DIAGNOSTIC UPDATE 



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Happy New Year! I hope 1999 

 brings a better growing season 

 than last year, or at least one that is 

 closer to 'normal'. The unusual 

 weather patterns that began last 

 March continued through early De- 

 cember with above-normal tempera- 

 tures (at least the heating costs were 

 reduced). Thanks to the mild tem- 

 peratures, the Plant Diagnostic Lab 

 continued to receive samples 

 through November. Most of the 

 samples were a continuation of 

 problems seen earlier in the season, 

 such as anthracnose and other foliar 

 diseases on trees and shrubs, rusts, 

 botrytis blight on annuals and pe- 

 rennials as well as on greenhouse 

 crops, root rots such as pythium, 

 anthracnose and red thread on turf, 

 and the development of stress-in- 

 duced cankers and diebacks on 

 woody species. Given the relatively 

 high incidence of plant diseases in 

 1998, the potential for disease prob- 

 lems in 1999 is significant. I think 

 its important to consider what the 

 major diseases were in 1998 and 

 what measures can be taken to re- 

 duce the likelihood of their occur- 

 rence if favorable environmental 

 conditions exist (prolonged wet 

 weather). 



WOODY ORNAMENTALS 

 Anthracnose and other leaf spots 

 and blights were widespread 

 throughout the northeast. Maple an- 

 thracnose was the worst I've seen in 

 17 years. Sycamore, oak, and flower- 

 ing dogwood were also common 

 hosts of anthracnose. Management 

 of most anthracnose diseases on 

 woody hosts can be achieved with 

 good sanitation. Remove and destroy 

 as many of the leaves as possible be- 



fore bud-break in the spring (the 

 leaves are the source of new infec- 

 tions). If the leaves can't be re- 

 moved, use a mulching mower to 

 reduce the leaves to small particles. 

 Valuable landscape specimens and 

 nursery stock should receive two to 

 three fungicide applications at 7-10 

 day intervals beginning at bud 

 break. Sycamores and flowering dog- 

 woods require the removal of dead 

 twigs and branches prior to bud- 

 break followed by fungicides. Re- 

 moval of fallen leaves is also very ef- 

 fective for the control of apple scab 

 on crabapples. Fungicides will prob- 

 ably be required for some highly 

 susceptible cultivars. 



Ascochyta leaf blight and bacterial 

 blight were the most common prob- 

 lems on lilacs. Ascochyta has two 

 phases, a shoot blight in the spring 

 (which resembles bacterial shoot 

 blight) and a foliar phase during the 

 summer and fall. Dead shoots and 

 branches should be pruned prior to 

 bud-break and fungicides should be 

 applied. Thinning dense bushes will 

 also help reduce disease severity. 



Shoot blight, caused by the fun- 

 gus Monilinia, was widespread on 

 most ornamental Prunus species, 

 particularly flowering almonds and 

 cherries. This disease has been very 

 damaging for last several years, so 

 protective fungicide sprays may be 

 warranted on nursery stock and 

 valuable landscape specimens. Fungi- 

 cides should be first applied when 

 the blossoms open followed by a 

 second application ten days later. 

 Once again, dead shoots should be 

 removed before bud-break. 



Spruce that were infected with 

 rhizosphaera needlecast last year 

 should be treated with fungicides 



this spring. The first application 

 should be made when the new 

 needles are half-expanded. Rust 

 diseases were phenomenal in 1998, 

 particularly on cedar, juniper and 

 serviceberry (amelanchier). Most of 

 these rusts have a two-year life cycle, 

 but there are usually overlapping 

 populations of the fungus. Removal 

 of galls from cedars and junipers can 

 help, but it is usually more practical 

 to treat the deciduous host with 

 fungicides beginning just after bud- 

 break. 



HERBACEOUS ORNAMENTALS 

 Botrytis blight was the most signifi- 

 cant problem during June and early 

 July, particularly on bedding plants, 

 Asiatic lilies, and peonies. All plant 

 debris from last year's crop should 

 be removed before growth resumes 

 this spring. Plants should be spaced 

 adequately to allow for good air cir- 

 culation. Overhanging branches 

 from nearby trees should be pruned 

 to reduce shading and promote the 

 rapid drying of wet foliage. If over- 

 head irrigation is used, water early 

 in the day to allow the leaves to dry 

 prior to nightfall. Fungicides will be 

 necessary if we have periods of pro- 

 longed wet weather. Management of 

 leaf spot diseases is the same as that 

 of botrytis blight. 



Stem cankers caused by the fun- 

 gus Phytophthora was fairly common 

 on sedums. (The stems develop a 

 water-soaked lesion which quickly 

 collapses and rots.) The easiest 

 method for control of this disease is 

 to rogue out the infected plants as 

 soon as symptoms are seen. Fungi- 

 cides should be applied to the re- 

 maining plants if wet weather pre- 

 vails or overhead irrigation is used. 



FEBRUARY / MAKCH 1999 



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