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DIAGNOSTIC LAB 



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I guess the saying about change- 

 able New England weather is 

 holding true for this season. The con- 

 ditions have certainly been wetter 

 than last summer (at least as of |uly 

 5), and the number of samples re- 

 ceived during May-|une is indicative 

 of the environmental conditions favor- 

 able for disease development. The 

 cool temperatures and high moisture 

 levels during June were favorable for 

 the development of botrytis blight, 

 leaf spots, anthracnose diseases, 

 needle-cast infections, root rots, and 

 bacterial blights. Problems related to 

 drought stress are still common on 

 nearly all woody ornamentals (tip die- 

 back, small leaf and needle size, and 

 sudden wilting during high tempera- 

 ture periods). Hemlocks and white 

 pines are showing significant needle 

 yellowing and browning as well as 

 needle loss. 



Fungal tip blights and cankers, in- 

 cluding DIPLODIA (SPHAEROPSIS) TIP BLIGHT 



and CYTOSPORA canker on conifers, kaba- 

 TiNA TIP BLIGHT On junipcrs, and phomop- 

 sis TWIG BLIGHT (junipers, rhododen- 

 drons) are more common this year. 

 The effects of drought stress predis- 

 poses plants to infection by these 

 (and other) fungi. Anthracnose has 

 been diagnosed on maples, dog- 

 woods, and oaks. (The wet weather 

 during leaf expansion was ideal for in- 

 fection.) Fire blight has been common 

 on crabapples and severe scab infec- 

 tions are beginning to cause early de- 

 foliation on susceptible cultivars. The 

 wet conditions during needle emer- 

 gence was also ideal for needlecast in- 

 fections (cyclaneusma on Scotts, plio- 

 derma on Austrian, rhizosphaera on 

 spruce), so we can expect to see 

 symptoms in 6-9 months. Symptoms 

 of Dutch elm disease are beginning to 

 show on elms (DED is accelerated by 

 drought stress. The same pattern de- 

 veloped in the 1993 growing season). 

 Birches, particularly B pendula cultivars, 

 have been hit hard by bronze birch 

 borers (drought stressed trees are 

 more prone to attack). Check for the 

 characteristic raised areas beneath the 

 bark. 



Several turfgrass diseases appeared 

 'on-cue,' while others appeared earlier 

 than usual. Snow mold was a common 

 problem, particularly on home lawns. 

 Damping off or seedling blight caused 

 by pythium was a problem in newly 

 seeded areas. In most cases, the dis- 

 ease was exacerbated by over-water- 

 ing. Brown patch is already evident in 

 some home lawns. 



The major problem in greenhouse 

 crops was botrytis blight. The high hu- 

 midity and cool temperatures were 

 ideal for fungal development. Remem- 

 ber: sanitation and good air circulation 

 go a long way in management of 

 botrytis . One case of bacterial blight 

 on geraniums was confirmed (refer to 

 earlier issues of The Plantsman for 

 symptom descriptions and controls). 

 Bacterial leaf spot on impatiens, 

 caused by pseudomonas, was de- 

 tected in two samples. The leaf spots 

 are tan with a light center; infections 

 may also appear as dark, water- 

 soaked areas between the veins. In- 

 fected plants should be removed. 

 Powdery mildew was a prob-lem on 

 New Guinea impatiens and petunias. 

 Increasing air circulation and fungicide 

 sprays held the problem in check. 



The usual diseases have begun to 

 appear on annuals and perennials, 

 but in greater intensity than last year. 

 Botrytis blight was diagnosed on pop- 

 py, tulip (tulip fire), peony, and roses. 

 ScLEROTiNiA STEM ROT was identified on 

 artemesia. Sclerotinia is characterized 

 by white, fluffy mold near the base of 

 the stem and hard black sclerotia that 

 form in the collapsed stems. Infected 

 plants should be removed immedi- 

 ately, as well as the soil surrounding 

 the roots. 



A few interesting problems have 

 shown up on vegetables. Bailing 

 twine that was treated with a petro- 

 leum-based preservative caused 

 twisted and distorted growth on any 

 portion of the plant that came in 

 contact with the twine. Once the 

 twine was removed, there was no 

 further development of symptoms 

 on subsequent growth. Several 

 cases of growth distortions (elon- 



gated leaves, curling) on tomatoes 

 grown in high tunnels was attributed 

 to uneven distribution of granular 

 fertilizer prior to planting. 



Most of the diseases that occurred 

 during May-|une will continue to cause 

 problems during the rest of the grow- 

 ing season, especially if we continue 

 to have frequent rainfall. As the tem- 

 peratures rise, additional diseases 

 such as BROWN PATCH and pythium blight 

 on turfgrasses usually become more 

 prevalent. Sclerotinia root rot on her- 

 baceous plants is also more severe 

 with moist soil conditions and warmer 

 temperatures. 



If you have had a problem with 

 needlecast on spruce in the past, re- 

 member that rhizosphaera often has a 

 second infection period during late- 

 August through early-September, so 

 you should apply a fungicide at this 

 time. Slime molds begin to appear (lit- 

 erally overnight) during moist periods 

 in )uly and August. They are most 

 commonly seen growing on bark 

 mulch. The fungi don't pose a threat 

 to plants, but they are unsightly. They 

 can be removed by raking or with a 

 strong stream of water. (But you can 

 expect them to reappear elsewhere!) 

 Remember to begin your sanitation ef- 

 forts during August. A little effort goes 

 a long way to prevent disease and in- 

 sect problems. 



1 also want to thank everyone for 

 their patience during our move to 

 Spaulding Hall. We are nearly settled 

 into the new facilities, although we're 

 still trying to locate a few 'lost' items. 

 Parking is a problem, but there is a 

 30-minute loading zone space at the 

 south end of Spaulding Hall (and an 

 elevator for those large samples). 

 If you wish to submit plant material to the 

 UNH-PDL lor diagnosis, send samples [with a 

 check for $12 00) to. The UNH Plant Diag- 

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

 ogy Department, 241 Spaulding Hall — 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 Exten- 

 sion Specialist in Plant Health, and can be 

 reached at (603) 862-3841 



THE PLANTSMAN 



