Damage Thresholds. Section 8

Transcription

1 Damage Thresholds Section 8

2 Relative yield Hypothetical yield of crop as affected by length of early season weed control Yield loss No yield loss Weeks of control

3 Relative yield Hypothetical yield of crop as affected by length of early season weed interference No yield loss Yield loss Weeks of interference

4 Relative yield Hypothetical example of critical period of interference Critical period Weeks

5 Weed Thresholds-Hypothetical Example 1 weed per 10 foot of row = 5% yield loss 2 weeds per 10 foot of row = 10% yield loss Herbicide Cost = 10% of crop value Damage threshold = 1 weed per 10 foot of row Economic threshold = 2 weeds per 10 foot of row

6 Factors Affecting Economic Thresholds Species and densities of weeds Cost of control measure Commodity price Yield potential in absence of weed complex and decrease in yield associated with interference from the weed complex

7 Can spraying lower weed populations be justified when Crop yield potential increases? As yield potential increases, the population of weeds to justify spraying decreases. Treatment cost decreases? As treatment cost increases, the population of weeds to justify spraying increases. Commodity price increases? As crop value increases, the population of weeds to justify spraying decreases.

8 Developing Weed Thresholds

9 Competitive Indices (1 = least, 10 = most) Weed Species Competitive Index Cocklebur 10 Velvetleaf 5.8 Smartweed 4.7 Common ragweed 4 Pitted morningglory 3 Sicklepod 2.5 Barnyardgrass 1.0 Crabgrass 0.5

10 Multi-Species Threshold Each unit of Total Competitive Load [TCL] = 0.3% Yield Loss for Corn 0.5% Yield Loss for Soybean 0.65% Yield Loss for Cotton 0.75% Yield Loss for Peanut

11 Example of Multi-species Threshold Weed Species # of weeds per 30 ft of row Competitive Index Competitive Load Cocklebur Smartweed Sicklepod Total Competitive Load 39.4

12 Multi-Species Threshold in Soybeans Each unit of TCL = 0.5% Yield Loss % yield loss without treatment: 39.4 X 0.5% = 19.7% Bushel yield loss without treatment: 30 bushels per acre X 19.7% = 5.9 bushels % economic loss without treatment 5.9 bushels X $6/bushel = $35.4/acre

13 Example: Given the following weed populations, calculate the percent yield loss if herbicides are not applied - soybean Weed Competitive index Field 1 Field 2 Cocklebur Smartweed Sicklepod Crabgrass Ragweed Velvetleaf If the soybean price is $6.60 per bushel and the yield potential is 48 bushels per acre, how much money can the farmer spend and still remain in the black on the herbicide investment? Field 1 Field 2

14 Example: Given the following weed populations, calculate the percent yield loss if herbicides are not applied - soybean Weed Competitive index Field 1 Field 2 Cocklebur 10 2 (20) 1 (10) Smartweed (0) 1 (4.7) Sicklepod (2.5) 2 (5.0) Crabgrass (2.0) 3 (1.5) Ragweed 4 1 (4) 0 (0) Velvetleaf (0) 2 (11.6) TCL If the cotton price is $6.60 per bushel and the yield potential is 48 bushels per acre, how much money can the farmer spend and still remain in the black on the herbicide investment? -Field X 0.5% = 14.25, X 48 = 6.84 bushels/acre lost, or $45.14/acre if herbicides are not applied -Field X 0.5% = 16.4, X 48 = 7.87 bushels/acre lost, or $51.96/acre if herbicides are not applied

15 Additional Research Needs -Determine Competitive Index for additional weeds -Continued verification of model in field -Evaluate factors affecting weed and crop interference Row spacing, plant populations, planting date, rainfall, soil characteristics, fertility, variety -Develop efficient scouting techniques -Determine effects of weeds below threshold on weed seed reserves and subsequent effects on future crops

16 Critical Periods of Interference How long after planting should crop remain weed-free How long can weeds remain in the crop without reducing yield

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34 Use in the Field

35 Using Pocket HERB to Demonstrate Benefits of Weed Scouting Perceived limitation of thresholdbased weed management is cost and time required to scout fields. Developing scouting methodology that makes scouting and use of HADSS more practical.

36 Percent of Samples Infested by Weeds in 52 Fields in NC from 1997 through 2001 From: Jordan et al Evaluation of scouting methods in peanut (Arachis hypogaea) using theoretical net returns from HADSS. Weed Technol. 17: Weed Species Yellow nutsedge, pitted and entireleaf morningglory, cocklebur Purple nutsedge, signalgrass, horsenettle, ragweed, prickly sida Lambsquarters, bermudagrass, dayflower, crabgrass, redroot pigweed, eclipta Spurred anoda, sicklepod, goosegrass, tall morningglory, trumpet creeper Percent of Samples 27.1 to to to to 2.8

37 Figure 1. Examples of Scouting Procedures used in 17 Fields with 12 or More Acres per Field Exit to other fields Sample 6 Sample 7** Sample 15 Sample 4 Sample 5* Sample 8* Sample 9** Sample 14 Sample 3* Sample 2 Sample 10* Sample 1* Sample 11** Sample 13 Sample 12* Field entrance Legend *six-sample ** three-sample

38 Percent of Time Recommendations Same as Whole-Field Recommendation. Data are from 17 fields with at least 12 acres. Paraquat Full sample Six Sample Three sample Grower standard Yes No Pooled

39 Percent of Times the Most Economical Herbicide Recommendation Following Various Scouting Procedures was the Same as the Optimum Whole-Field Approach Data are from 17 Fields Full 6-stop 3-stop Grower standard

40 % of yield % of yield % of yield PRE Herbicides Soybean NC data Aid in weed control Good agronomic practice Avoid early competition POST timing less critical Component of resistance management No PRE -13 % Plus PRE -34 % Timely 1 wk delay 2 wk delay Time of Roundup application Cotton NC data Corn NC data No PRE Plus PRE No PRE Lariat PRE % -24 % % -14 % Timely 1 wk delay 2 wk delay Time of Roundup application Timely 1 wk delay 2 wk delay Time of Roundup application