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DIAGNOSTIC LAB 



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Happy New Year! It sure is tough 

 to get back into the swing of 

 things after the holidays (and digging 

 out from snow storms!) Outside, The 

 'Blizzard of 1996' is in full swing as I 

 write this issue's column. I spent the 

 holidays in N). where they had the 

 first white Christmas in 12 years and 

 if it keeps going like this, they'll also 

 have a white Easter! 



Luckily, this is a relatively slow 

 time in the PDL. It's the time of year 

 for workshops and meetings, and 

 catching up on journal articles. 

 Speaking of workshops, the Christmas 

 Tree Pest IVIanagement Course was 

 held last week in Keene. The course 

 was a great success with over 100 at- 

 tendees and collaborators from three 

 states. The next course will be of- 

 fered in 1998. 



Although relatively few samples 

 were received in the last two months 

 of 1994, there were some notable 

 samples. 



Rhizosphaera needle blight was diag- 

 nosed on Tflxus and Hormonema needle 

 BLIGHT was diagnosed on balsam fir. 

 The fungus causes the needles to 

 turn red at the tips while the base of 

 the needles remain green. The symp- 

 toms are usually first noticed in Au- 

 gust. Once again, this is a disease we 

 pathologists know little about. A 

 Crimson King maple was diagnosed 

 with Verticillium wilt. The homeowner 

 has lost several trees over the last 

 five years, including three large lapa- 

 nese maples. It appears the fungus 

 came in on top soil brought to the 

 site, since several maples planted 

 into native soil have shown no symp- 

 toms of wilt. 



A few cases of Phomopsis Canker 

 and dieback were diagnosed on dog- 

 wood and maple. This is a problem 

 we will see more of during the next 

 two-to-three growing seasons as a re- 

 sult of the effects of stress induced 

 during the 1995 drought. 



Problems on greenhouse crops 

 were relatively few during November 



and December. FN-thium was isolated 

 from the roots of wilting New Guinea 

 impatiens and a chlorophytum that 

 was exhibiting browning of the 

 leaves. There was only one con- 

 firmed case of Powdery Mildew on 

 poinsettias this season. In general, 

 the crop was fairly clean throughout 

 the country. Several Asiatic lilies 

 were submitted with brown streaking 

 on the leaves. Although the samples 

 tested positive for Lily Symptomless 

 Virus, the problem was actually re- 

 lated to an iron imbalance induced 

 by high pH. 



|[J|n the coining months, 



remember that 



pythium root rot 



and botrytis blight are 



the most common problems 



in greenhouse crops. 



To avoid problems 



(especially to those 



tender bedding plants), 



remember nothing beats 



good sanitation, 



good air circulation, 



and careful monitoring . 



Bacterial Blight was diagnosed on 

 geraniums received in mid-Decem- 

 ber. Please be sure to scout your ge- 

 ranium crops for this potentially dev- 

 astating disease. ..There is no effec- 

 tive control for plants once they are 

 infected! The most common symp- 

 tom is wilting of one or more leaves 

 even though the soil is moist. Leaf 

 spotting, although less common than 

 wilt, may occur if severely infected 

 plants are present nearby. Leaf spots 

 develop when the bacterium is 

 splashed from one plant to another 

 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 geraniums are not as obvious as 

 those on seed and zonal types. On 

 ivy geraniums, the symptoms are 

 easily confused with edema or nutri- 

 ent imbalances. If bacterial blight is 

 suspected, a laboratory diagnosis is 

 necessary to confirm the presence of 

 the bacterium. If confirmed, plants 

 cannot be cured or protected by 

 pesticide sprays or drenches Strict 

 measures are needed to reduce po- 

 tential crop loss: 

 I. infected plants should be de- 

 stroyed and soil should not be 

 reused; 

 2 suspicious plants should be iso- 

 lated: and 

 3. tools, pots, flats, and bench tops 

 should be sterilized with 10% 

 bleach. 

 If you suspect the disease, please 

 submit whole-plant samples to the 

 PDL for diagnosis. The plants should 

 be removed from the potting 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. 



In the coming months, remember 

 that pythium root rot and botrytis 

 blight are the most common prob- 

 lems in greenhouse crops. To avoid 

 problems (especially to those tender 

 bedding plants), remember nothing 

 beats good sanitation, good air circu- 

 lation, and careful monitoring. 



If you wish to submit plant material to the 

 PDL for diagnosis, send samples {with a 

 check for Si 2.00 for each plant species) to: 

 The UNH Plant Diagnostic Lab. C/0 Dr. 

 Cheryl Smith. Plant Biology Department. 

 Nesmith Hall - UNH, Durham. NH 

 03824. Samples should be accompanied by 

 an identification form [available from your 

 county Cooperative Extension) Cheryl 

 Smith is the UNH Cooperative Extension 

 Specialist in Plant Health, and can be 

 reached at (603) 862-3841. 



FEBRUARY ♦ MARCH 1996 



25 



