Introduction
Overwintered vegetables, seeded in late summer or early autumn for harvest the following spring, are important new alternative crops in the Willamette Valley. These crops offer a source of cash flow in the spring, present the opportunity for three crops in two years, and may be less expensive to grow because of reduced needs for insecticides and irrigation. Cauliflower, onions, and spinach have shown the most promise as overwintered crops.
Recent cold winters have shown that these crops are marginally hardy in the Willamette Valley and might benefit from an inexpensive means of winter protection in some years. For all three crops, yield and quality decline when winter minima fall below 15°F. Temperatures in the low teens occur about every other winter on the average.
The objective of this trial was to determine whether these three overwintered crops would benefit from application of floating row covers, either shortly after planting or later in the autumn, for both early and late-seeded crops.
Materials and Methods
Cultivars used in this trial were 'Sweet Winter' Onion, 'Inca' cauliflower, and 'St. Helens' spinach. For all three crops, plot preparation before planting included disking, harrowing, application of 1,000 pounds/acre of 10-20-10 fertilizer and rotary tillage. The row covers used were a nonwoven polypropylene, Kimberly Farms, from Kimberly-Clark and a coextruded polypropylene-polyamide, Agronet, from Beghin Say-Kaysersberg. A summary of planting, covering, uncovering, and harvest dates for each crop is contained in Table 1.
Plot size was 20 feet of a three-row bed for spinach and onions, and 15 feet of a single row for cauliflower. Between-row spacing for cauliflower was 5 feet, within-row spacing was 1.5 feet. Cauliflower was transplanted from greenhouse-grown cell packs at 5 weeks after seeding. The spinach and onions were direct-seeded.
Herbicides used at planting (pounds/acre) were propachlor (4.0) for onions; chloro-IPC (1.5) for spinach, trifluralin (0.75) and propachlor (4.0) for cauliflower. The onions received applications (pounds/acre) of chloroxuron (3.0) on 2 December 1986, oxyfluorfen (0.10) on 15 December 1986, chloroxuron (3.0) and oxyfluorfen (0.12) on 11 March 1987. No insecticides or fungicides were used.
Additional fertilizer was applied as follows (pounds/acre): ammonium nitrate (50) to all crops on 3 February 1987, ammonium sulfate (50) to all crops on 10 March 1987, and urea (50) to onions on 8 May 1987.
Table 1. Dates of planting, row cover application, row cover removal, and harvest dates for cauliflower, onion, and spinach, 1986-1987 Cauliflower Onion Spinach Early Late Early Late Early Late Planting date 08/27/86z 09/18z 09/02 10/08 10/08 10/29 First cover applic. 10/14 10/14 09/30 10/08 10/08 10/31 Second cover applic. 11/02 11/02 10/20 10/20 11/05 12/02 Cover removal 02/23/87 02/23 03/23 03/23 03/30 03/30 Harvest 03/23-04/20 03/23-04/20 07/07 - 04/09 04/09 zTransplant dates. Seeding dates were 7/24 and 8/21, respectively.
Results and Discussion
Cauliflower
The winter of 1986-1987 was unusually warm and dry. The lowest recorded temperature was 22°F, insufficient to affect yield of these crops. Thus, the covers would not be expected to provide significant yield benefit but might still enhance quality. However, the percentage of Grade No. 1 heads (white, free of defects, 1.0 pound minimum) for the uncovered check plots in the early planting was the highest that has been obtained in 10 years of trials at this site (Table 2).
The Kimberly Farms cover reduced total yield, mean head weight, and percentage of Grade No. 1 heads (Table 2) for the early planting. Two factors may have contributed to the reduced yield and quality. The growing plants completely filled the available space under the covers and growth may have been restricted. However, the Agronet cover was similar in its restriction of growth but did not significantly reduce yield or quality. The greater temperatures under the Kimberly Farms cover may have stressed the plants either in the autumn or in early spring. This cover also advanced maturity by 7 to 9 days, indicating a warmer environment. This would be a distinct advantage in a colder winter. Plant size and appearance did not vary with treatment after cover removal.
For the second planting the yield of No. 1 heads and mean head weight tended to increase with row covers. Maturity was advanced only slightly by covering. The late covering dates for this planting may have prevented heating under the covers, leading to improved yield and quality.
Spinach
Onset of cold, wet weather indicated that applying covers immediately after planting might encourage earlier emergence and greater stands. This did not prove true. Stands and yields were lower when covers were applied at planting than when applied a month later (Table 4). With heavy rains and wet soil, the covers tended to stick to the soil surface rather than float and stands were reduced. A yellows disorder, probably Fusarium, was more pronounced on covered plots, perhaps because of more favorable temperatures for disease development. Where the covers did not stick to the soil surface, the spinach was cleaner and free of insect damage, compared to check plots.
Table 2. Effect of planting date, cover application dates, and type of row cover on yield and maturity of overwintered cauliflower, first planting, 1986-1987 Yield (tons/acre) Mean head wt.(pounds) % Harvest period Treatment No. 1 Total No. 1 Total No. 1 First Peak Last No cover 6.7 8.0 2.9 2.8 82 3/30 4/17 4/20 KF, first applic.Z 2.6 4.9 1.6 1.6 54 3/23 4/08 4/20 KF, second applic. 2.6 6.1 2.3 2.1 38 3/23 4/08 4/17 Agro, first applic. 5.4 8.2 2.6 2.6 65 4/08 4/14 4/20 Agro, second applic. 5.9 7.9 2.7 2.7 74 3/23 4/14 4/20 LSD(0.05) 2.0 1.4 0.6 0.5 21 Significance Cover vs. check **Y NS * * ** First vs. second applic. NS NS * * NS KF vs Agro ** ** * ** ** ZKF = Kimberly Farms, Agro = Agronet. Y**, *, NS: differences significant at 1% or 5% levels, or nonsignificant, respectively. Table 3. Effects of planting date, cover application dates, and type of row cover on yield and maturity of overwintered cauliflower, second planting, 1986-1987 Yield (tons/acre) Mean head wt. (pounds) % Harvest period Treatment No. 1 Total No. 1 Total No. 1 First Peak Last No cover 1.2 2.4 2.3 1.2 47 4/08 4/17 4/20 KF, first applic. 1.3 1.9 1.6 1.3 61 4/08 4/17 4/20 KF, second applic. 1.4 3.2 1.7 1.5 33 3/23 4/08 4/27 Agro, first applic. 1.5 2.8 1.5 1.4 57 4/08 4/14 4/20 Agro, second applic. 1.4 2.0 2.1 1.3 48 4/08 4/08 4/20 LSD(0.05) NS NS 0.5 NS NS Significance: Cover vs. check NS NS * NS NS First vs. second applic. NS NS NS NS NS KF vs. Agro NS NS NS NS NS Table 4. Effect of planting dates, cover application date, and type of row cover on yield and maturity of overwintered spinach, 1986-1987 Yield (tons/acre) Yellows Treatment First planting Second planting ratingz No cover 1.8 0.1 2.0 KF, first applic. 0.1 0.1 3.2 KF, second applic. 0.5 0.2 3.7 Agro, first applic. 0.2 0.4 3.8 Agro, second applic. 0.7 0.8 3.0 LSD(O.05) 0.8 NS 0.9 Significance: Cover vs. check * NS * First vs. second applic. * NS NS KF vs. Agro NS NS NS zFirst planting only. 0 = no yellow present, 5 = all older leaves affected.
Onion
Onion stands were reduced by the row covers, particularly in the second planting (Table 5). Onions are slow to emerge and lack vigor. The seedlings did not support the covers, which tended to become muddy and stick to the ground. The effect was less pronounced with Agronet as the seedlings tended to grow through the covers.
Vigor and stands for the second planting were so poor that it was abandoned in April. Row covers tended to reduce weed control in the first planting. Oxyfluorfen and chloroxuron were applied through the covers at 40 psi and 50 gallons/acre; the sprays tended to run off where the covers were supported by weeds or onions. The covers also provided a more favorable environment for weed growth. Nevertheless, some weed kill occurred under the covers and weed populations were maintained at an acceptable level.
Onion plant vigor was increased by Agronet but not by Kimberly Farms when rated in March. The vigor ratings mainly reflect plant height. Foliar color of covered onions in May was paler than that of check plot onions (Table 6), perhaps indicating that the covers interfered with even distribution of the spring-applied fertilizer. The covers tended to shed the fertilizer to the alleyways between plots. The tendency for reduced vigor on previously covered plots when rated in May, may also indicate uneven fertilizer distribution.
Row covers reduced yield of both jumbo and all grades of onions (Table 6). This was attributable both to the reduced stand and to smaller bulb size. Bulb size and yields were greater with Agronet than with Kimberly Farms.
Table 5. Effects of planting date, cover application date, and type of row covers on stand and vigor of onion, and weed control rating, 1986-1987 Stand/20 feet Weed control ratingz First Second First Second Vigor ratingy planting planting planting planting 30 Mar. 11 May No cover 98 48 7.3 5.8 4.3 4.8 KF, first applic. 59 0 5.5 6.0 3.3 4.0 KF, second applic. 68 0 5.0 7.2 3.8 4.4 Agro, first applic. 74 18 4.5 4.5 5.0 4.2 Agro, second applic. 83 24 5.0 5.0 5.0 4.3 LSD(0.05) NS 23 1.7 NS 0.9 NS Significance: Cover vs. check NS ** * NS NS NS Applic. date NS NS NS NS NS NS KF vs. Agro NS NS NS NS NS NS zRated on 30 Mar. 1987. 0 = no control, 9 = no weeds present. yFirst planting only. 5 = most vigorous, 0 = least vigorous. Table 6. Effects of planting date, cover application date, and type of row cover on yield of overwintered onion. first planting, 1986-1987 Yield (tons/acre) Mean bulb % Jumbo Foliar color Treatment JumboZ Total wt. (g) by number on 11 May No cover 4.7 20.9 5.3 12.8 dark green KF, first applic. 1.4 10.2 4.3 7.3 pale KF, second applic. 0.3 8.5 3.0 1.5 very pale Agro, first applic. 3.0 14.5 4.8 9.0 pale Agro, second applic. 1.5 15.0 4.4 4.3 pale LSD(0.05) 4.0 5.0 1.4 NS Significance: Cover vs. check * ** * NS Applic. date NS NS * NS KF vs. Agro NS * * NS ZJumbo = at least 3 inch diameter.
Conclusions
The winter of 1986-1987 did not provide an adequate test of row cover effects on plant survival, yield, or quality. However, a few conclusions can be made. Postemergence weed control chemicals can be applied through the covers but pressures or coverage may need to be adjusted to compensate for the partial barrier. Cauliflower might benefit greatly from wide covers which would not restrict foliar growth. Fertilizer distribution would be less of a problem on this crop since the roots extend over a large area.
Both onions and spinach appear poorly adapted to covering immediately after planting in high rainfall conditions. Covers could be applied later in areas where weather permits, or hoop-supported structures could be used.