Diseases of Concern for Ornamental Crops

This page contains background information on various diseases that attack ornamental plants in greenhouses and nurseries. The diseases are divided into two sections: foliar diseases and soilborne diseases. Visit our scouting page (coming soon!) to learn more about scouting for disease! 


Have you ever gone to the grocery store and noticed some gray, fuzzy growth on produce (such as strawberries?) This is gray mold, known as Botrytis cinerea. Botrytis is a fungus that can attack a wide range of plants, including ornamentals! Some common ornamentals afflicted by Botrytis spp. include geranium, petunia, pansies, fuchsia, zinnias, dogwood, and roses. Botrytis grows best when the environment is cool and moist, and what better place to find these conditions than a greenhouse!


Symptoms of Botrytis

Common symptoms of Botrytis include:

  • Brown or black lesions on leaves and stems
  • Wilting and browning of flowers and flower buds
  • In some cases, specks might appear on the flower petals first. These specks might start out small and then begin to get larger in size. Soon, the flower petals will turn brown. 

Signs of Botrytis

Watch for signs of Botrytis as well; this is that characteristic fuzzy appearance that can appear on flower buds, flowers, and leaves. This fuzz is actually a mass of spores, ready to spread to the next plant! Botrytis is hard to manage once it reaches this stage, so remember to scout regularly!                                                


Boxwood Blight

Boxwood blight is caused by a fungus called Calonectria pseudonaviculata. This pathogenic fungus attacks plants in the Buxus family (Buxaceae). The main hosts are Buxus, but C. pseudonaviculata can also be found on other plants, including Pachysandra and Sarcococca. Boxwood blight is a worldwide problem; it is found abroad as well as in the United States. The fungus produces very strong resting structures, called microsclerotia, which makes complete eradication difficult. Establish a robus scouting program to catch any signs or symptoms of this disease at an early stage. Please visit our page dedicated to scouting and other bilingual resources specifically for boxwood blight!

Symptoms of Boxwood Blight

  • Leaves can become bronzed
  • Defoliation (loss of leaves)
  • Light brown spots with darker brown to purple edges develop on the leaves. 
  • Black diamond-shaped lesions appear on the stem


Signs of Boxwood Blight

The most common and visible sign of the pathogen you will notice is sporulation. The fungus will produce many spores that will appear like fuzzy, white growth on the underside of the leaves. 

But remember, the survival structures of the fungus may be present on dropped foliage. Therefore, always immediately remove any foliage that is on the ground, even if it does not look 'diseased'.