Guess the Pest! Week #24 Answer: European Corn Borer

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations to Grier Stayton for correctly identifying the insect as a European corn borer and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #24 Answer: European Corn Borer

It’s hard to believe that a pest that once caused an estimated annual economic loss of $1 billion dollars in the United States is now a rare occurrence. The European corn borer (ECB), as the name implies, is actually native to Europe and was introduced into North American in the early 1900s. In addition to being a pest of corn (field corn and sweet corn), it is also considered a pest of many vegetable and field crops. Since the adoption of transgenic corn hybrids in the mid-1990s, losses due to ECB have been virtually eliminated in Bt crops and significantly reduced in other vegetable and non-Bt field crops. This is one of the pests that the UD Insect Trapping Program monitors with black light traps. The reason we continue to monitor ECB populations throughout the state is because even though generally speaking, populations have been low, there are still local pockets where ECB is causing damage. The photo above of the ECB larva was taken on the Eastern Shore of VA by Helene Doughty from a non-BT sweet corn plot that was 100% infested with ECB.

For information on the benefits of Bt adoption, read this article: Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growers http://www.pnas.org/content/early/2018/03/06/1720692115

Guess the Pest! Week #22 Answer: Helicoverpa zea, Corn Earworm

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations to Amanda Heilman for correctly identifying the insect as an adult corn earworm and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #22 Answer: Helicoverpa zea, commonly known as corn earworm

The moth in the photograph is an adult Helicoverpa zea, commonly referred to as a corn earworm. The adult moth is a nectar feeder and not considered a pest. However, corn earworm larvae are considered by some to be the most economically important crop pest in North America. They are highly polyphagous meaning they feed on many different species of plants. Corn, especially sweet corn, is a preferred host plant. However, they also attack soybean, sorghum, snap bean, tomato, and cotton to name a few. Larvae prefer to feed on reproductive plant structures including blossoms, buds, and fruits. It is because of this large host range, and the fact that Helicoverpa zea larvae are so destructive that they are known by several other common names including tomato fruitworm, cotton bollworm, and podworm.

Vegetable Insect Updates

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu and David Owens, Extension Entomologist, owensd@udel.edu

Fields that started silking at the beginning of the major 2018 moth flight are being harvested right now. Please let us know how well your spray program worked. Your feedback is important to us to evaluate if any recommendations need to be adjusted for 2019. Moth capture has declined slightly at several locations, and Monday captures (http://agdev.anr.udel.edu/trap/trap.php) were slightly lower than last week’s. Earworm flight may have peaked for the season.

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 4 8
Harrington 3 44
Milford 63 127
Rising Sun 6 17
Wyoming 4 30
Bridgeville 6 19
Concord 8 27
Georgetown 2 19
Greenwood 10
Laurel 2 84
Seaford 3 12

 

This will be the last trap capture for 2018. Many thanks to all of our cooperators who graciously host blacklight and/or pheromone traps at their locations. We are also grateful to Jon Baker with Trap Woods Inc., Harry Thompson with Thompson’s Roadside Stand, and Donna Hamilton for sharing their trap capture data with us; their data is posted twice a week on the website. You can view season catches and graphs of previous year trapping results at the above link.

Sulfur Deficiency in Sweet Corn

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

For the last couple of years, I have talked about and conducted research on sulfur (S) deficiencies in watermelon. At several meetings I was asked if the deficiency also appears in (field) corn. I could only relate the comments I have heard from several corn growers that they have often found their corn crop to be low or deficient in sulfur. I bring all this up again because I have seen several sweet corn fields lately that have sulfur deficiencies (Fig. 1). One of the possible reasons we are seeing more S deficiency is because less sulfur is being deposited into the soil from the atmosphere due to reductions in acid rain (Fig. 2). In 1986 about 24 lbs/a of sulfate were deposited in Maryland soils per year, however in 2011 it was closer to just 8 lbs/a each year. Organic matter supplies most of the sulfur to the crop, but sulfur must be mineralized to sulfate-S to be taken up by crop plants.

Because mineralization is carried out by soil microorganisms, soil temperature and moisture primarily determine when and how much sulfur is made available to the crop. Excessively wet (like we have had most of this summer) or dry conditions reduce microbial activity and reduce S availability from soil organic matter. Sulfate is relatively mobile in most soils and easily can be leached from soils, especially sandy soils. Soils low in organic matter are much more likely to be deficient in S.

In the field sulfur deficiency can be highly variable since soil sulfur availability varies considerably with soil organic matter and texture. Sulfur deficiency is often seen in sandier, lower organic matter, hillier areas of a field while low lying, greater organic matter areas usually have sufficient levels of S. Sulfur can be added to the crop in combination with several other nutrients such as ammonium or potassium and spray-grade ammonium sulfate is a good choice for foliar applications.

There are other deficiencies (and problems such as root diseases) that can cause striping (although the one pictured here was S) and only by conducting a tissue test can you be sure. Magnesium deficiency may cause striping and/or reddening of corn leaves. The yellow areas between the veins often appear as ‘beaded’ lines rather than solid stripes. Zinc deficiency may cause striping that begins at the base of the leaf and progresses to the tip. These stripes often coalesce to form a white band along the edge of the leaf or the midrib. Manganese deficiency causes striping that is olive green or dark yellow in color with veins remaining green. High pH, high organic matter, and dry soil conditions can cause Mn deficiency.

Figure 1. Striping in sweet corn leaf caused by S deficiency

 

Figure 2. Amount of sulfate deposited in soil from rainwater in 1986 vs. 2011.

Vegetable Insect Updates

David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Sweet Corn
Bill Cissel and David Owens
Corn earworm populations are higher than last week, and yesterday’s trap capture was higher in all but one location from Monday’s trap capture. At the research station, our trap captures increased significantly in the last two nights. Blacklight trap captures are also increasing. Focus more on the state-wide trends. Monday trap capture can be found at (http://agdev.anr.udel.edu/trap/trap.php). As a reminder, what is reported on the web is on a per night basis, the table below is cumulative over Monday, Tuesday, and Wednesday night. These trap captures correspond to a 3-day spray schedule, though some states recommend a 2-day schedule.

Joe Ingerson-Mahar at Rutgers in New Jersey recently wrote about the need for product rotation, citing pyrethroid resistance monitoring Virginia has been doing (https://plant-pest-advisory.rutgers.edu/corn-earworm-control-in-sweet-corn/). We have been using Virginia’s vial testing method and have seen similar results, near 30% of tested moths can fly after 24 hour exposure. Does this mean pyrethroids are ineffective? No, but it does highlight the need for chemistry rotation. We also do not know how vial tests translate to sweet corn efficacy where we apply products several times in a narrow time frame.

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 2 17
Harrington 1 28
Milford 2 41
Rising Sun 0 6
Wyoming 4 65
Bridgeville 3 63
Concord 3 56
Georgetown 4 32
Greenwood 2
Laurel 2 132
Seaford 5 52

Watermelon
David Owens
Spider mite populations have generally been decreasing, but can still be an issue with the warm weather. High humidity favors fungal pathogens of spider mites, but fungicide sprays can suppress them. Infected mites are going to look crumpled and may even be brown in color and a slightly fuzzy appearance as mite-killing fungi sporulate. Cucumber beetles are very active, as are various members of the rindworm complex. Yellow striped armyworms are present in fields.

Sweet Corn Insect Update

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu and David Owens, Extension Entomologist, owensd@udel.edu and

A whorl-stage sweet corn field on station had an economic infestation of fall armyworms, whorl thresholds are 15%. Be wary of fall armyworm in tassel-push corn, worms dislodged by the emerging tassel may go to the developing ear. Pyrethroids will not give complete worm control, scout fields soon after treatment. Other alternative mode of actions that are softer on beneficials include diamides (Coragen) methoxyfenozide (Intrepid), indoxacarb (Avaunt) and spinetoram (Radiant). Be sure to read the labels for use restrictions (indoxacarb cannot be used after tassel-push) and restrictions on the number of applications. A commonly used earworm product is Besiege which has chlorantraniliprole (Coragen) in it; earlier use of chlorantraniliprole may limit later use.

Corn earworm populations are higher than last week. Drier evening weather favors moth flight, and worms that developed in field corn are starting to emerge as adults. I expect moth flight activity to continue increasing state-wide until early-September. You may notice some trap locations that had been catching a lot of moths are now catching fewer; in some locations traps were adjacent to sweet corn that has since been harvested. However, other traps have been catching many more moths than they had been, especially in the Monday Laurel data. Blacklight trap captures are also increasing. Focus more on the state-wide trends. Monday trap capture can be found at (http://agdev.anr.udel.edu/trap/trap.php), and Monday trap captures were much higher from nearly all sites. As a reminder, what is reported on the website is on a per night basis, the table below is cumulative over Monday, Tuesday, and Wednesday night.

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 0 7
Harrington 1 4
Milford 5 11
Rising Sun 7 5
Wyoming 7 25
Bridgeville 2 23
Concord 4 20
Georgetown 2 14
Greenwood 6
Laurel 0 78
Seaford 1 21

Guess the Pest! Week #15 Answer: Stink Bug

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations Chris Leon for correctly identifying the damage in the photo as stink bug damage and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #15 Answer: Stink Bug

The damage on the corn stalk is stink bug feeding injury. Stink bugs will use their piercing-sucking mouthparts to probe into the stalk of the plant, removing plant fluids. If the stink bug hits the ear at this stage, the ear will often fail to develop kernels at the feeding site. This causes the ear to develop into the classic “C”-shaped or boomerang-shaped ear. This is why the greatest damage and yield loss potential due to stink bug feeding is prior to pollination. This is also why waiting until after tasseling (pollination), to control a stink bug infestation in field corn is too late. Here is a link to last week’s article discussing stink bug management in field corn: http://extension.udel.edu/weeklycropupdate/?p=12194

Guess the Pest! Week #14 Answer: Corn Rootworm

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations to Kathleen Heldreth for correctly identifying the damage in the photo as corn rootworm damage and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #14 Answer: Corn Rootworms

The corn plants in the photo are damaged by corn rootworm larvae. As you can see, the larvae feed on the roots and root tissue of the plants causing the plant roots to be “pruned”. Older larvae will tunnel into the roots leaving visible entrance holes and blackened root tips. Plants with excessive root pruning will usually lodge and in reaching for the sun, become “goosenecked”. Corn rootworm infestations are unusual for Delaware and not something we typically have to manage for. Crop rotation is the preferred method of control in regions with sporadic populations. Corn rootworm females prefer to lay eggs in corn fields in August and September. The eggs do not hatch until the following spring. If the field is rotated out of corn, the larvae will starve to death in the absence of a suitable host plant.

Vegetable Insect Update – July 6, 2018

David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Sweet Corn
by Bill Cissel and David Owens
Sweet corn trapping data is updated by Tuesday and Friday mornings and can be accessed here: http://agdev.anr.udel.edu/trap/trap.php. If there is one thing insects are really good at, it is making liars out of people. That said, I expect low earworm numbers until mid-July. Trap catches are as follows:

Trap Location BLT – CEW Pheromone CEW Corn spray schedule
3 nights total catch
Dover 3 0 4 day
Harrington 0 0 No spray
Milford 0 0 No spray
Rising Sun 1 0 6 day
Wyoming 1 0 6 day
Bridgeville 0 0 No spray
Concord 0 0 No spray
Georgetown 0 1 6 day – no spray
Greenwood 0 0 No spray
Laurel 0 6 4 day
Seaford 0 1 6 day – no spray

 Cucurbits
by David Owens
With the warm weather, it is not surprising that low levels of spider mites can be found in most fields. Check field edges and near wood lines. The action threshold we use as a benchmark is 1-2 mites per crown leaf, 20 – 30% of the crown leaves infested. During hot dry spells, try to limit mowing as much as possible, spider mites feeding on the grasses will be forced to look elsewhere for food once the plant they are on has been cut. I have also noticed a slight uptick in cucumber beetle activity.

Sweet Corn Insect Management

David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Sweet corn trapping data is updated by Tuesday and Friday mornings and can be accessed here: http://agdev.anr.udel.edu/trap/trap.php. As we suspected last week, trap captures have plummeted in part, I am sure, because we are trying to capture sizeable earworm moths for pyrethroid resistance monitoring. We typically experience a lull in moth activity until mid-July. Trap catches are as follows:

Trap Location BLT – CEW Pheromone CEW Corn spray schedule
(3 nights total catch)
Dover 1 3 5 day
Harrington 1 0 No spray
Milford 0 0 No spray
Rising Sun 0 15 4 day
Wyoming 0 1 6 day – No spray
Bridgeville 0 1 6 day – No spray
Concord 0 0 No spray
Georgetown 0 0 No spray
Greenwood 0 0 No spray
Laurel 1 1 6 day – No spray
Seaford 0 1 6 day – No spray