DIAGNOSTIC UPDATE 



C3 



The unusual weather patterns 

 that began in March continued 

 through the sunimer. Rain in 

 early May set us up for lots of 

 rots and foliar diseases. Although 

 the last half of May was some- 

 what "normal", the month of June 

 was wet, cloudy, and cool. Need-" 

 less to say the start of the grow- 

 ing season was slow and filled 

 with disease and environmental 

 problems. Mid-July brought a 

 relatively sudden jump to sum- 

 mer temperatures and near 

 drought-conditions. It was inter- 

 esting, to say the least. 



WOODY ORNAMENTALS 



The sudden shift in temperatures 

 and moisture availability has re- 

 sulted in early leaf color and pre- 

 mature leaf drop on many trees. 

 Widespread symptoms have been 

 noted on European birch and lin- 

 den. The sudden moisture shift 

 has also caused a condition 

 known as "semi-mature needle 

 blight" in eastern white pines. 

 The symptoms resemble acute 

 ozone damage (the tips of the 

 needles turn reddish). Shade tree 

 A.VTHRACNOSE is Still taking its toll, 

 particularly on sugar maples, 

 which have also been hard-hit by 

 pear thrips throughout much of 

 New England. Sycamore anthra- 

 cnose was very severe this year in 

 many areas. Oaks have been diag- 

 nosed with anthracnose and oak 

 leaf blister, and there was one un- 

 usual case of anthracnose on 

 hornbeam. Dogwood anthracnose 

 has been widespread with severe 

 blighting on many trees through- 

 out most of the northeast. Even 

 Kousa dogwood (usually highly 

 tolerant of anthracnose) succumbed 

 to minor leaf spots caused by 

 discula, the anthracnose fungus. 

 Powdery mh-DEW has also been com- 

 mon on dogwoods this year. 



Leaf spots were also common, 

 thanks to the prolonged wet weather. 

 Scab was severe on susceptible 

 crabapple cultivars, causing sig- 

 nificant defoliation by early Au- 

 gust. Lilacs were attacked by sev- 

 eral pathogens this year, resulting 

 in numerous 'panic' calls to the 

 UNH-PDL and county Coopera- 

 tive Extension offices. Ascochyta 

 leaf blight was problem on lilacs. 

 The disease has two phases, a 

 shoot blight in the spring (which 

 resembles bacterial shoot blight), 

 and a foliar phase during the 

 summer and fall that causes ol- 

 ive-green, water-soaked lesions. 



American elms are showing an 

 increase in symptoms of Dutch 

 ELM disease due to the lack of 

 moisture. As in the past, kabatina 

 dieback appears to be the most 

 prevalent problem on junipers, 

 but the disease has also been caus- 

 ing problems on chamaecyparis. 

 There has been lots of rhizo- 

 sphaera needlecast on spruce, and 

 in one case, rhizosphaera killed 

 all the new growth on a young 

 blue spruce. Once again, montlinta 

 SHOOT BLIGHT was widespread on 

 most ornamental Primus species. 

 This disease seems to be one we 

 can count on each spring (or at 

 least it has been for the last sev- 

 eral years), so protective sprays 

 may be warranted on valuable 

 landscape specimens. Fungicides 

 should be first applied when the 

 blossoms open with a second ten 

 days later. Rusts have been unbe- 

 lievable this year, particularly on 

 cedar and serviceberry (amelanchier). 

 So what should be done about 

 all these diseases and stress prob- 

 lems before next year? First, as 

 I've suggested in the past, sanita- 

 tion should be your primary fo- 

 cus this fall and winter. Where 

 foliar diseases have been a prob- 

 lem, rake and remove as much of 



the foliage as possible after leaf 

 drop, or use a mulching mower 

 to reduce the particle size and 

 speed degradation. Dead branches 

 on trees and shrubs should be 

 pruned and destroyed. 



HERBACEOUS ORNAMENTALS 



Botrytis remained a big problem 

 during June and early July, par- 

 ticularly for bedding plants and 

 herbaceous perennials. Asiatic lil- 

 ies were devastated by botrytis 

 blight (oriental lilies developed 

 only the 'typical' oval leaf spots). 

 The oriental lilies died from the 

 bottom up with the shriveled 

 leaves remaining hanging on the 

 stems. Unlike tulips with 'tulip 

 fire' lily bulbs are usually not in- 

 fected so the plants should be 

 healthy next year (unless we have 

 a repeat of this year's wet 

 weather). A stem canker caused 

 by the fungus colletotrichum was 

 diagnosed on osteospermum (cv 

 'wildside') and another basal can- 

 ker caused by fusarium was the 

 culprit killing phlox. 



Impatiens necrotic spot virus 

 (iNSv) was fairly common (as 

 usual) on impatiens and coleus. 

 The new 'seashell' impatiens 

 seemed to be particularly suscep- 

 tible, showing great ringspot 

 symptoms (don't forget, I do have 

 a different viewpoint than most 

 of you do). Other diseases on her- 

 baceous ornamentals included 

 POWDERY mildew on cascade petu- 

 nias and severe powdery mildew 

 on begonia. The mildew on the 

 begonias was so severe that it 

 caused the entire plant to col- 

 lapse, resembling bacterial blight. 

 If the plants had been treated at 

 the first sign of the disease, the 

 progression and subsequent loss 

 would have been minimal. (I'm 

 trying to emphasize the impor- 

 tance of scouting). 



OCTOBER. NOVEMBEI 



