Football season is here, and that means one thing — so are fall armyworms. Yes, it is that time of year, when superintendents throughout much of the country — and beyond — find themselves fighting off these annual invaders.
And these voracious feeders can devastate golf course turf as well as row crops. Other than their ravenous appetite, the life of the fall armyworm is as mysterious as the inner workings of college football's playoff system. A new tool from North Carolina State University can help superintendents manage this invasive feeder.
The caterpillars that invade golf courses throughout much of the country and parts of Canada are the larval stage of the fall armyworm moth (Spodoptera frugiperda). They are native to South Florida and South Texas in the U.S., as well as other tropical zones globally, however, evidence of their feeding habits stretch far beyond their native range. It is believed that the adult moths migrate hundreds, or even thousands of miles, on the wind.
They prefer Bermudagrass, but with multiple generations possible throughout the summer and fall, and each new adult able to move hundreds of miles, they can be found as far away as the Midwest, Northeast or even southern Canada by autumn under the right conditions.
Research indicates that hot, dry conditions are optimal for armyworm activity, but predicting severity from year to year is almost impossible.
The adult moths do not feed during their short stage of the armyworm life cycle, but they are voracious as they progress through the larval caterpillar stage. Fortunately, there are many effective tools available to manage them.
North Carolina State University recently published an infographic guide (right) to help turf managers identify the pest and life cycle stage as well as what to spray and when to apply it for maximum control. The steps to managing fall armyworm infestation and minimizing damage are:
Step 1: Identify the pest
Examine the turf canopy to see if you can find fall armyworms crawling across the surface during the day. If not, you can apply a soapy water flush or cut a section of the turf to find what is causing the damage. If you find caterpillars, do they have an “upside-down ‘y'” on the head capsule? If not, you need to investigate the source of damage further. Do not apply an insecticide until you have determined what is causing the damage. If the caterpillar has the “Y” marking, proceed to Step 2.
Step 2: Determine the life stage present
Once you have determined that fall armyworms are to blame, cut a small section of the turf and examine the top two inches of the soil profile. If you see more pupae (red-brown, inch-long capsules) than larvae (caterpillars), apply a diamide product (see “Insecticide Options” key for list of active ingredients) now or a pyrethroid product in 3-5 weeks. If you find more larvae (caterpillars) than pupae, proceed to Step 3.
Step 3: Caterpillar size
Get an approximate measurement of the length of a larva. If it is greater than one inch in length, apply a diamide product now or a pyrethroid product in 3-5 weeks. If it is less than one inch in length, you can spray a pyrethroid for a "quick-knockdown" that will not provide a long window of protection (1-2 weeks maximum) or apply a diamide that will take a few days to work but will provide several weeks of protection.
NC State also has launched an interactive fall armyworm locator map where users can report where and when activity occurs and severity of damage.
The female adults lay masses, each containing up to 1,000 eggs, on vertical objects in or adjacent to turf, such as ballwashers, 150-yard markers and directional stakes (right). The eggs hatch in just a few days, and the larvae fall to the ground where they begin feeding.
Larva can do little damage in the first through third instar stages, so that is when superintendents should treat to control them. Armyworms in the fourth or fifth instar stage can be a half-inch or more in length and are more difficult to control.
Damage first appears as what looks like drought stress. Damage can escalate rapidly and quickly can become catastrophic. Therefore, scouting can be critical, says the USGA Green Section.
Left untreated, hundreds of armyworms might be present once damage becomes noticeable. The NC State guide recommends pyrethroids, with active ingredients such as bifenthrin, lambda-cyhalothrin, zeta-cypermethrin, beta-cyfluthrin, gamma-cyhalothrin, deltamethrin and cypermethrin; and diamides with active ingredients like chlorantraniliprole, tetraniliprole and cyantraniliprole.
The migratory life cycle of the armyworm is a fascinating one. Multiple generations can occur throughout their migration. As adult moths are swept north, each successive generation of caterpillars pupates and eventually emerge as moths that continue their trek northward. Since the species is unable to tolerate cold, they cannot overwinter outside their native habitat and will die at the first frost. The process begins again the following year as new adults head north from Texas and Florida.