Euro­pean hor­nets strip bark from woody plants

Baltimore Sun Sunday - - GARDEN - By Ellen Nibali

Are these gi­ant Asian hor­nets? They eat bark off my young river birch. I’m wor­ried it will dam­age my tree and also I have two small chil­dren who play near the tree. I can’t find the nest.

There are no gi­ant Asian hor­nets in the United States. These are Euro­pean hor­nets. Black stripes on the ab­domen (as well as on our huge ci­cada killer wasps) look like the color is drip­ping.

Euro­pean hor­nets strip bark from woody plants (es­pe­cially lilac) to make their nests and ob­tain nour­ish­ment from the sap. They make pa­pery nests in a cav­ity, such as a hol­low tree or wall void, mak­ing them dif­fi­cult to lo­cate. On rare oc­ca­sions they make sus­pended, foot­ball­shaped nests like bald­faced hor­nets do.

Plants typ­i­cally with­stand strip­ping form Euro­pean hor­nets, but there may be some branch dieback when dam­age is ex­ten­sive.

These hor­nets are un­usual be­cause they fly at night as well as day, feed­ing on other in­sects. Do not at­tract them by leav­ing on lights at night. They are not ag­gres­sive, but keep your chil­dren at a dis­tance as much as you can. Like other so­cial hive-mak­ing wasps and hor­nets, all work­ers will die with cold weather and the new queens will over­win­ter else­where, never reusing an old hive.

I had to cut down an old white oak in my front yard that de­vel­oped an armil­laria in­fec­tion. I want to re­place it with an­other shade tree. Do I need to wait for the armil­laria fun­gus to clear from the soil?

With armil­laria, if you in­tend to re­plant, you need to re­move the stump. Armil­laria lives on dead wood. Keep­ing the stump helps armil­laria re­main in the area, be­cause the stump and re­main­ing root sys­tem are a good source of nour­ish­ment for it to keep grow­ing.

Have as much of the stump’s wood grind­ings re­moved off-site as is pos­si­ble. Re­fill the hole with clean top soil. Do not re­plant in the same hole. Plant your new tree about 30 feet away (or as far as pos­si­ble.)

It will not mat­ter whether your new shade tree is an oak or other species, as re­gards the armil­laria. How­ever, oaks are the premier species for sup­port­ing in­sects, birds and other wildlife.

Univer­sity of Mary­land Ex­ten­sion’s Home and Gar­den In­for­ma­tion Cen­ter of­fers free gardening and pest in­for­ma­tion at ex­ten­sion.umd.edu/hgic. Click “Ask Mary­land’s Gardening Ex­perts” to send ques­tions and pho­tos.

HAND­OUT

Euro­pean hor­nets are not usu­ally ag­gres­sive but fly at night as well as dur­ing the day hunt­ing in­sects.

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