D I A G N O S T 



UPDATE 



The flow of samples into the PDL 

 has been relatively slow during 

 lanuary and February. The samples were 

 primarily greenhouse crops, although a 

 few specimens of woody shrubs were 

 submitted. Thankfully, there was only 

 one major disease problem that showed 

 up during the last two months The 

 problem was botrytis cutting blight on 

 unrooted geranium cuttings shipped 

 from off-shore' sources. Botrytis blight 

 developed within days of receiving the 

 shipment, or in some instances, botrytis 

 was visible on the cuttings at the time of 

 arrival. The symptoms of botrytis cutting 

 blight resemble those of pythium black- 

 leg and include browning or blackening 

 of the stem at the base of the cutting, or 

 at wound sites Under humid conditions, 

 the typical gray fuzzy mold develops on 

 the blackened areas land may even be 

 present when the shipment is opened). 

 Besides refusal of infected shipments, 

 your options for control of botrytis blight 

 should include a fungicide treatment of 

 the cuttings at the time of planting 

 Recommended fungicides include Chipco 

 26019, Daconil 2787, Ornalin, and dea- 

 ry's 3336. Resistance to thiophanate- 

 methyl (Cleary's 3336 and Domain) has 

 been reported in several crops, so if 

 thiophanate-methyl is used, it should be 

 rotated with another fungicide. Cutting 

 back on the frequency and duration of 

 misting should also help reduce botrytis 

 cutting blight 



Thelaviopsis root rot was diagnosed 

 on several geranium samples. The inci- 

 dence of this fungal root rot on crops 

 grown in soilless media appears to be 

 increasing Diagnostic labs throughout 

 the northeast have noted thelaviopsis on 

 several crops, including geraniums and 



poinsettias Historically, thelaviopsis was 

 usually associated with soil-based me- 

 dia, and the reasons for the shift are un- 

 clear. The symptoms include stunting 

 and yellowing of the lower leaves The 

 irregular black or dark brown lesions 

 typical of thelaviopsis can be found on 

 the smaller feeder roots of infected 

 plants Fungicide drenches (Chipco, 

 Cleary's, Domain.) are effective in con- 

 trolling the disease. 



A few of the other interesting dis- 

 eases diagnosed during lanuary and 

 February included slime mold on the 

 leaves of New Guinea impatiens and 

 powdery mildew on rosemary. Botrytis 

 was not only a problem in the green- 

 house but was also causing problems in 

 perennial beds that had been covered 

 with plastic. The unusually warm weather 

 during February and lack of snow-cover 

 created ideal conditions for the develop- 

 ment of Botrytis Two samples, one P|M 

 rhododendron and one unnamed azalea, 

 were received from home owners with 

 heavy deposits of sooty mold caused by 

 azalea bark scale 



There have been no major outbreaks 

 of bacterial blight on geraniums, al- 

 though a few cases have been reported 

 in New England Because of the prob- 

 lems last year, however, 1 would suggest 

 you continue to inspect and monitor ge- 

 raniums during the next month or two 

 for bacterial blight (see the |une/|uly 

 1994 issue of The Planlsman for a descrip- 

 tion of symptoms). If you suspect the 

 disease, please submit whole-plant 

 samples to the PDL for diagnosis The 

 plants should be removed from the pot- 

 ting mix and the root system should be 

 wrapped in a plastic bag before shipping 

 (the mix should be moist but not 



soaked). The samples can be mailed in 

 a sturdy box (be sure to pad the plants 

 with newspaper). Or you can always 

 hand-deliver samples to the lab Other 

 problems to watch out for include downy 

 mildew on snapdragon, impatiens ne- 

 crotic spot virus on a wide range of 

 hosts, and the usual pythium and rhizoc- 

 tonia root rots. Remember to cut back 

 on watering during prolonged periods of 

 cloudy weather to prevent Pythium and 

 Botrytis problems Finally, remember 

 nothing beats good SANITATION, good 

 air circulation, and careful monitoring for 

 preventing disease problems (especially 

 during the early portion of the bedding 

 plant season). 



Finally, 1 want to remind everyone of 

 the new fee system for samples submit- 

 ted to the Plant Diagnostic Lab Begin- 

 ning May I, 1995, the fee will be $12. 

 per sample A sample consists of a 

 single plant species and may include 

 several specimens of the same species 

 (actually it's best to send several speci- 

 mens showing the range of symptoms 

 from healthy to most severely diseased). 

 We have avoided charging for samples 

 as long as possible, but due to contin- 

 ued decreases in funding, the fee is nec- 

 essary to defray a portion of the costs. 



If you wish to submit plant material 

 to the PDL for diagnosis, send samples 

 [with a check for $12.) to. The UNH 

 Plant Diagnostic Lab, C/O Dr. Cheryl 

 Smith, Plant Biology Dept.. UNH, 

 Durham, NH 03824. Samples should be 

 accompanied by an identification form 

 [available from your county Cooperative 

 Extension office). Cheryl Smith is the 

 UNH Cooperative Extension Specialist in 

 Plant Health, and can be reached at 

 603-862-3841. 



STEENBURG & CALLIORAS 



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603/868-1070 



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656 South Mammoth Road (Rte. 28A) 



Manchester, NH 03109-5049 

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