Scout for Aphids in Small Grains

Kelly Hamby, Associate Professor and Extension Specialist, University of Maryland and
David Owens, Extension Entomologist, University of Delaware

Figure 1. Barley Yellow Dwarf patch in a field of malting barley, March 2023. Photo: David Owens, Univ. of Delaware.

Last season, aphids transmitted an unusual amount of barley yellow dwarf virus (BYDV) to wheat and barley across the Delmarva Peninsula. BYDV is particularly important when it infects plants in the fall. Fall BYDV infections can stunt plants (noticed as early as green-up, Figure 1) and cause more serious yield loss than spring infections. Our most common small grain aphid species are bird cherry oat aphid (Figure 2) and English grain aphid, although bird cherry oat aphid are associated with greater and more severe incidence of BYDV.

Figure 2. Bird cherry-oat aphids.

Historically, planting after the Hessian fly-free date (Table 1) reduced the likelihood of fall BYDV infection. However, fly-free dates were calculated more than 100 years ago, and it is now not uncommon for our first killing frosts to occur in late October or even November. Long falls with milder weather allow more time for aphids to colonize fields and potentially transmit the virus. Small grains varieties vary in their susceptibility to BYDV, and planting varieties with at least some tolerance can help. Unfortunately, resistant varieties are not available in barley. Finally, monitoring and managing the aphid vectors may be necessary.

Identifying bird cherry-oat aphid: A magnifying hand lens is required to identify aphids. Bird cherry-oat aphid ranges from orange green to olive green to greenish black. Wingless individuals typically have a reddish orange patch around the base of the cornicles (tail pipes). Winged individuals tend to be very dark. Their legs, cornicles, and antennae are similar in color to their bodies and medium in size.

Monitoring and thresholds: Typically, monitoring aphids in the fall and at green-up provides the best chance of identifying and mitigating BYDV risk. Scout ten locations per field avoiding field margins and look at 1 ft of row in each, making sure to look at the crown (at or below ground level), at the stem, and on the undersides of leaves. English grain aphids tend to feed on the uppermost portions of the plants while bird cherry oat aphids tend to cluster on the lower portions, especially in barley.

University extension threshold recommendations vary by region. In southern states, 6 aphids/row-ft is considered justification for a treatment in the fall. North Carolina uses a threshold of 20 aphids/row-ft where BYDV has been a problem and cold weather is not in the 7 day forecast. For other small grains, consider increasing the threshold to 25-50 aphids per foot of row.

In 2022, one of the malting barley fields sampled averaged 17 aphids per row-ft in early November. Because of unusually warm winter weather in which average temperatures were greater than 38 degrees, aphid populations peaked in one field at 235 aphids per row-ft that had averaged 1.8 per row-ft in November. This highlights the need to regularly monitor aphid populations during periods of mild weather.

Natural enemies: A number of natural enemies feed upon or parasitize aphids and they often do a good job keeping aphid populations down. One natural enemy per 50-100 aphids should be sufficient to control aphid populations. In addition, they are good at finding aphids even when their populations are low. Small wasps that develop within aphids leaving behind “mummy” aphids (Figure 3A), lady beetles, lacewing larvae (Figure 3B), and flower fly larvae (Figure 3C) are especially common aphid natural enemies. Insecticides will also kill these natural enemies.

Figure 3. Aphid natural enemies A) parasitoid wasp and golden or tan colored “mummy” aphids, B) lacewing larva eating aphids, C) flower fly larva eating aphids. Images: David Cappaert, Bugwood.org.

Insecticides: Seed treatments (e.g., Cruiser, Gaucho) provide some protection from fall aphids, but do not continue to provide protection into the spring and are not economic in years where aphids do not occur. Due to the differences in economics and BYDV susceptibility of malting barley varieties, seed treatments may be more useful than in feed barley or wheat. We generally recommend a foliar insecticide when aphid populations reach threshold. Small grain aphids are generally quite susceptible to insecticides. Pyrethroid products (e.g., Warrior) or a pyrethroid-neonicotinoid mix (e.g., Endigo, labeled for barley only) work well for aphid control.

 

Table 1. Hessian fly-free dates for Maryland and Delaware counties

State County Date
Maryland Allegany Sept. 27
Anne Arundel Oct. 7
Baltimore Oct. 2
Calvert Oct. 8
Caroline Oct. 7
Carroll Sept. 28
Cecil Oct. 3
Charles Oct. 8
Dorchester Oct. 9
Frederick Oct. 2
Garrett Sept. 20
Harford Oct. 1
Howard Oct. 2
Kent Oct. 6
Montgomery Oct. 4
Prince George’s Oct. 7
Queen Anne’s Oct. 7
Somerset Oct. 10
St. Mary’s Oct. 9
Talbot Oct. 8
Washington Oct. 1
Wicomico Oct. 10
Worcester Oct. 11
Delaware Kent Oct. 8
New Castle Oct. 3
Sussex Oct. 10

More information:

Kleczewski, N., Cissel, B., Whalen, J. 2016. Barley Yellow Dwarf Management in Small Grains. http://cdn.extension.udel.edu/wp-content/uploads/2015/10/14051904/BYDV-Final-Draft-9-12-16.pdf.

Flanders, K., Herbert, A., Buntin, D., Johnson, D., Bowen, K., Murphy, J. F., Chapin, J., Hagan, A. 2006. Barley Yellow Dwarf in Small Grains in the Southeast. https://entomology.ca.uky.edu/files/efpdf1/ef150.pdf.

Owens, D. and B. Cissel. Insect Control in Small Grains (for Grain only) – 2020. https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/Insect_Control_in_Small_Grains_2020.pdf.

 

2023 Small Grain Variety Trials

Vijay Tiwari, Assistant Professor, Department of Plant Science and Landscape Architecture
University of Maryland, College Park

Results from the 2022/23 University of Maryland wheat and barley variety trials have been published. You can access the report by clicking the link.

Click here to view the report

For questions/comments, please email Dr. Vijay Tiwari at vktiwari@umd.edu. For more information on how to make the most of variety trial data, refer to our fact sheet: What do the Numbers Really Mean? Interpreting Variety Trial Results (FS-1119)

2023 Small Grain Field Day

wheat field

Date: May 23, 2023
Time: 3pm
Location: Wye Research and Education Center
211 Farm Lane, Queenstown, MD 21658

Registration link: http://bit.ly/smallgrain23

The program will start at the seed building and proceed to the fields. We will hear an update on the Agronomy degree program within the Department of Plant Science and Landscape Architecture, including highlights from the first semester teaching AGST401: Tractor and Equipment Operation, Safety and Maintenance. We will showcase a commercial variety strip trial organized by the Maryland Crop Improvement Association (MCIA) and industry reps will be on hand to discuss their entries in the trials. Dr. Vijay Tiwari will discuss the small grain variety trials and his wheat breeding program, Dr. Nidhi Rawat will discuss her pathology work in barley and wheat, and Dr. Kurt Vollmer will update us on weed control in wheat.

Dinner will be served at 5pm, sponsored by Maryland Crop Improvement Association and others.For additional program information, contact Dr. Nicole Fiorellino at nfiorell@umd.edu or 443-446-4275.

2022 Maryland Small Grain Variety Trials

Results from the University of Maryland Small Grain Variety Trials are in the tables below. To download a pdf copy of the report, click here.

University of Maryland also rates the relative susceptibility of select varieties of wheat and barley to Fusarium head blight. The results from this trial can be found here.

For questions regarding the small grain trials, contact Dr. Vijay Tiwari (vktiwari@umd.edu) or Dr. Nidhi Rawat (nidhirwt@umd.edu).

If you’d like to learn more about how to interpret variety trial data, view our fact sheet by clicking here.

Click to Download The 2022 Small Grain Variety Trials

Click to Download 2022 Wheat and Barley Disease Ratings

2021 Maryland Small Grain Variety Trials

Results from the University of Maryland Small Grain Variety Trials are in the tables below. To download a pdf copy of the report, click here or visit https://psla.umd.edu/extension/md-crops/small-grains-maryland.

For questions regarding the small grain trials, contact Dr. Vijay Tiwari (vktiwari@umd.edu) or Dr. Nidhi Rawat (nidhirwt@umd.edu).

If you’d like to learn more about how to interpret variety trial data, view our fact sheet by clicking here.

Click to Download The 2021 Small Grain Variety Trials

 

 

Scouting Fields for Fusarium Head Blight

Alyssa Koehler, Extension Field Crops Pathologist
University of Delaware

Most barley has made it past flowering, with wheat fields approaching anthesis. Over the past few weeks we have remained at low risk for Fusarium head blight (FHB) http://wheatscab.psu.edu/. There have been some rain events this week, and we will keep an eye on the model over the next 1-2 weeks. The recommended stage for fungicide application is when 50% of main tillers are flowering (yellow anthers visible) until 4-5 days after. Once wheat has flowered, symptoms of FHB are visible in 18-24 days, but cool weather can slow symptom development. Heads with FHB will have bleached florets or bleached sections of the head (Figure 1) and may have pink growth on spikelets. Glume blotch may also be present, but typically has more of a grey appearance. You can follow these steps to assess the level of FHB present in your field.

Wheat infected with fusarium
Figure 1. Symptoms of Fusarium head blight on wheat. Image: A. Koehler, Univ. of Delaware.
  1. For every 10 acres of field, randomly select one spot to survey.
  2. Keeping your line of sight above the wheat heads, walk 40-50 yards and randomly pick 10-20 heads to look at on the plant or detach and place into a bag. (You don’t want to be looking down and biasing the heads you select).
  3. Once you have randomly collected the heads, rate the percent of each head with symptoms of FHB (bleaching or pink growth on spikelets).
  4. After you have recorded values for each head, determine the average percent FHB severity by dividing the sum of disease severities by the total number of heads collected.

(Ex. You rate 10 heads with severity values: 0, 10, 30, 0, 0, 20, 10, 0, 0, 0. These add up to 70. 70/10 heads = 7% FHB severity).

Higher levels of FHB are typically associated with elevated levels of DON and possible issues with yield and test weight. It is possible to have delayed or lower levels of symptoms and still have DON.

  1. Repeat this assessment as needed to get an overall rating for the field. Fields with greater than 10% FHB severity are at higher risk for yield losses or elevated DON. Fields with elevated DON should be harvested as early as possible and you may want to consider increasing combine fan speeds and shutter openings to reduce the amount of scabby kernels harvested.

 

Can small grains get too big in the fall?

Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County

Temperatures have been unseasonably mild in our region in October and November. Warmer fall temperatures can make for an enjoyable harvest but can also force accelerated development in our small grains, resulting in excessive tillering and top growth. While this increase in vegetation may be less of a concern with a small grain grown strictly as a cover crop, it can be cause for concern for wheat or barley planted for grain.

Wheat and barley need adequate but not excessive growth in the fall in order to maximize overwintering survival and yield in the spring. Plants that have 1-3 tillers and 4-5 leaves should overwinter well and have excellent yield potential going into the spring. In normal years the plants have enough time between the Hessian fly-free date and winter dormancy to achieve 1-3 tillers. However, excessive tillering and top growth can occur if seeding occurs too early, and/or if temperatures in November are unseasonably warm. Rapid and excessive fall growth can be exacerbated if there are high residual nitrogen levels left in the field from the previous crop. This year I have seen some early planted barley that is approximately 10-12 inches tall now, which may cause some issues this spring.

Excessive top growth in the fall creates a stressful environment that can decrease the percentage of plants and tillers that survive the winter, and in extreme cases the growing point of the main stem can emerge (or be very close to emerging) from the soil. In this case, entire plants can die due to the freeze-thaw cycle. The main stem and first tiller of the plant contributes the most to yield, so if they die yield can be severely reduced; although if there are enough healthy secondary tillers, some yield can be recuperated. Excessive top growth also promotes the development of foliar diseases such as powdery mildew, which if established early, can create a real problem in the spring. Other snowmold diseases can cause serious plant injury to these larger, lush plants. Likewise, aphids are attracted to larger, greener plants; so excessive top growth will attract more aphids, which can vector Barley Yellow Dwarf Virus (BYDV). This would be especially true for seeds planted without an insecticide seed treatment for aphids. Another insect that likes larger plants is the Hessian fly, which will lay eggs in susceptible varieties of plants before the frost-free date (anywhere from September 30-October 13 depending on where you are in Maryland and the year/weather). These infestations can cause serious lodging issues in the spring. Finally, larger plants transpire more water than smaller plants. This means that if we have a dry winter/spring, the larger plants will have depleted the soil moisture faster than the smaller plants and the potential for drought stress increases (although our recent springs have not been dry).

If you have a situation where your wheat or barley for grain is putting on excessive growth, you may want to evaluate the stand after the spring thaw. If the stand is severely damaged, you might consider leaving that field as a cover crop rather than taking it to harvest. Stands with fewer than 15 plants per square foot are likely to have significant yield reductions. If you have cattle you could also try to graze the field in the fall (as long as it’s not too wet); or alternatively, mow the field to keep the growth at bay. Obviously this practice has significant costs associated with it, but has been done with success in our region.

Cause of Red Barley Heads & Wheat Leaf Tip Necrosis

Andrew Kness, Agriculture Extension Agent
University of Maryland Extension, Harford County

Over the past few weeks I have gotten questions about red/purple discoloration to barley heads (Figure 1). These symptoms are not widespread in the field; maybe 1% of heads exhibit this condition. To the best of our knowledge, these symptoms are not caused by a disease but likely a physiological response to an abiotic stress. This spring went from very mild in March to cool and even freezing in April. These symptoms could be a response to environmental conditions, genetic, or a combination of both. Affected heads appear to be viable and able to produce grain.

Discolored red/purple barley head
Figure 1. Discolored barley heads. Images: J. Semler, University of Maryland.

A second condition appearing this year is leaf burn or tip necrosis (LTN) in wheat (Figure 2). This disorder is often a response to cold injury or wind, but can also manifest as a result of heat and drought stress. These symptoms can be intensified by specific leaf rust and stripe rust resistance genes. In any case, there is nothing you can do to remedy the situation.

Wheat with brown leaf tips
Figure 2. Leaf Tip Necrosis on wheat caused by environmental stresses and/or rust resistance genes.

Leaf tip burn/LTN may be confused with barley yellow dwarf virus (BYDV). LTN tends to cause death of the leaf tip resulting in necrotic brown tissue (Figure 2), whereas BYDV can cause a range of symptoms from yellowing of the leaf, which may or may not be accompanied with bronzing/purpling of the leaf tips (Figure 3). Since BYDV is vectored by aphids, symptoms tend to be localized in hotspots in a field, whereas leaf burn and LTN more uniformly affect the entire field.

Purple wheat leaf tips indicate barley yellow dwarf infection
Figure 3. Barley Yellow Dwarf Virus symptoms on wheat.

Mild Winters Favor Greenbug Aphids and Winter Grain Mite in Small Grains and Orchardgrass

Kelly Hamby, Terry Patton, and Galen Dively
Department of Entomology, University of Maryland College Park

Summary. Weather stations in Baltimore, MD recorded the 3rd warmest winter on record in 81 years from Dec 2019 to February 2020, with 10% of our 30 year average snowfall (NOAA National Climate Report). Insects that overwinter as immatures or adults in above-ground protected areas are typically favored by mild winters, especially species that are not cold-hardy because much of the population would typically die during the winter. However, the lack of snowfall can also reduce overwintering survival because snow can insulate against freezing temperatures. Mild winter conditions favor green bug aphids and winter grain mite outbreaks in small grains and orchardgrass, and these pest populations can build rapidly. Fortunately, mild winters also favor many beneficial natural enemies. Greenbug aphid outbreaks have been observed in central Maryland orchardgrass (see Figure 1), and greenbugs have also been observed in Delaware. Overall, aphid populations have been spotty in Delaware and promising natural enemy activity has been observed (UD Weekly Crop Update, March 20). However, close surveillance is necessary when greenbug is the predominate species because greenbug injects toxic saliva during feeding and can be very destructive. It is important to carefully scout your fields for aphids multiple times to determine whether populations are building or crashing on your farm. Management interventions may be necessary to prevent economic losses. Winter grain mites may also be a problem this year and scouting close to the soil surface is necessary to catch this issue in a timely manner.

Figure 1. Heavy aphid populations have been observed in orchardgrass in central Maryland.
Figure 3. Aphid damage to orchardgrass in central Maryland.

Cereal Aphids and Greenbugs. Multiple species of aphid occur in Maryland small grains and orchardgrass (see Figure 2) and aphids can vector barley yellow dwarf virus. Bird-cherry oat aphids vector the most severe strain and may need to be managed in the fall to prevent damage from barley yellow dwarf, especially in intensive management wheat. Although the direct damage from aphid feeding is generally similar across species, it is especially important to record species if greenbugs are present. Greenbug saliva contains enzymes that break down cell walls, so their feeding is most damaging. They initially cause spotting on the leaf followed by discoloration and eventual leaf and root death if feeding continues. Grain cultivars vary in their tolerance for greenbug damage. One of the first noticeable symptoms of aphid outbreaks are circular yellow to brown spots with dead plants in the center (see Figure 3); however, aphid damage may be confused with moisture stress and/or nitrogen deficiency so make sure to scout for aphids especially in areas that are showing stress symptoms. Scout a minimum of 1 linear row foot in 10 sites, the more row feet and locations the better, and estimate the number of aphids per foot of row. The rule of thumb treatment threshold for small grains is to treat if counts exceed 150 per linear foot throughout most of the field, with few natural enemies detected (e.g., mummy aphids, lady beetles, fungal infections). One natural enemy to every 50 to 100 aphids can be enough to control the population. This threshold may be lower if greenbugs are the predominant aphid and greenbug populations should be carefully monitored. Foliar insecticides including pyrethroids (Group 3A), neonicotinoids (Group 4A), and organophosphates (Group 1B) can be used to control aphids.

Figure 2. Common cereal aphids. Notice color and length of antennae and cornicles (tail pipes). Greenbugs are light green with a dark green stripe, with black tips of the legs, cornicles, and antennae. Photos: Various Extension websites.

Winter Grain Mite. Winter grain mites are a cool season pest of small grains and orchardgrass that cause a silvery leaf discoloration from feeding damage that punctures individual plant cells. Feeding can also stunt plants. Winter mites have a dark brown to black body with bright reddish-orange legs (see Figure 4). Somewhat uniquely, their anal opening is on the upper surface and can appear as a tan to orange spot that is more visible under magnification. Two generations of winter grain mite occur per year and are active from the fall to early summer. They oversummer in the egg stage, with the first generation hatching around October and adult populations peaking in December or January. The second generation peaks from March to April and produces the oversummering eggs. Because spring eggs result in fall populations, rotating the crop away from grasses and managing wild grasses around field edges can be helpful to reduce populations. Adult activity occurs when temperatures are between 40 and 75°F, and they prefer cool, cloudy calm weather. Therefore, winter grain mites are easier to see during these conditions, and more likely to be higher on the plant during the early morning or late evening. If you are scouting on a hot, dry day or in the middle of the day, you should check under residue where the soil is moist, and may need to dig 4 or 5 inches into the soil to find the mites. Winter grain mite does not typically cause economic damage, and no thresholds have been developed. If large portions of a field show symptoms and mites are present, treatment may be warranted. No products are specifically labeled for winter grain mite; however, products labeled for brown mite such as dimethoate (Group 1B, in wheat only) are likely to be effective. Warrior II (pyrethroid, Group 3A) may also provide suppression.

Figure 4. Winter grain mite adult.

References and Useful Extension Articles:

Kansas State University Wheat Pests, Winter Grain Mite, https://entomology.k-state.edu/extension/insect-information/crop-pests/wheat/winter-grain-mite.html

NOAA National Climate Report Supplemental Material, https://www.ncdc.noaa.gov/sotc/national/202002/

Oklahoma State World of Wheat Blog, Winter grain mites in northcentral OK, https://osuwheat.com/2015/01/06/winter-grain-mites-in-northcentral-ok/

University of Delaware Weekly Crop Update March 20,2020. Agronomic Crop Insect Scouting, https://sites.udel.edu/weeklycropupdate/?p=14510

University of Delaware Fact Sheets and Publications, Winter Grain Mite Management in Small Grains, https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/winter-grain-mite/

Virginia Tech Insect Control in Field Crops, ENTO-335C, https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-016/ENTO-335C.pdf