Sweet Corn Insect Management Update. Rick Foster Department of Entomology Purdue University

Sweet Corn Insect Management Update Rick Foster Department of Entomology Purdue University

Goals of This Talk To update recent research results related to how to best use pheromone traps to manage corn earworms To convince growers to purchase and use their own pheromone traps To update pesticide recommendations, especially related to pyrethroid resistance

Corn Earworm Pest of sweet corn, seed corn, tomato and other crops Two generations per year where it overwinters 2 nd is usually most important

Corn Earworm Biology Females prefer to lay eggs on green silks

Corn Earworm Biology Females prefer to lay eggs on green silks When larvae hatch, they move directly into the ear tip Once inside the ear, the larvae are protected from insecticides

Corn Earworm Population Dynamics Northern Indiana is generally too cold for earworms to overwinter in appreciable numbers Southern Indiana has substantial overwintering First generation is usually small, but depends on location (north vs. south) The second generation is larger but many later season moths move northward from the southern US on storm fronts

Corn Earworm Control Must have insecticide present on silk when larvae hatches from egg Pyrethroids such as Brigade, Mustang Max Hero, and Warrior are no longer reliable due to resistance Coragen and Radiant are good alternatives

Corn Earworm Management Treat when fresh, green silks are present (start at 70%) and if threshold has been exceeded (more on that later) Threshold = 10 moths per night

Corn Earworm Management Make treatments every 2-5 days from 70% silks until silks are brown; generally 3-4 treatments Shorten interval if temperatures are high (highs >85 o F) Shorten interval if moth catches are high (>50)

CEW Management Tips The first application (70% silks) is the most critical, with each succeeding spray being less important Getting good coverage of the silks is imperative consider drop nozzles. Test with water sensitive paper.

Corn Earworm Management First generation populations are usually relatively low, but not always During much of the season, few earworms present Once the second generation hits, populations will likely be high for the rest of the season Date of arrival of second generation is variable

900 2014 Pheromone Trap Catches 800 700 Moths Per Week 600 500 400 300 200 100 0 Week Ending Lafayette Wanatah Vincennes

300 250 2008 - Lafayette Moths per Week 200 150 100 50 0 Week Ending

Trapping Information Dissemination For several years, we have had a network of traps around the state (6-10) Cooperators check the trap frequently and report the catch to me I maintain a website where trap catches are posted http://www.extension.entm.purdue.edu/corn earworm/index.php

Monitoring Costs White plastic mesh trap is $98.50 from Gemplers and will last about 3 years or about $33 per year. Wire screen traps from Bob Poppe s Service are $215 and will last about 10 years, about $21.50 per year. Hercon pheromone lures from Great Lakes IPM are $16.80 for 10, which will last the season Total sampling costs (not including your time) is $38.30 - $49.80, but let s round up to $50

Monitoring Benefits What if you miss one application because you don t have a trap and you lose 10% of one acre of sweet corn? 1000 dozen ears per acre/10 = 100 dozen $3 per dozen $300 lost That will pay your monitoring costs for 6 years

Relationship Between Pheromone Trap Catch and Egg Laying Jonathan Nixon, Rick Foster, and Rick Weinzierl

Relationship Between Pheromone Trap Catch and Egg Laying

Nightly Relationship Between Trap Catch and Egg Laying

What s Going On? The use of pheromone traps and the economic threshold of 10 moth/trap/night has been used effectively for several decades and yet we can t show a relationship between nightly trap catch and oviposition.

How Do Pest Managers Make Decisions? You must take all available information into consideration, not just last night s pheromone trap catch. Most growers will take into account the general trend in trap catches when making a spray decision. So, we decided to look at how trap catch and egg deposition were related when we looked at 10 days of silking for each of our plantings.

CEW Trap Catch and Oviposition 2010 1600 3 Pheromone Trap Catch 1400 1200 1000 800 600 400 Underestimation of egg laying Good agreement 2.5 2 1.5 1 0.5 Eggs per Silk 200 0 0-0.5 0 1 2 3 4 5 6 7 8 9 10 Planting

So, how do we use threshold? We should use the threshold of 10 moths per night when the neighboring field corn is silking Early in the season when field corn is not attractive to moths for egg laying, we propose that the threshold should be 1 moth per night Late in the season probably won t matter because moth catches are usually high

Testing the Hypothesis In 2014, we conducted a study to see how the new proposed threshold of 1 moth/night in the early season compared with the old threshold of 10 moths/night 8 planting dates April 18 May 28 April 27 June 6 May 8 June 16 May 23 June 26 4 treatments (Coragen for first 3 treatments; then Radiant if necessary) Untreated control 4 applications based on crop stage (Calendar sprays) Up to 4 applications, threshold = 10 moths per night Up to 4 applications, threshold = 1 moth per night

Planted April 18/Harvested July 14 Treatment # Sprays % Clean No Spray Control 0 42.3 b Calendar Sprays 4 76.5 a Threshold = 10 moths/night 3 (2 nd, 3 rd, 4 th ) 57.2 ab Threshold = 1 moth/night 4 79.7 a 1 st Silks Pheromone Catches June 23-12 July 1-48 June 24-1 July 2-13 June 25-0 July 3 1* June 26-2 July 4-2 June 27 25* July 5-18 June 28-25 July 6-17 June 29-24 July 7 17* June 30 24* July 8-16 * = Spray date Neighboring field corn not silking yet. First spray was applied on June 27, at 72% silk. Red text = Above 10 moths/night

Planted April 27/Harvested July 21 Treatment # Sprays % Clean No Spray Control 0 64.0 b Calendar Sprays 4 92.4 a Threshold = 10 moths/night 2 (2 nd, 4 th ) 80.2 ab Threshold = 1 moth/night 4 94.5 a Pheromone Catches June 30-24 July 8 16 July 1-48 July 9 10 July 2-13 July 10 0* July 3 1 July 11 18 July 4 2* July 12 18 July 5 18 July 13 18 July 6 17 July 14 18* July 7 17* July 15-7 Neighboring field corn not silking yet. First spray was applied on July 4, at 70% silk.

Planted May 8/Harvested July 28 Treatment # Sprays % Clean No Spray Control 0 90.1 b Calendar Sprays 4 98.5 a Threshold = 10 moths/night 2 (1 st, 2 nd ) 96.0 a Threshold = 1 moth/night 4 97.5 a Pheromone Catches July 5 18 July 13-18 July 6 17 July 14-18* July 7 17 July 15-7 July 8 16 July 16-0* July 9 10* July 17-0 July 10 0 July 18-0 July 11 18 July 19-1* July 12 18 July 20-0 Neighboring field corn began silking July 14. First spray was applied on July 9, at 72% silk.

Planted May 23/Harvested August 4 Treatment # Sprays % Clean No Spray Control 0 99.0 a Calendar Sprays 4 98.5 a Threshold = 10 moths/night 0 99.0 a Threshold = 1 moth/night 3 (1 st, 2 nd, 4 th ) 95.0 a Pheromone Catches July 12 18 July 20-0 July 13 18 July 21-0 July 14 18 July 22 0* July 15 7 July 23-3 July 16 0* July 24-0 July 17 0 July 25 0* July 18 0 July 26-0 July 19 1* July 27-0 Neighboring field corn beginning silking. First spray was applied on July 16, 65% silk.

Planted May 28/Harvested August 13 Treatment # Sprays % Clean No Spray Control 0 98.0 a Calendar Sprays 4 100 a Threshold = 10 moths/night 0 98.0 a Threshold = 1 moth/night 1 (2 nd ) 99.5 a Pheromone Catches July 18 0 July 26-0 July 19-1 July 27-0 July 20 0 July 28 0* July 21 0 July 29-0 July 22 0* July 30-0 July 23 3 July 31-0 July 24 0 August 1-0* July 25 0* August 2-0 Neighboring field corn silking. First spray was applied on July 22, at 68% silk.

Planted June 6/Harvested August 20 Treatment # Sprays % Clean No Spray Control 0 92.0 a Calendar Sprays 4 97.0 a Threshold = 10 moths/night 0 95.5 a Threshold = 1 moth/night 2 (3 rd, 4 th ) 98.0 a Pheromone Catches July 28 0 August 5-1 July 29 0 August 6-1 July 30 0 August 7-0* July 31 0 August 8-0 August 1-0* August 9-2 August 2-0 August 10-2 August 3-0 August 11-1 August 4-0* August 12-3* Neighboring field corn in late silking period. First spray was applied on August 1, at 71% silk.

Planted June 16/Harvested August 27 Treatment # Sprays % Clean No Spray Control 0 87.5 b Calendar Sprays 4 98.5 ab Threshold = 10 moths/night 2 (3 rd, 4 th ) 91.8 ab Threshold = 1 moth/night 4 99.5 a Pheromone Catches August 1 0 August 11-1 August 2-0 August 12-3 August 3-0 August 13-2* August 4-0 August 14-8 August 5-1 August 15-1* August 6-1 August 16-12 August 7-0* August 17-11 August 8-0 August 18-11* August 9 2 August 19-7 August 10 2 August 20-21 Neighboring field corn past silking. First spray was applied on August 7, at 79% silk.

Planted June 26/Harvested September 4 Treatment # Sprays % Clean No Spray Control 0 3.5 b Calendar Sprays 4 89.5 a Threshold = 10 moths/night 4 83.5 a Threshold = 1 moth/night 4 83.5 a Pheromone Catches August 15-1 August 23-23* August 16-12 August 24-49 August 17-11 August 25-48 August 18-11 August 26-84 August 19-7* August 27-83* August 20-21 August 28-41 August 21-48 August 29-114* August 22-91 August 30-126 Neighboring field corn well past silking. First spray was applied on August 19, at 69% silk.

Summary for 8 Plantings Treatment # Sprays % Spray Reduction Mean % Clean Range % Clean Untreated Control 0 100 72.1 3.5-100 Calendar Sprays 32 --- 93.9 76.5-100 Threshold = 10 moths/night 13 59 87.7 57.2-99 Threshold = 1 moth/night 26 19 93.4 79.7-99.5 Dynamic threshold 1 moth for PD 1, 2, 3, 7, 8 10 moths for PD 4, 5, 6 22 31 93.4 79.7-99.5

Conclusions for 2014 Study Using the 1 moth/night threshold for the entire season would have saved 6 sprays with no loss of control Using the 10 moth/night threshold for the entire season would have saved 19 sprays but would have resulted in unacceptable damage levels in 3 plantings Using the combination of thresholds would have saved 10 sprays and resulted in reasonably good control in all plantings Similar results with 5 plantings in 2013 Study needs to be repeated at least one more year

Conclusions Every serious sweet corn grower should have a corn earworm pheromone trap During early season production prior to silking of field corn and late in the season after field corn has dried down, the threshold should be 1 moth per night. During pollination of field corn, the threshold should be 10 moths per night. Pyrethroid resistance has reached the point where control cannot be counted on when used alone Coragen and Radiant are good alternatives Besiege (Premix of Warrior and Coragen) works well You can create your own premixes with either Coragen or Radiant + one of the pyrethroids (or Lannate)

Bonus!!!

Questions? Follow me on Twitter at: Rick Foster@PurdueFVInsect