DIAGNOSTIC II P D A T E 



CHERYL SMITH 



The 2003 growing season was an in- 

 teresting period tor plant diseases. Ac- 

 tually, it was railier exciting (& still 

 is) From my point of view, but ot 

 course my point oi view is a 'little 

 different' than most of yours! WET 

 would be the best descriptor tor 

 much of the season. This precipita- 

 tion was the culprit tor many ot this 

 year's prevailing problems. 



Woody Ornamentals 



Shade tree anthracnose was every- 

 where! Wet conditions prevailed dur- 

 ing most ot the early spring when 

 leaves were expanding. This created 

 the ideal conditions tor not only an- 

 thracnose diseases, but a wide range 

 ot leat spots as well. Anthracnose was 

 common on maples, sycamore, ash, 

 oak, and flowering dogwood. Apple 

 scab was severe on susceptible 

 crabapple cultivars, causing significant 

 defoliation by late-July. Another 

 prevalent leat spot was black spot on 

 rose. 



So what should be done about all 

 these toliar diseases betore next year? 

 Sanitation should be your primary lo- 

 cus this tall and winter. Where toliar 

 diseases have been a problem, rake and 

 remove as much ot the toliage as pos- 

 sible atter leat drop, or use a mulching 

 mower to reduce the particle size and 

 speed degradation. Although removing 

 infected leaves may not significantly re- 

 duce subsequent intections tor some 

 anthracnose diseases that also cause in- 

 fection ot the twigs (sycamore anthra- 

 cnose), it is effective tor most other fo- 

 liar diseases. If particular trees or spe- 

 cies have been problematic tor a num- 

 ber of seasons (minus the drought 

 years), you may want to consider fim- 

 gicides, especially if next spring is a re- 

 peat of this past one. 



Monilinia (European) shoot blight 

 was widespread on most ornamental 

 Prunus species particularly flowering 

 almonds and sand cherries. Although 

 this disease has been present for the 

 last six to eight years, it was particu- 

 larly severe this year. Shoots killed 

 earlier this year should be removed 

 during dry weather and destroyed. 



EARLY WINTER 2(10.^ 



Protective fungicide sprays may be 

 warranted next spring on nursery 

 stock and valuable landscape speci- 

 mens. Fungicides should be first ap- 

 plied when the blossoms open fol- 

 lowed by a second application ten 

 days later. 



Tip blights and cankers are still 

 very common on trees and shrubs 

 that have been subject to drought 

 stress and/or winter injiiry. Dieback 

 due to canker fungi is evident on 

 many hosts (juniper, pine, and oak). 

 Several fungi are associated with these 

 cankers and dieback. Many of the 

 fungi are considered "opportunistic;" 

 they attack trees and shrubs under 

 stress, particularly previous drought 

 stress. Prune dead shoots during dry 

 weather and destroy them. Protect ev- 

 ergreens from winter desiccation by 

 erecting wind-blocks. 



Herbaceous Ornamentals 



Annuals and perennials suffered from 

 root rots and lots of foliar problems 

 thanks to the wet conditions. Fungi 

 that are favored by moist soil condi- 

 tions caused most ot the root rots. 

 Pythium root rot was very common. 

 The best control for most of the root 

 rot diseases is to remove the symp- 

 tomatic plants and destroy them 

 (don't reuse pots if they were con- 

 tainer-grown). In the case of field 

 grown plants, include as much of the 

 soil surrounding the roots as possible. 

 Botrytis blight was a big problem on 

 bedding plants during June. It was 

 also a problem on other crops 

 throughout July and August (espe- 

 cially where the plants were crowded). 

 The best method for management of 

 Botrytis is to improve the air circula- 

 tion arotmd the plantings or produc- 

 tion area. Thinning plantings, increas- 

 ing plant spacing, removing overhang- 

 ing branches and locating production 

 areas away from "dead air" areas will 

 significantly reduce not only Botrytis 

 but also powdery mildew. 



Also worth noting is the fact that 

 viruses were more prevalent this year, 

 both in field- and 2,reenhouse-grown 



crops, than in recent yc.irs. It is im- 

 portant to remember that virus-in- 

 fected plants can't be "cured. " Any 

 plants suspected of being infected 

 with a virus should be destroyed (or 

 isolated from the rest of the crop 

 then destroyed if a virus is identified). 

 Cuttings should not be taken from vi- 

 rus-infected plants. 



Greenhouse sanitization between 

 crops is an essential management 

 practice. Be sure to thoroughly clean/ 

 sanitize your greenhouse before you 

 begin a new crop. Major sanitation 

 targets include eliminating weeds, 

 dust, plant debris, clutter and pet 

 plants. All surfaces should be sanitized 

 with products such as Oxidate, 

 Greenshield, or 10% bleach. Preven- 

 tion is much easier than trying to 

 correct a problem after it occurs! 



Finally, SANITATION is the most 

 important preventative measure. It has 

 been a very favorable year for the de- 

 velopment of diseases on nearly all 

 plants. It is important to remove all 

 plant debris at the end of the growing 

 season, particularly diseased material, 

 since it is often a source of infection 

 the following season. Infected leaves 

 should be removed and destroyed. In- 

 fected leaves should also be removed 

 from broad-leaved evergreens, and 

 dead shoots and twigs should be 

 pruned from trees and shrubs prior to 

 next spring (it helps to flag those 

 shoots now so they can easily be seen 

 later). Known diseased material 

 should not be composted. Be sure to 

 protect woody ornamentals against 

 winter damage and desiccation. A 

 little effort now can go a long way in 

 preventing future probletns. 



If you wish to submit plant mate- 

 rial to the PDL for diagnosis, send 

 satnples (with a check tor $15.00) to: 

 The UNH Plant Diagnostic Lab, 

 241Spaulding Hall— UNH, 38 Col- 

 lege Rd., Durham, NH 03824. 

 Samples should be accompanied by an 

 identification form (available from 

 your county Cooperative Extension 

 office). Dr. Cheryl Smith is a UNH 

 Extension Professor and the Plant 

 Health Specialist. 



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