UC Nursery and Floriculture Alliance

In this Spring 2025 issue, our Featured Articles present important updates on pests of nursery plants relevant to the nursery industry in California, including the Dotted Paropsine Leaf Beetle threatening Eucalyptus and the detection of invasive Thrips parvispinus in San Diego. In the Science to the Grower section, we discuss why nursery irrigation and fertilization methods should complement each other, assessing the benefits and drawbacks of liquid and controlled release fertilizers and how these methods relate to irrigation.

Eucalyptus trees are an iconic part of Californias landscape. The famous journalist Harold Gilliam once wrote, “the Eucalyptus seems an indispensable element of this State’s landscapes, as indigenously Californian as the redwoods, the poppy fields, the long white coastal beaches, and the gleaming granite of the High Sierra”. Introduced in the mid-1800s as a fast-growing source of timber, the trees were also used for firewood, oil production, and reforestation. Plantings peaked during the “eucalyptus craze” of the 1870’s and the “eucalyptus boom” of 1907.

Southern California is a hub for nursery and floriculture production in the United States, with a mild climate that allows many kinds of plants and flowers to grow. Unfortunately, this also makes the area vulnerable to a wide range of invasive pest species, among them, Thrips parvispinus. 

Plant-parasitic nematodes (PPN) are microscopic roundworms that primarily inhabit soil or plant tissues, feeding on living cells (Fig.1).

The economic damage caused by these pests in California is conservatively estimated at $2 billion annually. Preventing the arrival, establishment, and spread of additional non-native invasive PPN is crucial for healthy food, fiber, and ornamental crop production. Furthermore, this exclusion is essential to avoid market losses from quarantines on plant commodity exports.

The main two ways to apply fertilizer in nurseries and greenhouses are liquid feed, whereby water-soluble fertilizer is injected in the irrigation water, and controlled release fertilizer (CRF), whereby fertilizer granules are coated usually with a polymer for slower, longer term release of nutrients.  The CRFs are incorporated in the substrate at planting or topdressed to the containers.

In this article we will discuss the pros and cons of each strategy in relation to the irrigation method used.

The pH of soil and water and how it affects plant growth and chemical makeup of soils and media is somewhat detailed.  Over the course of five newsletters, we will present different aspects about pH.  Once complete, one should have a thorough understanding of pH and how it influences plant production.

Part I – What is pH?

Part II – How is nutrient availability affected by pH?

Part III – How is pH affected by fertilizers?

Part IV – How to adjust pH of soils

Part V – How to adjust pH of irrigation waters

Weeds are a common problem in container-grown plants and could require significant labor to remove before plants are shipped. No matter how well weeds are managed in the nursery, seeds can disperse for miles by wind or animals or arrive at the nursery from unpasteurized potting media. Reducing weed pressure in container plants typically requires manual removal or preemergent herbicide application to the potting media.

Each month, UCNFA hosts a free virtual Q&A session on a topic related to greenhouse and nursery management. Drawing on our members’ varied expertise, we hope to provide guidance on your production challenges.

Listen and ask questions about managing weeds in pots, gravel, concrete cracks, and everything in between.

Learn how to set your plants up for success with Haramrit Gill, Don Merhaut, and Jessie Godfrey.

Have you interacted with UCANR advisors and wondered how they are connecting with your community? If you are located within Los Angeles County, you may have attended workshops held by UC advisors regarding protecting groundwater from pollutants. The Los Angeles Regional Water Quality Control Board adopted water discharge requirements from irrigated lands to ensure that high water quality remains within the Los Angeles region.

We were delighted to host the workshop “Phytophthora Prevention in Habitat Restoration” on February 7th, 2025, at the beautiful California Botanic Garden in Claremont for a full-day workshop focused on critical plant pathogen issues. The session concentrated primarily on Phytophthora species impacting nursery production and ecological restoration efforts. Led by Dr. Johanna Del Castillo (UCCE Cooperative Extension Specialist, UC Davis), Dr. Sebastian Fajardo (Postdoctoral Researcher, UC Davis), and Dr.