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Some late season activity by corn earworm and fall armyworm in parts of Virginia

Although most of our sweet corn has been harvested for 2018, there are still some late-planted fields that may still be at risk to insect attack.  While most of the remaining pheromone traps around the state had low catch numbers, Mark Sutphin VCE Frederick County saw a great jump in corn earworm catch this week at one of the farms still growing sweet corn.  Keep in mind that corn earworm is also a pest of many other crops that may still be at risk this fall including tomatoes and beans (See images below).

Please keep in mind, In an effort to fend off any more pyrethroid insecticide resistance development in our corn earworm populations, rotating to another insecticide than a Class 3 (pyrethroid) is highly encouraged for at least one spray. Diamide insecticides such as Coragen or Besiege, the carbamate Lannate LV, or the spinosyn Blackhawk, are all effective non-pyrethroid options.

Also, Phil Blevins VCE Washington County reported some of the highest fall armyworm catch of the year >200 moths in the bucket trap this week.  These moths showed up late to southwest Virginia and are probably not going to be much of a pest concern in the state, and they will not successfully overwinter here as they are a tropical moth.

Fig. 1. Corn earworm damage to snap bean pods.

Fig. 2. Corn earworm (=tomato fruitworm) damage to tomato fruit.

 

 

Sweet Corn IPM Moth Trapping in Virginia – Week Ending September 7, 2018

This will be final trap catch alert of the year for the sweet corn IPM program as most corn has been harvested. I want to thank all of the VCE Extension folks who monitored traps on farms in their respective counties this year: Phil Blevins (Washington Co.); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Helene Doughty (Eastern Shore AREC Entomologist, Accomack Co.); Roy Flanagan (VA Beach); Bob Jones (Charlotte Co.); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.).
Click on the table below to view the trap catch results (moths per night) for some of the locations around Virginia for this final week. We will send out a synopsis of the season this winter. We are still seeing some high corn earworm moth activity on the Eastern Shore of Virginia, Westmoreland County on the Northern Neck, and Frederick County in the northwestern portion of our state. With the hot weather that we’ve experienced the past 2 weeks, moth activity has probably been a little higher than usual for September. Sweet corn growers are advised to keep control measures (spray intervals) as they were during August in most counties.
We still have caught very few fall armyworm moths in our traps around Virginia; however, this insect could contribute to some infestations in the ears of late corn. In an effort to fend off any more pyrethroid insecticide resistance development in our corn earworm populations, rotating to another insecticide than a Class 3 (pyrethroid) is highly encouraged for at least one spray. Diamide insecticides such as Coragen or Besiege, the carbamate Lannate LV, or the spinosyn Blackhawk, are all effective non-pyrethroid options.

Corn earworm average moth catch per night at farms around Virginia for week ending September 7, 2018.

Fall armyworm larva.

Mid-Atlantic Crop Management School Registration is Open!

Registration is open for the 2018 Mid-Atlantic Crop Management School for Certified Crop Adviser, Nutrient Management, and Pesticide Applicator Credits for Virginia, Delaware, Maryland, West Virginia, and Pennsylvania. The venue is the Princess Royale Oceanfront Hotel and Conference Center in Ocean City, MD on November 13-15, 2018. Register early so you can enroll in your preferred classes!

Registration: https://app.certain.com/profile/2876563
Schedule: https://sites.udel.edu/agronomy/cropschool/

 

Finishing out the soybean crop – when you can safely stop spraying

Soybean loopers have reared their ugly heads across southeastern and coastal Virginia this week. With many of us busy hauling corn, it is reasonable to ask  – when can we stop spraying beans?

In a normal year, we could safely ignore mid-September infestations. This year, the majority of double crop Virginia fields are completing pod fill. Research indicates that R3-R5 beans benefit from a spray when defoliation reaches 15% and you find more than 1 looper per sweep. I recommend that you at least double, and can safely triple, this threshold in R6 beans (i.e., 35-50% defoliation is acceptable). It benefits you to exercise restraint when treating fields after R5.5. There is no scenario when you need to spray R7 beans for loopers. Cooler evening temperatures will work in our favor when they arrive.

In Virginia, Intrepid Edge and Steward have been our most consistent treatments (see image below from 2017). Looper populations in Virginia have tested diamide resistant the past two years (e.g., Besiege, Prevathon). Spraying pyrethoids  will only make the problem worse.

 

Finishing Out the Soybean Crop – What do we need for Good Yields?

In general, we’ve had a good, but not great year for soybean in Virginia.  Although many areas were hit with a 3 to 4 week dry spell during July, August rains kept us in the game.  However, we did not see the ample  rains or cool temperatures that we experienced in August of 2017, which resulting in record yields.  Below is a summary of August rainfall and temperature anomalies for the U.S.

 

 

 

 

 

 

 

 

As you’ll notice,  we had about average or slightly below average precipitation and average to slightly above average temperatures for most of Virginia’s soybean growing areas.

So, I do not suspect that our yields will be as good as last year.  Still, our earlier-maturing varieties planted in April or May should yield quite respectably considering that most have made over 50% of their yield – they have reached the R6 stage (see photo below).  Yield of our later-maturing varieties, planted in May and early June, and our double-crop plantings are not quite there yet – much of our yield is yet to be determined – R5 soybean have only made roughly 25% of their yield at that time.

So, what do we need for good yields?  Rain is obvious.  Full-canopied plants with adequate soil moisture will draw about 0.25 inches of water/day from the soil.  But, we also need cool temperatures – soybean do not generally like 90+ degree days, especially when forming seed.

Below is the 10 day rainfall and temperature forecast for the U.S., and it does not necessarily look good for us.  Note that the rainfall is predicted accumulation and the temperature map shows anomaly.  Although we should get some rain this weekend only (more in northern parts), temperatures are supposed to be above average.  But, forecasts are only forecasts.  The weather does change.  I hope we will get the needed rainfall that they are predicting this weekend.  But a big ridge appears to be setting up over the Mid-Atlantic states for next week.  This usually means warm weather and only at the edges of ridges do we normally see rainfall – note the heavy rainfall predicted from Nebraska through Michigan.

 

 

 

 

 

 

I don’t mean to discourage, just to inform.  We still have decent soil moisture, at least in the subsoil.  With rain this weekend, we should get through next week without too much harm to the crop.

Our double-crop soybean (assuming late maturity group 4’s and group 5’s planted in late June to July) are just now in the R5 stage – it usually takes 80 to 100 days from planting to reach R6, depending on maturity and planting date.  So some timely September rains will usually result in good double-crop soybean.

When will our yield be “made”?  Below is table showing the number of days to soybean physiological maturity (R7; 95% of yield has made).  When can we expect to be harvesting our soybean?  Full maturity is reached about 2 weeks after R7 and harvest can proceed after the soybean have dried down to a harvestable moisture, usually within a week after R8.

Sweet Corn IPM Moth Trapping in Virginia – Week Ending August 24, 2018

Corn earworm moth catch data from sweet corn farms in Virginia can be found in the table below. In summary, corn earworm moth activity increased dramatically this week at several locations including lower Northampton County, Westmoreland County in the Northern Neck, Amelia County, Hanover County, and Frederick County.  Moth activity is quite variable right now, and should certainly be monitored carefully in the coming weeks. We still have caught very few fall armyworm moths in our traps around Virginia; however, it should be noted that the Amelia County Farm averaged 5.5 FAW moths per night, which is the highest of any trap this season so far. So, a late flight of this pest appears to have reached some part of Virginia.

In an effort to fend off  pyrethroid insecticide resistance development in our corn earworm populations, rotating to another insecticide than a Class 3 (pyrethroid) is highly encouraged for at least one spray. Diamide insecticides such as Coragen or Besiege (although it includes lambda-cy with the diamide), the carbamate Lannate LV, or the spinosyn Blackhawk, are all effective rotational insecticide options.

I want to once again thank Helene Doughty at the ESAREC and all of the VCE agents that are monitoring these pests on sweet corn farms in 17 different counties in Virginia: Phil Blevins (Washington Co. – See Photograph below); Chris Brown (Franklin Co.); Jason Cooper (Rockingham Co.); Ursula Deitch (Northampton Co.); Roy Flanagan (VA Beach); Kenner Love (Page and Rappahannock Co.); Laura Maxey Nay (Hanover Co.); Steve Pottorff (Carrol Co.); Stephanie Romelczyk (Westmoreland Co.); Beth Sastre-Flores (Loudoun Co.); Laura Siegle (Amelia Co.); Rebekah Slabach (Halifax Co.); and Mark Sutphin (Frederick Co.).

Corn earworm moth catch in pheromone-baited Heliothis traps around Virginia for week ending August 24, 2018.

Phil Blevins, Washington County VCE Agent – ANR, standing in front of his Bt sweet corn trial adjacent to a Heliothis trap for corn earworm and a bucket trap for fall armyworm monitoring.

Sweet Corn IPM Moth Trapping in Virginia – Week Ending August 17, 2018

Corn earworm moth catch data from sweet corn farm locations around Virginia can be found in the table below. In summary, corn earworm moth activity has dropped off this week at most locations with the exception of one of the farms in Frederick County where trap catch increased to 13 moths per night. Trap catch remained high at the Creeds location in Virginia Beach with over 20 moths per night being caught, which is high pest pressure still at that location. Moth activity is quite variable right now, and should certainly be monitored carefully in the coming weeks. We have caught very few fall armyworm moths in our traps around Virginia, which is good news. That insect can be quite devastating to late planted sweet corn. Keep an eye on brown marmorated stink bugs feeding on corn ears particularly on field edges (border rows). Fig. 2 below shows BMSB injury to sweet corn from feeding through the husk. Fig. 3 shows the same sweet corn ear after boiling in water. If more than 1 stink bug is found per 10 ears, a pyrethroid insecticide spray is recommended.

Corn earworm trap catch at sweet corn farms in Virginia – week ending August 17, 2018.

Fig. 2. Sweet corn damaged by brown marmorated stink bug.

Fig. 3. Sweet corn ear after being boiled in water. Note the appearance of stink bug feeding on the cooked corn.

Sweet Corn IPM Moth Trapping in Virginia – Week Ending August 10, 2018

Corn earworm moth catch data from sweet corn farm locations around Virginia can be found in the table below.  In summary, corn earworm activity has gone up this week in Accomack County, Virginia Beach, Amelia County, Frederick County, and Franklin County, but has dropped off in many other locations around Virginia.  Thus, moth activity is quite variable right now, but should certainly be monitored carefully in the coming weeks.

Corn earworm pheromone trap catch per night in Virginia.

Insecticide Options for Insect Control in Sweet Corn

Pyrethroids are the most commonly used insecticides in sweet corn.  They are relatively cheap, effective, and include many options such as (alphabetized):
Baythroid XL 1.6 to 2.8 fl oz/A
bifenthrin–2.1 to 6.4 fl oz/A Bifenture 2EC (Sniper, or others);
cyfluthrin–1.6 to 2.8 fl oz/A Tombstone 2EC (or OLF);
esfenvalerate–5.8 to 9.6 fl oz/A Asana XL;
lambda-cyhalothrin–1.28 to 1.92 fl oz/A Warrior II or 2.56 to 3.84 fl oz/A Lambda-Cy (LambdaT) permethrin–4.0 to 8.0 fl oz/A Perm-UP 3.2EC (or OLF)
zeta-cypermethrin–2.8 to 4.0 fl oz/A Mustang Maxx (or OLF)
zeta-cypermethrin+bifenthrin–4.0 to 10.3 fl oz/A Hero EC

Some drawbacks to pyrethroids are that they are broad spectrum contact poisons that are also quite toxic to natural enemies such as ladybeetles and minute pirate bugs, Orius spp., that frequent sweet corn in Virginia and which can destroy many eggs of CEW before the larvae can damage the ears. Pyrethroid insecticides are also toxic to bees.  Frequent use of pyrethroids can also cause outbreaks of corn leaf aphids, which can build up on the ears causing honeydew and sooty mold, which can reduce quality and marketability of the produce.  Corn earworm in Virginia is showing signs of resistance development to pyrethroids and therefore rotating different modes of action is recommended.

Other insecticide classes (different modes of action) that should be considered for use in sweet corn include:

  • Lannate LV methomyl –  Will not flare aphids.  HAs not provided as effective control of  corn earworm as the other products when used exclusively.  Is a good rotation or tank mix option.
  • Coragen 1.67SC  chlorantraniliprole–3.5 to 5.0 fl oz/A  – this diamide insecticide is virtually non-toxic to bees and natural enemies, and provides excellent control of corn earworm and other worm pests.  Only about two applications can be used per season.  It is an excellent choice during pollen shed.
  • Besiege lambda-cyhalothrin+chlorantraniliprole–6.0 to 10.0 fl oz/A  includes both the diamide and a pyrethoid.
  • Blackhawk 36WG spinosad–2.2 to 3.3 oz/A or Radiant SC spinetoram–3.0 to 6.0 fl oz/A are spinosysns that provide very good control of corn earworm and other worm pests and are less harmful to many natural enemies.

Is it too late to apply foliar fungicides in soybean?

Hillary L. Mehl, Extension Plant Pathologist & David Holshouser, Extension Agronomist

The wet weather conditions, along with relatively cool temperatures over the last few weeks have been nearly perfect for disease development in soybean.  As always, keep in mind the disease triangle – all 3 conditions must be met before a disease can form.

In most cases, one or more soybean pathogens are out there.  Refer to previous blogs for more information on common soybean diseases: Now is a Good Time to Evaluate Your Varieties for Foliar Diseases and Foliar Fungicides for Soybeans.  You can also access the Mid-Atlantic Soybean Disease Scouting Guide here. For a positive identification of the disease, send leaf samples to our diagnostic lab.

We also need a susceptible soybean variety (host).  Some varieties are resistant to specific pathogens; others have some tolerance; many have neither.

Of the 3 conditions, the environment is the most difficult to assess.  In general, we need high relative humidity (RH) for an extended period of time, usually over several days, and cool to moderate (e.g. not hot) temperatures.

Our research indicates that about 1/3 of the time, a foliar fungicide will result in yield increase.  The probability and amount of response will of course depend on the disease.  Frogeye leaf spot can be a quite devastating disease in susceptible soybean that have not been rotated.  Cercospora leaf blight (sometimes called late blight) is less devastating, but is common in almost all of our soybean when conditions are right.

We have attempted to create a foliar fungicide decision aid that would help decide on whether or not to spray.  The decision aid is based on the total number of favorable days for disease development, based on the data shown below.

We think that during the period of 1 week before and 1 week after mid-R3, yield-robbing disease levels may develop if we have 3 favorable days with 10 or more hours of relative humidity at or above 95%  and temperatures in the optimum range (77 to 86 F).  When these conditions are met, we would suggest a fungicide application.

However, after 3 years of on-farm testing we only improved the predictability of a yield increase slightly (approximately 50% versus the 33% we see on average).  Why?  We have not been able to predict the weather after the fungicide application.  If things turn dry, the disease will decline and a yield response is not likely.  If conditions remain favorable for disease, then a yield response to a fungicide application is more likely.

So, back to our original question, is it too late to apply a fungicide?

Most of our full-season soybean are past the R3 stage (though many acres were planted in June due to wet weather); so a yield response is not likely if fungicides are applied now.  Generally, it takes about 65 to 80 days after planting to reach the R3 stage, depending on planting date and relative maturity.

Double-crop soybean will usually take 40 (MG 4 planted in July) to 60 days (mid- to late-5 planted in June) to reach R3.  Since most double-crop soybeans recently entered or will enter the R3 stage, a yield response to a fungicide application is more likely.

What about seed quality?  We’ve seen little relationship between an R3 fungicide application and improved seed quality.  To insure good seed quality, we would suggest 2 applications (R3 and R5).  The R5 application might help with our biggest seed quality issue, Phomopsis seed decay, which tends to develop later in the season.  For seed growers, a late application is a good insurance treatment, but keep in mind that if long periods of wet weather delay harvest, seed quality will deteriorate even if a late fungicide was applied.  Be aware that most fungicide labels restrict applications once soybean enter the R6 stage.  Always follow label instructions.

In summary, there are several things that you need to keep in mind that will affect whether or not you will see a yield response to fungicides:

  • Non-rotated soybean will generally have more disease.
  • Variety Resistance. Many varieties have very good FLS resistance; some have only moderate resistance – this may work pretty well if soybean are rotated, but don’t depend on it if soybean were grown last year (or many of the previous years).  Generally, soybean are not resistant to Cercospora blight, but we have seen differences in varieties.  We measure % purple seed stain in our variety tests; however, this is not always a good indicator for resistance to the leaf spot and blight.
  • Timing & Soybean Stage. R3 applications are usually best; not always, but most of the time.  Still, we occasionally see a response with R5 applications.  I (David) have only seen a yield benefit from 2 applications (R3 and R5) once – this was in 80-bushel double-crop soybean in a very wet and cool year.
  • Historically, strobilurin fungicides were our most effective on most soybean disease.  However, FLS is now largely resistant to that class of fungicides, and control of our other diseases have declined.  However, the strobilurins still have utility.  We suggest a fungicide containing a strobilurin along with a good triazole. The 2018 soybean fungicide efficacy table can be downloaded here.
  • Spray Volume & Droplet Size. Good coverage of fungicide throughout the canopy is necessary.  Use at least 15 gallons per acre spray volume and make sure that your nozzles will deliver medium-sized droplets.  Small droplets will not penetrate the canopy to the lower leaves, where the fungicide is most needed.  Large droplets will not provide uniform coverage.  For more detail on this, see Application Equipment for Effective Insect Pests and Foliar Disease Control.
  • Seed Quality. Although, we don’t always see a seed quality benefit from an R3 application, two applications should improve seed quality.  Furthermore, a late-season (R5) application should help with certain seed diseases such as Phomopsis seed decay. However, keep in mind that if cool, wet conditions delay harvest seed quality will deteriorate even with a late fungicide application. Controlling late season insects such as stink bugs is also critical for preventing fungal infection and maintaining seed quality.