Fire ant (Solenopsis invicta) colonies surrounding strawberry plants in Chowan County, NC. Photo: HJB, 2008
In addition to crop pests, spring also brings other potentially problematic arthropods. Last week, I detailed spring pest management chores in strawberries, but I did not mention fire ants. Fire ants are an invasive pest in NC, but are common concerns in small fruit production in counties where they have become established. NCDA maintains a quarantine program for fire ants in these counties, and the 2010 quarantine areas can be found here. Fire ants are not crop pests in small fruits (although they can be in tobacco greenhouses) but are instead a public health hazard, particularly for pickers in commerical operations and customers in you pick operations.
Fire ants can often infest strawberry fields in the fall spring and may chose these sites because the ground stays warmer under black plastic and/or because they are attracted to water from drip lines.
There are 2 methods of controlling fire ants chemically: contact materials and baits. I prefer bait products because they are more likely to eliminate colonies when used properly. Contact materials (mound drenches) may provide a short term knock down, but unless the entire colony is treated, the fire ants will eventually rebound. Spring is a good time to use baits for fire ants because these materials take a few weeks to eliminate colonies, which means they will do their job by the time picking begins. Consult the NC Agricultural Chemicals Manual and the Southeastern Small Fruit IPM Guides for the specific baits registered and label rates in the crop you will be treating. (A note about pesticide recommendations)
In anticipation of some of the questions I may get from the strawberry community--applications through the drip may be tempting for fire ants, but these will probably not go deep enough into the soil to treat entire mounds and therefore will only offer at the most temporary benefit.
The most important consideration when using baits in the spring is timing. In order to be effective, baits must be applied when fire ants are actively foraging, because the ants must pick them up and return baits to the nest where they will kill the colony. The best time to apply baits is mid morning, on days where the temperature is greater than 70 F and ants are foraging. You can check for foraging activity by using the "potato chip test". Place a potato chip or cheese puff near mounds. If within 30 minutes, ants have found the chip, they are foraging and it's a good time to treat.
The "Two-Step Method", developed by extension specialists in Texas (of course!), follows bait treatments with a mound drench 2-3 weeks later and is a good tool for dealing with large, persistent infestations. It's best to contact your cooperative extension agent for recommendations on drench treatments because there are few products labeled for this purpose in small fruits.
There are organic bait and drench treatments which may be used in small fruits, and I or your cooperative extension agent can provide more information on these as well.
A group of NCSU extension entomologists conducted an Elluminate webinar on fire ant management in a wide range of cropping systems in February 2009. I participated in this webinar, which can be viewed online here. The entire webinar is 2.5 hours and covers fire ant management in homes, nurseries, field crops, fruits, and vegetables as well fire ant regulations in NC. Log in as a guest to view the presentation, which will download as a Java document. The password for the presentation is rifa. You will need speakers and/or headphones to hear the presentation.
More on fire ant biology and management can be found in this Structural, Residential, and Community Insect Pest Note by Charles Apperson & Mike Waldvogel from the NCSU Entomology Department.
Embedded below are the slides for my section of the 2009 Fire Ant Webinar for those of you who do not want to listen to the entire session.