Category Archives: Small Grains

New Crop Disease Management Resources

Though it has been around for several years, the Crop Protection Network (CPN) has recently added several publications on disease management in corn, soybean, and small grains that are relevant to growers, crop consultants, and extension personnel in Virginia and the surrounding region. These can be accessed at the CPN website cropprotectionnetwork.org. As stated on the website:

“The Crop Protection Network (CPN) is a multi-state and international partnership of university and provincial Extension specialists, and public and private professionals that provides unbiased, research-based information. Our goal is to communicate relevant information to farmers and agricultural personnel to help with decisions related to protecting field crops.

Extension specialists throughout the country (including myself) contribute to the publications and other resources posted on the website. An example of a recent publication on optimizing fungicide use for control of Fusarium head blight can be downloaded below. The CPN library includes over 30 publications on crop management, and additional publications are in development.

CPN-3001-Optimizing Fungicide Use for FHB

Wheat Disease Update – May 24, 2018

Fusarium head blight (FHB) risk for Virginia continues to be to high throughout the state due to recent wet, warm weather (http://www.wheatscab.psu.edu/). Most of the wheat is past the flowering stage and no longer at risk, but later flowering wheat may still need a fungicide application. Triazole fungicides including Prosaro, Caramba, and Proline are recommended. Do not apply fungicides containing a strobilurin since this can increase DON. For wheat that is past flowering, a fungicide application will not reduce FHB or DON contamination of the grain. Grain harvested from fields with signs and symptoms of FHB should be kept separate from non-infested grain.

For assistance with disease identification or management recommendations, contact Dr. Hillary L. Mehl, Extension Plant Pathologist (hlmehl@vt.edu).

armyworm in VA small grains

I have received several reports from Virginia Beach and Chesapeake of armyworms infesting wheat and hay in large numbers. Neighboring regions of NC are experiencing similar outbreaks.

Overall, these infestations are rare in our state, but scouting is recommended. Fields treated previously with pyrethroids may be at higher risk because they contain fewer natural enemies to combat pest outbreaks. Armyworms feed at night and may be found under residue and at the base of plants during the day. Oftentimes, they can be seen curled into a c-shape (see photos below). Thresholds are one larvae (0.75 in or longer) per linear foot in barley and 2-3 per foot in wheat. Refer to Chapter 4 of Virginia Tech’s “Pest Management guide: Field Crops” for products and rates labeled for armyworm control in our state. Pay attention to PHI before making an application. Pyrethroids can be effective against armyworm. Good coverage is critical, especially in high residue fields.

Photos courtesy of JB Rigg, Helena Chemical.

Wheat Disease Update – May 15, 2018

Three-day forecast for Fusarium head blight (FHB) risk on susceptible wheat varieties.

FHB risk is increasing in Virginia and will continue to increase over the next several days. Risk is highest on the Eastern Shore, but susceptible varieties such as Shirley that are flowering over the next week will be at moderate to high risk in many portions of the state. Growers should monitor the FHB risk tool (www.wheatscab.psu.edu) as their wheat crop begins to flower. Consider applying a fungicide if risk is moderate to high, especially on susceptible or moderately susceptible varieties. Wheat that has completed flowering is no longer at risk. Fungicides should be applied at early flowering or up to one week later. Do not apply a strobilurin-containing fungicide since this can increase DON contamination. Recommended fungicides include Prosaro, Caramba, and Proline.

Steve Rideout, Extension Plant Pathologist at the Eastern Shore AREC, confirmed stripe rust on research plots of Shirley on Monday. FHB risk continues to be high on the Eastern Shore, so growers in this part of the state with varieties that are susceptible to stripe rust should consider an application of Prosaro, Caramba, or Proline since these will control both FHB and rust.

Stripe rust on wheat.

For assistance with disease identification or management recommendations, contact Dr. Hillary L. Mehl, Extension Plant Pathologist (hlmehl@vt.edu).

 

Wheat Disease Update – April 30, 2018

As wheat starts flowering in the region, it is time to consider whether or not to make a fungicide application for Fusarium head blight (FHB). Currently, risk is low in most parts of Virginia. There are a few exceptions, including portions of the Eastern Shore, where risk is moderate to high.

The most effective fungicides for control of FHB and DON are Caramba (metconazole), Prosaro (prothioconazole + tebuconazole), and Proline (prothioconazole). Less expensive triazoles such as Tilt (propiconazole) and Folicur (tebuconazole) will provide some control, but if FHB risk is high these fungicides are unlikely to prevent unacceptable levels of DON contamination. Keep in mind that fungicides containing a strobilurin should not be applied after the flag leaf stage since they can increase DON contamination.

Current FHB risk in Virginia and the surrounding region. Green, yellow, and red indicate low, moderate, and high risk, respectively. FHB risk can be monitored using the Fusarium Risk Assessment Tool (http://www.wheatscab.psu.edu/).

To maximize their effectiveness, fungicides for FHB and DON control should be applied at early flowering or up to one week later. Fungicides that control FHB and DON will also control foliar diseases including powdery mildew, leaf rust, stripe rust, and leaf blotch. Stripe rust has been found in NC and was recently reported from a single field in Warsaw, VA so be sure to scout susceptible varieties for this disease. For specific wheat disease management recommendations or assistance with disease identification, contact Dr. Hillary L. Mehl (hlmehl@vt.edu).

 

Wheat Disease Update – April 19, 2018

Currently the wheat crop in Virginia is near flag leaf emergence, and flowering will start within a couple of weeks. As flowering begins, be sure to monitor the FHB risk in your area using the Fusarium Head Blight Prediction Center website. Currently, most of Virginia has low risk for FHB infection. The exception is the Eastern Shore where risk is moderate to high in many areas, especially on susceptible varieties such as Shirley. Powdery mildew outbreaks have been observed in some fields this season, and incidence of common rust has been sporadic. Stripe rust has been found in North Carolina, but it has not been reported from Virginia. The 2018 Wheat Fungicide Efficacy Table can be downloaded below. Once wheat approaches the heading stage, keep in mind that strobilurin fungicides should no longer be applied. For specific wheat disease management recommendations or assistance with disease identification, contact Dr. Hillary L. Mehl (hlmehl@vt.edu).

2018 NCERA 184 Wheat Fungicide Table

Wheat Disease Update – April 12, 2018

Currently the wheat crop is in the jointing stages, and we are several weeks away from flowering. Currently the Fusarium head blight (FHB) risk is low for most areas of the state except for the Eastern Shore. These conditions may change as the wheat crop approaches flowering, so be sure to continue monitoring the FHB risk tool (http://www.wheatscab.psu.edu/). Moderate to severe outbreaks of powdery mildew have been reported from several fields in the past week. Be sure to scout wheat fields at this time and apply fungicide when disease is first detected. The updated Wheat Fungicide Efficacy Table can be downloaded below. For specific wheat disease management recommendations or assistance with disease identification, contact Dr. Hillary L. Mehl (hlmehl@vt.edu).

 

NCERA 184 Wheat fungicide table 2017_Final

Time to start planning for horseweed/marestail

Charlie Cahoon and Michael Flessner, Extension Weed Specialists at Virginia Tech

Horseweed or Marestail

Horseweed is a winter or summer annual and a member of the asteraceae family.  In the winter annual cycle, horseweed germinates in the fall and overwinters as a basal rosette. The following spring, the rosette bolts, reaching 1.5 to 6 feet in height.  While most populations of horseweed in the region emerge in the fall, significant spring emergence can occur under certain conditions.  Spring germinating horseweed does not form a rosette.  Leaves are alternate, simple, linear to oblanceolate in shape, and lack petioles.  Leaf margins are either entire or toothed.  Flowers consist of numerous small heads arranged in a panicle with many white ray flowers and 20 to 40 yellow disk flowers.  Seed are small and have a pappus of tan to white bristles (resemble dandelion seed).  Seed are easily dispersed by the wind, allowing it to quickly spread to nearby fields and within fields.

Bolted horseweed. Virginia Tech Weed ID Guide.

Herbicide resistance:  Regionally, glyphosate- and ALS-resistant horseweed are widespread.  If you are unsure of the resistance status in your fields, assume resistance to glyphosate and ALS herbicides. Resistance to Gramoxone (PS I-inhibitor) has been reported in Delaware.

Management:  Horseweed is more prevalent in no-till fields compared to fields prepared conventionally.  Tillage can be useful in the long-term management of horseweed.  Chemical control of horseweed is more consistent when the weed is in the seedling or rosette stage compared to bolting plants.  Traditionally, glyphosate and ALS-inhibiting herbicides effectively controlled horseweed, however, biotypes resistant to these herbicides are wide-spread.  Chemical control of glyphosate- and ALS-resistant horseweed requires a postemergence herbicide to control emerged horseweed and depending on application timing a residual herbicide for horseweed yet to emerge.  Due to the prolonged germination period, horseweed seedlings can emerge 5 to 6 weeks after residual herbicide application, thus fall applications of residual herbicides often have limited effectiveness for spring emergence.

Herbicides used for emerged plants include 2,4-D (1 pt in the fall or 1 qt in the spring), dicamba, Liberty, Sharpen, or Gramoxone plus a triazine herbicide (atrazine or metribuzin).   Preliminary research from Virginia and North Carolina suggest Elevore (a new auxin herbicide from Dow) also controls horseweed well.  Fourteen days are required between Elevore application and corn or soybean planting and 30 days prior to cotton planting.  Herbicides providing residual control include Valor SX, triazine herbicides (atrazine, simazine, and metribuzin), and ALS-inhibiting herbicides (if horseweed is not ALS-resistant).

Horseweed seedlings do not tolerate shade.  Thus a well-established cover crop, or dense crop canopy can be very effective to manage horseweed infested fields.

Horseweed rosette. Virginia Tech Weed ID Guide.

Soybeans: The key to managing horseweed in in soybeans is to control it prior to planting. Horseweed needs to be controlled prior to bolting (grow upright); this may require an application weeks prior to planting.  Glyphosate plus 2,4-D (1 qt/A), glyphosate plus dicamba or glyphosate plus Sharpen will effectively control glyphosate- and ALS-resistant horseweed when they are small.  Pay attention to rotational restrictions of preplant burndown herbicides when planning burndown applications and planting.  If horseweed are susceptible to the ALS-inhibiting herbicides, Classic-containing herbicides (i.e. Canopy, Valor XLT, Envive, Surveil) are effective.  If applications are made early pre-plant, herbicides containing Valor SX or metribuzin or the Authority products can be included to provide residual control, or a second application of a non-selective herbicide may be needed at planting. Liberty or Gramoxone also control small horseweed and can be used as a part of the burndown application.  If horseweed is present at planting, Gramoxone plus a residual product (Valor SX, Authority products, metribuzin, or Sharpen) is suggested in regions with later emerging horseweed.    Foliar applied PPO-inhibiting herbicides (Blazer, Reflex or Flextar, Resource, and Cobra) DO NOT control emerged horseweed.  For Liberty Link varieties, Liberty applied postemergence controls small horseweed.   Classic and FirstRate are postemergence options where horseweed are susceptible to the ALS-inhibiting herbicides and are small.

Cotton:  Like soybean, horseweed needs to be controlled prior to cotton planting.  Burndown combinations of glyphosate plus 2,4-D/dicamba plus Valor SX is normally in order.  Again, pay attention to plant-back restrictions when timing burndown applications.  Glyphosate plus Sharpen is also effective, but requires a long waiting period between application and cotton planting.

Corn:  In no-till corn, Gramoxone plus triazine, glyphosate plus atrazine plus 2,4-D or dicamba, and Liberty plus atrazine applied burndown of emerged seedlings and residual control of glyphosate- and ALS-resistant horseweed.   Consult labels for waiting interval prior to planting corn.  Atrazine alone will provide good residual control of horseweed.  Dicamba and 2,4-D are the most effective postemergence herbicides.  For small emerged horseweed, foliar applied HPPD-inhibitors or Liberty plus atrazine are effective.

Sorghum:  Glyphosate plus Sharpen or Gramoxone plus a triazine applied burndown.  Atrazine alone or in combination with Gramoxone applied preemergence for residual control and control of small emerged horseweed.  Atrazine can be used postemergence for control of small horseweed.  However, similar to corn, 2,4-D and dicamba are the most effective postemergence options.

Small grains:  2,4-D, dicamba, Quelex, or Huskie will provide effective postemergence control of horseweed in small grains.  Harmony Extra is also very effective on small horseweed that is susceptible to ALS-inhibiting herbicides.

Fall fallow application:  In fields with a history of horseweed, fall applied herbicides can be helpful in managing the weed.  However, a fall herbicide application will not substitute for a spring burndown application.  Target applications for emerged horseweed plants in the late fall after one to two killing frosts.  2,4-D or dicamba should serve as the base for these applications.  Glyphosate is often suggested in combination with 2,4-D and dicamba to control other winter annual weeds.

To see similar information on other problematic weeds consult the Virginia Pest Management Guide: Field Crops at http://pubs.ext.vt.edu/456/456-016/456-016.html or the Mid-Atlantic Field Crop Weed Management Guide at https://extension.psu.edu/mid-atlantic-field-crop-weed-management-guide.

As always, don’t hesitate to contact Michael or myself with any questions or concerns.