Row Covers for Tomatoes By Henry G. Taber Department of Horticulture Iowa State University Updated: December 2008 Plastic row covers have been used in California since the late 1950s for early tomato production. They have not been widely used elsewhere because of the high labor requirements for ventilation. In the 1980s, double-slitted clear plastic tunnels and spunbonded floating row covers have been introduced to provide ventilation and lower the labor costs. Some in the industry refer to the plant row covers as low-tunnels to avoid confusion with the term ‘high tunnels’ which is more like a greenhouse structure. Combining row cover tunnels with translucent plastic mulches (clear or selective wavelength) may increase early tomato yields. However, a major disadvantage of this combination is a loss of frost protection. Also, air temperature in the tunnel may be considerably higher than ambient on sunny days and result in reduction of early tomato yield because of flower and/or fruit abortion. Our research work spans 10 trials since 1982 (see Tables 1 to 3). Row cover performance with tomatoes, unlike that of melons, has been inconsistent. I believe the major reason is the difference in heat tolerance between melons and tomatoes. Air temperatures under the row cover melon tunnels have exceeded 145oF for short periods and plant growth and early yields have not been affected. However, if air temperature exceeds 104oF for more than 3 continuous hours the tomato flowers will abort. See 1987 and 1988 data in Table 1 where row covers significantly reduced early yield because of high May temperatures, 4 to 5 ½ degrees above normal. Even though the slits in the clear plastic provide some ventilation, more should be provided by cutting a 5-inch diameter hole in the row cover over the top of the plant as the season progresses. Tomato flower at full anthesis that is subject to high temperature damage. Provide more ventilation when flower clusters are present in the tunnel or remove completely.
______________________________________________________________________________ IOWA STATE UNIVERSITY University Extension Horticulture Department , (515) 294-2751, taber at e-mail @iastate.edu Copyright © 2008, Iowa State University of Science and Technology. All rights reserved .
Iowa has a continental climate with considerable wind in the spring months. The floating row cover feathers against the plant, causing abrasion which results in stunting and distortion of the young transplant. Early yield is greatly reduced (Table 1 – 1983, 1984, and 1985). However, once the floating row cover is removed, total yield is the same, but the grower has lost his investment of material and labor.
The light weight spunbonded floating material is not recommended without wire hoop support. The tunnel may remain on longer than the slitted clear plastic tunnel because height is about 20inch compared to 14-inch for the clear plastic. However, light intensity is considerably less and may reduce plant growth and yield. Also, air temperature is about 5oF less than slitted, row cover and, thus, early yield reduced in cool springs compared to the slitted, clear plastic row cover. Dr. Stephen Reiners in New Jersey found that early tomato yield was less with spunbonded row cover material compared with the slitted, clear plastic (Table 4). Row cover (slitted clear) doubled early marketable yield when considering the 10 site year data (Table 1), from 33 to 66 cwt/acre. The data set includes the hot periods, 1986 and 1987, when row cover actually reduced early yields compared with the no cover control. Three site-years compared varieties: Pik Red, Jet Star, Superonic B, and Heinz 1810 in 1986 and 1987, and Sunstart, Sunshine, Indy, and Mountain Fresh in 2008. All experiments indicated there was no interaction between the variety chosen and row cover treatment, i.e. row cover performed similarly for all varieties. Of note is the relatively low percentage of marketable yield, about 60-64%, for varieties planted very early in the spring. Most of the cullage was the result of cat-facing (cold weather damage) and blotchy ripening. Cat-facing or blossom-end scarring is a serious problem for early planted tomatoes. Air temperatures over a week period in the low 50’s after setting transplants will induce abnormal flower development and result in increased number of locules in the fruit. The degree of sensitivity to low temperature is variety dependent and the early Sunstart is
______________________________________________________________________________ IOWA STATE UNIVERSITY University Extension Horticulture Department , (515) 294-2751, taber at e-mail @iastate.edu Copyright © 2008, Iowa State University of Science and Technology. All rights reserved .
particularly sensitive. Table 2, total seasonal yield, indicates that row cover does not enhance overall total yield. Thus, the effect is one of rate of fruit maturation rather than production of more flowers or enhancement of fruit set (see 2008 Research Progress Report on tomato row covers for more detailed information). Because there is no enhancement of total marketable yield, only early, the grower must receive a differential price in the marketplace to recover cost of the row cover operation. Thus, if the market price for late July production is $1.75/lb (compared to $0.85/lb for August production) then the row cover advantage would be worth $2970 per acre. Another advantage would be the capture of the early market leading to future sales throughout the season. Other materials were used In trials over the years – Dixie cups (blew away or transplants drown), solid clear plastic with slits manually generated (too labor intensive and too hot), perforated plastic with 3/8-inch drilled holes (much too hot with greatly reduced yields) – without success. Currently, the major row cover materials are the slitted, clear plastic at $0.04/foot or the spunbond polypropylene (AG-19) at $0.12/foot (reusable, if handled carefully). Remember, if you try tomato row covers be sure to monitor temperature daily and provide more ventilation as necessary. Table 1. Early fresh market tomato yield, cwt/acre, as affected by row cover treatment, 10 site years in central Iowa. --------------- Row Cover Materials ------------------None
Slitted Clear
Spunbonded
May weather
Year
Mkt
Total
Mkt
Total
Mkt
Total
Temp., oF
Rain, in.
1982
77
104
211
274
-
-
+ 2.5
+ 3.38
1983
52
71
156
240
9*
12*
- 6.0
+ 0.9
1984
-
33
-
52
-
9*
na
na
1985
19
28
31
46
7*
10*
+ 2.0
- 3.50
1986
11
16
30
40
-
-
0
+ 0.16
1987
32
36
22
28
-
-
+ 5.5
- 0.88
1988
53
97
26
53
43
85
+ 4.0
2001a
16
22
22
37
-
-
0
+ 0.73
2001b
9
23
20
25
-
-
0
+0.73
2008
25
96
63
169
56
153
- 2.6
+ 4.17
Average1
33
55
65
101
* Spunbonded was used without hoops resulting in plant damage by stunting because of constant wind action. In 1988 and 2008, the reemay was supported by wire hoops. 1 The 1984 values not included in the average of 9 years because of hail damage.
______________________________________________________________________________ IOWA STATE UNIVERSITY University Extension Horticulture Department , (515) 294-2751, taber at e-mail @iastate.edu Copyright © 2008, Iowa State University of Science and Technology. All rights reserved .
Table 2. Total season tomato yield, cwt/acre, as affected by row cover treatment, 10 site years in central Iowa. ---------------- Row Cover Materials ------------------None
Slitted Clear
Reemay
Year
Mkt
Total
Mkt
Total
Mkt
Total
1982
347
696
317
674
-
-
1983
241
513
292
596
382
571
1984
Hailed out on June 26, no total yields collected.
1985
Only early yield determined, not harvested total season
1986
277
409
356
490
-
-
1987
561
826
573
836
-
-
1988
Total seasonal yield not determined
2001a
176
325
202
357
-
-
2001b
95
351
87
331
-
-
2008
252
633
277
573
183
466
Average
278
536
301
551
Table 3. Useful field notes about the experiments in Table and 2 for each year.
Year 1982
Transplanted May 7
Row Cover in Place, days 23
Mulch Clear
1983
May 12
26
Black
1985
May 8
25
1986
May 1
1987
Training System Caged
Early Harvest Jul 27- Aug 16
Total Harvest Jul 27-Sept 18
Caged
Jul 26- Aug 3
Jul 26-Sept 1
Black
Stake, no prune
Jul 26- Aug 7
Jul 26-Aug 27
28
Black
None
Jul 14- Jul 21
Jul 14-Aug 20
April 29
23
Black
None
Jul 9- Jul 13
Jul 9-Aug 19
1988
May 4
27
Black
None
Jul 17- Jul 21
2001a
May 1
31
Olive
Stake, prune
Jul 17- Jul 26
Jul 17-Aug 9
2001b
May 16
24
Olive
Stake, prune
Jul 26
Jul 26-Aug 13
2008
May 5
26
Olive
Stake, prune
Jul 22- Jul 27
Jul 22-Aug 28
na
______________________________________________________________________________ IOWA STATE UNIVERSITY University Extension Horticulture Department , (515) 294-2751, taber at e-mail @iastate.edu Copyright © 2008, Iowa State University of Science and Technology. All rights reserved .
Table 4. Effect of two row covers on the early and total yield of fresh market tomatoes (Pilgrim) planted April 28 in central New Jersey (Dr. Stephen Reiners data).
Row Cover Treatment No cover Floating Clear, slitted
Early Marketable (cwt/acre) 58 88 118
Total Marketable (cwt/acre) 260 232 293
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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Jack Payne, director, Cooperative Extension Service, Iowa State University of Science and Technology, Ames, Iowa.
______________________________________________________________________________ IOWA STATE UNIVERSITY University Extension Horticulture Department , (515) 294-2751, taber at e-mail @iastate.edu Copyright © 2008, Iowa State University of Science and Technology. All rights reserved .
