June 9 2006.cdr
INSECTS
June 9,
2006
Issue 10
What's Hot!
Casey Sclar IPM Coordinator, Longwood Gardens LECANIUM SCALES. Two species of Lecanium scales are problematic in our landscapes and the next few weeks offer good management opportunities. Fletcher scale (Parthenolecanium fletcheri) affects a wide variety of coniferous plants such as Taxus, arborvitae, junipers, and even Taxodium spp.. European fruit lecanium (Parthenolecanium corni) affects a broad range of broadleaved woody plants such as redbud, hawthorn, dogwood, and oak. These soft scales appear like little brown lumps grouped along tree branches as adults. They feed in the phloem (on plant sap). Honeydew rain (clear sticky substance that is scale excrement) from the developing nymphs and adults of both species was noticeable in early May. A black fungus called sooty mold often grows on the honeydew. Lecanium scales have one generation per year. An adult female scale produces between 1000-3500 eggs. Penn-Del IPM Research group data reports eggs as early as May 9 and egg production from 319-1328 GDD (median=654) for European fruit lecanium. For Fletcher scale, eggs occurred as early as April 16 and egg (Continued)
DISEASES
For bagworm control, wait until hatch is more complete and you see the "dunce cap" stage or you will have to apply a product twice. Powdery mildew was diagnosed on a purplered leaved cultivar of ninebark, Physocarpus opulifolius. Unless severe pick-off infected leaves, powdery mildew rarely affects the health of the plant just its appearance. Control is usually easy with a number of fungicides labeled for powdery mildew (see previous issues). Look for red thread (coral red threads intertwined with the leaf blades) on turf after recent rains. Usually, no need for control but a preventative fungicide may be warranted if serious red thread has occurred in the past on a site. Sometimes a light fertilizer application 0.25-0.5 lb of actual nitrogen/1000 sq ft will help the turf grow out of the disease without any fungicide application.
Bob Mulrooney Extension Plant Pathologist
Honeylocust plant bug has been plentiful in the landscape this year.
DISEASE UPDATE. I have seen an increase of sycamore anthracnose this past week on native American sycamore with some accompanying leaf loss. Crabapple scab is increasing on susceptible cultivars. Cedar- apple rust on crabapple is very common. Phyllosticta leaf spot is everywhere on susceptible red and silver maples. It will infect box elder as well, but does not produce the red-brown rim around the spot.
Yucca plant bug has ravaged this “lowmaintenance” plant. New flushes of plant growth will obscure some of this damage in a few weeks.
DOGWOOD ANTHRACNOSE. Both anthracnose diseases of flowering dogwood, Cornus florida, can be found now. Spot anthracnose produces numerous small, less than 1/8 in. spots on the leaves. Discula anthracnose symptoms are irregular larger redbrown margined spots with tan to brown centers. It is not too late for fungicide applications for trees in locations prone to Discula anthracnose. Spot anthracnose usually does not necessitate control. Many commercial and homeowner fungicides are effective when applied preventatively. Kousa dogwoods are in bloom in the Newark area and are resistant to anthracnose and powdery mildew--while not the same tree, they offer a more disease-free choice as a flowering tree for the landscape. (Continued)
UNIVERSITY OF DELAWARE
Exobasidium gall has been found scattered on camellia and azalea. Scout and remove the large white masses from affected plants.
For more ion format n i on pests & practices covered in this Helpful numbers to know: Garden Line 831-8862 (for home gardeners only) New Castle County Extension 831-2506 Kent County Extension 730-4000 Sussex County Extension 856-7303
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.
Insects (Continued)
Diseases (Continued)
production from 171-1438 GDD (median=592). The crawler (hatchling nymph) stage for both species occurred about the same time. Earliest crawlers occurred about June 1 in our area with median crawler observations between 850-900 GDD. This number is rapidly approaching. The crawlers will migrate to the undersides of leaves/needles and spend the summer months there then migrate back to the branches to spend the fall and winter. They will resume growth, mate, and lay eggs the following spring. The settled crawler stage is the best time to control lecanium scales. Many insecticidal products are registered for this purpose but horticultural oils work quite well. Occasionally, a re-application is needed about 3 weeks after the initial application to ensure that all crawlers have emerged. Many naturally occurring parasites and predators often control lecanium scales, but parasites have been less active recently on a regional level. Still, many predators such as lady beetles feed on them. Insecticides sprayed later provide only limited effectiveness against nymphs and soil systemic insecticide applications must be properly timed.
GROWING DEGREE DAYS
AS OF J un e 5, 2 00 6
DAYLILY LEAFSTREAK, caused by the fungus, Aureobasidium, is just beginning to appear. Look for the long streaks of discolored tissue on the leaves of daylily. If it has been a problem in the past, try using fungicides such as Daconil, thiophanate-methyl (Cleary's 336 or Bonomyl), myclobutanil (Systhane, Eagle, Immunox), Heritage or Compass for control on a 14 day schedule from now until mid-July.
Editor: Susan Barton Extension Horticulturist
Fisch (New er Green h Cast le Co ouse unty ) = Rese 788 a ('05 = (Suss rch & Ed uc. C ex Co 5 62 ) enter unty , Geo )=N A ('0 rgeto 5=5 wn 90)
June 9,
2006
Issue 10
What's Hot!
Casey Sclar IPM Coordinator, Longwood Gardens LECANIUM SCALES. Two species of Lecanium scales are problematic in our landscapes and the next few weeks offer good management opportunities. Fletcher scale (Parthenolecanium fletcheri) affects a wide variety of coniferous plants such as Taxus, arborvitae, junipers, and even Taxodium spp.. European fruit lecanium (Parthenolecanium corni) affects a broad range of broadleaved woody plants such as redbud, hawthorn, dogwood, and oak. These soft scales appear like little brown lumps grouped along tree branches as adults. They feed in the phloem (on plant sap). Honeydew rain (clear sticky substance that is scale excrement) from the developing nymphs and adults of both species was noticeable in early May. A black fungus called sooty mold often grows on the honeydew. Lecanium scales have one generation per year. An adult female scale produces between 1000-3500 eggs. Penn-Del IPM Research group data reports eggs as early as May 9 and egg production from 319-1328 GDD (median=654) for European fruit lecanium. For Fletcher scale, eggs occurred as early as April 16 and egg (Continued)
DISEASES
For bagworm control, wait until hatch is more complete and you see the "dunce cap" stage or you will have to apply a product twice. Powdery mildew was diagnosed on a purplered leaved cultivar of ninebark, Physocarpus opulifolius. Unless severe pick-off infected leaves, powdery mildew rarely affects the health of the plant just its appearance. Control is usually easy with a number of fungicides labeled for powdery mildew (see previous issues). Look for red thread (coral red threads intertwined with the leaf blades) on turf after recent rains. Usually, no need for control but a preventative fungicide may be warranted if serious red thread has occurred in the past on a site. Sometimes a light fertilizer application 0.25-0.5 lb of actual nitrogen/1000 sq ft will help the turf grow out of the disease without any fungicide application.
Bob Mulrooney Extension Plant Pathologist
Honeylocust plant bug has been plentiful in the landscape this year.
DISEASE UPDATE. I have seen an increase of sycamore anthracnose this past week on native American sycamore with some accompanying leaf loss. Crabapple scab is increasing on susceptible cultivars. Cedar- apple rust on crabapple is very common. Phyllosticta leaf spot is everywhere on susceptible red and silver maples. It will infect box elder as well, but does not produce the red-brown rim around the spot.
Yucca plant bug has ravaged this “lowmaintenance” plant. New flushes of plant growth will obscure some of this damage in a few weeks.
DOGWOOD ANTHRACNOSE. Both anthracnose diseases of flowering dogwood, Cornus florida, can be found now. Spot anthracnose produces numerous small, less than 1/8 in. spots on the leaves. Discula anthracnose symptoms are irregular larger redbrown margined spots with tan to brown centers. It is not too late for fungicide applications for trees in locations prone to Discula anthracnose. Spot anthracnose usually does not necessitate control. Many commercial and homeowner fungicides are effective when applied preventatively. Kousa dogwoods are in bloom in the Newark area and are resistant to anthracnose and powdery mildew--while not the same tree, they offer a more disease-free choice as a flowering tree for the landscape. (Continued)
UNIVERSITY OF DELAWARE
Exobasidium gall has been found scattered on camellia and azalea. Scout and remove the large white masses from affected plants.
For more ion format n i on pests & practices covered in this Helpful numbers to know: Garden Line 831-8862 (for home gardeners only) New Castle County Extension 831-2506 Kent County Extension 730-4000 Sussex County Extension 856-7303
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.
Insects (Continued)
Diseases (Continued)
production from 171-1438 GDD (median=592). The crawler (hatchling nymph) stage for both species occurred about the same time. Earliest crawlers occurred about June 1 in our area with median crawler observations between 850-900 GDD. This number is rapidly approaching. The crawlers will migrate to the undersides of leaves/needles and spend the summer months there then migrate back to the branches to spend the fall and winter. They will resume growth, mate, and lay eggs the following spring. The settled crawler stage is the best time to control lecanium scales. Many insecticidal products are registered for this purpose but horticultural oils work quite well. Occasionally, a re-application is needed about 3 weeks after the initial application to ensure that all crawlers have emerged. Many naturally occurring parasites and predators often control lecanium scales, but parasites have been less active recently on a regional level. Still, many predators such as lady beetles feed on them. Insecticides sprayed later provide only limited effectiveness against nymphs and soil systemic insecticide applications must be properly timed.
GROWING DEGREE DAYS
AS OF J un e 5, 2 00 6
DAYLILY LEAFSTREAK, caused by the fungus, Aureobasidium, is just beginning to appear. Look for the long streaks of discolored tissue on the leaves of daylily. If it has been a problem in the past, try using fungicides such as Daconil, thiophanate-methyl (Cleary's 336 or Bonomyl), myclobutanil (Systhane, Eagle, Immunox), Heritage or Compass for control on a 14 day schedule from now until mid-July.
Editor: Susan Barton Extension Horticulturist
Fisch (New er Green h Cast le Co ouse unty ) = Rese 788 a ('05 = (Suss rch & Ed uc. C ex Co 5 62 ) enter unty , Geo )=N A ('0 rgeto 5=5 wn 90)
