The Effect of Herbicides and Plastic Mulch on Pumpkins

John Masiunas

Department of Natural Resources and Environmental Sciences

260 Edward R. Madigan Labs.

1201 W. Gregory Dr.

Urbana, IL 61801

masiunas@uiuc.edu

Introduction

Jack-O-Lantern pumpkin growers are using transplants for cultivars with high value seed and to ensure earliness and uniform stands. Transplants could be combined with plasticulture systems to shorten crop cycles and produce high quality fruit. Black plastic mulch is already widely used in muskmelon and watermelon grown in Illinois. Plastic mulch also provides weed control within the crop row. In the southern portion of Illinois, a shorter crop cycle may allow double cropping pumpkins with an early crop such as broccoli or cabbage. Double cropping will allow the costs associated with plastic mulch to be spread over multiple crops and will allow higher returns per acre.

There are problems with weed management in a plasticulture system using pumpkin transplants. How can weed management programs for multiple crops be integrated? The herbicides used on the first crop either can not persist or have to be registered for pumpkins. Pumpkin tolerance to herbicides may vary in systems using transplants and plastic mulch. Thus the standard pumpkin herbicides must be evaluated in this system. It will not be possible to use volatile herbicides, such as Command (clomazone), under plastic mulch. Even in current pumpkin cropping systems, voids exist in currently registered herbicides.

The herbicides that are currently registered for seeded pumpkins are for preemergent applications Curbit (ethalfluralin), Strategy (clomazone + ethalfluralin), and Sandea (halosulfuron). We also evaluated two possible new herbicides, Balance (isoxaflutole) and Outlook (dimethenamid). Strategy is a prepackaged mixture of ethalfluralin (18.2%) and clomazone (5.6%). It is the only herbicide containing clomazone labeled for jack-o-lanterns, Command (clomazone) although labeled for processing pumpkins is not registered for jack-o-lantern pumpkins because of injury concerns. Strategy is sold by Platte Chemical Company and is labeled for cucumbers, melons, watermelons, pumpkins, and squash. It should be surface applied after seeding or as a directed application after transplanting. Strategy can not use under row covers or plastic mulch, which will limit its utility as a broadcast application in a plasticulture system. Strategy, if used, would have to be directed between the rows of plastic mulch. The rate for Strategy varies depending on soil type with 2-3 pints on coarse soils to 4-6 pints on fine soils. The target weeds that Strategy controls are barnyardgrass, crabgrass, goosegrass, fall panicum, foxtails, wild proso millet, carpetweed, lambsquarters, pigweed, purslane, and velvetleaf.

Another newly registered herbicide for pumpkins is Sandea sold by the Gowan Company. The active ingredient in Sandea is halosulfuron-methyl. Sandea can be applied either prremergent or postemergent. The PRE activity can be enhanced by irrigation or rainfall after application. POST applications to pumpkins can cause some initial chlorosis and plant stunting from which pumpkins generally recover. For a POST application of Sandea use a nonionic surfactant at 0.25%. Sandea is registered for cucurbits under 24c labels so allowed uses vary from state to state. Table 1 indicates the cucurbits which Sandea is labeled on in the midwest. Target weeds which are controlled by Sandea are redroot pigweed, common and giant ragweed, cocklebur, and smartweed. Sandea will also suppress yellow nutsedge. It must be combined with a grass-active herbicide because it has no grass activity.

Balance is sold by Bayer Crop Science. Its active ingredient is isoxaflutole which inhibits carotenoid biosynthesis, causing bleaching of sensitive plants. Currently Balance is registered on field corn and not pumpkin. Its use rate varies depending on the soil type from 1.5 to 1.88 fl. oz on coarse soils to 2.25 to 3.75 on fine soils. The target weeds which Balance controls are barnyardgrass, crabgrass, foxtail, goosegrass, fall panicum, pigweed, chickweed, galinsoga, jimsonweed, lambsquarter, and eastern black nightshade. This wide spectrum of weeds controlled would make Balance a welcome addition if it was registered on pumpkin. Outlook is sold by BASF Ag Products. Its active ingredient is dimethenamid which is a chloroactemide. Outlook is currently registered on corn and dry beans but not pumpkins. The weeds controlled by Outlook include barnyardgrass, crabgrass, foxtail, goosegrass, fall panicum, witchgrass, carpetweed, pigweed, and purslane. Outlook could provide a preemergent grass herbicide that would complement Sandea.

Materials and Methods

The objective of our research was to evaluate the weed control and tolerance of transplanted pumpkin to herbicides either applied to bare ground or between the plastic mulch. The experiment was a split-plot design with three replications. The whole plot treatments were with or without pastic mulch and the subplot treatment was herbicides. The beds were shaped and black plastic laid to half the plots on June 5. On June 11, herbicides applied between plastic mulch with a CO₂ pressurized backpack sprayer delivering 28 gpa. Six week old ‘Howden” transplants planted between June 16 and June 17. The herbicide treatments were a weedy control, Command at 0.5 lb/acre, Strategy at 1.05 and 1.57 lb/acre, Sandea at 0.023 lb/acre, Strategy + Sandea at 1.05 + 0.023 lb/acre, Balance at 0.047 and 0.94 lb/acre, Balance + Sandea at 0.047 + 0.023 lb/acre, and Outlook at 1.0 lb/acre. The data we collected included at 4 and 6 weeks: plant stand and vigor. The stunting ratings were on a scale of 5 = no injury or stunting to 1 = complete plant death. The weed control data we collected were % control of pigweed, velvetleaf, and grasses. The ratings were based on 0 = no weed control to 100 = complete control. Data were analyzed with ANOVA and means separated using Fisher’s lsd at the 5% level.

Preliminary Results

Early pumpkin vigor was substantially greater in the black plastic mulch than in the bare ground treatment. Balance reduced early vigor in the bare ground treatment and not in the plastic mulch. The lack of injury in the black plastic mulch was because the pumpkins did not come in direct contact with Balance. By thee second rating the vigor in the bare ground was similar to the pumpkin vigor in the plastic mulch treatment. The pumpkins treated with Balance at 0.188 lb/A and growing without plastic had less vigor on August 6 then any other treatment.

All herbicide treatments provided good weed control. Command tend to be weak against pigweed. Outlook in the black plastic mulch treatment provided the best pigweed control. In the bare ground system several herbicides including Sandea, Balance, and Outlook provided good early season pigweed control. The other weeds were not common enough to detect significant differences in control.

Treatment List

The treatment list contains the herbicides and their rates along with the plot number that contains the particular treatment.

______________________________________________________________________________

Replication

Treatment Rate Plastic? 1 2 3

_____________________________________________________________________________

lbs a.i./A

1. Control – No 114 207 316

2. Command 3 ME 0.50 No 118 205 315

3. Strategy 2.1 SE 1.05 No 120 203 311

4. Strategy 2.1 SE 1.575 No 111 209 317

5. Sandea 75DF 0.031 No 117 208 312

6. Strategy + Sandea 1.05 + 0.031 No 119 202 319

7. Balance Pro SC 0.094 No 112 204 314

8. Balance Pro SC 0.188 No 116 210 318

9. Balance + Sandea 0.094+0.031 No 113 206 320

10. Outlook 1.0 No 115 201 313

...................................................................................................................................................

11. Control – Yes 105 219 310

12. Command 3 ME 0.50 Yes 103 213 306

13. Strategy 2.1 SE 1.05 Yes 102 212 308

14. Strategy 2.1 SE 1.575 Yes 107 216 307

15. Sandea 75DF 0.031 Yes 110 215 301

16. Strategy + Sandea 1.05 + 0.031 Yes 109 214 305

17. Balance Pro 4SC 0.094 Yes 106 211 309

18. Balance Pro 4SC 0.188 Yes 108 217 304

19. Balance + Sandea 0.094+0.031 Yes 104 220 302

20. Outlook 1.0 Yes 101 218 303

______________________________________________________________________________
Plot Plan

The plot numbering starts on the south side of the field. Fifteen feet nearest the pumpkin row was treated with the herbicide. Herbicides were applied over the bare ground treatment and between rows of plastic before planting. Herbicides were not applied under the plastic. The area between rows was also disced before vining.

101 Plastic 10 Outlook 1.0	111 Bare Grd 14 Strategy 1.575	201 Bare Grd 10 Outlook 1.0	211 Plastic 17 Balance 0.094	301 Plastic 5 Sandea 0.031	311 Bare Grd 13 Strategy 1.05
102 Plastic 3 Strategy 1.05	112 Bare Grd 17 Balance 0.094	202 Bare Grd 6 Strategy +Sandea	212 Plastic 13 Strategy 1.05	302 Plastic 9 Balance+ Sandea	312 Bare Grd 15 Sandea 0.031
103 Plastic 2 Comman 0.5	113 Bare Grd 19 Balance+ Sandea	203 Bare Grd 3 Strategy 1.05	213 Plastic 12 Comman 0.5	303 Plastic 10 Outlook 1.0	313 Bare Grd 20 Outlook 1.0
104 Plastic 9 Balance+ Sandea	114 Bare Grd 11 Control	204 Bare Grd 7 Balance 0.094	214 Plastic 16 Strategy +Sandea	304 Plastic 8 Balance 0.188	314 Bare Grd 17 Balance 0.094
105 Plastic 1 Control	115 Bare Grd 20 Outlook 1.0	205 Bare Grd 2 Comman 0.5	215 Plastic 15 Sandea 0.031	305 Plastic 6 Strategy +Sandea	315 Bare Grd 12 Comman 0.5
106 Plastic 7 Balance 0.094	116 Bare Grd 18 Balance 0.188	206 Bare Grd 9 Balance+ Sandea	216 Plastic 14 Strategy 1.575	306 Plastic 2 Comman 0.5	316 Bare Grd 11 Control
107 Plastic 4 Strategy 1.575	117 Bare Grd 15 Sandea 0.031	207 Bare Grd 1 Control	217 Plastic 18 Balance 0.188	307 Plastic 4 Strategy 1.575	317 Bare Grd 14 Strategy 1.57
108 Plastic 8 Balance 0.188	118 Bare Grd 12 Comman 0.5	208 Bare Grd 5 Sandea 0.031	218 Plastic 20 Outlook 1.0	308 Plastic 3 Strategy 1.05	318 Bare Grd 18 Balance 0.188
109 Plastic 6 Strategy +Sandea	119 Bare Grd 16 Strategy +Sandea	209 Bare Grd 4 Strategy 1.575	219 Plastic 11 Control	309 Plastic 7 Balance 0.094	319 Bare Grd 16 Strategy +Sandea
110 Plastic 5 Sandea 0.031	120 Bare Grd 13 Strategy 1.05	210 Bare Grd 8 Balance 0.188	220 Plastic 19 Balance+ Sandea	310 Plastic 1 Control	320 Bare Grd 19 Balance+ Sandea

Table 1. The effect of plastic mulch and herbicide treatment on pumpkin stand and vigor.

____________________________________________________________________________

Plant stand^a Vigor^b

Treatment Rate Plastic? July 17 Aug 6 July 17 Aug 6

____________________________________________________________________________

lbs a.i./A ---- #/ plot ----

1. Control – N 9 9 2.3 4.7

2. Command 0.50 N 9 9 3.2 5

3. Strategy 1.05 N 9 9 2.5 5

4. Strategy 1.575 N 9 9 3.3 4.7

5. Sandea 0.031 N 10 10 2.8 4.5

6. Strategy + Sandea 1.05 + 0.031 N 9 9 3 5

7. Balance 0.094 N 10 10 3.2 4.7

8. Balance 0.188 N 9 9 1.2 3.8

9. Balance + Sandea 0.094+0.031 N 10 10 2.2 4.8

10. Outlook 1.0 N 9 9 2.8 5

...................................................................................................................................................

11. Control – Y 10 10 5 5

12. Command 0.50 Y 8 8 4.7 4

13. Strategy 1.05 Y 9 9 4.7 5

14. Strategy 1.575 Y 9 9 4.7 5

15. Sandea 0.031 Y 9 9 4.7 5

16. Strategy + Sandea 1.05 + 0.031 Y 9 9 4.7 4.8

17. Balance 0.094 Y 9 9 4.3 5

18. Balance 0.188 Y 9 9 4.7 5

19. Balance + Sandea 0.094+0.031 Y 9 9 4.7 4.8

20. Outlook 1.0 Y 9 9 4.8 5

______________________________________________________________________________

^aThe maximum number of plants per plot was 10.

^bVigor was rated on the scale of 1 = lacking vigor to 5 = maximum vigor.

Table 2. The effect of herbicide treatment and plastic mulch on weed control.

______________________________________________________________________________

Velvetleaf Pigweed _Grass .

Treatment Rate Plastic? July 17 Aug 6 July 17 Aug 6 July 17 Aug 6

______________________________________________________________________________

lbs a.i./A ------------------------- % Control ------------------------

1. Control – N 89 92 87 72 83 77

2. Command 0.50 N 100 99 87 82 99 85

3. Strategy 1.05 N 97 97 93 87 99 97

4. Strategy 1.575 N 98 98 94 90 100 96

5. Sandea 0.031 N 95 95 98 88 91 87

6. Strategy + Sandea 1.05 + 0.031 N 98 98 100 88 98 99

7. Balance 0.094 N 99 99 95 87 98 94

8. Balance 0.188 N 100 99 96 92 100 96

9. Balance + Sandea 0.094+0.031 N 98 96 96 93 98 99

10. Outlook 1.0 N 95 99 99 94 100 99

............................................................................................................................................................

11. Control – Y 97 92 65 50 95 90

12. Command 0.50 Y 99 100 67 68 99 98

13. Strategy 1.05 Y 95 100 86 90 99 98

14. Strategy 1.575 Y 96 100 88 78 100 97

15. Sandea 0.031 Y 98 99 88 83 89 92

16. Strategy + Sandea 1.05 + 0.031 Y 99 100 89 86 99 97

17. Balance 0.094 Y 96 100 90 78 98 98

18. Balance 0.188 Y 100 100 96 88 99 100

19. Balance + Sandea 0.094+0.031 Y 99 98 82 70 100 96

20. Outlook 1.0 Y 96 100 98 100 100 100

______________________________________________________________________________