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All text & photos © Hilton Pond Center BLACK CHERRY KNOT Black Cherries, Prunus serotina, lead a tough life at Hilton Pond Center and elsewhere across the Carolina Piedmont. In spring tens of thousands of Eastern Tent Caterpillars build silken webs in their branches (below right), from which they conduct feeding forays that strip the trees bare of tender green leaves. Most trees rebound from this defoliation, but heavy infestations several years in a row can sap a tree's strength and eventually kill it. Black Knot disease causes thick, dark swellings on cherry twigs that look for all the world like--how can we put this delicately--elongated animal droppings hanging in the tree (top and below). In fact, many times on field trips we've had students who initially wouldn't pick up a cherry twig infested with Black Knot because they thought it was some form of scat--a polite word for feces. Their coprophobia was groundless, however, because the dark matter is actually the tree's own cells gone haywire because of the fungus.
Black Knot usually starts as an olive-green swelling at the base of a leaf petiole, but it eventually enlarges and turns dark. Smaller Black Cherry twigs that are attacked by the fungus usually perish within a year or so, and young trees with sizeable infestations often wither and die when the Black Knot growth interferes with transmission of water and minerals up from the roots and food products down from the leaves. Huge swellings occur even on the trunks of large trees, and these may or may not lead to the host's demise. Although the bark of young Black Cherry trees is relatively smooth, it is marked by distinctive thin horizontal lines called "lenticels"--tiny pores that apparently function in gas exchange. In older trees the outer surface becomes dark and crinkly, but at any age the species is still easy to identify up close by looking at its bark. Remarkably, the Black Cherries around Hilton Pond often can be spotted hundreds of feet away--not from of their bark characteristics but because their trunks and twigs are so heavily scarred by Black Knot disease (above left and below). It's unfortunate that Black Knot is so pervasive on the Black Cherries at Hilton Pond Center. Since the fungal spores are spread by wind and rain, there's not much one can do to stop transmission from one host to the next. Our numerous cherry trees are unlikely to achieve championship size under the on-going assault from insects and fungi, but at least those students who once wouldn't touch a Black Knot canker can use the disease to identify a Black Cherry with great accuracy. Before they get too confident, however, we should remind our young naturalists that that our shrubby native plums at Hilton Pond Center are likewise affected by the same fungus that causes Black Cherry Knot.
Comments or questions about this week's installment? NOTE: Be sure to scroll down for an account of all birds banded or recaptured during the week, as well as some other interesting nature notes. "This Week at Hilton Pond" is written & photographed You may wish to consult our Index of all nature topics covered since February 2000. You can also use the on-line Search Engine at the bottom of this page. For a free, non-fattening, on-line subscription to "This Week at Hilton Pond," just send us an E-mail with Subscribe in the subject line. Please be sure to configure your spam filter to accept E-mails from hiltonpond.org. |
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SPECIES BANDED THIS WEEK: * = New species for 2003 WEEKLY BANDING TOTAL 5 species 8 individuals
YEARLY BANDING TOTAL (2003) 61 species 1,037 individuals
BANDING GRAND TOTAL (since 28 June 1982) 123 species 43,151 individuals
NOTABLE RECAPTURES THIS WEEK (with original banding date, sex, and current age) Northern Cardinal (1) 01/21/02--after hatch year male White-throated Sparrow (2) All text & photos © Hilton Pond Center |
OTHER SIGHTINGS OF INTEREST
VAGRANT HUMMINGBIRDS --A hatch-year female Rufous hummingbird was banded on 5 Dec at Rock Hill SC, and a young male Rufous was banded the following day at Gastonia NC. This Week at Hilton Pond |
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Other insects attack the tree's buds while some species bore into its cambium layer. White-tailed Deer and small mammals such as Eastern Cottontails and Pine Voles consume the bark at ground level--a devastating problem for cherry seedlings and small saplings. Perhaps the most obvious and pervasive enemy of Black Cherry, however, is one whose handiwork is easily seen throughout the winter woods: Apiosporina morbosa, the Black Knot Fungus.
Obviously, such malignant growth makes the tree worthless for lumber purposes, but at least the sap that oozes from the cankerous sores may provide nutrition for a variety of birds, butterflies, and small mammals.
Oct 15 to Mar 15
Hilton Pond Center for Piedmont Natural History is a non-profit research & education organization in York, South Carolina USA; phone (803) 684-5852. Directed by