Crop protection with floating row covers interferes with tillage or other means of weed control. Therefore, herbicides or ground mulch are the likely means of weed control under covers. A successful weed control program depends on understanding the environmental and physiological interactions between the herbicide and other components of the cropping system. Results in 1983 with bunching onions (N. S. Mansour) indicated that paraquat residues on row covers might injure the subsequently emerging crop. It is also possible that row covers could alter the effectiveness of an herbicide program because of changes in soil moisture and temperature, more rapid weed seed germination, and decreased crop resistance to the herbicide in the warm, moist row cover environment.
The primary objective of this research was to broaden the information base available on the use of the currently accepted cucumber herbicide combination in conjunction with row covers and to evaluate the possibility of applying the contact herbicide paraquat through the covers. A second objective was to generate new information on the yield response of cucumbers to floating row covers and black plastic ground mulch.
Methods
Five weed control treatments [non-weeded, hand-weeded, bensulide plus naptalam (BN), bensulide plus naptalam plus paraquat (BNP), and black plastic ground mulch (GM)] were factorially combined with three row cover treatments (no cover, Reemay, Vispore) in randomized complete block design with four replications. The sequence of events is outlined below.
On April 24, 1985, and April 23, 1986, beds were formed by rotary tillage of a Willamette silt loam following application of a 14N-6.1P-11.7K fertilizer at 1,000 pounds/acre. On April 25, bensulide (Prefar) and naptalam (Alanap) were applied to the appropriate plots (1 bed x 4 m) at 5.0 and 3.0 pounds active ingredient/acre, respectively, in 100 gallons water/acre. The entire plot area was then rototilled to a depth of 2 inches to incorporate the herbicides. Biwall drip irrigation tubing with emitters at 12-inch intervals was laid the length of each bed, followed by application of 1.5 mil x 4 foot GM to the appropriate plots.
In 1985, plots were seeded with 'Sweet Success' parthenocarpic cucumbers at 5 hills/plot, 2 seeds/hill, on April 26. Reemay and Vispore row covers were applied to the appropriate plots on April 29. On May 6, paraquat was applied to the BNP plots at 1 pound/acre and also to the hand-weeded plots as a substitute for weeding. First emergence of cucumber seedlings was on May 8, but frosts on May 11 and 12 (29°F) reduced stands considerably. The decision was made to replant with transplants. Paraquat was re-applied to BNP and hand-weeded plots on May 17. On May 20, the entire plot area was replanted with greenhouse-grown transplants, 5/plot, which had been seeded on April 30. Row covers were removed on June 11 and harvesting commenced on June 21. An additional 30 pounds N/acre as ammonium nitrate was sidedressed around the plants on June 24. A 30N-4.3P-8.3K soluble fertilizer was applied through the drip system at 100 pounds/acre on July 22.
Air and soil temperatures were recorded from April 30 until June 11, 1985, for all combinations of row covers with GM or bare ground. Thermocouples were installed at 1.0-inch depth in soil and 1.0 inch above the soil surface. Temperatures were recorded every half hour with a Leeds and Northrup Speedomax 250 recorder.
Soil mechanical resistance or crusting was measured with a Technicon Products Co. penetrometer one day before cover removal.
Cucumbers were harvested two or three times a week from June 21 until September 23, when yields and quality declined markedly. Each fruit was weighed separately to determine variability in fruit weight. Yields reported here include only marketable fruit (more than 200 grams, straight). Cull fruit were not recorded, but the number appeared to be less than 20 percent for all treatments until late in the season.
Weed control ratings were made at cover removal on June 11. Weeds were counted by species on June 13.
In 1986, row covers were applied on May 8 and paraquat was applied to the appropriate plots on May 14. The cucumbers were transplanted on May 16 after lifting one edge of the covers. Covers were removed on June 6 and harvest started on June 13. Fruit was harvested weekly until August 20. Weed control ratings were made on June 9.
Results
Air and Soil Temperatures. Plastic ground mulch alone increased daily mean air and soil temperatures by nearly 2°F in 1985 and by over 4°F in 1986 (Tables 1 and 2), but the effect of the GM on average maxima and minima differed for air and soil temperatures. GM increased the average daily maximum air temperature but daily minima were not affected. In contrast, daily maximum soil temperatures were not greatly affected by GM, but minimum temperatures increased by an average of nearly 4°F in 1985 and 6° in 1986. Reemay and Vispore alone increased both air and soil temperatures and the combination of row covers with GM produced the highest temperatures. Heat unit accumulation more than doubled with either Reemay or Vispore plus GM. While the effects of row covers on mean temperatures were substantial, seedling loss to freezes on May 11 and 12, 1985 was severe.
Weed Control. The bensulide plus naptalam herbicide combination provided adequate weed control on most plots for up to four weeks after planting. The herbicides were much less effective on row-covered plots (Tables 3 and 4), but this may have been due primarily to row cover stimulation of weed growth rather than earlier breakdown of the chemicals. The reduction in weed control rating with row covers was similar for both weedy and BN plots, indicating no significant row cover x BN interaction. Thus, there was no evidence that row covers caused premature breakdown of BN activity. No sign of BN damage to cucumbers was noted, either with or without row covers.
Row covers tended to bring on early germination and growth of pigweed and other weeds which are normally not a problem until summer. BN provided partial control of most species, without a major shift in weed species present.
The BNP combination provided significantly improved weed control compared to BN alone when row covers were present. The BNP x row cover interaction was significant in 1985: weed control was poorer with row covers for weedy or BN plots, but weed control ratings were as good or better with row covers compared to bare ground when paraquat was added to the control program. It is possible that additional weed control was provided by paraquat adhering to the row covers. This explanation is unlikely, however, since no crop damage from paraquat residues was noted. The more likely explanation is that the paraquat was particularly effective with row covers because weeds emerged earlier under row covers and these flushes of weed growth were damaged or eliminated by the paraquat. Weeds may also have been more sensitive to paraquat under the row covers.
Emerged weed seedlings and cucumber seedlings surviving the May 11 and 12 frosts were severely damaged or killed by the paraquat application of May 17, indicating that this form of "stale seedbed" technique is possible with Reemay and Vispore. In most situations crop emergence would occur simultaneously with or closely follow weed emergence, so that a post-plant paraquat application would not be practical. An alternative for certain crops would be to spray milder contact herbicides such as chloroxuron, linuron, oxyfluorfen, and fluazifop through the row covers after crop emergence.
Soil Mechanical Resistance. Visual observations in past experiments indicated that row covers might act as an anticrustant and maintain the aggregate structure of soil particles at the soil surface, perhaps by breaking the impact of rainfall or irrigation water or by maintaining soil surface moisture. These observations have now been confirmed (Table 5). Both GM and row covers reduced soil crusting as measured by penetrometer, with Reemay providing slightly more reduction in crusting than did Vispore.
Plant Development. Seedling emergence, recorded on May 8, 1985, did not vary significantly with weed control treatment, but increased with row covers (Table 5). Following the freezes of May 11 and 12, the reduction in stand under row covers was similar to that on bare ground, indicating that the row covers did not provide adequate frost protection in this situation. Stand reduction with Reemay tended to be slightly greater than with Vispore, so that there was a significantly higher stand on Vispore-covered plots than on Reemay-covered plots when stands were re-evaluated on May 16. This result is in accord with the slightly higher mean soil and air temperatures recorded under the Vispore (Table 1). However, the minimum air temperature recorded during the freeze was 31°F for both row cover materials. After setting transplants on May 20, only insignificant plant losses occurred and stands did not vary with treatment. Weather conditions were nearly ideal in late May and early June for obtaining a response to row covers. Temperatures were mild and solar radiation was higher than normal. The effect of GM and row covers on development of the transplants can be seen in the number of flowers/plant on June 14 and the days to first fruit harvest (Table 5). GM alone did not affect early flower production but did reduce time to first harvest by 4 days compared to the hand-weeded plots. Reemay and Vispore significantly increased the number of flowers/plant and reduced time to first harvest by 7 to 8 days, respectively, in 1985 and 9 days in 1986 (Table 7). The earliest harvests occurred with the combination of GM and Reemay.
Early Yield. Both weed control program and row covers affected the very early yield (by July 1). Numbers of fruit from GM plots were greater than for any other weed control treatment, presumably because the GM affected temperatures and soil moisture as well as providing perfect weed control. Reemay and Vispore, when averaged over weed control treatments, increased very early yield by five to seven-fold in 1985 and more than two-fold in 1986, with the plants with a combination of Reemay or Vispore with GM significantly outyielding all other treatments (Tables 6 and 7).
Similar yield responses were obtained for cumulative yields through July 15. In both years, the highest yields were with GM and Vispore, followed by GM plus Reemay, and GM alone. Averaged across all weed control treatments, the yields from Reemay and Vispore-covered plots did not differ significantly. Among weed control treatments, GM plots had by far the greatest yield, again indicating the additional benefits of GM. Herbicide-treated and hand-weeded plots significantly outyielded the non-weeded plots, indicating significant weed competition with the crop on non-weeded plots. BNP plots tended to outyield BN plots, in agreement with the superior weed control of the BNP combination. Row covers did not affect mean fruit weight. Among weed control treatments, mean fruit weight was highest with GM, intermediate with hand weeding or herbicide, and lowest on non-weeded plots.
Total Yield. There were no significant interactions of weed control program and row covers in 1985. Only main effects are shown (Table 8). However, although not quite statistically significant, there was a tendency (P=0.06) in 1985 for yields to decrease with row covers on non-weeded plots, presumably because of increased weed competition. For the other four weed control treatments, yields consistently increased with either row cover. In 1986, this interaction was highly significant (Table 9). Row covers reduced yields on non-weeded, BN, and BNP plots but increased yield on hand-weeded GM plots. The highest cumulative yields in 1985 were with GM plus Vispore (32.7 fruit/plant), GM plus Reemay (27.7), hand-weeded Reemay (26.5), and hand-weeded Vispore (25.3). In 1986, the two highest yielding treatments were the same as in 1985, but the non-covered GM treatment produced the third highest yield.
When averaged over all weed control treatments, row covers increased the number of fruit harvested by about 20 percent in 1985 and 10 percent in 1986, without significantly reducing mean fruit weight. The percentage of large fruit (over 400 g) was reduced slightly by row covers, probably because of increased competition among the greater number of fruit present. Row covers had no effect on variability in fruit weight.
Among weed control treatments, GM produced the highest yields, with BNP again intermediate between hand-weeded and BN plots. Fruit size as well as number was reduced on non-weeded plots. Variability in fruit size, expressed as the coefficient of variation, tended to be highest with GM and lowest for non-weeded and hand-weeded plots. The lower level of variability on non-weeded plots was expected since the absence of significant numbers of large fruit tends to cluster fruit weights nearer the mean. The higher degree of variability for cucumbers on GM than on hand-weeded plots was not expected. The higher proportion of very large fruit and the very rapid development of fruit size on the GM plots may have contributed to a tendency to harvest at a more advanced stage of maturity.
Economic Return. As early as July 15, the additional materials costs of row covers (estimated at $600/acre) as well as any of the weed control practices ($200/acre for GM, less than $50/acre for herbicides) were easily recovered through increased yield (Tables 10 and 11). This analysis is very conservative since it assumes no price premium for early production and a low plant population of only 3,630/acre. The economic advantage of row covers was maintained throughout the 1985 season since previously row-covered plants continued to outyield the plants which had not been covered. In 1986, gross returns were not increased by row covers for BN, BNP, and non-weeded plots. Highest projected gross returns/acre in 1985 were for GM plus Vispore ($32,590), GM plus Reemay ($29,000), hand-weeded Reemay ($27,620), hand-weeded Vispore ($26,390), and GM without row cover ($26,140). It should be noted that the increase in gross return with GM as compared with hand-weeding is about the same as the increase for row covers over uncovered plots, and that the gross return for GM without row covers ($26,140) is essentially the same as that for Vispore with perfect weed control by hand weeding ($26,390). This indicates that, since GM is cheaper than row covers, it would be preferred in a case where only GM or row covers alone would be used. However, the much greater return for GM plus row covers indicates that they should be used together. If a price premium is assumed for earliness, the advantage of row covers would be enhanced.
Conclusions
Floating row covers increased early (July 15) yield of marketable cucumber fruit by nearly 33 percent when averaged over all weed control treatments and reduced time to first harvest by 7 to 9 days. The additional costs of row covers were easily recovered in the value of the increased early yields, even assuming no price premium for early fruit. However, for the total season, row covers were not a profitable cultural practice unless weed control was very effective. Parthenocarpic gynoecious cucumbers appear to be well adapted to row cover culture since the plants can tolerate fairly high temperatures and covers do not need to be removed at first bloom to allow for pollination by insects.
Row covers caused early germination and increased populations and growth of weeds, but did not appear to destroy the effectiveness of the standard herbicide program for cucumbers. Bensulide plus naptalam provided adequate early weed control. However, the tendency of row covers to reduce total season yield with bensulide plus naptalam indicates that row covers must be removed and cultivation accomplished before weed growth is excessive. Considering the small additional costs and the yield benefits derived from use of GM, the use of GM in combination with row covers appears to be the most profitable cultural practice. Row covers did not appear to make the crop more susceptible to herbicide injury. Contact herbicides such as paraquat may be applied through Reemay and Vispore before crop emergence or transplanting with good weed kill. In contrast to results reported previously for bunching onions, possible paraquat residues on the covers did not appear to damage transplants set three days after application.
Table 1. Floating row cover effects on soil and air temperatures and heat unit accumulation (50°F base), April 30-June 11, 1985 Mean air temperature Mean soil temperature Treatment Max. Min. Daily mean Heat units Max. Min. Daily mean Bare ground 79 45 63 544 79 48 64 Black plastic GM 84 45 64 689 79 52 66 Reemay 93 45 69 934 81 54 68 Vispore 99 46 72 1030 81 54 68 GM & Reemay 100 46 73 1267 82 57 70 GM & Vispore 102 48 75 1298 82 57 70 Table 2. Floating row cover effects on soil and air temperatures and heat unit accumulation (50°F base), May 9-June 6, 1986 Mean air temperature Mean soil temperature Treatment Max. Min. Daily mean Heat units Max. Min. Daily mean Bare ground 76 49 63 385 79 53 65 Black plastic GM 85 49 67 529 79 59 69 Reemay 86 51 68 518 78 56 67 Vispore 90 51 70 594 82 55 69 GM & Reemay 105 51 78 799 79 60 70 GM & Vispore 109 51 80 869 80 60 70 Table 3. Effects of weed control program and row covers on weed control ratings, 1985 WeedZ Total control no. of Predominant weed species, Treatment rating weeds/plot descending order, June 13 Weedy, No cover 4.3 132 Poa annua (41), groundsel (20), pigweed (20), scarlet pimpernel (20) Reemay 1.0 148 groundsel (32), Poa annua (32), pigweed (30), shepherdspurse (15) Vispore 0.8 149 scarlet pimpernel (44), pigweed (42), groundsel (21), Poa annua (17) BNY, No cover 7.0 56 Poa annua (15), groundsel (13), shepherdspurse (9), henbit (6) Reemay 4.0 94 scarlet pimpernel (30), Poa annua (19), henbit (15), pigweed (13) Vispore 5.3 72 pigweed (21), scarlet pimpernel (16), Poa annua (15), shepherdspurse (5) BNPX, No cover 7.3 71 henbit (18), groundsel (13), Poa annua (13), scarlet pimpernel (12) Reemay 7.5 27 pigweed (6), shepherdspurse (5), groundsel (5) scarlet pimpernel (4) Vispore 7.8 33 pigweed (8), shepherdspurse (5), scarlet pimpernel (5), Poa annua (5) LSD (0.05) 1.4 35 Main effects: Weedy 2.0 143 pigweed (31), Poa annua (30), scarlet pimpernel (28), groundsel (25 BN 5.4 74 scarlet pimpernel (17), Poa annua (16), pigweed (12), groundsel (9) BNP 7.5 43 scarlet pimpernel (7), groundsel (7), Poa annua (7), sheperdspurse (6) LSD (0.05) 1.1 26 No cover 6.2 86 Poa annua (23), groundsel (15), scarlet pimpernel (12), shepherdspurse (8) Reemay 4.2 90 scarlet pimpernel (18), Poa annua (17), pigweed (16), groundsel (14) Vispore 4.6 85 pigweed (23), scarlet pimpernel (22), Poa annua (12), groundsel (10) LSD (0.05) 1.1 NS ZNine point scale; 0= worst, 9= no weeds present. Hand-weeded and black plastic plots were weed free and were not included in the analysis. Rated on June 11. Y>BN: bensulide + naptalam XBNP: bensulide + naptalam + paraquat Table 4. Effects of weed control program and row covers on weed control ratings, 1986 WeedZ control Predominant weed species, Treatment rating descending order, June 9 Weedy, No cover 3.3 henbit, groundsel, pigweed, scarlet pimpernel, Poa annua Reemay 0.5 groundsel, Poa annua, henbit, pigweed, shepherdspurse Vispore 0.2 scarlet pimpernel, pigweed, hembit, groundsel, Poa annua BNY, No cover 5.0 shepherdspurse, henbit, dogfennel, groundsel Reemay 2.0 pigweed, henbit, shepherdspurse, groundsel Vispore 1.5 pigweed, shepherdspurse, groundsel, scarlet pimpernel BNPX, No cover 6.5 shepherdspurse, Poa annua Reemay 3.3 pigweed, henbit, scarlet pimpernel Vispore 2.8 pigweed, henbit, shepherdspurse,scarlet pimpernel Main effects: Weedy 1.3 henbit, dog fennel, shepherdspurse, Poa annua, pigweed BN 2.8 shepherdspurse, pigweed, henbit, groundsel, scarlet pimpernel BNP 4.2 pigweed, henbit, scarlet pimpernel, shepherdspurse, groundsel LSD (0.05) 0.7 No cover 4.9 henbit, shepherdspurse, groundsel, dog fennel, scarlet pimpernel Reemay 1.8 pigweed, henbit, scarlet pimpernel, groundsel, shepherdspurse Vispore 1.5 pigweed, shepherdspurse, scarlet pimpernel, groundsel, henbit LSD (0.05) 0.7 ZNine point scale; 0 = worst, 9 = no weeds present. Hand-weeded and black plastic plots were weed free and were not included in the analysis. Rated on June 9. YBN: bensulide + naptalam XBNP: bensulide + naptalam + paraquat Table 5. Main effects of weed control and row covers on cucumber plant emergence and development and soil crusting, 1985 Treatment Plants/plot Flowers/plant Soil mechanicalZ Days to first on May 8 on May 16 on June 14 resistance fruit harvest g.force Weed control Non-weeded 1.83 0.33 1.4 650 41 Hand-weeded 2.04 0.41 1.5 624 40 BN 2.05 0.67 1.2 645 39 BNP 2.80 1.17 1.8 650 39 GMY 2.70 0.67 1.3 563 36 LSD (0.05) NS NS NS 65 3 Covers No cover 1.27 0.20 0.2 733 43 Reemay 2.50 0.50 1.6 513 36 Vispore 3.05 1.25 1.8 633 35 LSD (0.05) 0.90 0.34 0.4 55 2 ZMeasured on June 10. YGround mulch Table 6. Yield of fruit/plant harvested by July 15, 1985 Number harvested by Weight harvested Mean fruit weight Treatment July 1 July 15 by July 15 on July 15 kg g Non-weeded, No cover 0.0 1.4 0.5 346 Reemay 0.8 2.0 0.6 298 Vispore 0.3 1.2 0.4 313 Hand-weeded, No cover 0.0 2.8 1.1 383 Reemay 1.1 5.9 0.2 403 Vispore 1.8 5.6 2.5 402 BN No cover 0.0 2.6 1.0 379 Reemay 0.9 4.5 1.7 367 Vispore 1.4 3.9 1.6 389 BNP No cover 0.0 2.3 0.9 375 Reemay 0.4 4.8 1.8 378 Vispore 1.0 5.6 2.1 379 GM No cover 0.9 8.0 3.4 429 Reemay 2.5 8.6 3.4 399 Vispore 2.9 10.7 4.3 400 LSD (0.05) 0.8 1.5 1.0 43 Main effects: Non-weeded 0.3 1.5 0.5 319 Hand-weeded 0.9 4.7 1.9 396 BN 0.7 3.6 1.4 378 BNP 0.5 4.2 1.6 377 GM 2.1 9.1 3.7 409 LSD (0.05) 0.5 0.8 0.7 32 No cover 0.2 3.4 1.4 382 Reemay 1.1 5.1 2.0 369 Vispore 1.5 5.4 2.1 377 LSD (0.05) 0.5 0.6 0.4 NS Table 7. Effect of row covers and weed control on days to first harvest and early yield/plant, 1986 Treatment Days to first Number of fruit harvested by Weight harvested by harvest June 30 July 15 June 30 July 15 --------g-------- Non-weeded No cover 42 0.3 1.0 103 366 Reemay 32 0.9 1.8 268 620 Vispore 31 1.1 1.8 359 600 Hand-weeded No cover 42 0.8 3.5 187 1092 Reemay 32 1.4 4.3 379 1183 Vispore 31 1.7 4.6 481 1420 BN No cover 44 0.3 2.1 102 758 Reemay 33 1.2 2.6 331 847 Vispore 33 1.6 2.7 474 911 BNP No cover 42 1.1 3.1 312 1045 Reemay 32 2.1 4.4 540 1408 Vispore 31 1.9 3.3 523 953 GM No cover 36 3.7 9.5 1179 3383 Reemay 30 7.0 12.2 2510 4578 Vispore 31 7.1 13.8 2353 4837 LSD(0.05) 4 0.9 1.4 260 491 Main effects: Non-weeded 35 1.0 1.5 243 529 Hand-weeded 35 1.3 4.2 349 1232 BN 37 1.0 2.4 302 839 BNP 35 1.7 3.6 764 1135 GM 32 5.9 11.8 2014 4265 LSD(0.05) 3 0.5 0.8 150 284 No cover 41 1.4 3.8 445 1569 Reemay 32 2.9 5.1 940 2003 Vispore 32 3.1 5.2 938 2030 LSD(0.05) 3 0.4 0.7 122 246 Table 8. Yield of cucumber fruit/plant for total season as affected by weed control and row covers, 1985 Total Total Mean wt., Number over % over Weight over Mean weight of Fruit wt. Treatment number wt. all fruit 400 g 400 g 400 g fruit over 400 g C.V. kg g kg g % Non-weeded 4.7 1.8 367 2.0 43 0.9 477 28.5 Hand-weeded 24.1 10.5 435 14.0 58 7.1 496 30.0 BN 15.9 7.2 418 8.7 52 4.5 524 32.1 BNP 19.8 8.5 431 10.6 54 5.5 523 33.0 GM 28.2 12.2 433 15.0 53 8.1 540 36.2 LSD(0.05) 4.0 1.6 27 2.1 5 1.3 21 No cover 16.1 7.0 428 9.2 57 4.8 517 32.1 Reemay 19.8 8.5 414 10.7 54 5.6 516 32.4 Vispore 20.3 8.6 409 10.3 51 5.3 504 32.4 LSD(0.05) 3.1 1.0 NS NS 4 NS NS Table 9. Fruit yield/plant for entire season as affected by weed control and row covers, 1986 Treatment Total Total Mean fruit number weight weight kg g Non-weeded, No cover 3.8 1.2 321 Reemay 2.3 0.8 366 Vispore 2.8 0.9 333 Hand-weeded, No cover 12.0 4.1 336 Reemay 14.8 4.7 320 Vispore 14.5 4.7 326 BN, No cover 6.0 2.2 346 Reemay 5.6 1.8 323 Vispore 5.1 1.8 352 BNP, No cover 8.6 3.0 347 Reemay 8.1 2.6 323 Vispore 6.3 2.0 313 GM, No cover 19.1 7.0 366 Reemay 23.8 8.9 373 Vispore 25.1 8.9 356 LSD(0.05) 3.1 1.2 42 Main effects: Non-weeded 3.0 1.0 333 Hand-weeded 13.6 4.5 327 BN 5.6 1.9 340 BNP 7.7 2.5 328 GM 22.6 8.3 365 LSD(0.05) 1.8 0.7 24 No cover 9.9 3.5 349 Reemay 10.9 3.7 335 Vispore 10.8 3.6 337 LSD(0.05) NS NS NS Table 10. Main effects of weed control program and row covers on estimated gross returnZ from cucumbers harvested by July 15, by July 31, and for the entire growing season, 1985 Treatment Gross return ($/acre) on July 15 July 31 Season Non-weeded 1,200 1,920 4,310 Hand-weeded 4,550 9,100 25,160 BN 3,350 5,990 17,250 BNP 3,830 7,430 20,370 GM 8,860 14,850 29,230 LSD (0.05) 1,100 1,760 3,950 No cover 3,350 6,950 16,770 Reemay 4,790 8,150 20,370 Vispore 5,030 8,390 20,600 LSD (0.05) 760 1,240 2,730 ZBased on $0.30/lb ($0.66/kg) and a plant population of 3,630/acre (2'x 6'spacing); no premium assumed for early production or extra fancy fruit. Table 11. Main effects of weed control program and row covers on estimated gross returnZ from cucumbers harvested by July 15, and for the entire growing season, 1986 Gross return ($/acre) on Treatment July 15 Season Non-weeded 1,267 3,830 Hand-weeded 2,952 10,780 BN 2,010 4,550 BNP 2,719 5,990 GM 10,219 19,890 LSD (0.05) 680 1,680 No cover 3,759 8,630 Reemay 4,799 9,100 Vispore 4,864 8,630 LSD (0.05) 589 NS Zbased on $0.30/lb ($0.66/kg) and a plant population of 3,630/acre; no premium assumed for early production or extra fancy fruit.