News

In this Fall 2025 issue of the UCNFA Newsletter, our Featured Article discusses current ongoing research evaluating the pathogen risks of irrigation with untreated recycled irrigation water on ornamental crops in San Diego County, including preliminary findings and potential grower implications. In Science to the Grower, we introduce an improved metric for measuring greenhouse light levels, Photosynthetic Photon Flux Density, to more accurately adjust lighting for optimal crop production.

Water scarcity continues to challenge California’s floriculture industry, leading many nurseries to rely on recycled irrigation water as a supplemental or primary water source. Although this approach conserves water, it also increases the risk of recirculating plant pathogens, particularly oomycetes such as Phytophthora, Pythium, and Phytopythium. These organisms move easily in water and can initiate new disease cycles each time crops are irrigated.

The tools available for growing our plants include testing a variety of parameters including specific ion nutrient testing, pH, salts, crop height, pathogen analysis, leaf tissue testing, and substrate testing to name a few. One overshadowed parameter is the amount of light we give our crops. Tracking light levels is important, but there are various ways to measure light, each with different implications for understanding plant growth.

Part I – What is pH?

Part II – How is nutrient availability affected by pH

Part III – How do fertilizers affect pH?

Part IV – How to adjust pH of soils/media

Part V – How to adjust pH of irrigation waters

Soilborne pests and weeds continue to pose significant challenges for nursery growers and gardeners seeking sustainable management solutions. To demonstrate practical, non-chemical approaches for addressing these issues, the University of California Cooperative Extension (UCCE) Fresno County, in collaboration with the Fresno County Master Gardener Program, conducted a soil disinfestation demonstration during the summer season at the Garden of the Sun in Fresno.

In this Summer 2025 issue of the UCNFA Newsletter, our Featured Articles focus on diseases on nursery crops, presenting the most recent diagnostics data from ornamental nurseries in California out of the Greenhouse and Nursery Pathology Lab at UC Davis. We will also discuss the impact and biology of powdery mildew in California nurseries, including practical guidelines for identification and management.

The disease diagnostics service for greenhouse and nursery crops was initiated in California in 2020 by Del Castillo Lab at UC Davis.

If you’ve ever seen a white, dusty coating on your ornamentals or nursery plants, chances are you’ve met powdery mildew, a common and frustrating disease affecting a wide range of nursery and floriculture crops.

Powdery mildew is caused by a group of fungi that are host-specific, meaning the one on your roses won’t necessarily infect your zinnias or begonias. Still, many ornamental crops are vulnerable, including roses, hydrangeas, snapdragons, phlox, chrysanthemums, begonias, kalanchoes, and many woody shrubs like crape myrtle, lilac, and dogwood.

Phytophthora species are recurrent pathogens infecting ornamental crops worldwide, with that, California is not the exception. From the disease diagnostics clinic from Del Castillo Lab, in 2024, Phytophthora root rot was the most prevalent disease diagnosed. Infected hosts include wax flower, gardenia, banksia, orchid rock rose, lavender, and boxwood, among other plants. From these plants, nine Phytophthora species were identified, with P. nicotianae, P. palmivora, and P. niederhauserii among the most common ones.