AGNOSTIC UPDATE 



H 



folks! It looks like the unusual 

 .weather may be keeping some of 

 the pathogens at bay Sample num- 

 bers are down by approximately 30% 

 compared to the same time period 

 last year. Although I did expect a drop 

 in sample numbers due to the institu- 

 tion of the SI 2 fee in May. 1 believe 

 the lack of rainfall during late May and 

 June has provided less-than-optimal 

 conditions for fungal and bacterial dis- 

 eases (unless of course, you have 

 been providing overhead irrigation! 

 Most areas of New Hampshire are now 

 (early (ulyl experiencing various levels 

 of drought stress. During the last two 

 weeks of |une. I received several calls 

 regarding sudden leaf drop of 'healthy' 

 leaves from deciduous trees and 

 shrubs (maple, ash, blueberry) These 

 plants are shedding leaves in re- 

 sponse to drought stress One thing to 

 keep in mind is that drought stress, 

 like any stress factor, weakens a tree's 

 (or any plant's! defense mechanisms 

 leaving them more susceptible to at- 

 tack by pathogens and insect pests 

 Be sure to provide adequate water (if 

 practical) during prolonged dry periods 

 (2 weeks or more) Hopefully, by the 

 time you receive this issue, we will 

 have had a few days of steady rains 

 (of course, rain may favor some dis- 

 eases, but its a worthwhile trade-off). 



Some fairly interesting diseases 

 have arrived in the PDL during the last 

 two months Three diseases, bacterial 

 blight on forsythia, tomato bushy stunt 

 virus (TBSVi on tomato, and bacterial 

 leaf spot on Impatiens were diagnosed 

 for the first time (at least to my knowl- 

 edge) in the UNH-PDL. The bacterial 

 blight on forsythia is caused by the 

 same bacterium that causes bacterial 

 blight on lilac. The controls for the dis- 

 ease are the same on forsythia as for 

 lilac. The TBSV occurred on a few 

 plants in a crop of greenhouse toma- 

 toes. Control of TBSV, as with all vi- 

 ruses, is to remove and destroy the in- 

 fected plants The symptoms of bacte- 

 rial leaf spot on impatiens were black 

 lesions which were limited by the 

 veins Thus, some leaves almost ap- 

 peared to be striped ' Infected leaves 

 28 



were shed soon after infection. Control 

 is the same as for any bacterial dis- 

 ease: avoid wetting the foliage and re- 

 move infected leaves/plants. Another 

 interesting problem was damage to 

 several species of evergreens caused 

 by improperly applied Wilt Pruf. The 

 foliage was off-color (sort of a gray- 

 green! and some of the needles and 

 shoots were killed Upon closer exami- 

 nation, globular deposits of a wax-like 

 material were found on the twigs, 

 needles, and stems. In all cases, the 

 Wilt Pruf was applied very late in the 

 season (temperatures below the rec- 

 ommended 50 F!. 



On woody ornamentals, the major 

 problems during May and June were 

 bacterial blight on lilac, fire blight on 

 crabapples, and anthracnose on oak 

 and maple leaves Kabatina dieback 

 seems to be the major problem on ju- 

 nipers Symptoms look similar to 

 phomopsis tip blight, but the control 

 measures are slightly different, so a 

 confirmation of the diagnosis is recom- 

 mended Azalea leaf and flower gall, 

 which causes a whitish gall-like growth, 

 began showing up in mid-lune It is 

 also common on blueberries and rho- 

 dodendrons Another problem that was 

 extensive this May and ]une, although 

 not a disease, was arborvitae leaf 

 miner The symptoms look similar to 

 winter bum, but upon closer examina- 

 tion, the damaged tissues are hollow. 

 Tiny exit holes or insect frass may also 

 be evident Monilinia is once again 

 causing shoot blight on Prunus species. 

 The infections take place during 

 bloom, so that is the key time for fun- 

 gicide applications 



The only major problem on fruit 

 was the worst case of mummy berry 

 on blueberry that I have ever seen 

 Other problems included two samples 

 of fire blight on pears, and freeze in- 

 jury to the new growth on raspberries. 



The most common problems on 

 herbaceous plants were botrytis can- 

 kers and blights Botrytis canker was 

 very common on zinnia, fuchsia, and 

 rosemar>' Botrytis blight lor tulip fire! 

 caused problems on tulips during late 

 May and early lune. Now is the time 



to apply sanitation measures to clean 

 up the tulips and help prevent the dis- 

 ease for next year Impatiens necrotic 

 spot virus was diagnosed on a Tonga- 

 nese' geranium (this was another host 

 ■first' for the UNH-PDL! Other common 

 diseases included anthracnose (colleto- 

 trichum) on lupine, anthracnose on 

 poppy, and leaf spots on phlox Plant 

 bugs, particularly the four-lined plant 

 bug, have been causing a lot of dam- 

 age on ornamentals, herbs, and veg- 

 etables. The damage looks like leaf 

 spots, often aggregated on a single leaf 

 or several adjacent leaves. The four- 

 lined plant bug is a rather attractive 

 green-and-yellow striped critter. Plant 

 bugs may be controlled with one of 

 several insecticides (consult your rec- 

 ommendations or your county office). 



Red thread seemed to be a fairly 

 common problem on turf grasses this 

 spring. The disease pressure on turf 

 was relatively light during |une (com- 

 pared to last June! Symptoms of 

 drought stress are beginning to show 

 up in many areas. The typical summer 

 diseases — pythium, brown patch, and 

 leaf-spot have not been major prob- 

 lems due to the lack of moisture. An- 

 thracnose, however, has been showing 

 up on samples, probably due to the 

 moisture stress. 



One again, most of the diseases that 

 show up during May and lune will con- 

 tinue to pose potential problems dur- 

 ing August and September In addition, 

 powdery mildew (which is already evi- 

 dent on lilac and phlox! will become 

 more prevalent during )uly-September. 

 When we do get some rainfall, be 

 ready for pythium and brown patch to 

 cause turf problems Rhizosphaera 

 needlecast of spruce often has a sec- 

 ond infection period from late August 

 through early September. If you have 

 had a problem with the needlecast in 

 the past, you should apply a fungicide 

 at this time Slime molds begin to ap- 

 pear (literally overnight! in late August, 

 although I've already received a few 

 calls from worried homeowners A 

 strong water spray or shovel will get rid 

 of the mold. 

 Continued on page 27 



The Plantsman 



