Field Crops Disease Management Resources and 2019 Guides

Alyssa Koehler, Extension Field Crops Pathologist;

The 2019 Fungicide Efficacy for Control of Corn Diseases table is now available through the Crop Protection Network This table is produced annually by the Corn Disease Working Group and provides efficacy ratings for fungicides to manage corn foliar diseases. A number of other resources for disease management in corn, soybean, and small grains are available through the Crop Protection Network

Small Grains Disease Updates

Alyssa Koehler, Extension Field Crops Pathologist;

For those that I have not met yet, my name is Alyssa Koehler and I am the new field crops Extension plant pathologist with the University of Delaware. I am located at the Carvel Research and Education Center in Georgetown and my email is

As temperatures warm up through March, begin to scout your field at least weekly to monitor for small grain diseases. Once temperatures are above 58-60 °F for 1-2 weeks, you may begin to see powdery mildew. Nitrogen applications offer a good time to check the field for these grey patches or “white fuzz” on leaves. In cases where you have high levels of foliar disease present, a fungicide application can be made at flag leaf, but remember that fungicides applied at this timing will not provide control for management of Fusarium Head Blight and DON levels. Fungicides for FHB are most effective when applied during flowering. In the next issue of WCU we will go over detailed management strategies for FHB. Please feel free to contact me if you have any questions as the season begins.

Weed Control in Wheat and Barley

Mark VanGessel, Extension Weed Specialist;

Since many small grain fields did not get an herbicide treatment last fall, they may need to be sprayed as soon as the fields dry out to control weeds before weeds get too large and before small grains get too large and interfere with spray coverage.

List of recommended herbicides for winter wheat and barley in Delaware (additional herbicides are labeled but not recommended).

Herbicide Maximum Stage Rotation to Soybeans Rotation to Vegetables
Axial XL Pre-boot No restrictions 30 days
Harmony Extra Before flag leaf emergence 7 days 45 days
Huskie Flag Leaf emergence 120 days 9 months
Quelex Flag leaf emergence 90 days 15 months
Starane Ultra Early boot stage 120 days in MD

90 days in DE, VA

4 months
Sentrallas Before flag leaf emergence 120 days

90 days in DE, MD, VA

4 months
2,4-D After tillering before jointing No restrictions 3 months
Dimetric EXT At “green up stage” No restrictions at least 4 months


Annual ryegrass populations with resistance to Group 2 herbicides (Osprey and PowerFlex) have been reported in Delaware. There have been no reported resistance issues with Axial XL in Delaware; however, resistance has been confirmed in Maryland. A word of caution, Axial XL is the same herbicide family as Hoelon (Group 1) and there was Hoelon-resistant annual ryegrass in the region in the past.

Common chickweed control is becoming more challenging with the spread of ALS-resistant common chickweed (resistant to Finesse, Harmony Extra, Osprey, and PowerFlex). Spring application of Starane Ultra, Quelex, and Huskie are options to suppress/control the resistant chickweed. Delaware Department of Agriculture and Winfield have approved a state label (24c) for use of Dimetric EXT for winter wheat and barley. The active ingredient is metribuzin. Dimetric is the only formulation of metribuzin with this special label in DE and MD. In addition to chickweed, UD Weed Science has also had encouraging results with control of ivyleaf speedwell, jagged chickweed, henbit, and knawel when applied to weeds 3 inches or less. We know some varieties differ in their sensitivity to metribuzin, and most varieties have not been tested. So, we recommend limiting Dimetric EXT to fields with ALS-resistant chickweed, treat early-spring, and being cautious on varieties with no previous experience.

  • Winter wheat is most tolerant if treated at green up timing. UD Research has used Shirley, a sensitive variety, and have not documented injury with green-up applications. When using a sensitive variety, applications in late March and into April did cause significant injury and yield reductions.
  • Do not apply with nitrogen.
  • Do not use on sandy soils with organic matter less than 0.75%; which includes sandy knolls in portions of some fields.
  • We recommend use of metribuzin only in fields planted with a grain drill (not recommend on fields where seeds were broadcast and incorporated with vertical tillage tool or disc).
  • Be sure to use the rate recommended for your crop stage.
  • Do not double-crop vegetables after small grain harvest.
  • Refer to the label for additional precautions, rates and timings.

Jagged chickweed control has not been very good with any herbicide or herbicide combinations when applied in the spring. In our trials, Dimetric EXT was the most effective treatment. Harmony Extra plus Starane Ultra provides some suppression. No other treatment provided better suppression in our trials.

Henbit is the most common weed in winter wheat and it can be difficult to control with most small grain herbicides applied in the spring. Harmony Extra, Huskie, and Quelex will suppress henbit, but seldom completely kill the plants. But suppression in combination with a competitive small grain canopy is often sufficient to stop henbit growth.

Ivyleaf speedwell control is another difficult weed to control. UD research has found suppression with a combination of Harmony Extra with either Starane Ultra or 2,4-D or Quelex applied alone (Quelex plus Harmony Extra was not included in our trial). PowerFlex also provides suppression but can cause injury to wheat with spring applications.

There is always interest in applying wheat herbicides with nitrogen, so be sure to read all herbicide labels carefully because some products can be tankmixed with nitrogen but only if the nitrogen is no more than 50% of the spray solution (nitrogen is mixed 1:1 with water.

A longer-term approach for weed control is to prevent winter annual weeds from producing viable seeds in the years the field is not planted with small grains. Jagged chickweed and henbit will start flowering in mid-March and need to be treated by early April to prevent seed production. Using a competitive cover crop is another alternative to limit seed production of these winter annual weeds.

Plan to Sample for Wireworms and Grubs

David Owens, Extension Entomologist,

In general, rates of wireworm and white grub injury are lower now than they have been historically due to good weed control. However, last year there were more weedy fields than usual due to weather interference with herbicide programs. These weeds are attractive to egg-laying adult wireworms and white grubs. The eggs hatch in the late summer and larvae feed on plant roots and organic matter until late fall when they move deep into the soil to avoid freezing. As the soil warms up between the end of March and mid-April, wireworms and white grubs will start moving to the surface. You can sample for them using a couple of different methods. The first method is useful primarily for wireworm sampling and involves baiting a field for 2-3 weeks. Place a half cup of wheat and corn seed in a shallow hole about 4 inches deep and 9 inches wide, cover the seed back up, and secure a piece of black plastic like a garbage bag over the soil. The plastic helps warm the soil, the seed will germinate, and wireworms will come to it. If 1 or more wireworms are found per bait station, a soil insecticide should be used. The second method is the compact soil sample, useful for both grubs and wireworms. This involves digging a hole 8 inches x 8 inches x 6 inches deep. Consider a treatment if you find more than 1 grub per field. Ideally, 1-2 bait stations per acre or 5 – 10 soil samples per field will provide good sampling confidence. Efficacy ratings for various seed treatments can be found here:

Note on Small Grain Weed Control

Mark VanGessel, Extension Weed Specialist;

Due to fall rain showers, a lot of small grain fields were not sprayed for weeds last fall. Be sure to scout your fields early and determine if a spring herbicide application is needed. Early spring applications of Harmony Extra, Axial XL, Huskie, Quelex, Starane Ultra, 2,4-D, Clarity, Dimetric (metribuzin), or Talinor have provided good weed control even with low temperatures. Be sure to read the label for crop rotation, required adjuvants, and restrictions for application with nitrogen.

New Mid-Atlantic Field Crop Weed Management Guide Available

Mark VanGessel, Extension Weed Specialist;

There is an updated “Mid-Atlantic Field Crop Weed Management Guide” developed by weed specialists from Penn State, Univ. of Delaware, Univ. of Maryland, Virginia Tech, and West Virginia Univ. The 260-page guide covers corn, sorghum, soybean, small grains, and hay and pastures. The guide includes information on commonly used herbicides for these crops, including relative effectiveness for burndown, preemergence, and postemergence control of most of the common weeds in the region. There are tables on premixes and what is included in the premixes, and a section on management of problem weeds. The guide is available in the Delaware county offices for $15 or can be ordered on-line at Available on-line are the printed copies for $25; an enhanced pdf copy for use on computers and tablets for $15 or both a hard copy and pdf for $35.

Delmarva Producers Should Double Check Double Cropping Coverage

Don Clifton, Farmers First Services,

As crop insurance deadlines for spring-planted crops near, make sure you have the right coverage package for your operation.

Double cropping is a common practice on Delmarva. Planting soybeans or vegetables after a small grain crop, or more than one vegetable annually on the same acreage, is routine for many area farmers. Producers need to be aware of special considerations when obtaining crop insurance for these crops.

Many Delmarva producers and agents have expressed frustration with the Double Cropping / Multiple Cropping provisions within current policy and procedure. Too often farmers find out about the full extent of certain coverage limitations only after a loss has occurred and the loss adjustment process has commenced. This has happened in cases of prevented planting claims as well as loss claims after harvest.

It is imperative that producers fully understand their options and responsibilities before making a final decision about their crop insurance package by the sales closing date. Depending on producer double cropping history or cropping history on the subject farm, it may be wise to change your coverage on either the first crop or subsequent crops. It is important to know your risk and any limitations to covering that risk. Ask your agent about your double cropping coverage NOW!

The applicable Crop Insurance Handbook language (par. 1223) reads, “1st insured crop limitations may apply to acreage planted to a 1st insured crop which has suffered an insurable loss. This excludes acreage that qualifies for double cropping. See the Loss Adjustment Manual for more information on double cropping.”

The issue of acreage qualification for double cropping is too important to ignore.

No producer can be expected to research the reference materials crop insurance professionals rely upon before making their crop insurance decisions. Crop insurance agents are prepared to answer your questions on a host of issues. Good communication with your agent is imperative. The agent needs to know which issues apply to your operation, which questions to answer.

In addition, information about these and any other crop insurance and/or revenue protection issues can be obtained by sending questions to or calling (302) 242-8806. We can help you know which questions to ask your agent.

If double cropping coverage limitations lead you to opt out of coverage for one or more crops, you may be able to obtain Whole Farm Revenue Protection (WFRP) as umbrella risk protection for your farm income. Once again, the time to inquire about WFRP is NOW!

Who Should Consider Whole Farm Revenue Protection (WFRP)?

Producers who derive income from:

  • Otherwise Non-insurable crops
  • A mix of insurable and non-insurable crops
  • Crops and livestock
  • Direct marketing
  • Growers of some greenhouse and nursery crops

In other words, just about every ag producer on Delmarva!

In addition, producers for whom crop insurance policy provisions have limited coverage for individual crops may want to consider supplementing their risk protection with WFRP.

WFRP is an umbrella (whole farm) policy covering a wide array of farm production, both insurable commodities and those for which insurance is not currently available or limited.

Talk to your crop insurance agent today to see how you might benefit from WFRP.

USDA and Cooperative Extension – a partnership to help you make the best-informed risk management decisions for your family. Only a licensed agent can sell you crop insurance, you can get current Information about these and any other crop insurance and/or revenue protection issues by sending questions to or calling (302) 242-8806.  We can help you know which questions to ask a crop insurance agent.

Insecticide Trial Results for Vegetable and Agronomic Crops

David Owens, Extension Entomologist, and Bill Cissel, Extension Agent – Integrated Pest Management;

Summaries of last season’s insecticide trials in peas, sweet corn, watermelon, field corn, soybean, and wheat can be viewed at

Scouting for Aphids in Small Grains

Phillip Sylvester, Kent Co., Ag Agent;, Bill Cissel, Extension Agent – Integrated Pest Management; and David Owens, Extension Entomologist,

Invariably I get asked, “What do you do this time of year?” or “Are the bugs dead yet?” The answers last week would’ve been: counting aphids in small grain plots, and not quite. Aphid populations coming out of winter are pretty low in research plots at Carvel in Georgetown, DE and at the Wye in Queenstown, MD. This is consistent with reports coming from other folks in the field. It may be tempting to tank-mix a pyrethroid with the initial nitrogen application for small grains in the next few weeks (assuming things dry out), but in the vast majority of cases, you will help your bottom line by leaving out an early insecticide. These low aphid populations also serve as important food for beneficial insects, and an insecticide will take them out, releasing spring migrants from predation. In fact, there are only two situations where we are concerned with the physical feeding injury caused by aphids, 1) infestations of Greenbug aphids and 2) English grain aphids feeding on small grain heads. However, aphids are important because of the role they play as vectors of Barley Yellow Dwarf Virus (BYDV). At this point in the growing season, an insecticide application may be warranted if you find ten or more aphids per row-foot. Remember, you may hit a small colony in one sample that has 10 or 15, but then go several samples without any. The only way to know how many and what species of aphid you have in your field is to scout it.

Read this fact sheet for more information about Barley Yellow Dwarf Virus:

Click here for a photo library of common aphid species in DE:

Click here for a photo library of Barley Yellow Dwarf Virus Symptoms: