CULT: Weed Control

From: HIPSource@aol.com

<< I have a large iris patch (about 5 acres) in New Jersey. I have tried the 
 product Preen to prevent weeds, with unsuccessful results. I have a 
 commercial herbicide/pesticide license. Is there any herbicide on the market 
 that would allow the irises to thrive while killing unwanted weeds? I am 
sure 
 large production iris growers use a form of weed control/herbicide. I have 
 contacted Rutgers University and the Hunterdon County Extension Center, but 
 they have not been able to give me much help because their knowledge of 
 irises is limited. >>

Hello, Mr. Hartpence.

As you know, the word 'weed' covers a lot of territory and apparently so do 
the weeds in North America, where they rarely respect iris beds. Weeds in 
iris beds are not only unattractive, they can harbor pests, sap nutrients, 
shade rhizomes and foster disease. So weed control is not only nice, it is 
necessary.

We have had several long conversations on weed control here on the list and 
these maybe viewed by searching the Archives at 
http://www.mallorn.com/lists/iris-l/

However, this is what I know on the subject, subject to the caveat that I 
have not done any research on the subject in a couple of years so what I tell 
you may be dated.

Preen, sold in bulk as Treflan, has been used to great advantage by many 
irisarians but timing is said to be important in its application and one must 
avoid getting it on wet foliage. The newly divided and transplanted irises 
must have had time to get established before application. This caution holds 
for any pre-emergent germination inhibitor since they work on the meristem 
and can adversely affect new growth on the iris unless it is growing 
strongly. Many other people rely on Surflan, and the local Extension office 
here recommended Dacthal a couple of years ago when I did some research for a 
pests and problems presentation.  These are also pre-emergent germination 
inhibitors. They won't do anything much for anything which is invading 
stoloniferously, but they will cut down on the annual seed sown stuff. To 
some extent the stoloniferous stuff like clover and wiregrass can be 
discouraged by cutting a deep edging.

For overspray of established irises to remove grasses and sedges one hears 
the products Vantage and Poast recommended, and I believe we determined they 
were the same chemical. 

Comprehensive herbicides such as Roundup can be used near irises, but great 
care must be taken to avoid drift. Use of a paint brush or wick spreader has 
been recommended.

The best means of weed control is prevention, and the next best is hand 
pulling. It is also possible to use a hoe or cultivator, but remember that 
many iris roots run wide and shallow. When possible, the best course is to 
pull them young and keep on pulling as they appear. 

It maybe useful to bear in mind that when weeds get the upper hand in an iris 
bed it is probably about time to divide and reset the irises anyway. If they 
get totally out of control I think one has little choice in the matter. Once 
the irises are removed one can address the weeds as necessary as a part of 
refurbishing the bed for replant.

Anner Whitehead
HIPSource@aol.com

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