Erika Crowl and Andrew Kness University of Maryland Extension
Recent interest has been generated in using drones to seed cover crops into agronomic crops in small, irregularly shaped fields with rolling terrain or those fields otherwise not suitable for aerial seeding using a fixed-wing aircraft or helicopter. However, little is known about how effective drones are at seeding cover crops and if they can deliver seed at the appropriate rate to establish a sufficient cover crop. In order to evaluate cover crop stand establishment seeded via drones, we conducted an on-farm trial with support from the Maryland Soybean Board.
A cover crop of radish was flown on to a 26 acre standing corn field in Baltimore County, MD on August 27, 2020 at the rate of 16 pounds of pure live seed per acre using a HSE-TTA drone equipped with a spin spreader capable of carrying 40 lbs of seed. The field was an excellent candidate for this trial because of its irregular shape, rolling terrain, and close proximity to power lines and wood lines (Figure 1). Corn grain was harvested on September 15, 2020 and cover crop establishment was measured on October 21, 2020 by counting the number of radish plants per square foot in a one square foot area at 20 random locations across the field. The average cover crop plant population in the field was 3.1 plants/ft2, with a minimum of 0 and maximum of 6. Radish plants averaged 5 inches in height at the time of rating.
Figure 1. Field location of drone-seeded cover crop (outlined in red). Image: Google Maps (bottom).
Figure 2. Unedited image (left) and percentage canopy cover image (right) calculated by Canopeo software showing 31% coverage.
Aerial establishment of cover crops is heavily influenced by soil moisture availability. August and early September saw sufficient rainfall in the region, contributing to conducive conditions for cover crop establishment. These data, representing only one field and one environment, demonstrate the potential that aerial seeding a radish cover crop with drones may be an effective method for establishing cover crops in these challenging fields. Future work will be done to replicate and gather additional data so that we can fully understand the feasibility of seeding cover crops with drones.
Acknowledgements: We would like to thank A-1 Aerials, K Drone Services, Graystone Farm, and the Maryland Soybean Board for supporting this work.
The Maryland Department of Agriculture (MDA) will issue a bonus payment to Maryland farmers based on a percentage (15%) of federal Coronavirus Food Assistance Program 1 (CFAP1) funds received for the CFAP1 period that ended Sept. 11, 2020. Deadline for the bonus payment is December 1 at 5:00 PM.
CFAP1 provides vital financial assistance to producers of agricultural commodities who have suffered a 5% or greater price decline or who had losses due to market supply chain disruptions from COVID-19, and face additional significant marketing costs. The commodities covered are: aquaculture (finfish and crayfish), corn, cut flowers, dairy, livestock (excluding poultry), nursery, small grains, soybeans and specialty crops.
Dale Johnson, Farm Management Specialist University of Maryland Extension
Corn
Harvested acres estimate was adjusted down 1 million acres and yield estimate was adjusted down 0.1 bushels per acre. Beginning stocks estimate was adjusted down 258 million bushels. The total effect of these changes decreased supply 436 million bushels. Domestic demand estimate was decreased by 100 million bushels which accounted for the decrease in Use total. The net effect of supply and demand decreased ending stocks 336 million bushels and the stocks-to-use ratio from 17.1% to 14.9%. These anticipated changes have been reflected in the market as December futures price for corn has increased $0.75/bu. from $3.23/bu. on August 11 to a high of $3.98/bu. on October 9.
Soybeans
Harvested acres estimate for soybeans was adjusted down 700,000 acres and beginning stocks were adjusted down by 52 million bushel. These two changes resulted in a decrease of 97 million bushel in estimated 2020/21 supply. On the demand side, there was an increase in export estimate of 75 million bushels. The resulting estimate of ending stocks was decreased by 170 million bushels decreasing the stocks-to-use ratio to a very low 6.4% from 10.4% last month. The November futures price for soybeans has spiked almost $2.00/bu. in the past two months from $8.83/bu. on August 11 to a high of $10.80/bu. on October 9.
Wheat
Yield estimate was adjusted down 0.4 bushels per acre. Demand was increased by 10 million bushel. The net effect was to decrease ending stocks by 42 million bushel and the stocks-to-use ratio from 44.3% in September to 42.1% in October. wheat futures prices (December) have followed corn and soybean prices and increased $1.03/bu. from $5.04/bu. on August 11 to $6.07/bu. on October 9.
Reports are for crop conditions up to October 6, 2020.
Western Maryland
Soybeans and corn are being harvested with wheat and cover crops being planted as soon as combines leave the fields. Manure is also covering many fields planted with cover crops. Welcome rains of early September have been followed by another dry spell. Hopefully the clouds of October will be more generous with their moisture.—Jeff Semler, Washington Co.
Central Maryland
The cooler weather has been a welcome change from this summer. September’s rain amounts and locations were scattered across the region. Corn grain harvest has begun. Soybean fields are drying down, with some ready to be harvested in the next couple weeks. It’s not too early to start thinking about weed control for next season, especially if dealing with herbicide resistant weeds like marestail. If planting a small grain, be sure to start clean and stay clean!—Kelly Nichols, Montgomery Co.
Northern Maryland
We were a tad dry in September and recent rains have been welcome. Corn harvest has been occurring for approximately 3 weeks now, although not at full force until the last few days. Corn yields are certainly down compared to last year’s record numbers; probably 10-20% lower. Even with that said, corn yields are better than anticipated considering how dry June/July was. Full season soybeans are drying down quickly and what’s been harvested so far has yielded exceptionally well. The double crop beans do not look nearly as promising, as a dry July severely inhibited establishment and dry September reduced pod set/bean size. Cover crop establishment has been good and the 2021 wheat and barley crop are going in the ground smoothly.—Andy Kness, Harford Co.
Upper & Mid Shore
Corn harvest is around half complete. Dryland yields are well above average, and may end up near all time highs. Irrigated yields are off 10-15%- probably due to too many cloudy, humid, hazy, poor light quality days. Soybean harvest is just beginning. Beans look really good. It’s still too early to predict yield, but we definitely grew a tremendous amount of forage. Early planted cover crops are off to a great start. Small grain planting is just beginning.—Jim Lewis, Caroline Co.
Lower Shore
Harvest is underway. Approximately 25% of corn has been harvested. Corn yield reports are 125 plus or minus bushels per acre. Sorghum is also ready to be harvested. Soybean harvest has not yet begun, although fields are now beginning to reach full maturity. We had a 2-3” rain event last week, which prevented entry to fields for several days. So far, the weather has been sunny and breezy this week, helping to dry crops down. Palmer amaranth is apparent in some fields, and we urge growers to harvest these fields last and thoroughly clean equipment to prevent the spread of seed. The planting of fall cover crops is underway.—Sarah Hirsh, Somerset Co.
Southern Maryland
Sunny conditions this week are finally allowing for good progress on corn harvest. Corn moisture levels are stubbornly running around 18-22% and saturated ground has made corn harvest a challenge this year. We continue to see a fair amount of ear rot issues. Cover crop planting is behind schedule as farmers struggle to get corn in. Soybean harvest has not yet begun, but there are some really good-looking soybean fields. We expect excellent double crop beans and a very good full season crop. The drier weather has provided some opportunities for getting in dry hay. We continue to struggle with orchardgrass persistence in this area. Fields that looked picture perfect in the spring and early summer are now looking more like fields of weeds with patches of crabgrass and the majority of orchardgrass gone. We have some work to do to figure out the persistence issue or rely more heavily on other species. Vegetable harvest is winding up. The pumpkin and cucurbit crop was hurt by heavy rainfall.—Ben Beale, St. Mary’s Co.
Kelly Hamby and Galen Dively University of Maryland, Department of Entomology
Insect Resistance Management in Bt Crops: Transgenic crops expressing insecticidal toxins sourced from Bacillus thuringiensis (Bt) bacteria reduce yield loss and insecticide use, delivering economic benefits for growers. Because this breakthrough in pest management is considered a public good and insect resistance is the largest threat to Bt crops’ durability, insect resistance management programs were developed and mandated by the EPA prior to the release of Bt crops. These plans included planting untreated refuge crops at high enough acreage to produce many susceptible adult insects that could interbreed with and dilute the resistance from insects surviving Bt crops (Figure 1).
Figure 1. Susceptible (white) corn borers emerge from the untreated block refuge (yellow) planted on the side of the Bt field (green). Resistant (red) corn borers emerge from the Bt field (green) and interbreed with susceptible moths to produce moths with diluted (white and red) resistance genes.
In addition, crops were supposed to express Bt toxins at a high enough dose that insects with diluted resistance genes (white and red) would be killed, called a “high dose” strategy. Finally, pyramided hybrids that contain multiple toxins targeting the same pest were developed to make it more difficult for pests to overcome the toxins. EPA also required monitoring for insect resistance and mitigation strategies to implement once resistance was detected.
The Issue: When best management practices for Bt insect resistance management are followed, for example, European corn borer (Ostrinia nubilalis) management in the U.S., resistance development has been slowed. In fact, all single and pyramided Bt traited corn hybrids still provide 100% control of corn borers. However, for some pests [corn earworm (Helicoverpa zea) and Cry toxins] Bt toxins were less effective and products were not high dose. This issue was further compounded by poor refuge compliance, which lead to the development of refuge-in-a-bag (RIB) seed mixes to increase refuge acreage. This technology was designed based on corn rootworm biology and is not as good as a separate block refuge for most other target pests. Finally, while pyramided multi-toxin hybrids were developed, hybrids that contained a single effective toxin for the management of some pests continued to be marketed. This enables insects to develop resistance to a single toxin first providing a “stepping stone” to resistance in pyramided hybrids that contain the same or similar toxins because they can already survive on some of the toxins that are being expressed. In addition, the same Bt toxins are used in both corn and cotton, so corn earworm (also known as bollworm) goes through multiple generations of selection pressure in the same year, increasing resistance. Reports of caterpillar pests resistant to Bt corn and cotton in the U.S. have occurred since 2014 for fall armyworm, since 2016 for corn earworm, and since 2017 for western bean cutworm. However, none of these resistance reports triggered EPA’s current regulatory definition of pest resistance and no mitigation actions were taken. Therefore, the EPA released a draft document outlining proposed changes to reduce resistance risks (especially for non-high dose pests at heightened risk of resistance), to increase the longevity of currently functional Bt traits and future technologies, and to improve the current caterpillar pest (Lepidopteran) resistance management program for Bt corn and cotton (USEPA 2020).
Proposed Changes: Changes build off current insect resistance management plans and incorporate feedback and recommendations developed by a July 2018 Scientific Advisory Panel, independent academic scientists, the Agricultural Biotechnology Stewardship Technical Committee, the National Alliance of Independent Crop Consultants, and Syngenta Crop Protection, LLC (USEPA 2020). The EPA has 1) confirmed Bt resistance to specific Bt toxins in corn earworm, fall armyworm, and western bean cutworm, 2) proposed a new resistance definition for non-high dose pests that acknowledges their heightened risk of resistance and enables more rapid response to unexpected injury, 3) proposed a resistance monitoring approach that will use sentinel plots to monitor unexpected injury in addition to reported cases of unexpected injury in Bt crops, 4) proposed an improved resistance mitigation strategy with best management practices to respond to unexpected injury within the growing season and moving forward, and 5) will continue to require reporting on refuge compliance, unexpected injury, and insecticides targeting the pests that are also targeted by Bt (USEPA 2020).
Changes Under Discussion: In addition to the above changes, three additional changes have been proposed that require further discussion and stakeholder comment (USEPA 2020). The first focuses on reducing the acreage of products that no longer effectively manage resistant caterpillar pests and that share or have similar toxins as multi-toxin pyramided hybrids that still provide control. Therefore, the EPA is proposing a short term (~ 3 year time frame) phase down of hybrids that contain a single toxin for control of caterpillar pests, capping acreage planted in these hybrids to a minimum. These include field corn (Table 1), sweet corn (Table 1), and cotton products. In addition, non-functional pyramids that do not contain effective toxins for control of resistant caterpillar pests would have a longer term (~ 5 year time frame) phase down to minimal acreage (Table 2). Even with the potential phase downs Cry toxins will still be available for planting in pyramided hybrids that include the Vip3A trait.
To improve refuge compliance nationwide, the EPA proposes to increase refuge-in-the-bag (RIB) seed blend technologies to 10% refuge and maintain current requirements to plant a separate 20% block refuge in cotton producing areas (USEPA 2020). This should help insect resistance management for all pests managed by Bt and may be especially important for pests at heightened risk of developing resistance.
To further increase refuge compliance, especially in cotton producing areas, additional strategies have been proposed. For example, sale of Bt corn products requiring block refuge must be followed up with mandatory on-farm visits [conducted by industry (registrants)] to assess refuge compliance during the growing season, which will be conveyed to growers at the point of sale and be included in the grower insect resistance management agreement (USEPA 2020). Visits will be reported to the EPA. Farmers out of compliance with block refuge standards in cotton producing regions for one year will not be allowed to purchase Bt products, including RIB and block refuge products, for two years. Seed dealers will be required to keep grower IRM agreement records for 3 years, with audits that could result in losing the opportunity to sell Bt seed if signature rates or record keeping are noncompliant [conducted and enforced by industry (registrants)]. The industry (registrants) must ensure the availability of non-Bt elite corn hybrids for refuge plantings (USEPA 2020), which should improve the quality and yield of these plantings.
Potential Impacts to Mid-Atlantic Seed Dealers and Growers: Phase downs of single toxin and non-functional pyramid hybrids will impact hybrid availability and selection; however, these toxins (which control corn borers) will be available pyramided with Vip3A. If you are planting hybrids that require 20% block refuge (such as is the case with the single traited hybrids that are being phased out), a mandatory on-farm visit by the registrants and/or seed dealers may be required. Non-Bt elite corn hybrids will have to be made available for block refuge and refuge-in-a-bag seed mixes which should make yield more comparable to Bt plants.
US EPA. 2020. EPA draft proposal to address resistance risks to Lepidopteran pests of Bt following the July 2018 FIFRA scientific advisory panel recommendation. Memorandum EPA-HQ-OPP-2019-0682-0007. https://www.regulations.gov/document?D=EPA-HQ-OPP-2019-0682-0007
Andrew Kness, Agriculture Agent University of Maryland Extension, Harford County
Stalk rot (left) and ear rot (right) of corn.
With corn harvest underway across much of the state, growers may be encountering ear rots and stalk rots in affected fields. The degree of severity is dependent on a variety of factors, so it is wise to scout fields prior to harvesting in order to identify problematic fields and give those harvest priority.
Several different pathogens can cause ear rots in Maryland; the main contenders are listed in the table below. Although they typically do not affect yield, they can cause grain quality issues through the production of mycotoxins. Furthermore, if infected grain is not dried quickly or to a low enough moisture content, infection can spread, even when in the bin. Therefore, it is important to scout and identify fields that are infected with ear rots and harvest those first. It is better to pay a few cents in propane to dry the wet grain than to wait and risk infection levels getting worse, and the potential for elevated mycotoxin concentration in the grain. Quickly dry infected grain to below 15% for short-term storage and to below 13% for long term storage. It is important to note that not all ear rotting fungi produce mycotoxins, so I would recommend sending samples to a lab (the UMD Plant Diagnostic Clinic is a free service) to get proper identification so that you know the species in question and thus if mycotoxin contamination is a concern.
Table 1. Common ear rots of corn.
Disease
Pathogen
Symptoms
Mycotoxin
Fusarium ear rot
Fusarium verticillioides
“Starburst” kernels, white kernels, infected kernels may be scattered on ear
Fumosin
Gibberella ear rot
Fusarium graminearum
Ear covered in white mat often with pink hue, infection starts at tip and can progress to butt end of ear
Vomitoxin (DON)
Diplodia ear rot
Stenocarpella maydis and S. macrospora
White fungal mat on ear, may cover the entire ear
None
Penicillium ear rot
Several Penicillium species
Blue-grey spores on kernels developing on damaged ears (hail, deer feeding, insects, birds, etc.), may infect the germ of the kernel
Some species may produce mycotoxins
Trichoderma ear rot
Trichodermaviride
Green spores in between kernels
None
Aspergillus ear rot
Aspergillus flavus
Olive green spores on ear, usually starting at tip, associated with damaged ears (feeding from insects, deer, birds, etc)
Aflatoxin
Stalk rots are also a harvest concern. Like ear rots, stalk rots are also caused by many different pathogens, several of which are listed in the table below. No one factor causes stalk rots; they are rather the end result of a host of factors that contribute to a net deficit in plant carbohydrates needed for grain fill. The grain fill process is a major carbohydrate sink for the plant. As the plant produces carbohydrates through photosynthesis, it allocates almost all of it’s carbohydrate production to filling the kernels. A healthy plant will have sufficient leaf area to maximize photosynthesis and therefore produce enough carbohydrates to fill the grain. However, when photosynthetic leaf area is compromised, the plant cannot make enough food to fill the kernels. So in order to compensate for the deficit, the plant will cannibalize carbohydrates from existing tissues. The first tissues to go are the stalks, which are then easily compromised by stalk-rotting pathogens.
Table 2. Common stalk rots of corn.
Disease
Pathogen
Anthracnose stalk rot
Colletotrichum graminicola
Diplodia stalk rot
Stenocarpella maydis
Charcoal rot
Macrophpmina phaseolina
Gibberella stalk rot
Fusarium graminearum
Fusarium stalk rot
Multiple Fusarium species
Any factor that reduces leaf area or reduces photosynthesis after pollination will predispose plants to stalk rots. These include reduced leaf area through insect feeding, lesions from foliar diseases, or mechanical damage (such as hail). Other factors include inadequate fertility, water stress, and excessive plant populations. Another significant factor is hybrid genetics; both resistance ratings to stalk rotting pathogens as well as ear and kernel size. High-yielding, large kernel hybrids are more susceptible to stalk rots if they are not kept healthy through grain fill.
Scout fields for stalk rots as early as black layer. The “pinch test” is one way to scout for stalk rots. Pinch the stalk in between the nodes at one of the lower two nodes. You should not be able to pinch healthy stalks but rotted stalks will fairly easily pinch. Do this at random to assess the field. Alternatively, you can do a “push test”, which involves pushing the corn stalks approximately 30 degrees from horizontal (8 inches laterally) at a height of about eye level. Healthy stalks will return to vertical while infected plants will not. If more than 10% of plants tested exhibit stalk rot symptoms, you may want to harvest as soon as possible or risk a not-so-fun harvest of lodged corn.
Attached is the summary for the September 11 WASDE.
Corn
Harvested acres estimate was adjusted down 0.5 million acres and yield estimates were adjusted down 3.3 bushels to 178.5 bushels per acre. Beginning stocks were adjusted up slightly but the net effect in total supply was a decrease of 353 million bushels. Domestic demand estimate was decreased by 200 million bushels but exports were increased by 100 million bushels so the net effect in demand total was a decrease of 100 million bushel. So the ending stock estimates were down by 253 million bushel decreasing the stocks to use ratio from 18.7% to 17.1%. This anticipated decrease in ending stocks has been factored into the market as the December futures price increased this past month from $3.27 on August 12 (last WASDE) to $3.70 on September 11.
Soybeans
Yield estimates for the 2020/21 crop year were adjusted down from 53.3 bushels per acre estimated in August to 51.9 bushels per acre current estimate. Beginning stocks were also adjusted down by 35 million bushel. These two changes resulted in a decrease of 152 million bushel in estimated 2020/21 supply. On the demand side, the only change was a decrease of 2 million bushel in residual. The resulting estimate of ending stocks was decreased by 150 million bushels decreasing the Ending stocks to use ratio from 13.7% from 10.4%. Just like corn, soybean futures market prices (November) have spiked during the past month from $8.83 per bushel on August 12 to $9.93 on September 11.
Wheat
There were no changes in the wheat supply and demand estimates. However, wheat futures prices (September) have followed corn and soybean prices and increased from $4.91 per bushel on August 11 to $5.35 on September 11.
There was an adjustment of a minus 20 million bushel to the 2019/20120 crop estimate which carried forward to the beginning stocks of the 2020/2021 crop year. Yield estimates for the 2020/21 crop year were adjusted up from 178.5 bushels per acre estimated in July to 181.5 bushels per acre current estimate. These two changes resulted in an increase of 258 million bushel in estimated 2020/21 supply. On the demand side, feed & residual and export estimates were increased by a total of 149 million bushel. The resulting estimate of ending stocks was increased by 108 billion bushel increasing the Ending stocks to use ratio to 18.7% from 18.1% in July. These bearish numbers continue to suppress prices. Futures market prices have been in decline since the up tick in prices at the end of June/beginning of July so today’s WASDE report had little effect on prices and December corn settled at $3.27 per bushel.
Soybeans
There was a slight decrease of 5 million bushel to the 2019/20120 crop estimate ending stocks which carried forward to the beginning stocks of the 2020/2021 crop year. Yield estimates for the 2020/21 crop year were adjusted up from 49.8 bushels per acre estimated in July to 53.3 bushels per acre current estimate. These two changes resulted in an increase of 285 million bushel in estimated 2020/21 supply. On the demand side, the crushing estimate was adjusted up 20 million bushel, export estimate was adjusted up by 75 million bushel and residual was adjusted up by 5 million bushels. The resulting estimate of ending stocks was increased by 185 million bushels increasing the Ending stocks to use ratio to 13.7% from 9.8% in July. Just like corn, soybean futures market prices have been in decline since the up tick in prices at the end of June/beginning of July so today’s WASDE report had little effect on prices and November soybeans settled at $8.83 per bushel.
Wheat
There were minor adjustments in wheat supply and demand resulting in a 17 million bushel decrease in ending stocks estimate decreasing the Stocks-to-use ration from 45.6% in July to 44.3% in August. There was little movement in wheat prices and September 2020 SRW prices settled at $4.90.
Maria Cramer, Galen Dively, and Kelly Hamby University of Maryland, Department of Entomology
It is not unusual to see groups of Japanese beetles feeding on corn silks, which is known as “silk clipping” Figs.1 and 2). While Japanese beetle numbers tend to peak in July, there are multiple beetles that may clip corn silks, and with later maturity field and sweet corn silking in August, it is important to still be on the lookout But how much of a concern is silk clipping, what should you be looking for, and what should you do about it?
Figure 1 (left). Japanese beetles feeding on corn silks. Figure 2 (right). Silk regrowth after clipping. Images: M. Cramer, University of Maryland
Silk clipping is often not as much of a concern as it initially appears. If silks are clipped after pollination, which occurs within the first 4-5 days of silk emergence1, kernel set will not be affected2. If clipping reduces the number of kernels, the kernels may develop to be larger and offset the reduction in number2. However, under drought conditions, yield loss from silk clipping is more likely2,3.
Drought slows silk emergence and pollination, which means there is a longer window where silk clipping can hurt yield. Indeed, severe drought stress can cause incomplete silk emergence and cause a mismatch between pollen shed and silks that results in nearly blank cobs1. Drought can also make it harder for plants to compensate for poor pollination1. If leaf rolling begins in the early morning and continues until evening1, the field is stressed enough to be of concern and it is important to scout for silk clipping beetles during the first several days of silk emergence.
The culprits. Japanese beetles are the most noticeable silk clippers in Maryland because they are large, shiny, and congregate in groups (Fig. 3). They are a sporadic pest4 and their populations will vary yearly. However, their populations may be higher in corn following sod, soybean, or perennial ryegrass or clover covercrops4. Other beetles that may clip silk include the western, northern, and southern corn rootworm adults (Fig. 4)5. Western corn rootworm (WCR) has several look-alikes that do not clip silks, so make sure check the stripes; WCR will not have crisp black stripes, but instead has smudged stripes.
Figure 3 (left). Japanese beetle. Image: E. Hodgson, Iowa State. Figure 4 (right). Adults of southern corn rootworm (left), western corn rootworm (middle), and northern corn rootworm (right). Image: Varenhorst, South Dakota State
Scouting. Silking typically begins 3 days after tasseling5, so plan your scouting accordingly. You want to evaluate the silk stage and pollination. Silks naturally senesce about 10 days after emergence, browning and drying out. At this point, pollination can no longer occur1. To determine if green silks have been successfully pollinated, you can dissect the ear and do a shake test. Pollinated silk starts to discolor and drop away at the base of the silk where it attaches to the ear. Bob Nielson with Purdue Extension has produced a great video describing the pollination shake test: https://www.youtube.com/watch?v=K7DiwD4N0T0&feature=youtu.be
You should scout if pollination is incomplete. When scouting, make sure you sample both the edges and the interior (at least 40 feet into the field); while you may see alarming numbers of Japanese beetles on the edge of the field, there are usually much fewer inside the field2. Sample a minimum of 20 corn plants in 5 locations spaced evenly though the field. Count the number of beetles per ear and measure the length of the silks.
Thresholds. For Japanese beetles, three conditions need to be met to before an insecticide application will pay off: 1) there are three or more beetles per ear, 2) silks are clipped to less than ½ inch in length, 3) and pollination is less than 50% complete4 (most silks in the field are still green and/or shake test indicates about half of the silks are still attached). Conditions are similar for rootworm beetles, but the threshold is five or more beetles per ear.
Treatments. Because broad-spectrum insecticides may cause flare ups of other pests (for example, aphids or spider mites), only spray if thresholds are met. Pollen-shed is a time when there are large numbers of beneficials in the corn field doing important pest control work (Fig. 5), and foliar sprays may decrease their numbers.
Figure 5. Lady beetle larva eating corn pollen. Image: M. Cramer, University of Maryland
For Japanese beetles, consider a perimeter spray if most of the damage is on field edges (where they tend to feed more heavily). Japanese beetles are difficult to control, but pyrethroids should provide some control (e.g., Baythroid®, Brigade®, Warrior II®, Hero®, etc.). Good adult corn rootworm control has been found for indoxacarb products (e.g., Steward®), pyrethroids (e.g., Warrior II®, Brigade, etc.), and neonicotinoid pyrethroid mixes (e.g., Endigo®)6,7. When using insecticides, always consult and follow the label.
If silk clipping by Japanese beetles is a consistent problem, consider cultural controls like avoiding ryegrass and clover cover crops. Because female beetles lay eggs more easily into soft ground, it is also possible to reduce egg laying in nearby fields by pausing irrigation during the peak of Japanese beetle activity4.
Steckel, S., Stewart, S. D. & Tindall, K. V. Effects of japanese beetle (Coleoptera: Scarabaeidae) and silk clipping in field corn. J. Econ. Entomol.106, 2048–2054 (2013). https://academic.oup.com/jee/article/106/5/2048/878220
Shanovich, H. N., Dean, A. N., Koch, R. L. & Hodgson, E. W. Biology and Management of Japanese Beetle (Coleoptera: Scarabaeidae) in Corn and Soybean. J. Integr. Pest Manag.10, (2019). https://academic.oup.com/jipm/article/10/1/9/5454734
DeVries, T. A. & Wright, R. J. Evaluation of Foliar Applied Insecticides for Control of Adult Corn Rootworm in Corn, 2015: Table 1. Arthropod Manag. Tests41, tsw080 (2016). https://academic.oup.com/amt/article/41/1/tsw080/2658080
DeVries, T. A. & Wright, R. J. Evaluation of Foliar-Applied Insecticides for Control of Adult Corn Rootworm in Corn, 2015C: Table 1. Arthropod Manag. Tests41, tsw096 (2016). https://academic.oup.com/amt/article/41/1/tsw096/2658095
Kelly Hamby1, Maria Cramer1, Galen Dively1, Sarah Hirsh2, Andrew Kness2 Alan Leslie2, Kelly Nichols2, Emily Zobel2, and David Owens3 1University of Maryland, Department of Entomology | 2University of Maryland Extension 3University of Delaware Extension
A few hot spots where corn earworm (also known as tomato fruitworm, soybean podworm, and sorghum headworm) activity is starting to rise have been identified in central Maryland and Delaware. The warm 2019-2020 winter allowed for overwintering in our area, and some parts of the state experienced a higher than normal first flight in early June. The warm weather through June and July made for speedy development and earlier activity for the second summer generation. Because corn earworm has developed resistance to most Bt hybrids, significantly more adult moths are emerging compared to levels a decade ago. Some areas continue to capture few moths and are experiencing low pressure, while others have been experiencing moderate pressure that may continue to increase towards heavy pressure (>65 moths captured per 5 days). Captures for select sites in Maryland and Delaware are pictured below, and values within the gray box indicate low pressure (<7 for weekly captures, and <5 for four to five day captures).
Corn earworm larva feeding damage to corn
Although corn earworm prefer fresh corn silks for egg laying, they will lay eggs on wilted and brown silks if the plants remain green and unstressed. As corn matures further over the next several weeks, corn earworm activity will shift to other host plants including soybeans and vegetables. See last summer’s articles for scouting and management recommendations in vegetables as well as sorghum and soybeans.
Podworm outbreaks have historically occurred in growing seasons where the corn crop was drought and heat stressed, with corn senescing earlier than normal. However, narrow row spacing in soybeans makes the plants less attractive to female moths and increases the likelihood that fungal pathogens will infect the larvae. Therefore, it is important to scout bean fields, especially paying attention to those fields with a more open canopy in areas where the nearby maturing corn is no longer attractive to earworm moths. North Carolina State University has produced a helpful economic threshold calculator for podworm in soybean: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html
Acknowledgements: Corn earworm trapping efforts in were supported by the Crop Protection and Pest Management Program [grant numbers 2017-70006-27171 and 2017-70006-27286] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
