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Controlling the spread of little fire ants

Updated: 
July 6, 2014 - 12:05am

Markets and more

Farmer-direct markets: Hooulu Farmers Market, 9 a.m. to 2 p.m. Wednesdays and Saturdays, Sheraton Kona Resort & Spa at Keauhou Bay; South Kona Green Market, 9 a.m. to 2 p.m. Fridays and Sundays, Amy B.H. Greenwell Ethnobotanical Garden in Captain Cook; Keauhou Farm Bureau Market, 8 a.m. to noon Saturdays, Keauhou Shopping Center.

Plant advice lines are answered from 9 a.m. to noon Thursday at the University of Hawaii Cooperative Extension Service in Kainaliu, 322-4892 and 9 a.m. to noon Monday, Tuesday and Friday at UH CES at Komohana in Hilo, 981-5199.

Recently, a number of infestations of little fire ants have been found on products shipped from East Hawaii. These discoveries are a reminder for us to be vigilant about checking the latest information on little fire ant control to prevent the spread of this pest.

The little fire ant (also known as the electric ant) Wasmannia auropunctata, is native to Central and South America, but has spread to many areas around the world. It is currently established in several areas on Hawaii Island, stinging its victims and causing injurious allergic reactions in people as well as animals. Infestations have been reported in agricultural and residential areas as well as in parks and forests. Their ability to nest almost anywhere including high tree tops, leaf litter and inside homes makes controlling their spread difficult.

Ants have developed well-organized survival systems during their 100 million years on Earth. We have a lot to learn if we hope to control their numbers. Though little fire ant populations may be reduced in small areas, ways to eradicate their colonies entirely seem elusive. Some online information offers helpful solutions. If you want to consult an area expert about baiting and controlling little fire ant infestations, contact Reggie Hasegawa at reggie.hasegawa@cpsagu.com.

The first step in pest control is positive identification. Whenever and wherever new plants or materials are introduced they should be checked for little fire ants. “How to Test for LFA” is a three-minute video viewable online at vimeo.com/97558997. It advises smearing chopsticks with peanut butter and placing them in shady areas on and off the ground to attract ants.

If the ants are red-orange and very tiny, about as long as a penny is thick, they may be little fire ant. If you find red ants, bag them in a zip-close bag and put it in the freezer overnight to kill them. When the ants are dead, deliver or mail the sealed bag with your contact information to a Hawaii Department of Agriculture office for positive identification. You might also want to contact the HDOA pest hotline at 643-7878 or 643-PEST, the Hawaii Ant Lab at 315-5656 or the Big Island Invasive Species Committee to make a report and get some help. Refer to “Stop the Little Fire Ant” online at ctahr.hawaii.edu/oc/freepubs/pdf/ip-lfa.pdf for more information.

If you have little fire ants, you should begin control practices as advised by the HDOA or as found in the various publications at littlefireants.com. The East Hawaii Master Gardeners also have information on little fire ant identification and control at ctahr.hawaii.edu/uhmg/EastHI/little-fire-ant.asp.

Research has shown the product Tango, when mixed with bait and applied properly, is very effective against little fire ant. The method depends on worker ants carrying the baited insecticide into the colony and to the queen. See littlefireants.com/tango%20package.pdf for more information on this product and its use. Though slow acting, Tango can reduce ant populations significantly over a period of months.

For minimally infested areas that are shipping products, soaps and detergents can help prevent ants from traveling on fruit, vegetables or flowers. Any crop that can be safely immersed in cold soapy water for up to 15 minutes can be treated by this method. Since soaps break the surface tension of water, ants can’t float on soapy water or survive in the air bubbles. Soap also disrupts the ant’s protective cuticle layer causing them to drown quickly in the soapy water.

Agitating ¼ teaspoon of liquid soap or detergent per gallon of cold water and completely submerging the commodity in the solution for 15 minutes will kill the ants and they can then be washed off with clean, clear water. This technique is not recommended for sensitive commodities or those that are bruised, cut or torn. Treated products must be placed in a little fire ant-free holding area to prevent further contamination. A moat of soapy water can serve as a barrier. Placing table legs in a container of soapy water can prevent ants from crawling up them and re-infesting clean products.

Since little fire ants pose such a dangerous threat to farming, gardening, hiking and picnicking in Hawaii, it is very important that we all continue checking for them on our property and at our workplace. If positively identified, immediate treatment should begin. We are more likely to succeed at controlling their spread if all farmers, gardeners and property owners maintain vigilance in detecting and controlling their populations.

Tropical gardening helpline

Sarah asks: I was happy to see lots of little peppers developing on my pepper plants but I was upset when young peppers started falling off the plant. I opened a few and found a white worm inside. What’s the problem and what can I do to save my peppers?

Answer: It sounds like you have an infestation of the pepper weevil, Anthonomus eugenii. This pest was first discovered in 1933 on Oahu and has since spread to all of the Hawaiian Islands. The adult is a small brown-black beetle that is a little more than one-tenth of an inch long. The dark body has a slight luster with a typical weevil snout and long thin antennae.

The female adult beetle can lay hundreds of eggs in a season. If not controlled, an established infestation can wipe out this season’s crop and threaten future crops. Once the eggs have hatched and the larvae are feeding inside the young peppers or the pepper blossoms, it is too late to save that blossom or pepper but the larvae should be destroyed to prevent them from becoming adults.

Since it seems likely that you have the weevils in your crop, you should collect and destroy all infested fruit and begin a program to eliminate the adults. Pepper weevils are very hard to get rid of, especially in a mild climate like ours. You can monitor the extent of the infestation by setting out pheromone-baited yellow sticky traps mounted on poles at a level just below the top of the plants. Though you may catch some in the traps, stronger measures will be needed to completely eliminate the problem. Pesticides, even systemic chemicals which aren’t approved for vegetables, won’t kill the larvae. Though parasitic wasps will attack the larvae, they won’t significantly reduce the population.

The best approach is to contact the adults directly by spraying with a pyrethrin insecticide. Though most pyrethrin products are organically approved caution in application is recommended. If you are unable to control the problem this season, you might want to consider planting your peppers for the next season as far away as possible and begin monitoring and controlling as soon as the plants start to flower.

Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.

Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook.