6 . Lenz, F. and C.N. Williams. 1973. Effect of fruit removal on net assimilation and gas eous diffusive resistance of soybean leaves. Angew. Bot. 47:57-63. 7. Mondal, M.H., W.A. Brun, and M.L. Brenner. 1978. Effects of sink removal on photosynthesis and senescence in leaves of soybean (Glycine max. L.) plants. Plant Physiol. 61:394-397. 8 . Monselise, S.P. and F. Lenz. 1980. Effects of fruit load on stomatal resistance, specific leaf weight, and water content of apple leaves. Gartenbau. 45:188-191. 9. Nafziger, E.D. and H.R. Roller. 1976. In fluence of leaf starch concentration on C 0 2 assimilation in soybean. Plant Physiol. 57:560-563. 10. Proctor, J.T.A. 1979. Stomatal conductance changes in leaves of McIntosh apple trees before and after fruit removal. Can. J. Bot. 59:50-53. 11. Raschke, K. 1975. Stomatal action. Annu. Rev. Plant Physiol. 26:309-402. 12. Schaffer, A.A., K. Liu, E.E. Goldschmidt, C.D. Boyer, and R. Goren. 1986. Citrus leaf chlorosis induced by sink removal: starch, nitrogen, and chloroplast ultrastructure. J. Plant Physiol. 124:111-121. 13. Schaffer, B., J.A. Barden, and J.M. Wil liams. 1986. Net photosynthesis, stomatal conductance, specific leaf weight, and chlo rophyll content of strawberry plants as influ enced by fruiting. J. Amer. Soc. Hort. Sci. 111:82-86. 14. Schaffer, B., J.A. Barden, and J.M. Wil liams. 1986. Whole plant photosynthesis and dry-matter partitioning in fruiting and de- blossomed day-neutral strawberry plants. J. Amer. Soc. Hort. Sci. 111:430-433. 15. Schaffer, B. and S.K. O’Hair. 1987. Net C0 2 assimilation of taro and cocoyam as af fected by shading and leaf age. Photosyn thesis Res. 11:245-251. Effects of Simulated Insect Injury on Net Photosynthesis of Potted Grapevines T.J. Boucher1,2, D.G. Pfeiffer2, J.A. Barden3, and J.M. Williams3 Virginia Polytechnic Institute and State University, Shenandoah Valley Research Station, Steeles Tavern, VA 24476 Additional index words. Vitis vinifera, Japanese beetle, Popillia japonica, leaf area loss Abstract. Grape (Vitis vinifera L.) leaves on potted vines were injured artificially by removing leaf disks with a paper punch. The leaves showed decreased net photosyn thesis (Pn) for the remaining leaf area as leaf area loss (LAL) increased. This reduced P„ in the remaining leaf area at low levels of injury was more pronounced after 12 days than after either 1 or 5 days. The effects of LAL and lowered Pn were additive by 20% LAL for all days tested. H ort S cience 22(5):927—928. 1987. Artificial defoliation studies with grape usually have involved removal of whole leaves or portions of shoots (1, 6 , 9, 10) and have been useful for determining the effects of foliar loss resulting from mechanical har vesting or disease on yield and berry matu rity. Research with other crops, however, has indicated that it may not be adequate to simulate certain insect injury (5, 11). Studies on the effects of simulated insect injury on Pn of apple determined that “ the amount of cut surface exposed by injury was more important than the amount of leaf area removed” (5). It is important to avoid cut ting the midrib or the main lateral veins of the leaf when simulating damage by insects that feed on interveinal areas. (5, 11). It fol lows that arthropods that remove portions of a shoot, large portions of leaves, or many Received for publication 7 Jan. 1987. This re search was supported in part by a grant from the Virginia Agricultural Council. The cost of pub lishing this paper was defrayed in part by the pay ment of page charges. Under postal regulations, this paper therefore must be hereby marked ad vertisement solely to indicate this fact. 'Present address: New Haven Co. Coop. Ext. Serv., 670 Wintergreen Ave., Hamden, CT 06514. 2Dept. of Entomology. 3Dept. of Horticulture, V.P.I. & S.U., Blacks burg, VA 24061. smaller portions, and sucking anthropods (e.g., mites) may all produce different amounts of damage to the plant, even when the amount of leaf area injured or removed is similar. Pn increased in the remaining leaves on potted grapevines following removal of whole leaves (7). Pn of the remaining leaf area of grape after removal of a portion of many leaves by insects has not yet been investi gated to the best of our knowledge. Re searchers have demonstrated a decline in Pn of apples due to mite damage (4) and have shown that a “ secondary reaction” occurs in apple leaves that further reduces Pn when > 20 % of the leaf area is removed with a cork borer (5). If a similar drop in efficiency occurs in grape leaves from such insect in jury [e.g., Japanese beetle, (Popillia japon ica Newman)], this drop might increase the leaf area required to mature the fruit com pared to estimates based on other forms of defoliation ( 1 , 6 , 10 ). Information gained in this area may be helpful in determining economic injury lev els (E1L) and economic thresholds (ET) for certain insect pests. Studies on effects of simulated insect damage on soybean Pn re veal that certain artificial injury techniques (e.g., paper punch) adequately simulate damage by certain defoliators (11). This study was initiated to determine if a drop in Pn (based on remaining leaf area) occurs in grape after leaf area removal and, if so, at what level of interveinal leaf area loss (LAL) it occurs. Five grafted ‘Meurier 7‘Elvira’ grapevines were grown in 15-cm pots containing peat- vermiculite (Promix) in an open-ended greenhouse from Mar. through July 1984. The vines were fertilized at a rate of 200 ppm N weekly, beginning in April, using a so lution of 20N-8.6P-16.6K. On 1 Aug., four adjacent leaves near the midlength of the shoots (=«10 to 18 nodes from the shoot apex) were selected and Pn of attached leaves was determined with a Beckman model 865 infrared gas analyzer as previously described (12). Pn again was de termined 24 hr after treatment and 5 and 12 days later. The air flow rate into the leaf chamber was 5 liters• min - air temperature was 28° ± 2°C. Photosynthetic photon flux was maintained at 850 |xmol*s_ '-nrr2. The leaves were randomly reassigned to one of four treatments (=0, 10, 20, or 45% LAL) based on leaf size as estimated by length x width measurement. Leaf disks (0.31 cm2) were removed from the interveinal area using a paper punch. The outline of each leaf was traced and a paper cut-out was made at the conclusion of the experiment. The tracings and the dam aged leaves were measured with a Ll-COr model 3000 leaf area meter. The actual per cent LAL was determined from the differ ence between the two measurements and ranged from 9-12% (10% treatment), 20- 28% (20% treatment), and 42-52% (45% treatment). Pn was calculated using posttreatment leaf area to determine the photosynthetic effi ciency of the remaining leaf tissue (actual Pn) (5). Posttreatment Pn rates are presented as a percent of the pretreatment rates. A gen eral linear model procedure was used to ana lyze the data (3). There was a drop in the Pn of uninjured leaves (0% treatment) throughout the 14 days of the study. The mean Pn values for the undamaged leaves on days 0, 1, 5, and 12 were 16, 13, 13, and 12 (mg C 0 2/dm2 per hr), respectively. This gradual decline in Pn may have been due to both the handling of the leaves during measurements (2 ) and/or leaf aging (8 ). Pn values below those of the H ort S cience , V ol . 22(5), O ctober 1987 927