This report is intended to share information that is relevant to the greenhouse grower community throughout the eastern portion of the state. It reflects the challenges and successes that growers encountered and shared with MSU Extension during the 2025 growing season. Observations during Jan-Mar covered 3 counties with multiple visits in each county (Wayne: 9, Monroe:2, Oakland: 2). During Apr-June, information is included from 10 counties with at least one visit in each county listed (Oakland: 11, Wayne: 10, Genesee: 5, Macomb: 5, Tuscola: 5, Monroe: 3, Lapeer: 3, St. Clair: 2, Livingston: 1, Washtenaw: 1). During July-Sept, information is included from 9 counties with at least one visit in each county listed (Wayne: 5, Huron: 2, Sanilac: 2, Tuscola: 2, Jackson: 1, Monroe: 1, Genesee: 1, Lapeer: 1, Oakland: 1).
Diseases
January-March: Powdery mildew was observed in succulents. Conditions in early spring and fall especially favor this disease, which thrives at relative humidities greater than 90% and at temperatures between 65-85 F. Powdery mildew on succulents can look very similar to the damage caused by edema, or sunscald, presenting as brown, scabby patches on leaves. Among succulent crops, kalanchoe, crassula, and echeveria tend to be more susceptible. Fungicides with FRAC code 3 are going to be your best control products (myclobutanil, metconazole and triflumizole). However, it is critical to rotate to other FRAC codes such as 7, 8, 11 or 12 with subsequent applications to avoid developing resistance.
April-June: Monkshood, Aconitum, tested positive for Cucumber Mosaic Virus (CMV). A member of the buttercup family (Ranunculaceae) and native to the Eastern United States, this poisonous perennial can harbor diseases like CMV, tomato spotted wilt orthotospovirus (TSWV), and potato leafrool virus (PLRV) among others. It's best practice to keep this perennial pest-free to avoid spreading virus to other genera that may have more susceptibility to these viruses.
July-September: This summer brought pleasant conditions for growers, leading to relatively minimal disease issues. Some powdery mildew was observed on certain monarda varieties. Some chrysanthemum producers also saw root rot symptoms following abundant rain events, but incidences of this were minimal.
Weeds
January-March: Liverwort, Marchantia polymorpha, management continues to be an active area of research for MSU Horticulture Department professor and researcher, Debalina Saha. Growers can struggle with controlling this weed, a primitive species that will form dense mats in wet environments. This weed is primarily an issue in long-term crops like perennials but was spotted this season in annual bedding crops like spikes as well.
April-June: Marsh parsley, Cyclospermum leptophyllum, was an interesting find at one greenhouse. This weed is a member of the carrot family and is a summer annual that will emerge mid-spring through mid-autumn with multiple generations per season. It prefers to grow in moist environments, making it well suited to grow underneath greenhouse benches as we found. There are limited herbicide options for controlling this species, with only dimethenamid-p (Tower) showing efficacy for control and labelled for use in the greenhouse.
July-September: One grower noted purslane and cottonwood tree seedlings being abundant in their mum crop this season outdoors in their nursery pad. Another grower observed horseweed, Erigeron canadensis, under benches in the greenhouse. Upon closer inspection they seem to do a wonderful job at harboring whitefly. A helpful reminder that good weed control goes hand-in-hand with pest control.
Pests
January-March: Among the issues reported during the early season for pests were thrips being difficult to manage in some pepper and other flower crops. Shorefly were also noted at one site, and growers were looking into options of using biological control agents such as nematodes to provide control in addition to chemical sprays for pests like fungus gnats, shorefly, and thrips. One grower was also looking to options for low-spray volume applications using a fogger to gain better control.
April-June: While thrips continued to be a challenging pest throughout the season, spider mites, fungus gnats and aphids started to become more problematic at points during the season. Spider mites were particularly an issue with many tropical and houseplant crops brought in from Florida this season. Aphids were tricky to control in hanging baskets and edible crops, such as strawberries, especially when infestations popped up close to when plants were marketable. Growers were especially interested in sprays or biological controls that could be used on edible crops that would be safe for consumers at retail.
July-September: Spider mites continued to be an issue on tropical plants like elephant ears and palms for some growers. Blotch leafminer and red headed flea beetle were also observed on a chrysanthemum crop. This summer Box tree moth also became a frequently asked about topic for many retailers. The current quarantine area for this invasive pest includes 13 southeast and central Michigan counties: Clinton, Eaton, Ingham, Lapeer, Livingston, Oakland, Jackson, Washtenaw, Wayne, Lenawee, Monroe, Macomb and St. Clair. Several new and updated publications regarding boxwood and box tree moth have been published this year covering everything from diagnosing damage to selection of alternative landscape shurbs.
Abiotic Issues: Throughout the entire season, abiotic stressors were among the most frequently reported issues. Nutrient deficiencies and toxicities were encountered by some growers, which led to exploration of water quality concerns. Most often a simple pH or EC adjustment to irrigation water resolved the issue at hand. This speaks to the importance of conducting routine pour-through testing of crops to make sure pH and EC are within range. Additionally, some growers were seeing purpling of young petunia plants that had recently been stuck as unrooted cuttings. This purpling of foliage on young plant material, especially in petunias and begonias, is linked to LED lighting that is too intense, and greenhouse temperatures are too low.
April-June: As the season progressed, growers encountered some different abiotic issues in the greenhouse. The cold spring resulted in some growers experiencing cold damage with malfunctioning heaters. Heaters were also being run fairly regularly without much ventilation and ethylene exposure impacted some sensitive crops. A good reminder to service and maintain heaters throughout the season. Additionally, some growers experienced herbicide damage to plants this season. Some instances were due to a product misformulation of an insecticide, which led to some plants being dosed with herbicide. Other growers saw phytotoxicity from herbicides that were either improperly applied within the greenhouse or through drift from nearby farm fields.
July-September: Amongst those that produce mums, most growers are aware of the many challenges this crop can encounter related to lighting and temperature conditions. This year was no different with some growers experiencing early crown budding due to a series of cool nights, plus some experiencing heat delay on early flowering varieties. Though it's nearly impossible to control the weather, there are some techniques that can be used to ensure chrysanthemum crops flower on schedule. For instance, to mitigate heat impacts that could delay flowering, several cultural and environmental control strategies can be utilized. Adjust photoperiod for early-season varieties to 10-12 hours of light. Pull black cloth in the early morning rather than late in the day to minimize hot air building up underneath. Optimize irrigation, since water stress can further suppress growth. Last, but not least, monitor fertility; high temperatures can alter nutrient uptake especially if you're relying on controlled-release fertilizers.
Source: Michigan State University
