Summaries of last season’s insecticide trials in peas, sweet corn, watermelon, field corn, soybean, and wheat can be viewed at https://cdn.extension.udel.edu/wp-content/uploads/2013/12/15092741/Delaware-Field-and-Vegetable-Crop-Insect-Pest-Management-Trials.pdf.
Jarrod O. Miller, Extension Agronomist, email@example.com
We avoided most of the flooding seen in the Carolinas with Florence, but hurricane season lasts until the end of November. Some later planted corn is still drying down, so saturated soils and winds may cause lodging, but there are no hurricanes on the horizon that may cause those issues. Full season and double crop beans are more likely to have issues if another storm heads for the Delmarva. Depending on development stage, storm conditions could increase disease pressure, cause lodging and shattering. For more detailed information, check out NC State extension as they dealt with the aftermath of Florence (https://soybeans.ces.ncsu.edu/2018/09/soybean-considerations-following-hurricane-florence/)
For fields along tidal streams and shorelines, hurricanes could bring salt water across fields. It may be necessary to perform soil tests in these fields to check for salt levels prior to next year’s crop. In general, if Na makes up more than 15% of the cation exchange capacity, lower yields could be observed. Total salts (which can include Ca and Mg) may also cause issues in fields flooded with tidewater. Gypsum works well if Na is the only issue, but irrigation is needed to leach soils high in Ca, Mg and Na.
Insect populations are generally lower this week. Loopers can still be found in some fields, as can stink bugs and bean leaf beetle. Defoliation thresholds for R6 beans are considerably higher than earlier R-stage beans. Now that our earlier planted fields are starting to senesce or have dropped leaves completely, this is a good time to take stem samples for Dectes stem borer, especially in fields that had large numbers earlier or have a history of Dectes problems. If your field has a large stem infestation, prioritize that field for as timely a harvest as possible. Lodging loss potential increases with the percent of infested stems and late harvest.
Continue to scout for corn earworm and soybean looper. Last weekend’s storm activity from the south could have brought up more loopers from that region. I have received a couple of reports of pockets of loopers in fields. They often show up in localized sections, typically in drier, less robust parts of fields. Defoliation thresholds prior to R6 are 15%, at R6, plants can tolerate greater defoliation. R7 beans are safe. Also, be sure to check the lower canopy if you do see significant looper activity, they sometimes start first in the lower canopy unlike our other defoliators that concentrate in the upper canopy. NC only recommends Intrepid Edge, VA recommends Intrepid Edge and Steward. Both products are ‘worm’ products and will clean up corn earworm. Steward has some, but not great activity on bean leaf beetle, and neither has stink bug activity. We also had a report of armyworm activity in some isolated fields. Armyworms can feed on pods, but are not as aggressive as corn earworm. There doesn’t seem to be much consensus in different states’ recommendations; some combine them with corn earworm thresholds, others treat them as defoliators, and others use a threshold in between.
Bill Cissel, Extension Agent – Integrated Pest Management; firstname.lastname@example.org
Congratulations to Lamar Witmer for correctly identifying the disease as sudden death syndrome of soybean 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 #23 Answer: Sudden Death Syndrome of Soybean
by Nancy Gregory, Plant Diagnostician; email@example.com
Sudden death syndrome of soybeans (SDS) is caused by the fungus Fusarium virguliforme. We started seeing this disease in Delaware in 2002 in cool and wet seasons, but have seen it more often in the past few years. SDS can be confused with other stem diseases such as Phomopsis stem canker and charcoal rot. Leaf symptoms of yellowing and browning between the veins are typical, and leaves shrivel and fall off, leaving petioles still on the stems. If stems are pulled up and placed in a plastic bag overnight, blue spore masses of the fungus may be seen at the base of stems. The internal stem tissue (cortex) may show dark discoloration. There is a toxin produced by the fungus that is responsible for the symptom pattern showing up at the top of the plant. The fungus overwinters in debris, and disease is most severe when infection occurs early. Improving drainage, alleviating compaction, and treating seed may help get seedlings established.
Several fields in the SW portion of Sussex County have experienced above threshold corn earworm activity lately. I have not heard of any excessive populations or populations for which pyrethroids did not provide good control. Soybean loopers are present in many fields at low numbers, as are green cloverworm. Its important to distinguish them, cloverworms are easy to kill and are not aggressive defoliators while loopers are less susceptible to many materials. Cloverworms have a narrow body, three sets of prolegs in addition to the last abdominal segment’s prolegs. Larger larvae often have white stripes and hold their last set of prolegs out in a V shape. Cloverworms also wriggle violently when poked. Loopers tend to be narrower near the head and wider near the abdomen, and have two sets of prolegs. There are some reports of unusually high soybean aphid populations in drought stressed fields. The threshold for soybean aphid 250 per plant on 80% of plants with an increasing population. If you hit threshold, you have about a week before they might reach a damaging population. Check back in a couple of days to see if populations continue to increase, they might not if beneficials are present. Soybean aphids cause inconsistent plant injury after R5.5, and are not considered a threat once beans hit R6. Check labels for pre harvest intervals. Pyrethroids all do a good job, some have pretty long PHIs.
Bill Cissel, Extension Agent – Integrated Pest Management; firstname.lastname@example.org
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.
The most economically important insect present in soybean fields right now is corn earworm. There are reports from south and southwest Delaware of a few fields above threshold. Pay special attention to late planted, open canopy fields. Pyrethroids should do a good job unless a field is 4x above threshold, in which case you may want to look at an alternative or additional mode of action. Stink bugs are present in low numbers in most fields, mostly greens but also with browns and the occasional brown marmorated. As a reminder, thresholds are 5 bugs in 15 sweeps, 2.5 for seed production. Defoliator complex members include green cloverworm, bean leaf beetle, aphids, and the occasional soybean looper. Virginia has been experiencing significant looper pressure in the last couple of weeks.
As you walk into fields, you may also see flagged leaves – 1 trifoliate that has wilted. This is a sign of possible Dectes infestation. Examine the wilted petiole where it would attach to the stem. If the petiole core is red and hollowed out, Dectes is present. Fields where you see a lot of this activity should be prioritized for timely harvest.
Corn earworm, stink bugs, bean leaf beetles, and soybean loopers are the primary insect pests present in soybean. So far, only low numbers of earworms and loopers have been found, but we are seeing moth activity in fields and our pheromone traps have been capturing more earworms than last week. If loopers are present, use defoliation thresholds and keep in mind that pyrethroid resistance is prevalent in southern states. Corn earworms are also demonstrating reduced pyrethroid susceptibility. If a field is at threshold or only slightly above threshold (please visit the CEW threshold calculator and enter your application cost, soybean value, row spacing: (https://soybeans.ces.ncsu.edu/2015/08/managing-corn-earworm-in-soybeans/) and the worms are small, pyrethroids should knock them back enough. If large numbers of worms are present, other useful products include Intrepid Edge, Steward, Radiant, or a diamide containing product (Besiege, Prevathon). Also note that if stink bugs are present at threshold (5 per 15 sweeps grain, 2.5 per 15 sweeps for seed) a pyrethroid will be necessary. We also continue to find low numbers of aphids. Thresholds are 250 per plant on most plants, with increasing numbers of aphids up until R6. After R6, aphid injury is inconsistent. In addition to defoliating, bean leaf beetles can feed on pods. Treatment may be necessary if 3- 4 beetles are present per sweep and 10% of the pods have been fed upon.
Primary insect pests present in fields include green cloverworm, bean leaf beetles, aphids, stink bugs, and yellow striped armyworm. Aphid populations can increase quickly, so keep an eye out. Corn earworm trap captures have been low in some areas, high in others. Within the last few days, counts have come up quite a bit. Be on the lookout for earworm larvae in fields. Fields that are most attractive are later planted open canopy fields at R2. Worm development will coincide with the susceptible R4 to R6 stages. Worms at or before R2 do not typically require treatment. NC State has a very useful threshold calculator that takes into account row spacing, control cost, and price of beans: https://soybeans.ces.ncsu.edu/2015/08/managing-corn-earworm-in-soybeans/.
We have been conducting adult vial tests for monitoring corn earworm pyrethroid resistance, and have observed close to 30% survivorship. If you face a heavy infestation, 2-3 times above threshold, pyrethroids alone might not give enough control. We picked up our first small soybean loopers this week. This can be a significant defoliator. Base treatment decisions on defoliation estimates, and keep a close eye on fields that have loopers in them. Mississippi also uses defoliation and a ballpark figure of 10 loopers per 15 sweeps. Pyrethroid insecticides are generally ineffective on loopers. 2018 Spray trials from NCSU highlight high rates of Prevathon and Intrepid Edge as the most efficacious products. Other products that have resulted in good efficacy from other states include Steward and Radiant.