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DIAGNOSTIC LAB 



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Spring is finally here (I thini<)! If 

 April showers bring May flowers, 

 then what do April snowstorms 

 bring? One disease that was favored 

 by the abundance' of winter was 

 SNOW MOLD. We had perfect conditions 

 (early snowfall on green turfgrass 

 with moist, unfrozen soil) for the de- 

 velopment of both pink and gray 

 snow mold. The snow acts as an in- 

 sulator, keeping out the cold and 

 dry air while maintaining the moist 

 conditions necessary for fungal 

 growth. Last year, problems with 

 pink snow mold continued into the 

 early summer, thanks to cool night 

 temperatures, a pattern that seems 

 to be repeating itself this year. 



The cloudy, wintry weather also 

 brought the 'typical' problems to 

 greenhouse crops. Pythium root rot 

 and BOTRYTis blight caused problems 

 on many crops. Oedema was very 

 common on ivy geraniums, resulting 

 in defoliation of the plants in two 

 severe cases. All three of these dis- 

 eases are favored by over-watering, 

 while excess humidity and poor air 

 circulation favor the development of 

 botrytis and oedema. Thelaviopsis 

 root rot has been diagnosed on ge- 

 raniums and columbine. This fungal 

 root rot is becoming more common 

 since the loss of benlate, particu- 

 larly when field soils are added to 

 the growing medium. Preventative 

 measures include using sterilized 

 potting mix and fungicide (thiopha- 

 nate methyl) drenches. 



Impatiens necrotic spot virus 

 (iNsv) has reared its ugly head in 

 the last few weeks (mid-April to 

 early-May). The virus has been diag- 

 nosed on impatiens, tomatoes, pep- 

 pers and begonias Remember — the 

 key to controlling INSV is to control 

 thrips and to rogue and destroy in- 

 fected plants (See the lune/|uly 1995 

 issue of The Plantsman for a review of 

 symptoms and management of insv). 



Twig dieback due to winter in- 



jury/drought stress is beginning to 

 show up on a wide range of woody 

 species. We can expect to see more 

 of this as the season progresses, 

 thanks to drought stress effects from 

 the last three seasons. Trees and 

 shrubs that were installed last sea- 

 son will require extra care this grow- 

 ing season (pruning, ample water 

 during dry periods, and fertilization 

 to promote new root growth). 

 Drought stress symptoms are also 

 becoming more evident on conifers, 

 especially hemlock. Reddish-brown 

 needles may appear scattered 

 throughout the tree or may be con- 

 centrated on the side of the tree 

 exposed to winter winds. Spruce in 

 exposed locations are exhibiting these 

 one-sided symptoms. The symptoms 

 should not be confused with rhizo- 

 sphaera needlecast symptoms. Spruce 

 infected with rhizosphaera have 

 purple-to-reddish one-year-old nee- 

 dles. Fungicides to control rhizo- 

 sphaera should be applied when the 

 new grovrth is 1-1 1/2 inches long. 



lune and |uly traditionally bring a 

 number of plant diseases and prob- 

 lems to New Hampshire growers. 

 Bacterial blight on lilac and for- 

 sythia was a common problem last 

 year. A combination of pruning and 

 copper fungicides provide effective 

 control. Shoot blight (Monilinia) 

 continues to be a severe problem 

 on Prunus sp. Fungicides should be 

 applied during bloom, and infected 

 twigs should be removed during dry 

 weather. Primary apple scab lesions 

 should be evident on Malus sp. by 

 early June. Secondary scab infec- 

 tions should be controlled with fun- 

 gicides to reduce the likelihood of 

 early defoliation on susceptible 

 crabapple cultivars. We can expect 

 TWIG blights and cankers such as 

 kabatina, phomopsis, sphaeropsis 

 (diplodia), botryosphaeria, and 

 cytospora to be common on 

 drought-stressed trees and shrubs. 



Removing the affected twigs should 

 provide satisfactory results. Arbor- 

 viTAE LEAF MINERS were a problem 

 last year The damage to the shoot 

 tips resembles winter burn. Insecti- 

 cides should be applied from mid- 

 )une to mid-)uly to prevent egg lay- 

 ing by the adult moths. 



Turfgrass diseases and problems 

 to watch for during May-june are 



snow mold, RED THREAD, DOLLAR SPOT, 



and LEAF SPOTS. Prolonged spring- 

 like weather favors the development 

 of red thread and pink snow mold. 

 Once the night temperatures be- 

 come warmer (65F), diseases such 



as BROWN PATCH, PyTHIUM BLIGHT, AND 



ANTHRACNOSE become more common. 

 Leaf spots on annuals and peren- 

 nials (i.e., SEPTORIA, TULIP FIRE, DIDY- 



MELLA on iris) should be controlled 

 with a combination of sanitation, 

 proper spacing, and fungicides. The 

 damage caused by botrytis blight to 

 annuals and perennials can be re- 

 duced by thinning the plantings to 

 allow for better air circulation. Plant 

 bug feeding injury usually appears 

 in late )une-|uly. The damage ap- 

 pears as circular spots with brown- 

 reddish borders that often occur in 

 clusters on the leaves of herbaceous 

 crops. 



Mid-May through mid-july is the 

 critical period for managing most 

 plant diseases. Remember — sanita- 

 tion is the most important cultural 

 method for preventing disease 

 problems. 



If you wish to submit plant material to the 

 PDL for diagnosis, send samples {with a 

 check for $12.| to. The UNH Plant Diagnos- 

 tic Lab, C/O Dr. Cheryl Smith, Plant Biol- 

 ogy Department, Spauldina Hall , UNH, 

 Durham, NH 03824. Samples should be 

 accompanied by an identification form 

 [available from your county Cooperative 

 Extension). Cheryl Smith is the UNH Coop- 

 erative Extension Specialist in Plant Health, 

 and can be reached at (603) 862-3841. 



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THE PLANTSMAN 



