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Ask Your PCA: What are ways to protect flowers from fungal diseases?

Issue Date: Jan 12 2022
Chris Boisseranc, PCA, Southwest Ag Consulting, Inc., Redlands

Southern California grows warm-weather flowers throughout the year such as sunflowers and marigolds. The region also has perennial plants that flower in the winter—South African and Australian natives, and a wax flower plant—that are used as filler flowers in bouquets all over the world.

Southern California is ideal for growing these flowers. The arid climate means there is reduced pest pressure compared to other regions of the world as far as fungal pathogens are concerned.

The main issue for Southern California cut flowers are fungal diseases. Weather changes during transitional times of the year—fall and spring—will result in fungal diseases. While there are several disease problems, botrytis cinerea is one of the biggest issues, and is also a problem for grapes.

Humidity, cooler temperatures, and rain saturating the flowers that have sugar inside of them create problems with botrytis, and defoliation of the flowers. In turn, the flowers will be lost before harvest or during transportation in the boxes.

Powdery mildew can also be problematic, but it's mainly a problem on the new growth that emerges in the fall. It can also happen in the spring, but fall treatment is critical coming into winter.

Management involves keeping the plants pruned and properly spaced, and using varieties that have tolerance to various diseases.

Fungal spray applications and some chemigation through irrigation water are used for control. Some of the more susceptible varieties will be treated twice a month leading into Valentine's Day for fungi, and any type of pest, to protect the flowers.

Chemical rotation with either a tank mix of multiple chemistries or rotation of chemistries is advised to reduce the risk of resistance building.

With supply-chain issues, consider ordering chemicals six months in advance. It's expected that these supply chain issues will continue until mid-2022, and higher prices are anticipated as well.

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