Mary Lou Gripshover, Ohio

Question on herbicide use

May 19, 2014

Categories: Basal Rot, Diseases and Pests, Fungus, Growing Daffodils, Weed Control

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A good friend of mine says that she thinks repeated use of Preen has a deleterious effect on her daffodils.  She says she has lost lots of bulbs, and thinks Preen is the cause, even though it’s registered for use on daffodils.  I’ve had some losses as well, so can’t really argue the point with her.  I’ve seen Organic Preen, which contains corn gluten, so I’m wondering if anyone has used that formulation of Preen, and what the results were.  Thanks for any help.

Mary Lou

11 responses to “Question on herbicide use”

  1. Loyce McKenzie, Mississippi Loyce McKenzie, Mississippi says:

    Rod Armstrong knows a lot about corn gluten,,maybe he can share experiences.

  2. Rod Armstrong, Texas says:

    I’ve not used corn gluten as a herbicide but understand it’s effects are controversial.  Check this link for more information –

    I have used horticultural cornmeal, which is quite different than corn gluten meal, as a fungicide.  It too has its critics; however, laboratory studies have shown that trichoderma, a good fungicide that attacks other pathogenic fungi, increases 5 to 10 times faster in cornmeal media than in normal soils. There has been scientific research in New Zealand in using trichoderma as a fungicide in the prevention of the narcissus basal rot fungus in daffodils.  I believe our friend Peter Ramsay has written about this research and hopefully can add to this post.

  3. Mary Lou Gripshover, Ohio Mary Lou Gripshover, Ohio says:

    Rod, thanks for the information on both corn gluten and horticultural cornmeal.  Do you dig the cornmeal into the soil when you plant, or broadcast it over the beds?  And I may try the Preen with corn gluten next spring as pre-emergent weed control, as apparently it’s too late now to do any good.

  4. Rod Armstrong, Texas says:

    When planting I just put a dollop or so of the cornmeal in the hole with the bulb before covering with soil.  For bulbs already down in the past I’ve spread it on the top of the soil; however, critters including squirrels are attracted to it so I’ve not done so recently.



  5. Ceci Brown, Virginia says:

    I remember at an ADS lecture by Kathy Welsh at the Richmond convention where she stated never use Preen on Daffodils as it will do extreme damage to your show bulbs.


  6. Lesley Ramsay, New Zealand Peter Ramsay, New Zealand says:

    Hello All,

    Trichoderma is now used by many daffodil lovers in NZ.  Our prime target is basal rot – we sprinkle the product in the bottom of the trench at planting time.  The product we use is Tenet – very fine cornmeal with the trichoderma mixed in.  The trichoderma attaches itself to the emerging roots.  Since starting the use of this product our loss to basal rot has reduced dramatically.  John McLennan was one of the first to use trichoderma on daffodils and has reported a high rate of success.  – you might like to report on this John.  One drawback is that you can only purchase large quantities at a time and that it is  very expensive.  Groups of growers split the contents up thus reducing the cost per person.

    For the rose lovers out there Trichoderma in a pelatised form which has given us control of silver blight.  You  drill  holes in the base of the rose and tap the pellet in.  This has been very successful for me.


    There have been no controlled field trials on daffodils – however trials on onions have had a very high success rate



    Hope this helps  Cheers,  Peter

  7. Jason Delaney, Missouri Jason Delaney, Missouri says:

    Trichoderma harzianum is the specific fungus needed to control basal rot in daffodils.  Before spending lots of money, make sure to read the label and its active ingredients to make sure you are indeed purchasing the correct product.

    Also, note that these products have a limited shelf life, as they are an active pathogen.   Refrigeration will prolong their life, but after 6-8 months they begin to lose efficacy (per the label).

    I have been using the wettable powder formula, to dip the bulbs in just prior to planting. As it’s only been two seasons and I also began HWT at the same time, I cannot claim that this product specifically has made any difference–yet, the resulting plants have been bigger and more lush and robust than ever before.  i think the HWT had something to do with that…  Still, I plan to continue using it into the future.  I can’t hurt.

    Despite being a natural product, still be sure to wear a dust mask and nitrile, vinyl, or latex gloves and long sleeves when handling.  The wettable powder formulation (WP), has an extremely fine dust.

    Hummert International, of Saint Louis, sells this product and ships world-wide.

    Thanks, New Zealand friends, for discovering this wonderful product and promoting it on the world market.


  8. Loyce McKenzie, Mississippi Loyce McKenzie, Mississippi says:

    Peter, this is very helpful, especially to those of us who garden in the Basal Rot belt.

    And that last sentence: Keith Kridler has always taught us, when in doubt, ask about what they would do for onions. That is officially what you specify on the forms for Mississippi State University when you send soil samples!!

    Loyce McKenzie

  9. Bob Huesmann, Maryland says:

    Here is what I think I’ve learned during my research over the past several years.

    1. The product used in New Zealand which has been researched for and is used on onions, and is used informally (and reportedly with good effect) on narcissus, is Tenet (Brand name).  The active ingredient is trichoderma atroviride Strain LC 52.  According to a EU source, t. atroviride is a new name for t. harzianum.  However, I don’t see the term atroviride used in American sources.  I can’t find a source for Tenet in the U.S.  The product sold by Hummert is Rootshield, of which the active ingredient is t. harzianum.   (See below.)

    2.  The active ingredient in Rootshield is t. harzianum Rifai either Strain T-22 or KRL-AG 2, depending on which label you believe. (Maybe they are the same strain, or maybe it doesn’t make any difference?)  Rootshield contains 1.15% active ingredient, which in turn contains 1 x 10 to the 7th power Colony Forming Units (CFU) of t. harzianum per gram.  The pricing on Rootshield looks a little out of synch to me.  Although the proportion and concentration of active ingredient are exactly the same on the labels, you can buy 4 oz of Rootshield for about $17 or $18, but the 1 lb size (4 x as large) will set you back about $120.

    3.  There is another natural fungicidal product on the market called Soilgard.  Its active ingredient is gliocladium virens Strain G21. In research a few years ago, I found that gliocladium and trichoderma are different names for the same thing.  I am assuming that they are the same, and that the so-called gliocladium virens in Soilgard is substantively the same as the t. virens in Rootshield Plus (See below) and Die-hard Bio Rush (See further below.) According to its label, Soilgard contains 12% active ingredient, which in turn contains 1 x 10 to the sixth power CFU per gram (I assume per gram of active ingredient?)  You can get 5 lb of the WP (wettable powder) for about $70.  Somebody who’s a better scientist and mathematician than I am will have to figure out the cost per CFU of each of these products, which is what I think we would want to know.

    4.  There is yet another, newer product now available.  It is Rootshield Plus, and–no surprise–the Plus is t. virens, the same bug that is the single active ingredient in Soilgard, although of a different Strain–in this case G 41.  So, the active ingredients in Rootshield Plus are t. harzianum T-22 (1.15%, same as regular Rootshield), plus t. virens G-41 (0.61%).  The t. harz comes 1 x 10 to the 7th power CFU per gram, same as Rootshield.  The t. virens comes 5.3 x 10 to the sixth power CFU per gram.    You can get Rootshield Plus WP for $125 per lb.  Rootshield Plus also comes in granular form.  According to the label, the active ingredient content is exactly the same as Rootshield: 1.15% t. harzianum and 0.61% t.virens, in the same concentrations as for the WP formulation.  However, you can buy Rootshield Plus for $200 for 10 lb.  This is a heck of a lot cheaper than the WP.  Either I’m making a mistake or one of the labels (in this case, probably the one for the Granular formula) is wrong.

    5.  Another product is DIEHARD Bio Rush, from Horticultural Alliance in Florida.  Bio Rush is a compound product which contains many ingredients which are said to be growth-promoting micorrhizae and soil conditioners, as well as trichoderma.  There is no way to calculate the percentage of trichoderma to total product weight. However, the label states that the product contains 5,500,000 CFU per cubic centimeter of a combination of four trichoderma types: t. hamatum, t. harzianum, t. viride and t. reesei.  It doesn’t specify the proportion of each of these in the total trichoderma count, and the label doesn’t give enough information to calculate the total trichoderman count. (5,500,000 CFU per cc of what?)  BioRush costs $28.74 per lb.

    6.  I have been using DIEHARD products for about 5 years.  I have used a more “complete” product called DIEHARD Flower Bed when planting my bulbs–putting about a tablespoon in the hole and a bit more mixed in with the fill dirt.  Actually, I augmented the trichoderma content of the Flower Bed by mixing in some BioRush. This applies only to my new plantings.  Last year I used (once)
    a separate application of BioRush (easily mixed in water and applied with a watering can) after bloom, on all beds, in hopes that this would fortify the effect of the trichoderma already in the soil.  This is all very unscientific, but I do think there has been some suppression of basal rot.  I’m beginning to understand that trichoderma don’t last forever in the soil.  They do suppress, but not eliminate, basal rot.  And their numbers in the soil do dwindle, so that repeated applications are needed to maximize their effect. This would suggest a regime of 3 or 4 applications per season–certainly one when planting, then drenches (or some other, better, means of getting the trichoderma down to the root level) early in spring, once or twice during the summer, and again as rooting begins again in fall.  This year, I have drenched one of my beds with Rootshield (using that product for the first time) and I will use BioRush on the others.  The DIEHARD products don’t specify a strain (e.g. Rifai T-22) for their trichoderma, and I don’t know if that distinction makes a significant difference in performance.

    7.  I think  trichoderma may be the most effective means available to control basal rot, but it is rather expensive, and we certainly need some research to figure out how and when to apply the various products to get the maximum effect.


  10. Bob Huesmann, Maryland says:

    Just to clarify, my recent message about trichoderma was titled “Natural Fungicides”, but seems to have circulated under the “herbicide” title.  I think this discussion started with corn gluten, which is a natural herbicide and does not, as far as I know, have any fungicidal properties.

  11. Ted Snazelle, Mississippi Ted Snazelle, Mississippi says:

    I stopped using Preen several years ago after I had rowed out a number of bulblets of daffodil seedlings only to see that it killed virtually every bublet.  I am still sick at heart as a number of these bulblets were from standard daffodils X  N. jonquila.  This loss set back my jonquil hybridizing considerably!