May 14 2004.Cdr
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INSECTS May 14, 2004 Issue 7 Derby Walker Extension Agent What's Hot! BOXWOOD PESTS. Boxwood leaf miner adults are emerging from As temperature increases, so does the their pupa and the gnat-like flies will soon be laying eggs into the possibility of spray burn. Material undersides of young leaves. The eggs will hatch in about three selection, formulation, time of day, plant weeks. Females, on average, lay 29 eggs and perish soon condition and plant sensitivity determine afterwards. There is only one generation per year. The mines will the magnitude of risk. Leaves are more be evident in a few weeks. Infested leaves are spotted yellow and sensitive when high temperatures and high may drop off the plant early. The mines or blisters will become humidity follow cool and cloudy more obvious as the larvae increase in size. The larvae pupate in conditions. Check the label for guidance. the mine and will emerge next spring. Continuous infestation may kill twigs and weaken the plants making them more prone to There still is evidence of winter damage in disease problems. Malathion, Merit, Marathon, Conserve and the UDBG on several hosts that generally Cygon all have labels for boxwood leaf miners. do not display winter injury. Common China fir, Cunninghamia lanceolata, has Also look for boxwood psyllid nymphs, which hatch as soon as the dead branch tips and browned foliage. buds open in the spring. The eggs were laid last summer in the Virginia sweetspire, Itea virginica, has bud scales. As the nymphs develop, the leaves become cupped quite a bit of branch or twig dieback that protecting several nymphs. Marathon, Merit and Orthene will appears to be winter related. Prune back to control psyllids. Also insecticidal soaps, neem oil, or azadirachtin new green leaves and discard the prunings. (derived from neem) can be used for control. Aphids have been spotted on spirea in DISEASES Newark. Birches have a large yellow aphid (Hamamelistes spinosus) feeding on leaf Bob Mulrooney Extension Plant Pathologist undersides. Infested birch leaves look corrugated with aphids packed into every FORSYTHIA. Twig blight is appearing now in Newark. Flowers fold. Remember that aphids are usually become infected by spores of the fungus, Sclerotinia sclerotiorum, controlled by early summer as a result of during wet, cool weather and invade the stem tissue causing twig predators and parasites. If excessive dieback. The dead twigs are orange-brown with a zonate pattern honeydew is objectionable, use insecticidal originating from the infected flower. It's too late for any fungicide soap, neem oil or horticultural oil for control now. Prune and destroy dead, infected twigs. The fungus control. If leaf curling becomes will form hard, black structures called sclerotia, which look like objectionable, consider using foliar- rat droppings. They can be on the surface of the twig, but more absorbed insecticides but they will knock often will be packed into the pith of the infected twig. These are out beneficials for a while. responsible for the spores that infect the flowers. Removing them with the infected twigs will help reduce the amount of disease. Imported black willow leaf beetle damage There is less of this disease now than in 2003, but it is present. on willow has also been noted. Look for clusters of oval yellow eggs on leaves and SYCAMORE ANTHRACNOSE is easy to spot now on Platanus leaf skeletonization caused by larvae. Bt occidentalis. Some later emerging leaves are dead; leaves on provides control on early instar larvae. branch tips are healthy; and leaves inside the plant canopy have re large brown blotches that follow the veins. This may look bad now For mo but the trees recover and put out another flush of leaves by mid- ation June. This is happening about the same time as last year. inform on pests & practices covered in this CEDAR APPLE RUST. Last week’s rains caused a spectacular Helpful numbers to know: appearance of cedar-apple rust galls on eastern red cedar, Garden Line 831-8862 Juniperus virginiana in Sussex County. The gelatinous, orange (for home gardeners only) telial horns are very conspicuous on infected trees. If possible, New Castle County Extension 831-2506 prune out old galls. The disease can cause small twig death. Kent County Extension 730-4000 Sussex County Extension 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. Fischer Greenhouse (New Castle County) = 369 ('03 = 318) GROWING Kent County Extension Office (Kent County) = 437 ('03 = 342) DEGREE DAYS Research & Educ. Center, Georgetown AS OF May 11, 2004 (Sussex County) = 416 ('03 = 339) Extension Horticulturist Extension Susan Barton Susan Editor: Newark, Delaware 19717 Delaware Newark, Townsend Hall Townsend Cooperative Extension Cooperative ritage, ritage, unox, unox, infection becomes aesthetically objectionable. objectionable. aesthetically becomes infection were observed early in the week. This is a minor disease that does not require control unless the amount of leaf leaf of amount the unless control require not does that disease minor a is This week. the in early observed were portant to remove infected leaves. leaves. infected remove to portant SPOT ANTHRACNOSE ON DOGWOOD. The first symptoms of spot anthracnose on the leaves of flowering dogwood dogwood flowering of leaves the on anthracnose spot of symptoms first The DOGWOOD. ON ANTHRACNOSE SPOT prox. 1/8 inch raised, raised, inch 1/8 prox. ercial applicators can use Banner, Compass, He Compass, Banner, use can applicators ercial with another mimosa. another with branches, it is probably Fusarium wilt. The tree will eventually die from wilt and should be removed. Do not replant replant not Do removed. be should and wilt from die eventually will tree The wilt. Fusarium probably is it branches, emoval, homeowners can try spraying a fungicide such as Imm as such fungicide a spraying try can homeowners emoval, be due to winter damage or Fusarium wilt. If you can find brown discoloration under the bark on the affected affected the on bark the under discoloration brown find can you If wilt. Fusarium or damage winter to due be MIMOSA is just leafing out in Newark. If a tree is not leafing out now and/or has considerable branch dieback, it may may it dieback, branch considerable has and/or now out leafing not is tree a If Newark. in out leafing just is MIMOSA res that can re-infect the hollyhock so it is im is it so hollyhock the re-infect can that res ible cultivar near you. Look for the small ap small the for Look you. near cultivar ible Eagle, Daconil 2787 and others. and 2787 Daconil Eagle, Infuse, or Bayer Advanced Garden Disease Control. Comm Control. Disease Garden Advanced Bayer or Infuse, If there are too many infected leaves for hand r hand for leaves infected many too are there If yellow spots. This rust produces spo produces rust This spots. yellow ) d e orange-red to red pustules on the underside of the leaves. The upper surface will have many small light green to to green light small many have will surface upper The leaves. the of underside the on pustules red to orange-red u n i t n o C HOLLYHOCK RUST is now appearing on a suscept a on appearing now is RUST HOLLYHOCK ( s e s a e s i D.