Arkansas Fruit, Vegetable and Nut Update

Fire Ant Management in Strawberry

by Aaron Cato - April 10, 2020

Worried about fire ants in your strawberry? Provided here are some recommendations for managing this pest and mitigating future infestations.

We’re off to a warm start and I think everyone is either starting harvest or watching green berries grow. The mild winter and warm start to the spring most of us got has also led to fire ant (Solenopsis invicta) springing up earlier than usual, and I know I have noticed all the active mounds in Little Rock (Picture 1). There are a few growers in the state that are already seeing mounds pop up among their plants and are worried about harvest and the health concerns related to these feisty ants. I had a chance to talk to the University of Arkansas’s resident fire ant specialist, Dr. Kelly Loftin, and he’s offered some advice for control.

Picture 1: Fire ant Mound in Little Rock, AR.

Along with the recommendations from Dr. Loftin mentioned here, check out the 2020 Southeast Regional Strawberry Integrated Pest Management Guidefor more product recommendations and use rates.

Are fire ants an expected issue on my farm?

I think everyone reading this could tell you whether they have dealt with fire ants before on their property. This species has a bad habit of making itself known through aggressive bites and stings. I worked in West Alabama last summer where this species runs rampant, and let’s just say this is a major reason I was ready to come back to Arkansas.

In Arkansas we are on the edge of the fire ant range and the winters in the northern parts of the state are usually enough to deter overwintering populations outside of warmer city hotspots (Picture 2). Although that range cuts right through the state, anyone in the northern part would tell you that it’s not uncommon to see this species. Usually what we see is that it is sporadically introduced all the way up through Missouri, but as soon as we have a hard winter it dies back about to where the map indicates.

If you produce strawberries in a county not colored green in the map in picture 2, I wouldn’t expect you to have issues in the spring unless mild winters have been prevalent.

Picture 2: Established range of fire ant in the United States.

How do I determine if fire ants are in my strawberry field?

Monitoring for fire ants is necessary not only for determining if you will have an issue in your field, but also because effective control measures only work if active foraging is occurring. Dr. Loftin indicated that fire ants usually begin foraging by April 15^th in Arkansas, and he wouldn’t recommend an application of Esteem or Extinguish before that date unless you have confirmed that the ants are active.

The go to method for determining fire ant activity is by using the hot dog test (Picture 3). First, place slices of hot dogs out where you want to monitor for fire ants. Return 30 minutes later and look for fire ants present on the slices. In Picture 3 you can see active foraging occurring, which means that fire ant mounds are active and that workers are searching for food to bring back to the mound. This is important because the best control measures are baits that need to be brought back into the mounds by workers. These baits then make the queen lay sterile eggs, leading to a collapse of the colony.

Picture 3: Slice of hot dog being fed on by fire ants. Photo by B. Royals - NC State.

How do I manage fire ants in strawberry?

Once you’ve determined that you have a fire ant issue control is relatively easy using granular baits. Esteem and Extinguish are both labeled in Arkansas for use in berries, although you should read the specific label of what you buy to make sure it is labeled for strawberry. These granular baits do a great job of collapsing colonies, but the caveat is that they are relatively slow acting. After applying these baits, you should expect to see colonies collapsing in three to four weeks. Determine if control after this lengthy time period will benefit your production system before choosing this strategy.

Dr. Loftin indicated that the best way to manage fire ant in strawberry is to apply control measures in the fall. If you determine that you have actively foraging fire ants in the fall (before October 15^thand ideally in mid September) make an application of either Esteem or Extinguish. This will collapse colonies in this area before they become dormant, meaning that little to no colonies will exist in that area in the spring. Monitoring can begin again in the spring, but most strawberry will be harvested in Arkansas before any mounds will establish in your fields.

Directions for use of fire ant baits

Fire ant baits need to be collected by workers and brought into the mounds to be effective. Dr. Loftin indicates that these baits need to be applied when the ground is not moist. If you apply following a rain the bait could dissolve into the wet soil, making it impossible for ants to bring it back to the mound. Moisture from sprinkler irrigation or rain events can also lead to baits dissolving. Make applications where they can be collected by ants at least 12 hours before any rain or overhead irrigation event, and avoid applications until the soil is relatively dry.

If you are trying to get control before April 15^th, pay attention to the forecasted temperatures for the next week. If you apply the bait just before a cooldown (below 65 degrees), ants may not forage before the bait is dissolved by your next rain.

Fire ants can cause a lot of hassle and headache in our handpicked crops, especially when considering businesses based in agritourism. Granular baits offer the best control of fire ants when used correctly and are also the safest option. Fall applications offers efficient and effective control in areas that see yearly infestations, but spring applications can also offer delayed control.

If you have any questions please give me a call at 479-249-7352.

Aaron Cato