August 22 2008
INSECTS
August 22, 2008
Issue 20
Casey Sclar IPM Coordinator, Longwood Gardens
FALL WEBWORM. This year is another “epic” performance by Fall Webworm (Hyphantria cunea) for best defoliation and webbing by a caterpillar. The characteristic “ghostly webs” are on branch terminals everywhere hickory, pecan, black cherry, but especially mulberry and mountain ash. Over 88 tree species have been noted in the USA as being susceptible.
What's Hot! The dry weather is beginning to cause tulip poplars to loose leaves. Look for the oldest leaves to turn yellow and drop. This is a normal drought response for these trees.
There are two generations per year. The white adults emerged and laid eggs earlier this year after overwintering as a cocoon in soil or debris. It usually takes approximately 6 weeks for full larval development, and the maturity of the second generation is definitely upon us. The larvae are yellow with white hairs when young. Once more mature, their hairs will be longer and come from orange or black spots so larval appearance will vary. These caterpillars have either a black or red head. There are actually two “races” of this pest in our region thus the difference in larval appearance. The caterpillars usually feed together in the same tent, but wander once older.
In general, diseases are hard to find in the landscape at the present time because of the prolonged dry weather. Powdery mildews are probably the exception; they thrive in dry weather as long as there is enough humidity for their growth.
Scouting for and pruning out small webs is a good option. At this point, it may be best to prune out this year's infestations and avoid spraying for it entirely. Damage from fall webworm is cyclical and reaches its peak once every four years or so. Several birds, wasps, yellowjackets, and other parasites will feed on them. Spraying through the large webs has limited effectiveness even with broad spectrum contact pesticides and coverage will be an issue. B.t. is not a good option against mature caterpillars and has had limited effectiveness against fall webworm for us. Plus, you'll still have the webs to deal with anyway. The damage is mainly aesthetic.
WINTER ANNUAL WEED CONTROL IN LANDSCAPE BEDS. Apply premergence herbicides to control winter annual weeds in landscape beds before the end of August. Common winter annuals include chickweed, henbit, purple deadnettle, field violet, annual speedwells and mustard family weeds including bittercress. Winter annual grasses include annual bluegrass, annual ryegrass, and downy brome. Several short lived perennials and biennials will also be germinating at this time such as mouseear chickweed and marestail (horseweed). OH2 and Rout are examples of preemergence materials highly effect in landscapes on mustard family weeds, speedwells, Lamiums (henbit
DISEASES Bob Mulrooney Extension Plant Pathologist
Nancy Gregory Plant Diagnostician
SOUTHERN BLIGHT OF HOSTA, caused by Sclerotium rolfsii, was diagnosed in the clinic last week. This can be a serious disease in the garden and is very difficult to control. Symptoms include yellowing, browning and wilt beginning on lower leaves. Petioles and stems may rot and fall over at the base. White mats of the fungus may be seen, but the overwintering structures of the fungus called sclerotia are very diagnostic. The small round sclerotia turn from white to yellow to brown and are sometimes compared to mustard seeds. The sclerotia will form at the base of the petioles or on debris in the soil, and are very resistant and persistent in soil. The best control is prevention; inspect all new plants to be sure that they are free of symptoms. If S. rolfsii is present, sanitation is important, remove infected plants and the surrounding soil, being careful not to let the sclerotia fall onto (Continued)
UNIVERSITY OF DELAWARE
WEEDS Gordon Johnson Agricultural Agent, Kent County
(Continued)
Fornfomromrae tion i
on pests & practices covered in this newsletter, call your County Extension Office 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
View pictures at http://ornamental diagnostics.blogspot.com/
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)
Weeds (Continued)
non-infested soil. There are no chemical controls labeled for home use, so a professional may need to be consulted to treat areas larger than a single plant. Southern blight is a disease that infects many annuals, perennials and vegetables.
and purple deadnettle), horseweed, and annual bluegrass. They are weak however on chickweed which is better controlled with herbicides containing isoxaben (Snapshot, Gallery), pendamethalin (Pendulum, others), trifluralin (Snapshot, others), or prodiamine (Barricade). Preemergence herbicides can be effective in reducing late summer germinating winter annuals; however, many of these weeds germinate from fall through spring requiring long residual materials or repeat applications. Check with each product label for compatibility with specific landscape plants and efficacy on specific winter annual weeds.
FOLIAR NEMATODE. In spite of the current dry spell, symptoms of foliar nematodes were observed on windflower, Anemone x hybrida 'September Charms'. Foliar symptoms are distinctive on many perennials including hosta, ferns, peony and others. Look for yellow to brown discolored areas on the leaves bordered by the leaf vein pattern. Symptoms will be evident from now through the fall. Fortunately foliar nematodes do little harm to plant health, but can make perennials fade faster. An infested hosta planting can look very unthrifty. If only a few leaves are infected, picking and destroying them is best. There are no labeled pesticides for foliar nematodes in the landscape. Often foliar nematode injury is misdiagnosed as premature senescence.
Editor: Susan Barton Extension Horticulturist
Cooperative Extension Townsend Hall Newark, Delaware 19717
GROWI DAYS DAESGORF EAuEgust 18, 2008 NG
4 5) = 26 ('06 e ous ) = NA wn y enh geto) Gre Count eor her e r, G 2590 Fisc Castl = ente w c. C A ('06 (Ne N Edu h & nty) = u earc Res sex Co ( Su s
August 22, 2008
Issue 20
Casey Sclar IPM Coordinator, Longwood Gardens
FALL WEBWORM. This year is another “epic” performance by Fall Webworm (Hyphantria cunea) for best defoliation and webbing by a caterpillar. The characteristic “ghostly webs” are on branch terminals everywhere hickory, pecan, black cherry, but especially mulberry and mountain ash. Over 88 tree species have been noted in the USA as being susceptible.
What's Hot! The dry weather is beginning to cause tulip poplars to loose leaves. Look for the oldest leaves to turn yellow and drop. This is a normal drought response for these trees.
There are two generations per year. The white adults emerged and laid eggs earlier this year after overwintering as a cocoon in soil or debris. It usually takes approximately 6 weeks for full larval development, and the maturity of the second generation is definitely upon us. The larvae are yellow with white hairs when young. Once more mature, their hairs will be longer and come from orange or black spots so larval appearance will vary. These caterpillars have either a black or red head. There are actually two “races” of this pest in our region thus the difference in larval appearance. The caterpillars usually feed together in the same tent, but wander once older.
In general, diseases are hard to find in the landscape at the present time because of the prolonged dry weather. Powdery mildews are probably the exception; they thrive in dry weather as long as there is enough humidity for their growth.
Scouting for and pruning out small webs is a good option. At this point, it may be best to prune out this year's infestations and avoid spraying for it entirely. Damage from fall webworm is cyclical and reaches its peak once every four years or so. Several birds, wasps, yellowjackets, and other parasites will feed on them. Spraying through the large webs has limited effectiveness even with broad spectrum contact pesticides and coverage will be an issue. B.t. is not a good option against mature caterpillars and has had limited effectiveness against fall webworm for us. Plus, you'll still have the webs to deal with anyway. The damage is mainly aesthetic.
WINTER ANNUAL WEED CONTROL IN LANDSCAPE BEDS. Apply premergence herbicides to control winter annual weeds in landscape beds before the end of August. Common winter annuals include chickweed, henbit, purple deadnettle, field violet, annual speedwells and mustard family weeds including bittercress. Winter annual grasses include annual bluegrass, annual ryegrass, and downy brome. Several short lived perennials and biennials will also be germinating at this time such as mouseear chickweed and marestail (horseweed). OH2 and Rout are examples of preemergence materials highly effect in landscapes on mustard family weeds, speedwells, Lamiums (henbit
DISEASES Bob Mulrooney Extension Plant Pathologist
Nancy Gregory Plant Diagnostician
SOUTHERN BLIGHT OF HOSTA, caused by Sclerotium rolfsii, was diagnosed in the clinic last week. This can be a serious disease in the garden and is very difficult to control. Symptoms include yellowing, browning and wilt beginning on lower leaves. Petioles and stems may rot and fall over at the base. White mats of the fungus may be seen, but the overwintering structures of the fungus called sclerotia are very diagnostic. The small round sclerotia turn from white to yellow to brown and are sometimes compared to mustard seeds. The sclerotia will form at the base of the petioles or on debris in the soil, and are very resistant and persistent in soil. The best control is prevention; inspect all new plants to be sure that they are free of symptoms. If S. rolfsii is present, sanitation is important, remove infected plants and the surrounding soil, being careful not to let the sclerotia fall onto (Continued)
UNIVERSITY OF DELAWARE
WEEDS Gordon Johnson Agricultural Agent, Kent County
(Continued)
Fornfomromrae tion i
on pests & practices covered in this newsletter, call your County Extension Office 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
View pictures at http://ornamental diagnostics.blogspot.com/
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)
Weeds (Continued)
non-infested soil. There are no chemical controls labeled for home use, so a professional may need to be consulted to treat areas larger than a single plant. Southern blight is a disease that infects many annuals, perennials and vegetables.
and purple deadnettle), horseweed, and annual bluegrass. They are weak however on chickweed which is better controlled with herbicides containing isoxaben (Snapshot, Gallery), pendamethalin (Pendulum, others), trifluralin (Snapshot, others), or prodiamine (Barricade). Preemergence herbicides can be effective in reducing late summer germinating winter annuals; however, many of these weeds germinate from fall through spring requiring long residual materials or repeat applications. Check with each product label for compatibility with specific landscape plants and efficacy on specific winter annual weeds.
FOLIAR NEMATODE. In spite of the current dry spell, symptoms of foliar nematodes were observed on windflower, Anemone x hybrida 'September Charms'. Foliar symptoms are distinctive on many perennials including hosta, ferns, peony and others. Look for yellow to brown discolored areas on the leaves bordered by the leaf vein pattern. Symptoms will be evident from now through the fall. Fortunately foliar nematodes do little harm to plant health, but can make perennials fade faster. An infested hosta planting can look very unthrifty. If only a few leaves are infected, picking and destroying them is best. There are no labeled pesticides for foliar nematodes in the landscape. Often foliar nematode injury is misdiagnosed as premature senescence.
Editor: Susan Barton Extension Horticulturist
Cooperative Extension Townsend Hall Newark, Delaware 19717
GROWI DAYS DAESGORF EAuEgust 18, 2008 NG
4 5) = 26 ('06 e ous ) = NA wn y enh geto) Gre Count eor her e r, G 2590 Fisc Castl = ente w c. C A ('06 (Ne N Edu h & nty) = u earc Res sex Co ( Su s
