A G N O S T 



UPDATE 



□ 



This has certainly been a season 

 of false starts where spring is 

 concerned. Near 70 degrees one 

 day and freezing the next. Rain, 

 then snow, then rain . . . Hopefully, 

 by the time you read this, spring 

 will be shedding its winter cloak 

 and another growing season will be 

 underway. As usual for this time of 

 year, the Plant Diagnostic Lab has 

 been relatively sample-free. There 

 have been a few interesting prob- 

 lems to note, however. 



Phytophthora root rot, also 

 known as shanking, was diagnosed 

 on tulips. The symptoms include 

 yellowing at the tips of the leaves, 

 poorly developed and discolored 

 roots, and shriveling of the devel- 

 oping flower. Like pythium, shanking 

 is favored by high moisture levels 

 in the growing medium. A geranium 

 sample was submitted with se- 

 verely chlorotic, nearly white 

 younger leaves. The problem was 

 caused by temperatures that were 

 too high; plants grown in a cooler 

 area of the greenhouse were unaf- 

 fected. 



The three major problems to 

 watch for during the next two 

 months on greenhouse crops are 



BOTRYTIS, PYTHIUM, and OEDEMA. 



Oedema is most common on Ivy ge- 

 raniums. BOTRYTIS BLIGHT and PYTHIUM 



ROOT ROT can infect any greenhouse 

 crop. All of these are related to wa- 

 tering practices and humidity lev- 

 els. Proper plant spacing, good air 

 circulation, good sanitation prac- 

 tices, and avoiding over-watering go 

 a long way in preventing problems 

 with these diseases. Impatiens ne- 

 crotic SPOT VIRUS (iNsv) continues to 

 be one of the greatest threats to 

 bedding plants and other green- 

 house crops. Symptoms vary with 

 the host and may include ring 

 spots, mosaic, necrotic spots, black 

 stem lesions (common on impa- 

 tiens) and stunting, to list a few. In- 



coming plant material should be 

 isolated, if possible, and monitored 

 for symptom development and 

 thrips. Remember, thrips control is 

 essential for managing INSV and 

 don't forget the importance of 

 weeds and leftover plants as a 

 source of the virus. Additional 

 problems common to bedding 

 plants and other spring greenhouse 

 crops include powdery mildew on pe- 

 tunias, snapdragons, roses and 

 rosemary, and various leaf spots. 



Two 'new' leaf spots to watch for 

 are acidovorax on geranium and 

 cercospora leaf spot on pansy. The 

 symptoms of acidovorax, a bacterial 

 leaf spot, are variable brown 

 sunken lesions that are associated 

 with chlorosis. It has been found on 

 many cultivars in Florida, Indiana, 

 and Michigan. It is a disease of 

 young plants — first seen at the two- 

 leaf stage, but disappearing as 

 plants get larger. It is often seen in 

 mixed infections, so it may be 

 missed. Early cercospora leaf spot 

 symptoms include tiny purple spots 

 and flecks on the upper foliage. In- 

 termediate lesions have a light cen- 

 ter with a purple rim, and, in the fi- 

 nal stages, large spreading purple 

 lesions that dry and turn necrotic 

 often appear on the lower leaves. 

 This disease starts as a problem in 

 southern plug production and then 

 moves into northern states. The 

 disease may be seed-borne. If you 

 suspect you have either of these 

 diseases, submit a sample to the 

 UNH-PDL for confirmation. 



During the next month or two, 

 inspect woody ornamentals for win- 

 ter injury. Prune any branches and 

 limbs damaged by ice and snow, 

 remove leaves that are dead or se- 

 verely winter-burned from broad 

 leaf evergreens, and after bud- 

 break, remove any branches that 

 fail to leaf-out. 



The fungi that cause anthracnose. 



LEAF SPOTS, and needlecasts usually 

 infect the leaves/needles during the 

 period between bud-break and full 

 leaf/needle expansion. Thus, April- 

 May is the key time to control 

 many of these foliar diseases. Sani- 

 tation measures, such as raking the 

 previous year's leaves, can greatly 

 reduce the levels of infection. Fun- 

 gicides may be required, however, 

 for valuable specimens or where 

 disease pressure is high. Control 

 measures for shoot blights, such as 

 PHOMOPSis TIP blight (juniper), bacte- 

 rial BLIGHT (lilac and forsythia), and 

 monilinia shoot blight (Prunus spp.) 

 also need to be applied as growth 

 resumes in the spring. We will 

 likely continue to see problems in- 

 duced by the '95 (and late '96) 

 drought on many woody plants dur- 

 ing the upcoming growing season. 



Although we have not had per- 

 sistent snow cover this winter (at 

 least in the southern portion of the 

 state), PINK SNOW mold can still be a 

 problem on turfgrasses in the early 

 spring. Cool temperatures (below 

 50F|, abundant soil moisture, and 

 the absence of extended dry peri- 

 ods favor the growth of snow mold 

 fungi. The severity of gray snow 

 MOLD infections should not be as 

 great as last spring due to the lack 

 of persistent snow cover. 



If you wish to submit plant material to 

 the UNH-PDL \or diagnosis, send 

 samples \mth a check for $12.00) to-. 

 The UNH Plant Diagnostic Lab, C/O 

 Dr. Cheryl Smith, Plant Biology Depart- 

 ment. 241 Spaulding Hall, UNH, 

 Durham, NH 03824. Samples should be 

 accompanied by an identification form 

 {available from your county Cooperative 

 Extension office, or call 603-862-3200). 

 Cheryl Smith is the UNH Cooperative 

 Extension Specialist in Plant Health, and 

 can be reached at phone-. 603-862-3841, 

 FAX: 603-862-2717, e-Mail. 

 cheryl.smith@unh.edu. 



APRIL «^ MAY 1997 



27 



