Leaf Strip

Alternative Borer Control Methods

Iris Borer Deterrent by Garden Shield


Following twenty years of research, Garden Shield is marketing this non-toxic, 98%+ effective, and environmentally safe iris borer spray. The spray comes in a one-quart size plastic spray bottle and sells for around $25 with some discounts available. You probably will not find it in garden stores because it is a new, specialized product. You can, however, read all the details about Iris Borer Deterrent at the Garden Shield online website. The address is www.gardenshield.com. You can also call the company toll free at 1-866-690-4000. You can order either online or over the telephone.

Garden Shield reports that Iris Borer Deterrent is extremely effective against iris borers in all stages. They recommend that it be used throughout the growing season from the first warm days of spring; whenever you are transplanting; and whenever new growth appears. The directions indicate that you should spray only on cloudy days or during dusk or dawn to prevent possible leaf spotting. You may spray leaves, rhizomes, and even the soil in which the irises are growing.

This product is nontoxic because it repeals iris borers (and many other critters both mammal and insect) instead of killing them. The active ingredient, Methyl Nonyl Ketone, was used as an ulcer drug in 1950s. It is presently used as a fragrance enhancer in cosmetics and perfumes.

Garden Shield conducted five years of intensive field testing with the Iris Borer Deterrent before it became registered with the Environmental Protection Agency. The following is a brief summary of the results of field-testing. In year one of the trials no borers were found in the Iris Borer Deterrent treated plot. In a plot of equal size that was left unprotected, 49 borers were found. In year two the figures were 1 borer in the treated plot and 56 borers in the non-treated iris plot. In year three 2 borers were found in the treated plot, while 52 borers were observed in the unprotected plot. In the fourth year 3 borers were noted in the sprayed plot with 57 in the unprotected plot. In year five no borers were found in the treated plot, while 75 were observed in the untreated plot. These results are, indeed, rather impressive.

One question remains to be answered relative to your use of the Iris Borer Deterrent, and that is, "Is this right product for me to use?" First, the product appears to meet all the EPA's safety and effectiveness requirements, and presently is in a patent pending process. If you have a very large iris garden Iris Borer Deterrent could prove to be rather expensive and labor intensive compared to other forms of iris borer protection and treatment. On the other hand, if you have a small iris collection and controlling borers without resorting to toxic pesticides is important to you, then Iris Borer Deterrent might be a good choice for you.

Parasitic Nematodes

Parasitic nematodes are microscopic roundworms that feed on insects and have used successfully control insect pests. In a study reported in the April 1998, Bulletin of the American Iris Society, parasitic nematodes were shown to equal or more effective than Cygon 2-E or Merit. Cygon and imidacloprid (Marathon) both showed an reduction in borers of 87% while nematode Steinernema carpocapsae had a 100% reduction and nematode Heterorhabditis bacteriophora gave an 87% reduction.

Parasitic nematodes pose no threat to humans, wildlife or plants so they are exempt from EPA regulation. Nematodes hunt down and kill borer larvae within 48 hours and are easy to apply because no safety equipment is required. Both species, Steinernema carpocapsae and Heterorhabditis bacteriophora are very effective against moth larvae including iris borers. There are now many suppliers worldwide and nematodes are now a cost-effective method to control iris borers. Care should be taken to purchase the correct species of parasitic nematodes since several species are now available.

It is important to apply nematodes correctly to get the best results. In the study the nematodes were applied in the spring when the soil temperature was above 50 degrees. The irises and the surrounding soil was drenched with water (2 quarts per square foot) to allow the nematodes to swim close enough to the borers to kill them. The nematodes are most effective against the borer larvae so application should be done in the spring. The Wisconsin Cooperative Extension has found that a nematode treatment is effective for 4 to 5 weeks. They have treated iris as late as June or early July and still got some success controlling borers which suggests that the nematodes can successfully attack borer larvae that have moved down into the rhizome and pupae located in the soil.

Ten million nematodes treat about 225 square feet of soil or 60 linear feet of conventional garden row. Application rates vary so it is important to follow the manufacturer directions. Nematodes are available in packs of 1 million juvenile nematodes or more. Spraying is not as effective as drenching the area. Nematodes can also be added to irrigation water. The nematodes will not over winter in most of New England so they will need to be reapplied in the spring. Rain or watering every 4 days will increase the effectiveness of the nematodes. Ultraviolet light is hard on the nematodes. Ideally application should be done on overcast or rainy days. If there are none in the weather forecast, try late afternoon or early morning. If the soil is very dry, water the area ahead of time.

Gardeners can purchase their nematodes in several forms: a nematode impregnated sponge, gel, a clay like residue or a "sawdust" like material which can be shaken on the iris and then wetted. Nematodes delivered on a sponge usually have to be stored in the refrigerator. When the soil temperature exceeds 50 degrees, the sponge is just tossed into a bucket of lukewarm water and allowed for to sit for a few minutes to let the nematodes swim out. Gently squeezing the sponge is helpful. The bucket is then poured out on the iris. If you are treating a lot of iris, it is helpful to wet the plants and surrounding soil with water ahead of time so you can use less water to apply the nematodes.

A summary of the study on the effectiveness of parasitic nematodes appeared in the Bulletin of the American Iris Society, series number 309, (April 1998), pages 35 to 37. Another version of the article can be found on the internet at
www.agnr.umd.edu/users/ipmnet/98-2nmn2.htm A definitive article on parasitic nematodes by Randy Gaugler, Department of Entomology, Rutgers University, complete with color photos and a source list can be found on the internet at www.nysaes.cornell.edu/ent/biocontrol/pathogens/nematodes.html Dr. Parwinder Grewal, an entomologist at The Ohio State University, produced nematode reference center on the internet at www2.oardc.ohio-state.edu/nematodes/default.htm

Spring Burning

In the March, 2002 issue of Tall Talk (Tall Bearded Iris Society), Opal and Henry Wulf of Lincoln, Nebraska, describe their experiences with using controlled burning to control borers. The Wulfs learned about their technique from Alan Ensminger who showed them how to construct a burner attached to a 20-pound tank of propane on wheels since they both have large commercial iris gardens. The irises are burned in the spring to remove the dead foliage from the previous year contaminated with borer eggs. The key to successful burning is to burn when the debris is dry enough to burn quickly so the rhizomes will not be damaged. The Wulfs treated the few damaged rhizomes by digging them and giving them a Chlorox soak.

The Wulfs clean their beds of leaves in the fall and cut the iris back. Their spring burning removed the residual iris leaves, any tree leaves that may have blown onto the iris and a few early weeds. Burning should only be done on windless days. It could be difficult to find enough days to complete the burning in a windy and/or wet year.

The Wulfs are emphatic that burning is a job for two responsible persons: one person to control the burner and one person to watch for unruly flames that threaten to get out of hand. A small hand held weed burner should work well for small gardens but it still would be essential to have two people present for safety's sake.

If you can't locate a copy of "Tall Talk", an issue can be order for $5 from TBIS, P.O. Box 555, Pawnee, OK 74058. The March, 2002 issue is well worth the $5.

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