Kansas State University Field Pansy Control In No-Till Fields Going To Soybeans

Transcription

1 Field Pansy Control In No-Till Fields Going To Soybeans Trial ID: BEANS Location: Wayne Albertson Study Dir.: Jason Miller Investigator: David L Regehr CROP AND WEED DESCRIPTION Weed Code Common Name Scientific Name 1. VIORA Pansy, field Viola rafinesquii SITE AND DESIGN Plot Width, Unit: 6.7 FT Plot Length, Unit: 25 FT Reps: 4 Site Type: CROPLAND Tillage Type: NO-TILL Study Design: FACTORIAL Previous Crops Previous Pesticides Year 1. FIELD CORN Various 2002 SOIL DESCRIPTION Texture: silty clay loam Soil Name: Grundy Fert. Level: good APPLICATION DESCRIPTION Application Date: 22/Nov/2002 5/Apr/2003 Time of Day: 11:45 AM 11:30 Application Method: SPRAY SPRAY Application Timing: Fall Spring Applic. Placement: BROADCAST BROADCAST Air Temp., Unit: 48 F 46 F % Relative Humidity: Wind Velocity, Unit: 5 NW 7 N Dew Presence (Y/N): N N Soil Temp., Unit: 41 F 45 F Soil Moisture: ADEQUATE ADEQUATE % Cloud Cover: 0 50 WEED STAGE AT EACH APPLICATION Weed 1 Code, Stage: VIORA COT-1 DIA VIORA COT-3 DIA Stage Scale: 0-1/2 IN 0-3 IN APPLICATION EQUIPMENT Appl. Equipment: BACKPACK BACKPACK Operating Pressure: Nozzle Type: TT TT Nozzle Size: Nozzle Spacing, Unit: 20 IN 20 IN Nozzles/Row: 4 4 Boom Length, Unit: 6.7 FT 6.7 FT Boom Height, Unit: 20 IN 20 IN Carrier: WATER WATER Spray Volume, Unit: 15 GPA 15 GPA

2 Trial Comments This experiment was designed to evaluate field pansy control in a no-till field ahead of soybeans. In Brown County, KS, identical treatments were applied either in the fall ( ) or in the spring (4-5-03). The spring application was later than we would have liked, but windy weather pushed back the application date. All treatments contained a base of 0.5 lb/a 2,4-D (1 pt/a LV4) and 2 fl oz/a dicamba () in order to control other winter annual broadleaf weeds. This was our first major effort to control field pansy, and herbicide rates were on the high side. The range in cost of treatments in the experiment was approximately $10 to $30/A. A goal of future research is to reduce treatment costs while maintaining weed control efficacy. Visual ratings were taken in January, April, and May. The main interest is in the May 6 rating just prior to soybean planting. There was no precipitation for almost two months following the fall applications, and many treatments showed very little activity at first. Also, the presence of corn residues at fall application raised questions about how effective the spray coverage was. In addition, herbicide activity is difficult to score while winter annuals are largely dormant, as at the January rating. However, by April, all but one of the fall applications showed 88% or greater control of field pansy. After application in early April, only five of 14 treatments gave 85% or greater control of field pansy. The factorial design of this experiment allowed us to directly compare the control from fall- vs. spring-applied treatments. Average field pansy control, rated on early May, was 92% after fall application vs. 77% for the same treatments after application in spring. The only treatment that gave better control after being applied in spring was 0.5 oz/a plus 2,4-D plus dicamba. When applied in fall, this treatment was shaky with only about 75% control, but the 85% control following spring application, plus it being one of the lowest cost treatments, suggests that this treatment merits further attention. Another treatment that performed fairly well in spring was 26 fl oz/a RoundupUltra Max plus 2,4-D plus dicamba, a treatment that costs about $13/A. This may be a good option for field pansy, but many soybean growers would prefer a spring burndown treatment with more residual activity, hoping to reduce in-crop weed management costs. The winter of was drier than normal, and there appeared to be little spring germination of field pansy. Consequently, fall applications of non-residual treatments such as glyphosate or paraquat with 2,4-D and dicamba, gave over 90% control at modest cost. At this point, we don't know how much spring germination to expect, and whether spring-germinated field pansy is much of a threat to soybean production. Given the advantages of controlling winter annuals in fall rather than in spring, and the gaps in our understanding of field pansy germination and establishment, it seems prudent to favor a fall herbicide treatment with foliar burndown and adequate residual to control spring germinators. Several treatments meet these criteria, and the one that does it at least cost appears to be 2 oz/a Canopy XL plus 2.5 oz/a plus 2,4-D plus dicamba plus crop oil concentrate at about $14/A. Several other treatments have potential and merit further study.

3 1 Fall 43 fgh 94 a 98 a 93 a 2 Fall 48 e-h 96 a 97 a 94 a Resource 3 fl oz/a 3 Fall 35 gh 99 a 100 a 96 a BackDraft 2.5 qt/a 4 Fall 88 a 95 a 98 a 92 a Gramoxone Max 1.67 pt/a 5 Fall 70 a-d 95 a 94 a 89 ab 6 Fall 80 abc 99 a 100 a 94 a 7 Fall 73 a-d 99 a 99 a 91 a 8 Fall 65 b-e 99 a 100 a 95 a 9 Fall 53 d-g 99 a 99 a 100 a 10 Fall 60 c-f 100 a 100 a 97 a 11 Fall 30 h 85 a 91 a 75 a-d

4 12 Fall 53 d-g 96 a 99 a 95 a 13 Fall 83 ab 74 a 95 a 88 ab 14 Fall 80 abc 98 a 98 a 94 a 15 Fall 0 i 0 b 0 i 0 f Untreated Check 16 Spring 58 cde 89 ab 17 Spring 50 ef 84 abc Resource 3 oz/a 18 Spring 60 cde 84 abc BackDraft 2.5 qt/a 19 Spring 80 b 64 cd Gramoxone Max 1.67 pt/a 20 Spring 55 de 46 e 21 Spring 73 bc 66 bcd 22 Spring 35 g 58 de

5 23 Spring 63 cde 78 abc 24 Spring 38 fg 90 ab 25 Spring 48 efg 90 ab 26 Spring 23 h 85 abc 27 Spring 63 cde 85 abc 28 Spring 38 fg 79 abc 29 Spring 70 bcd 81 abc 30 Spring 0 i 0 f Untreated Check LSD (P=.05) CV Means followed by same letter do not significantly differ (P=.05, Student-Newman-Keuls) Mean comparisons performed only when AOV Treatment P(F) is significant at mean comparison OSL.