AGNOSTIC 



UPDATE 



I can usually tell when spring has 

 arrived (or at least is on its way) 

 by the increase in the number of 

 samples arriving the Plant Diagnos- 

 tic Lab, and this year is no excep- 

 tion. The number of samples 

 doubled during April and early 

 May. Although there were numer- 

 ous conifer and broad-leaf ever- 

 green samples, the majority were 

 from greenhouse crops. The prob- 

 lems diagnosed on greenhouse 

 crops were primarily edema on ivy 

 geranium, botrytis pythuim, and 

 three cases of bacterial blight of 

 geraniums. Thanks to the whims of 

 Mother Nature, weather conditions 

 during January-March were very 

 conducive to development of 

 edema. In several cases, the sever- 

 ity of the edema was such that the 

 leaves shriveled and died. BACTE- 

 RIAL BLIGHT in this years gera- 

 nium crop has been confirmed by 

 diagnostic labs throughout most of 

 the northeast. In greenhouses, the 

 most common symptom is wilting 

 of one or more leaves even though 

 the soil is moist. Leaf spotting, al- 

 though less common that wilt, may 

 occur if severely infected plants 

 are present nearby. Leaf spot de- 

 velops when the bacteriums 

 splashed from one plant onto an- 

 other or drips from hanging baskets 

 onto plants below. Leaf spotting is 

 usually accompanied by yellowing, 

 often in a V-shaped pattern. The 

 symptoms on ivy geranium are not 

 as obvious as those on seed and 

 zonal types. On ivy geraniums, the 

 symptoms are easily confused with 



edema or nutrient imbalances. If 

 bacterial blight is suspected, a 

 laboratory diagnosis is necessary to 

 confirm the presence of the bacte- 

 rium. If confirmed, strict measures 

 are needed to reduce potential 

 crop loss. Plants cannot be cured 

 or protected by pesticide sprays or 

 drenches. Therefore: 



1. Infected plants should be 

 destroyed and soil should not 

 be reused 



2. Suspicious plants should be 

 isolated 



3. Tools, pots, flats, and bench 

 tops, should be sterilized with 

 10% bleach. 



Many conifers and broad-leaf ev- 

 ergreens took a beating this winter, 

 particularly hemlocks. Besides the 

 usual damage caused by salt injury 

 to roadside planting, many hem- 

 locks are showing symptoms of 

 desiccation caused by the combi- 

 nation of the extremely cold tem- 

 peratures and dry winds of this 

 past winter. Last summer's drought 

 also stressed many trees that were 

 accustomed to growing in relatively 

 wet sites. Trees less that six feet 

 that have turned completely brown 

 will probably not survive. However, 

 wait a few more weeks to evaluate 

 their condition before you replace 

 or remove them. 



)une and July are 'big' months 

 for plant diseases. Watch for 

 BROWN PATCH, PYTHIUM BLIGHT, 

 and LEAF SPOTS on turf (water in 

 the morning and avoid excessive 

 nitrogen). Lilac shoots infected with 

 bacterial blight should be pruned 



during dry conditions. FIRE BLIGHT 

 infected shoots (strikes') on crab 

 apples, hawthorn, cotoneaster, or 

 mountain ash should be pruned 

 during dry conditions (sterilize 

 tools between each cut). Watch for 

 the leaf spots or dieback associ- 

 ated with DOGWOOD ANTHRA- 

 CNOSE and prune any severely in- 

 fected or dying twigs and branches. 

 The severity of LEAF SPOTS and 

 POWDERY MILDEWS can be re- 

 duced through the use of sanitation 

 measures plus cultural techniques 

 that increase air circulation. One 

 interesting 'disease' often shows up 

 on bark mulch at this time of 

 year.. SLIME MOLD (simply rake or 

 shovel them up. or wait and they'll 

 either blow away during dry 

 weather or wash away during the 

 next good rain). Remind your cus- 

 tomers (as well as yourselves) that 

 proper planting (depth and spac- 

 ing) and cultural techniques (sani- 

 tation and mulching) go a long way 

 toward preventing plant problems. 



If you wish to submit plant material to 

 the PDDL for diagnosis, send sample to-. 

 Dr. Cheryl Smith, Plant Disease 

 Diagnostic Lab, Nesmith Hall, UNH, 

 Durham, NH 03824. Samples should 

 be accompanied by an identification form 

 (available from your county Cooperative 

 Extension office). There is no fee [at this 

 time). Cheryl Smith is the UNH 

 Cooperative Extension Specialist in 

 Plant Health, and can be reached at 

 (603) 862-3841. »» 



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