November 2003

The Latest in Disease Control By Margery Daughtrey

Now that I have the chance to explain to you what is new inthe disease control sphere, I find myself thinking that you might not havetaken advantage of what was new last year, or the year before last. The flowerindustry is conservative about switching to new materials for diseasemanagement. Sometimes this heel dragging stems from contentment, sometimes frommisinformation and sometimes from fear or frugality. But if you’re reading thisarticle you are doing exactly what you ought to be doing: learning about whatis available and what is coming, so you are not caught without any knowledge ofoptions when a particular need arises. File this away so you can drag it outthe next time you want some additional guidance on an intriguing chemical.

Not Old Hat Yet

I’ll start with the category of fungicides that are not oldhat yet . . . and that many of you haven’t even tried. Strobilurins wasironically named after a mushroom, Strobilurus tenacellus, which was theoriginal source of the chemical. Currently, we have three syntheticstrobilurins available to the flower industry: Compass-O (Olympic), Cygnus(BASF) and Heritage (Syngenta). These are all considered”reduced-risk” materials by the EPA. The strobilurins have anexcellent broad range of effectiveness against many common flower diseases,particularly in the categories of leaf spots, anthracnose, scab, Botrytis,downy mildew, powdery mildew and rusts. They can help with most of the fungi oroomycetes (such as downy mildews) that spot plants. With spots caused bybacteria, excessively low pH or furnace misbehavior, you’ll need a differentsolution.

The three strobilurin fungicides on the market now aresimilar but not identical: If you are looking for primarily a powdery mildewmaterial, something for rusts or something for an anthracnose, you may preferone over another. Keep an eye on researchers’ test results to help you with thefinesse of which strobilurin to use when. And pay attention to the labels. Thematerials are not to be used repeatedly all season long — you’ll need torotate with materials that have complementary modes of action.

Strobilurins have the advantage of going beyond mere contactaction, but being systemic increases the likelihood of resistance developing inthe target population — hence the strict usage instructions. Lest you thinkthat this kind of chemistry is only useful for foliar diseases, let me hastento add that trials of Heritage 50WDG in both New York and Florida are showingextremely good control of Pythium and Rhizoctonia on impatiens at a low rate.

Another fungicide that is not new but still not well utilizedis Stature (SePRO). This product contains a mixture of dimethomorph andmancozeb, and thus is ideally suited for use against downy mildews since itcontains two effective ingredients. Our trials with this material against thethree different downy mildews of pansy, mini-rose and snapdragon show it to bean excellent protectant.

Still in the Pipeline

One new strobilurin from BASF is not available forornamentals use yet, but is showing a superb effectiveness against powderymildew in my trials. The test name is BAS-500. Additionally, a new,still-being-tested formulation of Heritage is also looking very promising. Thusyou can anticipate that there will be even more effective strobilurins on themarket before long. But please note that the ones already available to you arevery good, broad-spectrum fungicides with low potential for phytotoxicity.While we are talking about things not yet available, the combination ofmefenoxam and fludioxonil known as Hurricane continues to Á give goodresults in trials of Pythium and Rhizoctonia root/stem base problems onimpatiens in both Florida and New York.

New Chemicals

Generic products have recently become available forphosphites, iprodione, cholorothalonil, mancozeb and cupric hydroxide. They mayperform similarly to products with the same active ingredient, but they mayvary in phytotoxicity or residue or even effectiveness, so test them beforeuse.

Another new option in the powdery mildew department isMilStop, a new potassium bicarbonate product marketed by BioWorks,complementing its biological for root diseases, PlantShield HC. The initialforté of MilStop will be powdery mildew, and its one-hour re-entryinterval (REI) gives it a special attractiveness for many operations.

One long-awaited new product for ornamentals and somegreenhouse vegetables, including cucumber and tomato, is Rhapsody 1.34% AS, abiological control for foliar disease management (both bacterial and fungal)from AgraQuest. The active ingredient in Rhapsody is the QST 713 strain of Bacillussubtilis. You may already have an appreciation for Bacillus subtilis as theactive ingredient in Companion (Growth Products), which is a different strainof the same species. There is a four-hour REI for Rhapsody. Rhapsody is alsolabeled as a post-harvest dip on cut flowers. The information provided byAgraQuest indicates that it has a multiple-site mode of action.

Trials at Chase Research Gardens have shown good benefit ofRhapsody against bacterial diseases, including Pseudomonas leaf spots on delphiniumand impatiens and Xanthomonas leaf spots on geranium. Trials by David Norman atthe University of Florida-MREC have shown good powdery mildew suppression withRhapsody at 1 percent on gerbera. We have seen powdery mildew control onmini-roses, verbena, petunia and poinsettia, as well as control of Botrytis onpoinsettias and geraniums, in trials at the Long Island Horticultural Research& Extension Center. Chase Research Gardens has also noted some control of adowny mildew and excellent control of the nasty Cercospora leaf spot on pansyusing Rhapsody. The label allows a 3- to 10-day treatment interval; moststudies have been conducted with a seven-day interval.

Biophos 43.07% L is a dipotassium phosphate product fromAgBio that is newly available for management of Phytophthora and otherdiseases. It is labeled for drench at rates from 0.1-0.5 percent, and as aspray at 1-2 percent. In our trials, a drench at 0.25 percent has completelyshut down Phytophthora drechsleri, which attacks at the stem base ofpoinsettias. Biophos is similar in active ingredient and mode of action to thefamiliar Phytophthora control Chipco Aliette WDG, which contains fosetyl-Al,but it is likely to perform somewhat differently. Biophos and Aliette are ofspecial value in those cases in which the Phytophthora strain assaulting a crophappens to be resistant to Subdue/Subdue MAXX (Syngenta). Biophos will be agood choice to rotate with Subdue/Subdue MAXX for water mold root diseasemanagement. It will also have other, yet-to-be-delineated control attributes,because the phosphite type materials act by stimulating host plant defenses ingeneral.

The new Alude from Olympic is another new product in thissame category that has 45.8 percent phosphorous acid salts as its activeingredient.

At the risk of repeating something that my entomologicalcounterpart might be simultaneously describing, I would like to point out adisease-fighting use for the miticide Pylon 21.4% Á EC from Olympic,which was recently registered for foliar nematode control on greenhouseornamentals. Foliar nematodes are occasionally seen on many greenhouse cropsand other herbaceous perennials in the nursery trade. When Vydate, Oxamyl andTemik were lost to ornamentals producers due to their innate toxicity andpotential for groundwater contamination, foliar nematode symptoms began to beincreasingly common. Now Pylon, though developed as a miticide, has shown amajor side benefit in terms of foliar nematode control, and a supplementallabel has been written to legitimize this use. Nancy Rechcigl of YoderBrothers, Inc., reported applications made to Japanese anemone of Pylon at 4oz. per 100 gal. at 14-day intervals were extremely effective at killing thenematodes within the plants. Skillful use of this new chemical tool bypropagators should result in a marked improvement in the quality of crops proneto foliar nematode within the next few years.

All in all, the industry should feel pleased at the recentdevelopments in ornamental plant health protection tools. There are newsolutions for the stubborn problem of foliar nematodes, a new biologicalcontrol with broad spectrum activity, some products that stimulate host plantdefenses and some reduced-risk chemistry that works against powdery mildews,downy mildews and leaf spots. Given these new developments, it’s time for me toadjust my wish list!

Author’s Note: With a subscription to Plant ManagementNetwork, fungicide and nematicide test (F&N Tests) results for allagricultural crops, including ornamentals can be found atwww.plantmanagementnetwork.org.