DIAGNOSTIC UPDATE 



E3 



It's raining outside as I write this 

 update. The prolonged rainy pe- 

 riod and relatively mild tempera- 

 tures will likely result in significant 

 disease pressure from fungal LEAF 

 SPOTS and BLIGHTS such as APPLE 

 SCAB, ANTHRACNOSE diseases and 

 NEEDLE-CASTS. And the potential 

 for serious FIRE BLIGHT problems 

 appears to be very high. 



The greenhouse problems from 

 March through early May have 

 been fairly typical, although there 

 have been more virus problems 

 than usual. TOMATO RINGSPOT 

 VIRUS was diagnosed on lipstick 

 plants showing symptoms that are 

 usually associated with cold water 

 injury (similar to cold water injury 

 on African violet). TOBACCO STREAK 

 and POTY viruses were found on 

 hele-nium. The symptoms were a 

 very subtle mottling of the foliage. 

 IMPATIENS NECROTIC SPOT VI- 

 RUS (INSV) was confirmed on 

 snapdragons, coleus, and felicia. 

 INSV usually causes white, circular 

 spots on the foliage of snapdrag- 

 ons, but in this case also caused a 

 bronzed, sunken stem canker. Two 

 viruses, LILY SYMPTOMLESS virus 

 and poty virus were diagnosed on 

 oriental lilies (the cultivars 

 'Espresso' and 'Moonshine'). The 

 double virus infection caused 

 growth distortions and chlorotic 

 streaking of the foliage. Extensive 

 SHOOT DIEBACK on coleus was 

 caused by the fungus phomopsis. 

 Other more 'typical' problems in- 

 cluded PYTHIUM ROOT ROT on 

 felicia, verbena and geranium; 

 EDEMA on geraniums; and iron/ 

 manganese toxicity on geraniums. 

 Iron-manganese toxicity symptoms 

 on geraniums are similar to those 

 caused by high soluble salts (brown- 

 ing) of the leaf margins and 

 interveinal necrosis), except the 

 interveinal chlorosis and browning 

 are usually more severe. IRON/ 

 MANGANESE TOXICITY is com- 



mon with poor drainage and/or 

 low pH. The pythiuni infections on 

 the geraniums had advanced to the 

 point of causing "black leg" symp- 

 toms and, as a result, most of the 

 crop was lost. If the problem had 

 been diagnosed sooner, fungicide 

 drenches may have helped. 



Although we had a relatively 

 mild winter, WINTER BURN or 

 DESICCATION was evident on 

 many conifers. The symptoms of 

 bronzed or reddened needles was 

 especially common on trees and 

 shrubs that suffered from drought 

 stress last year. Another disease 

 problem that is most likely related 

 to previous drought stress was 

 noted throughout the native range 

 of balsam fir last summer and is 

 evident again this spring. The fun- 

 gus cylospora is causing a TWIG 

 CANKER on balsam fir. The canker 

 eventually girdles the twigs at the 

 base of the previous season's growth, 

 causing the needles to drop and 

 eventually resulting in "bird foot- 

 like" bare shoot. PHOMOPSIS TWIG 

 BLIGHT, also favored by drought 

 stress (and winter injury), has been 

 a common problem this spring. 



Other problems on woody orna- 

 mentals included VOLUTELLA 

 BLIGHT on pachysandra and a 

 couple of cases of STEM CANKER 

 on vinca, caused by the fungus 

 Phoma. As mentioned above, the 

 potential for fire blight seem to be 

 high this spring. Many of the host 

 plants (apple, pear, cotoneaster, 

 hawthorn, mountain ash, quince, 

 etc.) were in bloom during the ex- 

 tended wet weather in late April to 

 early May. The late frost that oc- 

 curred during the third week of 

 April may confound the identifica- 

 tion of fire blight infections since 

 blight-injured blossoms look similar 

 to those injured by frost. Suspected 

 fire blight strikes should be pruned 

 during dry weather. 



GRAY SNOW MOLD has been 



the primary problem on turfgrass 

 samples received mid-March through 

 mid-May. Although consistent snow 

 cover was lacking in many south- 

 ern areas, wet soil conditions com- 

 bined with cold temperatures fa- 

 vored disease development. 



The most common problems on 

 turfgrass during late spring-early 

 summer include RED THREAD, 

 BROWN PATCH, LEAF SPOTS, and 

 PYTHIUM BLIGHT. Red thread was 

 fairly common on both perennial 

 ryegrass and fescues last year, thus 

 we can expect it to be a problem 

 this year if cool, moist weather oc- 

 curs during June and again in Sep- 

 tember. The easiest management 

 practice is to collect the clippings 

 when mowing. 



One disease has already ap- 

 peared on herbaceous annuals and 

 perennials. COLLETOTRICHUM LEAF 

 SPOT on pansy causes tan-to-straw- 

 colored spots surrounded by a 

 purple-red border on the leaves. 

 The disease is easily spread by wa- 

 ter splash from overhead irrigation 

 or during rains. Several fungicides 

 are registered for control, but ap- 

 plications are usually only required 

 during prolonged wet conditions. 

 BOTRYTIS BLIGHT was also com- 

 mon on field-grown pansies that 

 were covered with mulch. The 

 problem occurred in plantings where 

 the mulch was left in-place during 

 the warm spell in late March, creat- 

 ing ideal hurrud conditions. 



To submit plant material for 

 diagnosis, send samples (with a 

 check for $12.) to: The UNH Plant 

 Diagnostic Lab, C/O Dr. Cheryl 

 Smith, Plant Biology Department, 

 Spaulding Hall-UNH, Durham, NH 

 03824. Samples should be accompa- 

 nied by an identification form (avail- 

 able from your county Cooperative 

 Extension). Cheryl Smith is the 

 UNH Cooperative Extension Special- 

 ist in Plant Health, and can be 

 reached at 603-862-3200. 



lUN E.JULY. 1998 



