AGNOSTIC 



UPDATE 



Well, it certainly looks like 

 the plant pathogens have 

 been busy during the 

 months of May and June, as well as 

 the early part of luly. The number 

 of sannples submitted to the lab 

 doubled between May and )une 

 Although typical spring and sum- 

 mer diseases of field-grown orna- 

 mentals are beginning to show up 

 in the lab, a few diseases contin- 

 ued to plague greenhouse opera- 

 tions. Botrytis and pytfiium became 

 more problematic as the tempera- 

 tures (and humidity) increased, and 

 three additional cases of bacterial 

 blight of geranium were confirmed in 

 May (see the diagnostic update in 

 the lune/july issue). 



Symptoms of early winter dam- 

 age began to appear shortly after 

 our first hot spell in lune. Woody 

 shrubs and small trees, particularly 

 those planted within the last two 

 years, began to leaf-out; then the 

 leaves suddenly wilted during the 

 hot weather. The injured tissue is 

 usually at the soil line. The dam- 

 age likely occurred during the first 

 few bouts of freezing temperatures, 

 before we had any significant snow- 

 cover. Since 1 mentioned snow, it 

 seems appropriate to discuss snow 

 molds on turf Snow molds were the 

 most frequently diagnosed dis- 

 eases on turf samples received in 

 the Diagnostic Lab during May and 

 early June. The more 'typical' 

 warm-weather turf diseases, such as 

 brown patch, pythium. and leaf spot 

 (helminthesporium) have begun to 

 show up in the last three weeks 

 throughout the southern half of the 



state. In addition, anthracnose and 

 ascockyta leaf blight is showing up on 

 turf that was stressed by last 

 summer's drought. 



The shoot blight phase of brown 

 rot (monilinia) was a problem on 

 Prunus species again this spring, 

 particularly flowering almond and 

 ornamental cherries. The symptoms 

 are usually blighted blossoms, but 

 in severe cases, entire twigs may 

 be killed. Crabapples have been 

 hit hard by apple scab this spring. 

 The youngest 7-to-8 leaves on a 

 shoot are often completely blighted, 

 and in severe cases defoliation has 

 already begun. Sanitation (removal 

 of infected leaves after they fall in 

 the autumn) is a very effective 

 means of control for apple scab. 

 Numerous cases of anthracnose on 

 maples and ash have been diag- 

 nosed in the lab in the last few 

 weeks. During my recent travels 

 around the southern part of the 

 state, I have noticed significant 

 twig death and dieback on sy- 

 camore trees that were hit with an- 

 thracnose last year. I haven't yet re- 

 ceived any sycamore samples this 

 year, so hopefully we've escaped 

 at least one problem. 



Botrytis blight and leaf spots have 

 been showing up on annuals and 

 perennials for the last few weeks 

 During the last week of )une, two 

 cases of fusarium wilt were diag- 

 nosed on china asters. The fungus 

 is soil-borne and may also be 

 seed-borne. The symptoms of the 

 disease include stunted growth (of- 

 ten one-sided), wilt, and black 

 streaks that extend up the stem 



from the soil line. Infected plants 

 should be removed and destroyed 

 (do not compost them). 



Most of the diseases we are see- 

 ing now will continue to plague us 

 for the rest of the growing season. 

 Hazy, hot. and humid weather (af- 

 fectionately called the three H's' 

 by the weather forecasters) will fa- 

 vor brown patch and pythium on turf, 

 botrytis blight, and the progression 

 of wilt diseases (such as Dutch elm 

 disease and verticillium) By the be- 

 ginning of August, powdery mildews 

 should be appearing on a wide 

 range of hosts (I have already seen 

 some growth on a few lilacs around 

 campus). Sanitation in the autumn 

 is also effective in reducing the in- 

 cidence of powdery mildew. If our 

 summer is hot and dry, as it was 

 last year, expect to see spider mite 

 feeding damage on a wide range of 

 hosts. Many conifer species were 

 particularly hard-hit by spider 

 mites last summer To check for 

 mites, place a white piece of paper 

 beneath a branch and tap the 

 branch a few times, if the specks 

 on the paper begin to crawl around 

 you have a potential mite problem. 

 If you wish to submit plant material to 

 the PDL for diagnosis, send samples to. 

 Dr. Cheryl Smith, Plant Diagnostic Lab. 

 Nesmith Hall. UNH, Durham, NH 

 03824. Samples should be accompanied 

 by an identification form [available from 

 your county Cooperative Extension office). 

 There is no fee {at this time] Cheryl 

 Smith is the UNH Cooperative Extension 

 Specialist in Plant Health, and can be 

 reached at (603) 862-3841 



The More You Qdw, The More You Know. 



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AUGUST /SEPTEMBER 1994 



