Total-release fungicides for disease control

One of the most important elements of disease spread and development is water. Foliar diseases caused by many fungi and most bacteria are spread through rainfall and irrigation splashing. Pathogen spores germinate and infect leaves in a film of water. In some cases, the spores can even swim in water films to reach an appropriate site for infection.

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At Chase Horticultural Research, most of our fungicide trials are conducted with an excess of water on leaves to promote disease. Overhead, intermittent mist or plastic bags are used depending on the time of year and the type of disease that is sought. This is a necessity in the dry western environment as much as it was in the humid environment of Florida when I worked for 14 years at University of Florida.

Eliminating water

The key cultural control plant pathologists often recommend is elimination of overhead irrigation or exposure to rainfall to limit and in many cases eliminate foliar diseases. This may not be possible in the nursery but is a critical element of foliar disease control in a greenhouse.

Even with the availability of effective fungicides, when plants are exposed to overhead irrigation or rainfall, they often become infected with foliar diseases. Fungicides can be overwhelmed by the environment, which favors diseases as well as washes off fungicide residues needed to maintain their maximum efficacy.

All that being said, did you ever wonder whether or not spraying a fungicide in a large volume of water was helping the disease or controlling it? While the development of low-volume applicators greatly reduces spray costs through reducing personnel requirements, it also should reduce the negative effects of wetting the leaves that makes some disease outbreaks to be worse and reduces fungicide efficacy. This would be especially important if the wrong fungicides were chosen and you were ultimately just spraying leaves with water. Since many foliar diseases look similar, misdiagnosis is more common than you would think.

Total-release fungicides

More than 10 years ago, Chase Horticultural Research started working with Whitmire Micro-Gen to develop information on total-release fungicides. A greenhouse was constructed with portals, fans and other special characteristics to facilitate research studies. I did not originally have much faith in the method of application since disease control is very different than insect and mite control where total-release and low-volume were proven effective.

Pathogens like Alternaria and Pseudomonas do not move around the leaf surface the way aphids do. For these pathogens to come into contact with a fungicide or bactericide is mainly a matter of thorough coverage, which for years has depended on the use of a lot of water to deliver the chemical control. However, we were pleasantly surprised to see how effective these total-release fungicides were for a variety of diseases.

Fungaflor TR

This year Whitmire Micro-Gen finally has a registered product called Fungaflor TR. The active ingredient in this product is Imazalil, which is not labeled for other uses in the greenhouse ornamental industry, to my knowledge. Imazalil belongs to the sterol-inhibitor class of fungicides which includes Eagle, Banner MAXX, Strike and Terraguard. The labeled sites are greenhouses for application on a wide range of plants from bedding plants to cut flowers to flowering hanging baskets and foliage plants. The target diseases include Alternaria leaf spot, Botrytis blight and leaf spot, downy and powdery mildews and rust diseases. The use rates are given in cans per 3,000, 1,500 and 1,000 square feet and the restricted-entry interval is 24 hours.

Comparing Fungaflor to other controls

Numerous trials have been conducted with Fungaflor TR and other labeled chemical controls. The best control was achieved with Alternaria leaf spot on impatiens, downy mildew on stock and powdery mildew on gerbera.

Control of downy mildew on stock (Matthiola incanae) was especially effective. The best control was Stature DM (6.4 ounces per 100 gallons) and Heritage (1 ounce per 100 gallons) but statistically, Fungaflor TR was the same as these two fungicides.

Fungaflor TR provided good control of Botrytis, but higher labeled rates needed to be applied to ensure optimal results. Four trials were conducted on Botrytis blight to narrow down the rate range and each trial employed a different chemical standard. In each trial the Fungaflor TR performed as well as the fungicide standard, which was applied as a wet spray at the rate given per 100 gallons. Unfortunately, none of the trials sought to evaluate the possibility that the Fungaflor TR could control disease better than an Imazalil wet spray.

Comparing total release to wet sprays

We also worked on another active ingredient, and in that case, the total-release product was directly compared to a wet spray of the same active ingredient. The target diseases were Alternaria leaf spot, Botrytis and Rhizoctonia for this product.

Results were consistent and equivalent control of the two foliar diseases when the total-release product was compared to the wet spray. No benefits were observed from using the total-release product over the wet spray but efficacy was very high. We have also looked at a total-release copper product that showed a high degree of efficacy.

If the total-release application method does not result in better control than a wet spray we will still have achieved benefits in reducing worker exposure and costs of labor in applying these products. In the future, we hope to see more total-release products available.

Fungaflor TR trial results at Chase Horticultural Research Inc.

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- Ann Chase

June 2008