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2003 Potomac Division Meeting Abstracts

March 16-18, 2003 - Harrisburg, Pennsylvania
(Joint with Eastern Branch of the Entomological Society of America)

Posted online January 23, 2004


Puccinia lagenophorae: Invasive or beneficial? WILLIAM L. BRUCKART, III. USDA-ARS-FDWSRU, 1301 Ditto Ave., Ft. Detrick, MD 21702. Publication no. P-2004-0001-PTA.

Puccinia lagenophorae
, cause of a rust disease on common groundsel (Senecio vulgaris) may be useful for biological control in the U.S. During evaluations in containment, it was found in the U.S. (California and the East Coast). Is it damaging to groundsel and will it attack native Senecio spp.?

Overwintering behavior of Colletotrichum acutatum in dormant highbush blueberry. A. DeMARSAY and P. V. Oudemans. Dept. of Plant Biology and Pathology, Rutgers University, Blueberry and Cranberry Research and Extension Center, Chatsworth, NJ 08019. Publication no. P-2004-0002-PTA.

Colletotrichum acutatum
is the causal agent of anthracnose fruit rot of highbush blueberry. Overwintering inoculum largely determines disease incidence in the next growing season. Identifying how and where the pathogen overwinters in dormant blueberry tissue is crucial to risk assessment and improved disease management. Samples of dormant twigs from the susceptible cv. ‘Bluecrop’ and the resistant cv. ‘Elliott’ were taken from unsprayed commercial fields in New Jersey. The twigs were incubated in moist chambers and emerging spore masses were tallied to determine the number of infections arising in various tissue types. Buds, especially flower buds, were the primary source of overwintering inoculum in both cultivars, accounting for 73 and 95 percent of infections in ‘Bluecrop’ and ‘Elliott’, respectively. ‘Bluecrop’ twigs were more likely to be infected and had higher average numbers of infections than ‘Elliott’ twigs, suggesting a greater carryover of inoculum. The spatial pattern of C. acutatum in sampling plots was highly aggregated for both cultivars.

A new isolate of Ramularia crupinae for biological control of Common Crupina. F. ESKANDARI and W. L. Bruckart, III. USDA-ARS-FDWSRU, 1301 Ditto Ave., Ft. Detrick, MD 21702. Publication no. P-2004-0003-PTA.

A French isolate of R. crupinae, which causes significant stem and foliage necrosis on common crupina (Crupina vulgaris), has been under evaluation for biological control. Recently, we found a new, pink isolate of R. crupinae that produces abundant conidia on both solid and liquid media. Spore yields are very high (2 × 10(^7) spores/ml), compared with approximately 2 × 10(^3) spores/ml for the original isolate. One of 11 species in the Asteraceae, Carthamus tinctorius (safflower), was infected with the new isolate of R. crupinae, developing a limited number of small, necrotic lesions on older leaves. Damage to safflower and crupina was measured after repeated inoculations with R. crupinae. Root dry weight of crupina was reduced by 53.1% and there were no significant differences (P = 0.05) in root dry weights of inoculated safflower compared with controls. Similar results were noted for data on height, number of flowers, and top dry weight.

Integrated control of potato leafhopper (Homoptera: Empoasca fabae) on apple (Malus domestica): Implications for fire blight (Erwinia amylovora) management. K. P. LEAHY (1), D. W. Greene (1), W. R. Autio (1), J. L. Norelli (2), and T. C. Leskey (2). (1) Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003; (2) Appalachian Fruit Research Station, USDA-ARS, Kearneysville, WV 25430. Publication no. P-2004-0004-PTA.

Work done in Virginia in the 1990’s suggested that potato leafhoppers were able to facilitate the bacterial disease fire blight on apple seedlings in growth room conditions. An abundance of research shows that the plant growth regulator Apogee (prohexadione-ca, a gibberellin synthesis inhibitor) has a significant effect in suppressing diseases, including fire blight, and some insects, on apple. We wished to see whether potato leafhopper feeding on apple was affected by Apogee, and whether potato leafhopper feeding and fire blight incidence would correlate under field conditions. An 8 × 8 field factorial trial was conducted using +/- Apogee, +/- potato leafhoppers (using imidacloprid insecticide as an exclusion technique), and +/- Erwinia amylovora mist inoculation. Mature Gala apple trees on M26 rootstock were used for the trial. Significant suppression of fire blight incidence was seen where potato leafhopper feeding was reduced, as well as significant suppression of both potato leafhopper feeding and fire blight incidence where Apogee was used. It is still possible that other insects besides, or in addition to, potato leafhoppers are involved; further research is planned in order to clarify whether these leafhoppers do play a significant role with fire blight in the Northeast and mid-Atlantic U.S.

Comparison of pepper anthracnose isolates using Biolog. J. K. MARVEL (1), S. A. Alexander (1), and E. L. Stromberg (2). (1) Dept. of Plant Pathology, Eastern Shore AREC, VPI & SU, Painter, VA 23420; (2) Dept. of Plant Pathology, VPI & SU, Blacksburg, VA 24061. Publication no. P-2004-0005-PTA.

Pepper anthracnose has become a serious problem over the last four years on Virginia’s Eastern Shore. The identity of the species causing this disease has been in doubt. To assist in characterizing the pathogen(s), the Biolog™ identification system was used on locally and regionally collected isolates. Different Colletotrichum species were obtained from the American Type Culture Collection as standards. The Biolog system utilizes 96-well titer plates with a different carbon source in each well; fungi have signature patterns of carbon metabolism providing a unique “fingerprint”. Five replicate plates were inoculated with each isolate using specifications recommended by Biolog Inc. Plates were kept at 28°C and read with a plate spectrophotometer every 24, 48, 72, 96, and 168 hours. Isolates within a region were more closely related to each other than to isolates from other regions; however, reproducibility of the identification was low. Suggested modifications may increase the accuracy of Biolog identification of pepper anthracnose pathogens.