A G N O S T 



UPDATE 



It looks like mother nature has 

 decided to give us a little (I 

 emphasize "little") reprieve from 

 the drought! It rained for the first 

 time in a month last night (9/7), 

 and more is predicted for the next 

 24 hours. Needless to say, the 

 drought in the Northeast is a hot 

 topic (no pun intended). During the 

 last three weeks, I have been seeing 

 increasing symptoms of drought 

 stress on all plant material that has 

 not received supplemental water. 

 There are several symptoms of 

 drought stress now evident besides 

 the obvious symptoms of wilting, 

 marginal burning, and reductions in 

 growth and yield. Many plants are 

 showing nutrient deficiency symp- 

 toms because the nutrients are un- 

 available for absorption by plant 

 roots without sufficient soil moisture. 

 Many trees and shrubs have chlo- 

 rotic leaves and premature leaf drop 

 is evident in most species. Although 

 the yellowing and shedding of the 

 older needles of conifers is normal 

 in the fall, more than one year's 

 complement of needles will be shed 

 by trees under drought stress. The 

 younger needles will turn reddish- 

 brown. Additional symptoms on 

 woody plants may include twig die- 

 back and cracks in the stems and 

 trunks. Shrinking of the stems is also 

 common with herbaceous plants An- 

 other, often over-looked, problem 

 associated with drought is over-wa- 

 tering. In several instances, recently 

 transplanted material has been over- 

 watered. 



It is important to keep in mind 

 that a prolonged drought usually has 

 long-term (2-3 years) effects on plant 

 health. Drought-stressed plants are 

 more susceptible to diseases, in- 

 sects, and winter injury. For instance, 

 powdery mildew will have more of 

 an impact than usual this year be- 

 cause the fungus draws moisture 

 (what little there is) from the leaves. 

 Spider mite populations have ex- 

 ploded this summer due to the hot, 

 dry conditions. Many conifers appear 

 "bronzed" due to spider mite feed- 

 October & November 1995 



It IS important to keep in mind 



that a prolonged drought usually has 



long-term (2-3 years) effects 



on plant health. Drought stressed 



plants are more susceptible to 



diseases, insects, and winter injury. 



ing damage. A good source of addi- 

 tional information on the effects of 

 drought on trees and shrubs can be 

 found in an article by Robert Childs 

 and Melissa Castonguay in the Au- 

 gust 10, 1995, issue of Tree News 

 (UMass). 



Although the drought is, and will 

 continue to be, the major plant 

 health problem during the 1995 

 growing season, there were a few 

 other problems during June and July 

 as well. We may not have had much 

 rain, but we certainly had high hu- 

 midity for much of the summer. 

 Botrytis was a problem on most her- 

 baceous plants Botrytis stem can- 

 kers were common, and flowers were 

 particularly hard-hit where overhead 

 irrigation was used. Several cases of 

 fusarium stem rot of delphinium 

 and one case of fusarium wilt of 

 chrysanthemum were diagnosed. 

 Plant bug feeding injury was very 

 prevalent during July on a wide 

 range of herbaceous plants. Plant 

 bugs typically cause brown or tan 

 necrotic spots, often several in a lo- 

 calized area, that have a darker 

 "dot" in the center (the actual feed- 

 ing site). The feeding usually occurs 

 near the top of the plants. Spider 

 mites and aphids have also caused 

 problems on a wide range of hosts. 



Viruses have been more prevalent 

 this year than in recent years, partly 

 due to the increase in insect pres- 

 sure. Viruses diagnosed included 

 peony ring spot on peony, tomato 

 spotted wilt and tomato mosaic on 

 tomato, and watermelon mosaic-2 

 and squash mosaic on cucurbits An- 

 gular leaf spot, a bacterial disease, 

 was diagnosed on melons and 

 pumpkins. Rainy periods and over- 

 head irrigation help to spread the 

 angular leaf spot bacterium. 



The usual summer diseases on 

 turf, brown patch and pythium, have 

 not been as much of a problem this 

 summer because of the lack of mois- 

 ture. We haven't escaped unscathed, 

 however. Heat and drought stress 

 have been a primary problem, par- 

 ticularly on shallow or sandy soils. 

 Anthracnose is a common problem 

 on stressed turf Summer patch was 

 diagnosed on three turf samples in 

 the last month, and one case of 

 take-all was diagnosed in July. 



Diplodia tip blight was diagnosed 

 on scotts and Austrian pine. Several 

 juniper samples were received with 

 kabatina twig blight and one with 

 phomopsis tip blight The honey lo- 

 custs have taken a beating this year 

 from honey locust plant bugs and 

 gall midges. 



What can we look forward to in 

 the next couple of months? Certainly 

 we can expect the development of 

 more problems associated with the 

 drought. If we get several periods of 

 rain, we can expect some of the turf 

 diseases such as brown patch, leaf 

 spot, and pythium to occur. Remem- 

 ber that late autumn is the key time 

 for fungicide control of snow mold 

 on turf. Now is the time to 

 apply fungicides for control of rhizo- 

 sphaera needlecast on spruce 



If you are growing snapdragons, 

 be sure to scout the crop and get a 

 fungicide on at the first sign of gray 

 fungal growth on the undersides of 

 the leaves. The lower leaves of poin- 

 settias should also be examined 

 regularly for powdery mildew. Look 

 for small chlorotic or yellow lesions 

 on the upper surface of the lower 

 leaves, then check the underside for 

 the white to gray growth of the fun- 

 gus. It is good practice to carry a 

 small zip-loc bag around to put in- 

 fected or suspicious leaves in. If any 

 powdery mildew infections are 

 found, fungicides should be applied 

 immediately — be sure to get good 

 coverage on the undersides of the 

 leaves. 



The most important thing to con- 

 sider during the next two months is 



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