August 11, 1993
Crown gall was recently diagnosed on a euonymus samplesubmitted to the Plant Disease Clinic. Crown gall is a bacterialdisease caused by Agrobacterium tumefaciens. Crown gall can affectmany species including ornamental shrubs and vines, particularilyeuonymus, honeysuckle, and rose. Certain perennial flowers, suchas chrysanthemums, asters, and daisies, are also susceptible.Blackberry, raspberry, and tomato are hosts. The disease can alsooccur on young nursery stock including shade trees, nut-bearingtrees, pome fruits (apple and pear), and stone fruits (peach,cherry, etc.).
Proper preparation and careful maintenance maximizes the vase life of any cut flower whether grownyourself or purchased at the local flower shop. Properconditioning or hardening of flowers is critical. Recut stemsunder water to prevent air bubbles from forming within the stems.Remove 2 inches from the bottom of each stem, cutting at an angle.Transfer the cut flowers into the container in which they will beconditioned. To condition flowers, immediately immerse flowers intepid water (110 F) containing floral preservative almost up to theflower heads.
A leaf blight on hawthorn was diagnosed recently in the PlantDisease Clinic. The disease is caused by the fungus Fabraeathuemenii. Symptoms of leaf blight begin in spring and earlysummer as small, angular, reddish-brown spots on the upper surfaceof leaves. The spots increase in size and run together, causingpremature defoliation during wet years. From a plant pathologist'sview point, the disease is very interesting because of thecharacteristic spores, which resemble minute, winged insects.
Peonies can be leftundisturbed for many years. Sometimes, however, it becomesnecessary to move established peonies. Peonies shaded by largetrees or shrubs bloom poorly and should be moved to a sunny site.Large, old plants may become overcrowded and flower poorly. Large,old plants should be dug, divided, and transplanted to improveperformance. The best time to move or divide peonies is September.
The 1993 gardeningseason has been frustrating for many home gardeners. Manygardeners have simply been unable to do much yard work because ofthe nearly constant rain. However, the 1993 gardening season isfar from over. Much can still be accomplished over the nextseveral weeks. Late summer and early fall is an excellent time toseed lawns and plant trees, shrubs, spring-flowering bulbs, andperennials.
Black Rot of Grape
Black rot of grape is caused by the fungus Guignardiabidwellii. On leaves, the first symptoms are small, yellowlesions. These spots develop into brown lesions that aresurrounded by dark irregular margins. Fungal fruiting structures(pycnidia) form within these spots and appear as small, black dots.