armyworm moth, the yellow striped armyworm moth, the beet armyworm or small mottled willow moth and the true armyworm moth. Out of these four species, the fall armyworm is the insect that causes the most problems to turf grasses, on golf courses and home landscapes.
In the Order Lepidoptera and family Noctuidae, the fall armyworm has four life stages: egg, larva, pupa and adult. Adult females lay egg masses that can contain several hundred new worms and are deposited on or near plant food supplies. The caterpillar that hatches is about 1/8” long and will grow to a length of 1 to 1 /2”. The caterpillar hides in plant litter during the middle of the day, preferring to eat early in the morning or late in the evening. These armyworm caterpillars eat the blades of grass above the soil. If you have a major infestation they can eat the grass down to the soil level. Because the first three stages are very small they do little damage as they feed, the last two stages, however, consume 80 – 85% of the total foliage. These caterpillars are able to overwinter underground in the southern regions of Texas in the pupal stage. The full grown larvae will enter the soil and form the pupal stage, adult moths emerge from the soil and begin the life cycle over again.
Armyworms should be controlled when they occur in large numbers or you find excessive plant damage in your turf. Examine your grass blades to see if any damage is apparent, damaged lawn will appear off-color and turn brown in the damaged areas. Weather and natural enemies can act together to keep the armyworm population under control. Parasites such as wasps and flies are very effective against the armyworm. Predators, such as ground beetles, help limit outbreaks, birds and rodents also consume large numbers of larvae and pupae.
I prefer not to use chemical pesticides in my yard, however, sometimes it is necessary. I would suggest checking the level of infestation before taking any drastic measures with pesticides as most are indiscriminate killing the good bugs as well. Bacillus thuringiensis (Bt) will kill caterpillars, just remember it kills all caterpillars that come in contact with it. Spinosad is a natural substance found in many pesticide products sold in spray, dust, granular and pellet forms. Some of these products have been approved for use in organic gardens. Halofenozide is an insect growth regulator, which when ingested affects the hormones that regulates the insects’ molting process. Just a tiny amount will activate premature molting. The insect will stop eating and literally die of starvation. This process usually takes from 1 to 3 weeks. With all this said, if you decide to use pesticides it is very important that you READ AND FOLLOW the directions found on the product label. The label will also provide you with any precautions you need to take before mixing or applying the chemical.
If you have any gardening questions, you are welcome to call the Ector County Extension office at 432-498-4071 or the Midland County Extension office at 432-686-4700. You can also check out the Permian Basin Master Gardener website at westtexasgardening.org for tips on gardening in West Texas.