Revisiting Soybean Aphids How does soybean price effect the threshold? And what s next. By: Lesley Lubenow NDSU Extension Service Area Specialist/Agronomy Use of slides from: Jan Knodel, NDSU Extension Service
Soybean Aphid (Aphis glycines) From Asia In the U.S. since the year 2000 Roy Scott, SDSU Mike Rankin, UW-Extension
Populations will vary
Soybean aphid Life cycle
Soybean aphid - Biology Parthenogenesis in fields No males needed! Birth to Live young Short generation time (only 5 days) Telescoping of generations Aphids are born pregnant 6 to 9 aphids per day Population doubles every 1.8 days Grandmothers contain their daughters & granddaughters
Soybean aphid - Biology Hot temperatures reduce populations Beneficial Insects reduce populations Aphids can wash off in heavy rain storms
Soybean Aphid Damage Symptoms Stunted, yellowing plants Leaf distortion Sooty mold on leaves from honeydew Transmit viruses that infect soybean
Quiz
Where do they overwinter? Option One: Buckthorn Option Two: Chokecherry Option Three: Box-Elder
Where do they overwinter? Option Two: Chokecherry Answer: Buckthorn Option Three: Box-Elder
The 250 aphid threshold! NDSU and regional universities recommendation Spray when: 250 aphids per plant and increasing Up to R5 growth state
Timing of Application 250 aphids per plant Threshold increases. Yield benefit often less. Do Not treat Veg stages R1 R2 bloom R3-R4 pods forming, growing R5 seeds forming filling R6 full seed R7 maturing R8 mature
The 250 aphid threshold! NDSU recommendation: Spray when there are 250 aphids per plant and increasing up to R5 Heard and read talks where much lower numbers are encouraged What happens when the price goes up?
The Reason for 250 Back to the Basics IPM EIL= Economic Injury Level This timing is when insects are hurting yield! EIL = (C*N)/(V*I) ET= Economic Threshold This timing is when it is time to spray!
Number of Insects Soybean Aphid IPM Economic Injury Level Economic Threshold Time (days, weeks) Economic threshold for soybean aphid. J. Econ. Entomol. 100(4): 1258-1267.
Number of Insects Soybean Aphid IPM Economic Injury Level Economic Threshold =250 aphids Time (days, weeks) Economic threshold for soybean aphid. J. Econ. Entomol. 100(4): 1258-1267.
Number of Insects Soybean Aphid IPM Economic Injury Level =674 aphids Economic Threshold =250* aphids Time (days, weeks) *Rounded number, actual no. = 273 aphids Economic threshold for soybean aphid. J. Econ. Entomol. 100(4): 1258-1267.
Number of Insects Soybean Aphid IPM 7 days Economic Injury Level =674 aphids Economic Threshold =250* aphids Time (days, weeks) *Rounded number, actual no. = 273 aphids Economic threshold for soybean aphid. J. Econ. Entomol. 100(4): 1258-1267.
19 location-years (n=464) Basis of the calculated Economic Threshold for Soybean Aphid Data from Ragsdale, et al. 2007. JEE 100(4): 1258-1267
Plots sprayed at the Threshold - aphid # doesn t reach the EIL - residue still present during midseason aphid flight -Formula uses a 7 day lag time to get spraying accomplished Aphid number EIL 674 ET 250 Spray EIL ET Residue Time
The Real World Application of EIL What happens if aphids are sprayed at too low numbers? What happens if aphids are sprayed late? What happens if soybean price increases?
Plots sprayed too early (fewer than 250 aphids/ plant) - remaining aphids rebound in absence of natural enemies - residue breaks down before midseason aphid flights SBA number EIL 674 ET 250 Spray aphid #s rebound Time
19 location-years (n=464) Treating low aphid populations results in no detectable yield increase (cannot detect difference when <1-2 bu/acre).
The Real World Application of EIL What happens if aphids are sprayed at too low numbers? What happens if aphids are sprayed late? What happens if soybean price increases?
Plots sprayed late (more than 674 aphid/ plant) - some yield loss already occurred Spray Yield loss occurs Aphid number EIL 674 ET 250 Time
The Real World Application of EIL What happens if aphids are sprayed at too low numbers? What happens if aphids are sprayed late? What happens if soybean price increases?
The price of beans needs to be factored into the threshold in some way. Do $15 soybeans mean we lower the economic threshold below 250 aphids per plant? Based on research, at $15/bushel soybeans would decrease the EIL to 450 aphids per plant.
EIL 674 at $6.50/bushel EIL Aphid number EIL 450 at $15.00/bushel ET 250 Spray Residue EIL ET Time Lead time is reduced to 3-4 days instead of 7 days. No change in IPM recommendation.
What s the future for Soybean Aphid IPM? Rag1 and Rag2 genes for soybean aphid host plant resistance Work done in IA. NDSU is working with Rag1. Resistance genes may change aphid doubling time, and new thresholds would need to be calculated. Soybean maturity groups, not available here Yield penalty, less so with Rag1 and Rag2 beans In Iowa, aphids are overcoming the genetics in some fields.
Current IA rec s for Resistant Beans Consider Genetics for Fields sprayed 2 out of 4 years Organic Soybeans Difficult to Spray Fields In Aphid Hot Spots Farmers who are motivated by reduced chemical application Resistant Beans vs. susceptible, photo courtesy of IA Extension
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