Where Do We Go
From Here?
by: Tommy Hebert
Golden Triangle Rose Society

Lawn and garden buffs face constant challenges. Not only are our growing skills tested, but almost constant changes occur in our lawn and garden care products. Their effectiveness and availability vary dramatically. Safety and health concerns drive new products both on and off the market. And perhaps the most demanding of the parameters which effect availability or care chemicals is profitability.

Chemical manufacturers are faced with astronomical registration and labeling costs, and it is logical that they can't afford to label a chemical that produces poor returns. If it does, it doesn't stay on the market very long. If environmental or health concerns become a problem, the product is pulled down or its applications are narrowed and made more restrictive.

The manufacturers operate on the "tin cup" theory. They are allowed to produce a volume of chemicals whose cumulative toxicity does not exceed a defined quota. It would appear logical that as new products emerge from their research and production lines, old products of less profitability or greater toxicity are removed from the "tin cup" to make room for the newcomers. Thus, some of those chemicals on which we growers had placed high hopes are sacrificed in the name of safety or profitability, or both.

One such promising chemical has been removed from the market before really realizing its full potential to rose growers. Sentinel was introduced as a turf fungicide and was also labeled for use on field grown roses. Despite the fact that it was not labeled for home use, some home growers tried it and found it to be, in most cases, tremendously effective in controlling some of the common fungal diseases of roses. Sentinel has now been removed from production because it is a suspected carcinogen.

Its loss produced a wave of disappointment among rose growers. Many felt that Sentinelís lower toxicity rating and 28-day frequency of application requirement could not be recognized as anything less than a great advantage to both the rose and the rosarian. The long anticipated, happily ever after marriage ended before the honeymoon was over.

Zenca Professional Products tried to tell us a few months ago that relief was in sight and that their new fungicide, Heritage, is a broad spectrum, preventative fungicide with systemic properties and would make us forget the Sentinel family of cyproconazoles. The active ingredient in Heritage is azoxystrobin, from the family of fungicides called "strobilurins", which are naturally occurring materials found in mushrooms. Heritage is claimed to be much safer and environmentally friendlier than Sentinel.

Although the effectiveness of Heritage against fungal diseases of roses has been confirmed by reputable research organizations, results were less than impressive as a blackspot preventive. Heritage's effectiveness against blackspot, when compared to that of Sentinel, revealed the obvious superiority of Sentinel. Even further depressing of fans of Sentinel was the fact that Heritage is only marginally effective when applied at frequencies exceeding 7 days while Sentinel has been found to be effective on 28-day applications.

Not to worry, says Novartis Crop Protection, Inc. Their new fungicide, Compass, is firmly mounted on its white charger and galloping to the rescue of the rejected Sentinel suitors. Another strobilurin, isolated from mushrooms, Compass' active ingredient is trifloxystrobin and will be marketed in the form of 50% wetable powder.

Compass is a turf grass fungicide which is also labeled for use on ornamentals. It has very favorable human and environmental profiles. Novartis claims that Compass is a so-called "mesostemic" fungicide. This type of activity is characterized by a high affinity of the fungicide for the waxy layers of the plant surface. It also penetrates the plant surface but does not significantly move through the plant's vascular system. It binds itself so tightly with the plant surface that it is very weather-resistant.

Even more novel is Novartis' claim that the wetting of the applied fungicide by dews aids its redistribution, not only by additional spreading and penetration buy by redistribution in the vapor phase. The manufacturer claims that this vapor phase activity can cause movement for short distances throughout the plant canopy. Another environmental plus for Compass is its claim to compatibility with Integrated Pest Management programs.

Compass is so new there is very limited data on its effectiveness by independent researchers. What little application data that this writer has located is, however, quite encouraging. Its blackspot control properties compare very favorably with Sentinel. The verdict on frequency of application, however, is still in question. Novartis claims that over 90% of the fungicide remains on plant surfaces after 21 days, but most test on which data are available were conducted on 14-day applications.

Compass is, to the surprise of few, going to be pricey. So was Sentinel, but I didn't hear any complaints when considering its other advantages.

One caution, which this writer is concerned about, is the prospect for development of insensitivity, or diminishing effectiveness, of the strobilurins. For that matter, many of the modern fungicides have the same problem. Because of this, it will probably be advisable to alternate these fungicides with others which have different modes of activity, or perhaps limiting repeat application to no more than two consecutive applications. The smart rosarian will exert any measure necessary to avoid an insensitivity problem by rotation of fungicides (editors note: Consesus seems to be alternating Compass with Banner Maxx), tank mixing and avoiding multiple, sequential applications of the same chemical. Undoubtedly the most important habit to practice is punctuality in applications. Many of these problems go away if you stay ahead of infections, because most insensitivity problems occur during periods of escalated applications of fungicides to eradicate established fungal infections.

In summary, there is good reason to believe that the "Strobies" will be effective fungicides. This writer is optimistic that the strobilurin family will be expanded to overcome any weaknesses found in the first introductions, and innovative application methods will be developed to avoid insensitivity problems.