AGNOSTIC UPDATE 



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Hazy, hot, and humid .did we 

 si<ip spring? Lii<e the saying 

 goes, if you don't iii<e the weather 

 in New England just wait a day and 

 it will change. We certainly went 

 from cool, cloudy weather to hot, 

 relatively dry weather in a short pe- 

 riod The hot weather brings with it 

 a new' set of seasonal problems. 



The high humidity favors many 

 fungal diseases. Although botrytis 

 prefers cooler temperatures, BOTRY- 

 TIS BLIGHT can be a significant 

 threat when the evening tempera- 

 tures are slightly cooler 155-70 F), 

 High humidity and warm evening 

 temperatures favor the develop- 

 ment of turf diseases such as 

 BROWN PATCH and PVTHUIM BLIGHT. 

 Luckily, the relatively low rainfall 

 has helped to keep a some of the 

 fungal diseases at bay, but they are 

 still there waiting for the right 

 moisture conditions! DROUGHT 

 STRESS symptoms are still very 

 common on nearly all woody orna- 

 mentals (and will continue to be for 

 the next year or two). Symptoms in- 

 clude tip dieback, small leaf and 

 needle size, marginal browning (ne- 

 crosis), and sudden wilting during 

 high-temperature periods. Hem- 

 locks and white pines are showing 

 significant needle yellowing and 

 browning as well as needle loss 

 due to drought stress and winter 

 desiccation. Drought-stressed trees 

 and shrubs are more susceptible to 

 winter injury and fungal tip blights 

 and cankers (to say nothing about 

 insect attack). 



Kabatina DIEBACK on junipers has 

 been the most common problem on 

 junipers during the last two months 



DiPLODIA (SPHAEROPSIS) TIP BLIGHT 

 has been a common problem on Aus- 

 trian and Scots pine CytospORA has 

 been isolated from small cankers on 

 maples and oaks. Although few 

 samples with ANTHRACNOSE have 

 been submitted to the PDL, there is 

 plenty of evidence of infections on 

 sycamores and ashes in the south- 



ern areas of New Hampshire (the 

 wet weather during leaf expansion 

 was ideal for infection). Elms are 

 showing symptoms of Dutch elm 

 DISEASE (DED), and many have died 

 since )une (DED is accelerated by 

 drought stress. The same pattern de- 

 veloped in the 1993 and 1996 grow- 

 ing seasons.) White birch, particularly 

 B. pendula cultivars, are again being 

 hit hard by BRONZE BIRCH BORERS 

 (drought-stressed trees are more 

 prone to attack). Check for the char- 

 acteristic raised areas beneath the 

 bark on the trunk and larger branches. 



Drought-stressed trees 



and shrubs are 



more susceptible to 



winter injury and 



fungal tip blights and 



cankers (to say nothing 



about insect attack). 



Many Prunus spp showed damage 

 this spring from SHOOT BLIGHT 

 caused by Monilinia laxa. For the last 

 several years, this fungus has 

 caused significant dieback on flow- 

 ering almond, cherry, and sour 

 cherry and this year was identified 

 on flowering quince REPEATING 

 SPRUCE RUST, a 'new' disease on 

 spruces, was confirmed on two 

 samples this spring. You can distin- 

 guish this rust from other spruce 

 rusts by noting the time of year the 

 rust pustules appear on the 

 needles. The orange pustules of re- 

 peating spruce rust appear just 

 prior to bud break. The pustules of 

 all other spruce rusts do not ap- 

 pear on the needles until mid-sum- 

 mer. A few other diseases have 

 also been common on woody orna- 

 mentals this season: PEACH LEAF 

 CURL; RHIZOSPHAERA NEEDLE BLIGHT 

 on firs; and LEAF and FLOWER GALL 

 on azalea. 



Brown patch is already evident 

 in some home lawns, thanks to the 

 warm, humid weather. AntHRACNOSE 

 seems to be a prevalent problem on 

 turfgrass, particularly on golf courses. 

 Summer patch is also starting to ap- 

 pear in home lawns Remember, 

 proper turf management goes a long 

 way towards preventing, or at least 

 reducing, turfgrass diseases Keep 

 thatch to no more than an inch, use 

 slow-release nitrogen fertilizer formu- 

 lations, keep mower blades sharp 

 and water deeply (1" per week). 



The major problem in green- 

 house crops was IMPATIENS NE- 

 CROTIC SPOT VIRUS (INSV), specifi- 

 cally on impatiens and New Guinea 

 impatiens. Suspect plants should 

 be isolated and infected plants 

 should be destroyed Thrips control 

 is critical for prevention and man- 

 agement of INSV. Bacterial leaf 

 SPOT on impatiens, caused by 

 Pseudomonas, was detected in two 

 samples. The leaf spots are tan 

 with a light center, or infections 

 may appear as dark, water-soaked 

 areas between the veins. Infected 

 plants should be destroyed 



The usual diseases, have begun 

 to appear on annuals and perennials. 

 SlerOTINIA stem rot was identified 

 on marigold, but has a very wide 

 host range. Sclerotinia is character- 

 ized by white, fluffy mold near the 

 base of the stem and hard black 

 sclerotia (they resemble rodent drop- 

 pings) that form on and in the col- 

 lapsed stems. Infected plants, as 

 well as soil surrounding the roots, 

 should be removed immediately. 

 The fungus is favored by high hu- 

 midity, so space or thin plants to 

 allow for adequate air circulation 

 BOYTRYTIS BLIGHT was diagnosed 

 on tulip (tulip fire), peony, and lily. 

 Plant bug feeding damage is al- 

 ready evident on a wide range of 

 plants. The damage, usually on the 

 upper third of the plant, looks like 

 clusters of orange leaf spots. When 

 the leaf is held up to the light, the 



24 



THE PLANTSMAN 



