Production of muskmelons in the Willamette Valley is limited by low air and soil temperatures, particularly early in the growing season. Daily minimum temperatures are commonly between 50 and 55°F even during the warmest months.
Several methods have been used to stimulate early melon production or to increase yields, including transplanting, clear or black plastic ground mulches, and hoop-supported plastic tunnels. The major effect of the various plastic materials is to increase soil and air temperatures, improving vine growth and fruit set. A recent development is the production of "floating row covers", materials which can be laid directly on the crop or seedbed and which do not need structural support. These materials are usually perforated or slit to allow some air movement and to avoid excessive temperatures under the material. The following trials were designed to evaluate the effects of floating row covers on muskmelon earliness and yield.
Methods
1983.
Three 200-foot long beds were prepared by rotary tillage in early April 1983, after a broadcast application of 800 pounds/acre of 10-20-10. Drip irrigation tubing was run the length of the beds and the beds were then covered with 4 feet x 12 mil black plastic ground mulch. Transplants seeded in a heated glasshouse on March 17 or seeds of 'Gold Star' muskmelon were planted on April 14 through holes cut in the ground mulch. Floating row covers were applied immediately after planting.
Plot size was 20 feet long with 8 feet between rows and 6 plants/plot on 3-foot spacing in the row. Nine treatments were replicated three times in randomized block design. Treatments included 1) black ground mulch (check); 2) Vispore, a finely perforated clear polyethylene (Ethyl Visqueen Corp.), removed on May 13, 1983; 3) Vispore removed on June 1; 4) Reemay, a spunbonded polyester (DuPont Co.), removed on May 13; 5) Reemay removed on June 1; 6) Xirofilm, a slit clear polyethylene, removed on May 13; and 7) Xirofilm removed on June 1. Each of the above treatments was on transplanted melons. In addition, Xirofilm was applied over direct-seeded melons and removed on 8) May 27 or 9) June 9, 1983.
Irrigation was through the drip system as needed. An additional 20 pounds N/acre was also applied through the drip system. Thermocouples were placed at one-inch soil depth and between the ground mulch and floating covers for all treatments. Temperatures were recorded every half hour from April 14 until June 1. Melons were harvested at least twice weekly from mid-July until all fruit had matured in mid-October 1983.
1984.
Methods were as above except that transplants were started on April 2 and May 3 and planted on April 25 and May 29, 1984, respectively. These treatments included black ground mulch on transplants (1); black ground mulch on direct-seeded (2); Vispore removed on June 22 for transplants(3); June 27 for direct-seeded (4); Vispore removed on July 2 for transplants (5); July 9 for direct-seeded (6); Reemay removed on the above early removal dates (7, 8); Reemay removed on the above late removal dates (9, 10). Temperatures were recorded every half hour until July 1.
Results and Discussion
1983.
A frost (29°F one inch above the ground mulch) occurred the night after planting. Minimum air temperature recorded at the same time under each of the floating row covers was 32°F, indicating significant frost protection. Most plants on the black plastic ground mulch were killed as were several under the row covers. All frost-killed plants were reset the following day. Some further losses occurred, with significantly fewer check plot plants surviving to produce fruit than survived under row covers (Table 1).
Daily mean soil temperatures were increased by 5 to 9°F by row covers compared to bare ground; the ground mulch increased the mean daily soil temperature by only 2° (Table 2). The row covers increased minimum air temperatures by 2 to 3° but increased mean maximum air temperature by as much as 31°. Heat unit accumulation [summation of (daily mean air temp minus 50°)] nearly tripled under the row covers compared to over bare ground. Air temperatures were often in excess of 115°F under the row covers, particularly the Vispore and Xirofilm. These excessive temperatures may have offset some of the positive effects of increased temperatures on plant growth. Although vine growth was greatly increased under the row covers, leaf size was also noticeably reduced. Since the growing plants were unable to force open the slits in the Xirofilm, this material was not used in 1984.
Early row cover removal occurred at close to first bloom for each treatment, with the late removal treatments designed to sacrifice fruit set on early blooming flowers in exchange for continued plant protection and increased vine growth. Since late May was unusually warm and sunny, all treatments might have benefited from earlier plastic removal in 1983. However, time of plastic removal had no significant effect on any yield parameter (Table 1). Late removal of row covers did tend to increase the percentage of fruit harvested by the end of August (Table 3), but this effect was not statistically significant.
Within the transplanted treatments, type of row cover had no significant effect on yield/plant, number of fruit/plant, mean fruit weight, or percentage of small and large fruit (Table 1). Use of row covers with transplants tended to increase the number of fruit harvested/plant (Table 1) when compared to the check treatment, but this effect was statistically significant only for the late removal of Vispore. All row covers reduced mean fruit weight and percentage of large fruit (more than 2 pounds), probably as a result of greater fruit set on covered plants.
Direct-seeded plants covered with Xirofilm tended to have greater fruit set and reduced fruit weight when compared with any of the transplanted treatments.
Effects of row covers on number of days required for ripening the first fruit were striking. For transplanted treatments, the first fruit harvest occurred from 5 to 28 days earlier with row covers than with ground mulch only. Type of cover and time of removal did not significantly affect first fruit harvest. Row covers did not substantially increase early production, however, as there were only a few very early fruit. Only in mid-September was the percentage of fruit harvested from row-covered treatments significantly higher than for the uncovered treatment (Table 3). Row covers usually brought peak production 7 to 10 days early (Table 3). All fruit were harvested from most row-covered plots by September 23 (data not shown); substantial numbers of fruit from check plots were not harvested until mid-October. October in the Willamette Valley brings rain and cool weather, generally reducing fruit quality. Thus, the earlier final harvests with row covers may be a distinct advantage.
Direct-seeded plants under Xirofilm had very concentrated production. First harvest was comparable to that of transplants on black plastic ground mulch, while peak and final harvests were considerably advanced (Table 3). Although fruit size was reduced as a result of increased set on the direct-seeded plants (Table 1), use of the Xirofilm produced yield and earliness of direct-seeded plants comparable to standard culture with transplants and black plastic mulch. The cost of raising transplants versus cost of the row covers must be considered before conclusions can be drawn regarding the profitability of direct seeding with row covers versus use of transplants.
Table 1. Floating row cover effects on survival and yield of muskmelon, 1983 Plants Total Yield/ Fruit/ Mean fruit Fruit less Fruit more Treatment surviving yield plant plant weight than 1 lb than 2 lb % T/A lb No. lb % % Transplanted Ground mulch 56 8.6 18.9 8.5 2.4 1 72 Reemay, early removal 83 11.6 16.9 10.5 1.6 15 31 Reemay, late removal 67 9.8 17.4 9.5 1.8 5 36 Vispore, early removal 100 15.4 18.9 11.0 1.7 8 34 Vispore, late removal 83 12.9 20.0 12.1 1.7 14 32 Xirofilm, early removal 94 14.2 18.2 11.6 1.7 14 29 Xirofilm, late removal 100 13.4 16.7 10.5 1.7 18 33 Direct-seeded Xirofilm, early removal 100 13.5 16.5 12.9 1.3 32 10 Xirofilm, late removal 100 15.2 18.7 14.8 1.3 28 4 LSD (0.05) 33 5.0 NS 3.4 0.6 20 34 Table 2. Effect of floating row covers on air and soil temperatures Mean air temperature (°F)Z Mean soil temperature (°F)Y Treatment Max. Min. Daily mean Heat units Max. Min. Daily mean 1983 Bare ground 76 44 60 461 78 50 64 Black plastic 82 44 63 651 75 56 66 Reemay 102 47 75 1204 80 58 69 Vispore 104 47 76 1294 78 59 69 Xirofilm 107 47 77 1313 89 57 73 1984 Bare ground 78 49 64 461 76 57 66 Black plastic 86 49 67 589 79 60 70 Reemay 102 52 77 913 80 64 72 Vispore 112 51 81 1062 85 63 74 ZMeasured 1 inch above ground or black plastic, 1 inch above black plastic but beneath row cover. YMeasured at 1-inch depth. Table 3. Effect of floating row covers on earliness of muskmelon, 1983 % fruit harvested by: Days from planting or seeding to harvest: Treatment 8/15 8/22 8/31 9/15 9/30 First Peak Last Transplanted Ground mulch 1 4 11 50 88 124 157 184 Reemay, early 3 6 20 83 100 96 150 161 Reemay, late 8 10 23 86 100 110 150 158 Vispore, early 1 1 13 73 99 110 150 180 Vispore, late 9 17 27 72 100 107 150 161 Xirofilm, early 3 6 19 78 100 96 150 169 Xirofilm, late 1 4 33 79 96 119 147 176 Direct-seeded Xirofilm, early 0 1 20 96 100 119 147 158 Xirofilm, late 0 0 26 96 100 128 145 155 LSD (0.05) NS NS NS 25 NS
1984.
As in 1983, a severe frost (27°F) occurred shortly after planting. Also as in 1983, the minimum air temperature recorded under the floating row covers was 2 to 4° higher than over bare ground or black plastic mulch during the frost period, but not sufficiently higher to prevent frost-kill of all transplants. All plots were replanted on May 29, about the normal time for planting melons in the Willamette Valley. Thus, the row covers were not used to extend the length of the growing season in 1984 as they were in 1983.
Mean temperatures and heat unit accumulations for May 29 - July 1 are listed in Table 2. The black plastic ground mulch increased mean daily soil temperature at 1-inch depth by 4°; the combination of ground mulch and row covers increased mean soil temperature by 6° (Reemay) or 8° (Vispore). Vispore raised soil maximum temperatures more than did Reemay but their effects on soil minimum temperatures were essentially equal. The ground mulch increased the mean daily air temperature at 1 inch above ground by 3°, mainly through an increase in the maximum temperature. This was probably caused by heat reflected from the plastic surface. Row covers raised the mean low temperature by 2 to 3° and maximum temperature by an average of 24° (Reemay) or 34° (Vispore). Maximum temperatures often exceeded 115° under row covers, particularly the Vispore. Heat unit summation more than doubled under the row covers. Greater vine growth under row covers (Table 4) and no apparent reduction in leaf size or leaf injury indicated no heat injury from the covers in 1984. Both mean temperatures and solar radiation were lower than normal between May 29 and July 1, which may have prevented injury.
Direct-seeded plants generally took almost 20 days to emerge. On June 25, transplants averaged above 15 leaves/plant, direct-seeded about 2.5 leaves/plant. Row-covered plants were also more advanced in development than were non-covered plants (Table 4). Type of row cover had no effect on transplant development but development of direct-seeded plants was slightly more advanced under Vispore. On July 2, flowers were present only on transplants. More flowers were present on row-covered plants and more flowers were present on plants with late row cover removal. Early fruit set showed a similar pattern: more fruit with late removal and no difference between Reemay and Vispore.
Ripening of the fruit was advanced 10 to 20 days by transplanting and 12 to 21 days by row covers (Table 4). Direct-seeded, non-covered plants did not produce ripe fruit until late September compared to August 15 for non-covered transplants. Generally, type of row cover made no difference for transplants, but first harvest was earlier with Vispore for direct-seeded plants. Early fruit ripening was usually promoted by late row cover removal.
Total yield/plot was also increased by transplanting and row covers (Table 5). On August 22, all row-covered transplants had produced significant yields, compared to no yield from non-covered transplants and direct-seeded plants. Yield did not vary with type of row cover but tended to be increased by late removal. By August 31, all transplants and two of the direct-seeded treatments had produced significant yields. Again, late removal produced higher yields. At final harvest on October 5, most of the direct-seeded plants still did not reach the yield level of the transplants. This was caused, in part, by less than desired stands on the Reemay early and late removal and non-covered, direct-seeded treatments. However, even when yields were expressed on a per plant basis (Table 6), transplants outyielded direct-seeded plants. On a per plant basis, yields with Reemay and Vispore were not significantly different, whereas on a per acre basis, Vispore tended to outyield Reemay for direct-seeded plants.
In contrast to 1983, fruit size in 1984 did not vary significantly with treatment (Table 6) and most yield differences can be explained on the basis of numbers of harvested fruit.
Since the first planting was lost to freeze damage, first ripe fruit production occurred more than two weeks later in 1984 than in 1983. Total yields were also lower. However, even with the late May planting, row covers significantly advanced maturity and yield. Some growers in the Willamette Valley attempt to direct-seed melons in May without any row cover protection or ground mulch. In 1984, they would not have been able to produce ripe fruit of a main-season variety before late September, missing more than a month of the potential marketing season.
Muskmelons are a very limited acreage crop in this area and the price does not vary greatly during the season. A grower's roadside stand sold his own melons for 29C/pound throughout the season, even though the supermarket price for California melons fell below this figure.
If this price situation held true every year, the cost of row covers must be recovered in higher yields, or locally produced melons must have enough drawing power to increase overall business at the stand.
Assuming a price of 29/pound and an additional cost of $600/acre for using row covers, it is evident that for the entire season, use of row covers yielded increased return for all treatments except the Vispore late removal transplants (Table 5). Even more striking, on August 22, after only one week of harvest, the additional cost of row covers had already been recovered on all transplanted treatments.
In summary, row covers are a useful and profitable means to increase earliness and, to a certain extent, yield of muskmelons in the Willamette Valley. Both Vispore and Reemay are excellent covers, with higher maximum temperatures under the Vispore. If temperatures are not excessive (more than 120°F), row covers should not be removed until several days after bloom.
Table 4. Effects of row covers on plant development and days to harvest, 1984 Leaves/plant Flowers/plant Fruit/plant Days to harvest Treatment on 6/25 on 7/2 on 7/19 First Peak Transplanted Ground mulch 11.5 4.6 0.0 92 103 Reemay, early 15.1 9.5 0.6 78 100 Reemay, late 18.2 13.2 1.8 78 90 Vispore, early 15.3 6.8 0.8 78 107 Vispore, early 15.4 11.1 1.8 80 85 Direct-seeded Ground mulch 0.2 0.0 0.0 111 129 Reemay, early 2.3 0.0 0.0 96 112 Reemay, late 1.0 0.2 0.0 92 114 Vispore, early 3.8 0.0 0.0 94 113 Vispore, late 4.0 0.6 0.0 90 95 Table 5. Total yield and value of muskmelons, 1984 Total weight harvested by: Gross return on: Net increase over check: Treatment 8/22 8/31 9/24 10/05 8/22 10/05 8/22 10/05 Transplanted ---------------T/A----------- ------------------$/A--------------------- Ground mulch 0.0 3.3 10.3 12.6 0 $7335 -- -- Reemay, early 1.3 3.2 10.5 14.0 $761 8104 $161 $169 Reemay, late 3.9 6.4 13.3 14.2 2242 8218 1642 283 Vispore, early 2.3 3.7 14.3 16.4 1317 9487 717 1552 Vispore, late 3.0 6.7 10.4 12.9 1712 7499 1112 (436) Direct-seeded Ground mulch 0.0 0.0 0.4 3.6 0 2077 -- -- Reemay,early 0.0 0.0 4.6 8.2 0 4749 -- 2072 Reemay, late 0.0 0.7 2.9 4.7 0 2751 -- 74 Vispore, early 0.0 0.4 6.2 10.0 0 5827 -- 3150 Vispore,late 0.0 3.5 10.3 11.2 0 6503 -- 3826 LSD (0.05) 2.3 3.2 7.2 8.4 Main Effects Transplanted 2.1 4.6 11.7 13.7 Direct-seeded 0.0 0.9 4.9 7.5 **Z ** ** * Row covers 1.0 3.1 9.0 11.2 Ground mulch 0.0 1.6 5.4 8.1 * * * NS Early removal 0.9 1.8 8.9 12.1 Late removal 1.7 4.3 9.1 10.3 NS * NS NS Reemay 1.3 2.6 7.8 10.3 Vispore 1.3 3.5 10.2 12.6 NS NS NS NS Z**, *, NS: Means significantly different at 1% and 5% levels, and not significantly different, respectively. Table 6. Yield per plant and mean muskmelon fruit weight, 1984 Yield/plant harvested by: Mean fruit Treatment 8/22 8/31 9/24 10/5 weight Transplanted -----------------lb------------------------- Ground mulch 0.0 3.2 10.0 12.2 3.5 Reemay, early 1.3 3.1 10.1 13.5 3.6 Reemay, late 3.7 6.2 12.8 13.6 3.1 Vispore, early 2.2 3.6 13.8 15.8 3.2 Vispore, late 2.8 6.4 9.6 10.7 2.8 Direct-seeded Ground mulch 0.0 0.0 0.6 6.8 2.9 Reemay, early 0.0 0.0 5.5 9.9 2.7 Reemay, late 0.0 0.7 2.8 7.2 3.4 Vispore, early 0.0 0.4 5.9 9.7 3.3 Vispore, late 0.0 3.3 9.9 10.8 3.0 LSD(0.05) 2.2 3.0 6.9 8.0 NS Main Effects: Transplanted 2.0 4.5 11.3 13.2 3.2 Direct-seeded 0.0 0.9 4.9 8.9 3.1 **Z ** ** * NS Row covers 1.0 3.0 8.8 11.4 3.1 Ground mulch 0.0 1.6 5.3 9.5 3.2 * * * NS NS Early removal 0.9 1.8 8.8 12.2 3.2 Late removal 1.6 4.1 8.8 10.6 3.1 NS * NS NS NS Reemay 1.3 2.4 7.8 11.1 3.2 Vispore 1.3 3.4 9.8 11.8 3.1 NS NS NS NS NS Z*,*,NS: Means significantly different at 1% and 5% levels, and not significantly different, respectively.