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M.T. Windham, W.T. Witte, R.J. Sauve, and P.C. Flanagan

Sixty cultivars of lilac obtained from two commercial nurseries were planted 18 May 1994 and immediately placed under drip irrigation and fertilized regularly. Powdery mildew appeared in July. Each plant was rated in July, August, and September for powdery mildew on a scale of 1 (healthy) to 5 (totally mildewed). There were 22 cultivars in the most resistant group (0–1.8) in July, 13 in August (0–1.0), and 11 in September (0–1.0). Mildew-free were: `Miss Kim', `Royalty', `Palibin', `Summer Snow', `White Summers', `Minuet', `Ivory Silk', `Anna Amhof', `Donald Wyman', but these were not significantly different from `James MacFarlane' and `Superba' (<10%of plant mildewed). Data on growth will also be presented.

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M.T. Windham, W.T. Witte, R.J. Sauve, and P.C. Flanagan

Eighty-one oak taxa were established at the Nursery Crops Research Station in McMinnville, Tenn., in Fall 1993 and Spring 1994. Drip irrigation was applied as needed beginning 18 May 1994 and plants were fertilized regularly. Powdery mildew began to appear in July on some taxa. Each plant was rated on a scale where 0 = healthy plant and 5 = totally mildewed. Height and caliper were recorded in Fall 1994 and the 1994 growth increment calculated. Quercus robur fastigiata was most severely affected by powdery mildew (4.1), followed by a group of six taxa, including douglasii, oglethorpensis, macrocarpa, virginiana, prinus, and aliena (2.3–1.4). There were slight amounts of mildew on 26 taxa and 48 taxa were mildew-free. Growth increment in height and caliper will also be presented.

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W.T. Witte, M.T. Windham, R.J. Sauve, and P.C. Flanagan

Sixty accessions of commercially available lilac cultivars were planted May 1994 and immediately placed under drip irrigation and fertilized regularly. Powdery mildew appeared in July 1994 and was rated on a scale of 0 (healthy) to 5 (totally mildewed) in July, August, and September. Mean growth index (GI = cm height + cm mean width) was calculated for each cultivar in Fall 1994 and 1995. Fastest growth (GI = 75 to 45 respectively) occurred in the group including chinensis `Rothomagensis', meyeri `Dwarf Korean', reticulata `Ivory Silk', prestoniae `Isabella', `Mrs. Harvey Bickle', `Excel', `Katherine Havemeyer', `Mme. F. Morel', `Silver King', `Leon Gambetta', `Mount Baker', and microphylla `Superba'. Data will be presented on powdery mildew ratings for the 1995 season.

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William E. Klingeman, Gregory R. Armel, Henry P. Wilson, Thomas E. Hines, Jose J. Vargas, and Philip C. Flanagan

Mugwort (Artemisia vulgaris) is a perennial invasive weed species that has infiltrated row crops, turfgrass, ornamentals, and various noncrop areas. Currently, multiple mimics of indole-3-acetic acid can provide control of this species; however, these herbicides can damage certain sensitive ornamental plants. When applied at reduced rates, the p-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides mesotrione and topramezone have demonstrated some selectivity among certain ornamental plants. Field and greenhouse studies were initiated to evaluate whether these herbicides could control mugwort when applied alone, or in mixtures with photosystem II (PSII)-inhibiting herbicides that often provide synergistic weed control. In the field, mesotrione controlled mugwort between 30% and 60% by 21 days after treatment when applied at 0.093 to 0.187 lb/acre. When the PSII-inhibiting herbicide atrazine was added, control increased to 78% and 79%. In the greenhouse, similar rates produced greater control in mugwort, and all mesotrione treatments limited mugwort regrowth by at least 95% when compared with untreated control. When HPPD inhibitor rates were reduced further, the addition of the PSII inhibitors atrazine or bentazon was not sufficient at providing acceptable control of mugwort.