Issue 16
July 13,
INSECTS
2012
Issue 16
Casey Sclar Plant Health Care Division Leader, Longwood Gardens
What's Hot!
ELONGATE HEMLOCK SCALE. No scale insect is more frustrating than elongate hemlock scale, Fiorinia externa (EHS). It is a major threat to conifers in our landscapes. Hemlock (Tsuga), fir (Abies), douglas fir (Pseudotsuga), spruce (Picea), and cedar (Cedrus) may be infested. Damage from feeding causes eventual needle drop and branch dieback, beginning at the lower branches and progressing upward. There is no honeydew produced.
A recent reader question about controlling weeds in a large daylily bed prompted the following suggestions:
This is the scale insect that breaks all the rules-it has no set “crawler” periods in our climate and overwinters in the egg, nymph, or adult stage. Retired Entomologist Jim Stimmel (PA Dept. of Ag.) observed that development resumed with warmer weather in early spring and stopped only after prolonged cold. The use of GDD's or plant phenology to predict crawler emergence with EHS is simply futile. Further work indicates EHS developed an increased cold tolerance, which assisted their northward spread. Brown, 1.0 mm long oval shells house the adult females; male “pupal cases” are slightly shorter, white and oystershell-shaped. Minute non-feeding winged adult males emerge to mate and die. Eggs are contained and hatch from within the female shell cover and crawl out through a one-way flap at its rear. The orange crawlers quickly settle, molt, and develop. Adult females are completely protected within their hard shell; only their mouthparts protrude through its bottom to feed. These shells remain on the plant after the females have died, so detailed scouting to ensure that infestations are active is very important. Biological control does not provide meaningful suppression of EHS. Rarely encountered are a small lady beetle, Cybocephalus nipponicus and the fungus Aschersonia marginata. Several different researchers have investigated EHS management, and few come up with consistent results. Safari (dinotefuran) drenches showed promise in Connecticut studies and seem to be the most consistent. Remember that some neonicotinoid applications may lead to mite outbreaks a concern for hemlocks.
DISEASES
(Continued)
Use a preemergent in the spring to reduce the number of annual grass and broadleaf weeds. Use products containing trifluralin, dithopyr, isoxaben, prodiamine, pendimethaline, metolachlor and oryzalin. You can control emerged grasses over the top with clethodim and sethoxydim. Finally, you can use a directed spray of glyphosate to control emerged weeds but you should protect the daylilies, possibly with a piece of cardboard, to keep the spray from contacting daylily foliage. Handpulling is also an option, but be sure to get all the plant parts. Insects (Continued) University of Maryland saw suppression of EHS using spring applications of horticultural oil, Merit (imidacloprid) soil drenches, and Distance (pyriproxifen). Previous work at Longwood had great results with October applications of 2% v:v horticultural oil, while Merit soil drenches and Distance sprays were ineffective. PSU work by the late Paul Heller showed that spring applications of a dozen materials in Christmas Trees were largely ineffective, with the exception of Cygon (dimethoate). Bottom line choose products selective against armored scales, and maybe wait until fall for any oil applications.
Fornfomromrae tion i
on pests & practices covered in this newsletter, call your County Extension Office
Nancy Gregory Plant Diagnostician POWDERY MILDEW has been observed on several woody ornamentals in the UDBG this week. Powdery mildew on Leucothoe is common in warm, relatively dry, but humid conditions. Plants in shady sites tend to have more powdery mildew due to the higher humidity there. Leaf symptoms include blotches that turn brown to reddish, with mycelium and spores on the lower or
Helpful numbers to know: Garden Line (for home gardeners only) New Castle County Extension Kent County Extension Sussex County Extension
831-8862 831-2506 730-4000 856-7303
(Continued)
UNIVERSITY OF DELAWARE
COOPERATIVE EXTENSION
Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. Janice A. Seitz, Director. Distributed in furtherance of Acts of Congress of March 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin.
Diseases (Continued) upper leaf surface. To control, rake up fallen leaves and discard, and trim shrubs to increase air circulation. At the first symptoms and signs, fungicides such as thiophanate-methyl may be applied, according to the label. Neem oil and potassium bicarbonate salts may also offer some control if applied when symptoms are first observed. Powdery mildew has also been observed on crape myrtle, mostly on the new growth and flower buds. The fungal species of Erysiphe is specific to Lagerstroemia, and probably overwinters in leaf buds, so trimming in the early spring may reduce infection. As above, powdery mildew is favored by relatively dry and warm weather, with high humidity. Control includes selective pruning to increase air circulation, and fungicides when symptoms first appear, according to label directions and rates. FOLIAR NEMATODES. I have not seen symptoms of foliar nematodes on Leucothoe since it has been so dry; they need a film of water to travel on the plant. Editor: Susan Barton Extension Horticulturist
67 =1 (’ 11
G N I W GREGOREE DAYS D
, 2 01 2 0 1 y l Ju AS OF
5)
0 1 72 ge ) olle , PA) = 6 56 C =1 y re t o 1 n m Cou '1 rth 5 ( Swa laware use ) = 171 wn o h eto n (De org 848) ree ounty e G G r, 1 = 1 her le C nte 1 Fisc w Cast . C e 19 (' c e u 7 d (N 1 E = & ch unty) ear o Res sex C s ( Su
INSECTS
2012
Issue 16
Casey Sclar Plant Health Care Division Leader, Longwood Gardens
What's Hot!
ELONGATE HEMLOCK SCALE. No scale insect is more frustrating than elongate hemlock scale, Fiorinia externa (EHS). It is a major threat to conifers in our landscapes. Hemlock (Tsuga), fir (Abies), douglas fir (Pseudotsuga), spruce (Picea), and cedar (Cedrus) may be infested. Damage from feeding causes eventual needle drop and branch dieback, beginning at the lower branches and progressing upward. There is no honeydew produced.
A recent reader question about controlling weeds in a large daylily bed prompted the following suggestions:
This is the scale insect that breaks all the rules-it has no set “crawler” periods in our climate and overwinters in the egg, nymph, or adult stage. Retired Entomologist Jim Stimmel (PA Dept. of Ag.) observed that development resumed with warmer weather in early spring and stopped only after prolonged cold. The use of GDD's or plant phenology to predict crawler emergence with EHS is simply futile. Further work indicates EHS developed an increased cold tolerance, which assisted their northward spread. Brown, 1.0 mm long oval shells house the adult females; male “pupal cases” are slightly shorter, white and oystershell-shaped. Minute non-feeding winged adult males emerge to mate and die. Eggs are contained and hatch from within the female shell cover and crawl out through a one-way flap at its rear. The orange crawlers quickly settle, molt, and develop. Adult females are completely protected within their hard shell; only their mouthparts protrude through its bottom to feed. These shells remain on the plant after the females have died, so detailed scouting to ensure that infestations are active is very important. Biological control does not provide meaningful suppression of EHS. Rarely encountered are a small lady beetle, Cybocephalus nipponicus and the fungus Aschersonia marginata. Several different researchers have investigated EHS management, and few come up with consistent results. Safari (dinotefuran) drenches showed promise in Connecticut studies and seem to be the most consistent. Remember that some neonicotinoid applications may lead to mite outbreaks a concern for hemlocks.
DISEASES
(Continued)
Use a preemergent in the spring to reduce the number of annual grass and broadleaf weeds. Use products containing trifluralin, dithopyr, isoxaben, prodiamine, pendimethaline, metolachlor and oryzalin. You can control emerged grasses over the top with clethodim and sethoxydim. Finally, you can use a directed spray of glyphosate to control emerged weeds but you should protect the daylilies, possibly with a piece of cardboard, to keep the spray from contacting daylily foliage. Handpulling is also an option, but be sure to get all the plant parts. Insects (Continued) University of Maryland saw suppression of EHS using spring applications of horticultural oil, Merit (imidacloprid) soil drenches, and Distance (pyriproxifen). Previous work at Longwood had great results with October applications of 2% v:v horticultural oil, while Merit soil drenches and Distance sprays were ineffective. PSU work by the late Paul Heller showed that spring applications of a dozen materials in Christmas Trees were largely ineffective, with the exception of Cygon (dimethoate). Bottom line choose products selective against armored scales, and maybe wait until fall for any oil applications.
Fornfomromrae tion i
on pests & practices covered in this newsletter, call your County Extension Office
Nancy Gregory Plant Diagnostician POWDERY MILDEW has been observed on several woody ornamentals in the UDBG this week. Powdery mildew on Leucothoe is common in warm, relatively dry, but humid conditions. Plants in shady sites tend to have more powdery mildew due to the higher humidity there. Leaf symptoms include blotches that turn brown to reddish, with mycelium and spores on the lower or
Helpful numbers to know: Garden Line (for home gardeners only) New Castle County Extension Kent County Extension Sussex County Extension
831-8862 831-2506 730-4000 856-7303
(Continued)
UNIVERSITY OF DELAWARE
COOPERATIVE EXTENSION
Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. Janice A. Seitz, Director. Distributed in furtherance of Acts of Congress of March 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin.
Diseases (Continued) upper leaf surface. To control, rake up fallen leaves and discard, and trim shrubs to increase air circulation. At the first symptoms and signs, fungicides such as thiophanate-methyl may be applied, according to the label. Neem oil and potassium bicarbonate salts may also offer some control if applied when symptoms are first observed. Powdery mildew has also been observed on crape myrtle, mostly on the new growth and flower buds. The fungal species of Erysiphe is specific to Lagerstroemia, and probably overwinters in leaf buds, so trimming in the early spring may reduce infection. As above, powdery mildew is favored by relatively dry and warm weather, with high humidity. Control includes selective pruning to increase air circulation, and fungicides when symptoms first appear, according to label directions and rates. FOLIAR NEMATODES. I have not seen symptoms of foliar nematodes on Leucothoe since it has been so dry; they need a film of water to travel on the plant. Editor: Susan Barton Extension Horticulturist
67 =1 (’ 11
G N I W GREGOREE DAYS D
, 2 01 2 0 1 y l Ju AS OF
5)
0 1 72 ge ) olle , PA) = 6 56 C =1 y re t o 1 n m Cou '1 rth 5 ( Swa laware use ) = 171 wn o h eto n (De org 848) ree ounty e G G r, 1 = 1 her le C nte 1 Fisc w Cast . C e 19 (' c e u 7 d (N 1 E = & ch unty) ear o Res sex C s ( Su
