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Manage Greenhouse Plant Diseases and Insect Damage


Published: Friday, April 19, 2024

The following is from Heidi Lindberg, Mary Hausbeck and Jeremy Jubenville of Michigan State University Extension.

Michigan State University Extension has updated their insect and disease management recommendation guides for the 2024 greenhouse season. These documents are updated yearly to reflect the efficacy of pesticides as Michigan State University (MSU) Extension specialists and their nationwide colleagues perform research trials evaluating the products against common greenhouse insects, mites or diseases.

The MSU Extension floriculture team has updated their "Greenhouse Insect Pest Management 2024" guide. It provides a list of recommended products for controlling the most common insect and mite pests found in greenhouse floriculture production systems. Products are presented in a table format that includes the trade name, active ingredient, mode of action (MoA) group, and restricted entry interval (REI). This format is intended to deliver quick and easy access to the information that growers need to manage pests effectively.

Growers of greenhouse vegetables and greens can use the guide "Recommended Insecticides for Common Greenhouse Pests on Vegetables, Herbs, and Leafy Greens" when considering an insecticide application. The guide provides the names of the products, active ingredients, labeled crops and the pests they control.

MSU Extension plant pathologist Mary Hausbeck has released her updated "2024 Greenhouse Disease Management" guide. Based on years of efficacy trials, the products are graded from "A+" to "B/B-." The "A" team products provide a high level of disease control, and "B" team products provide good, but more limited control.

At the outset of disease symptoms or during a time when disease pressure may become high (wet, cloudy conditions), choosing a fungicide product that has been graded as an "A" could provide the level of plant protection needed. In other situations when prevention is important, disease symptoms are not evident and the conditions are sunny and dry, a wider range of products can likely do the job.

It's of utmost importance that fungicides be alternated over the course of the growing season based on their FRAC codes. The FRAC code appears on the first page of the pesticide label and is based on the fungicide's mode of action. Ensuring that the fungicides included in a program have different FRAC codes is the best way to prevent a pathogen from developing resistance to fungicides.

Over-reliance on a particular fungicide or group of fungicides with the same FRAC code greatly increases the risk that the target pathogen will become resistant to that chemistry which could result in control failure.

Are you looking for recommendations for vegetables and herbs? Hausbeck and colleagues developed a guide for disease management specifically for vegetable and herb crops. It includes information on registered products' active ingredient, trade name, FRAC code and re-entry interval and is categorized by crop group and target pathogen.

It's especially important to remember that the vegetable or herb crop must be explicitly stated on the pesticide label. Also, be sure to check that use of the fungicide in the greenhouse is not prohibited. Some fungicides may list a particular vegetable or herb on its label but then include a statement that the use of the product is not allowed in the greenhouse.

The disease management recommendations for the 2024 growing season are consistent with those of the previous year, with some notable changes.

There have been considerable changes to the products recommended for Botrytis control based on exhaustive MSU research and testing. Broadform (fluopyram plus trifloxystrobin) is now included on the "A" team due to its consistent effectiveness in protecting plants even under high-pressure situations. The former "B" team products have been removed from the recommendations as research has clearly shown a significant level of Botrytis resistance to some fungicides among pathogen populations in the state.

The product Emblem (fludioxonil, group 12 FRAC group) was added for Botrytis control. Emblem/Medallion/Spirato (fludioxonil) were also added to the Thielaviopsis management list.

In the 2023 disease management guide, the impatiens downy mildew program provided a distinction in the fungicide program for susceptible and resistant cultivars.

While new genetic improvements to some varieties of impatiens have improved their resistance to impatiens downy mildew, growers should consider a fungicide program for extra assurance.

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