Category Archives: Pest Group

Distribution of Herbicide-Resistant Italian Ryegrass in Eastern Virginia

Charlie Cahoon, Extension Weed Specialist

Eastern Shore AREC-Virginia Tech

Italian ryegrass is one of the most common and troublesome weeds Virginia small grain producers face.  The weed competes with wheat for essential nutrients, sunlight, and moisture and also interferes with harvest.  In the past, growers have relied upon herbicides, such as Axial XL, Hoelon, PowerFlex, and Osprey, for control of Italian ryegrass.  However, herbicide resistant Italian ryegrass biotypes have developed, limiting the herbicide options available to growers.

During the summer of 2016, the weed group at the Eastern Shore AREC traveled Eastern Virginia in search of resistant Italian ryegrass.  To broaden the survey, we solicited samples from extension agents and members of the agriculture industry.  In total, 82 samples were collected throughout Eastern Virginia (Image 1).  The objective of this survey (and subsequent resistance screening) was to determine the distribution of resistant biotypes in Virginia; allowing growers to tailor management strategies specific to biotypes in their area.

Italian ryegrass heads collected during the summer were allowed to dry down and then threshed to separate the seed.  Approximately 400 seed from each population were planted in a seed tray.  Once Italian ryegrass reached 3.5 to 4 inches in height (1 to 2 leaf), plants were treated with a 1X rate of Axial XL (16.4 oz/A), Hoelon (43 oz/A), PowerFlex HL (2 oz/A), and Osprey (4.75 oz/A). A non-treated check from each sample location was included for comparison purposes.  Visual injury was recorded at 28 days after treatment (DAT) for Italian ryegrass treated with Axial XL and Hoelon.  PowerFlex HL and Osprey are both ALS-inhibiting herbicides and act much slower than the ACCase-inhibiting herbicides (Axial XL and Hoelon).  Therefore, ryegrass treated with these products were evaluated 42 DAT.  Also at 42 DAT, Italian ryegrass biomass (and subsequent % biomass reduction) was determined by cutting and weighing the above ground portion of ryegrass.

Image 1. Locations of 2016 Italian ryegrass samples collected.

Overall, approximately 23% of all samples collected were resistant to Axial XL (Image 2) compared to 30% that were resistant to Hoelon (data not shown).  Most samples resistant to Hoelon were also resistant to Axial XL.  However, for 6 samples, Axial XL remained effective despite poor Hoelon activity.  Axial-resistant Italian ryegrass is widespread in two of Virginia’s major wheat producing regions (Eastern Shore and southern Chesapeake/Virginia Beach).  Of the 14 samples collected in Northampton Co., 9 were found to be resistant to Axial XL (64%).  In contrast, none of the 5 samples collected from Accomack Co. were Axial-resistant.  In southern Virginia Beach and Chesapeake, 5 of 6 samples collected were resistant to Axial (83% of samples).  Excluding the Eastern Shore and southern Chesapeake/Virginia Beach, only 9% of remaining samples were resistant to Axial XL; 1 samples east of Stony Creek in Sussex Co.; 1 sample south of Waterview in Middlesex Co.; 1 sample northeast of Newtown in King and Queen Co.; 1 sample northwest of Loretto in Essex Co.; and 1 sample south of Somers in Lancaster Co.

Image 2. Distribution of Axial-resistant Italian ryegrass in Virginia.

ALS-resistant Italian ryegrass is more widespread throughout eastern Virginia.  Of the surveyed populations, 92 and 93% were resistant to Osprey and PowerFlex HL, respectively.  Producers should keep in mind the presence of herbicide-resistant Italian ryegrass nearby does not automatically mean they have a resistant biotype on their farm.  Fields with escaped Italian ryegrass were purposely chosen for this survey.  It is best to rely on field history and performance of herbicides in the past when making management decisions.  However, it is always a good idea to rotate modes of action to delay the development of resistant biotypes.

Unfortunately, if ryegrass is resistant to Axial XL and the ALS-inhibiting herbicides (Osprey and PowerFlex HL), there are no postemergence options left.  In this situation, a residual product that includes pyroxasulfone (Anthem Flex and Zidua) is suggested delayed-preemergence or early postemergence.  These products offer residual control of ryegrass only (they will NOT control emerged ryegrass).  It is imperative that these products are applied and activated by a timely rainfall prior to ryegrass emergence.  Rotating away from wheat also presents an opportunity to control Italian ryegrass (and prevent seed production) with glyphosate early burndown prior to planting corn or full-season soybean.  Be aware that glyphosate-resistant Italian ryegrass is suspected in northeast North Carolina and eastern Virginia.  In this situation, paraquat plus a residual herbicide like s-metolachlor applied to fallow ground during the fall would be in order.

Image 3. Axial XL-susceptible Italian ryegrass collected near Nassawadox, VA treated with no herbicide (left), Axial XL at 16.4 fl oz/acre (middle), and Hoelon at 43 fl oz/acre (right).

Image 4. Axial XL-resistant Italian ryegrass collected near Cheriton, VA treated with no herbicide (left), Axial XL at 16.4 fl oz/acre (middle), and Hoelon at 43 fl oz/acre (right).

 

 

Eastern Shore AREC Field Day CANCELED!

Due to impending rain Tuesday and Wednesday and already saturated soils, the Eastern Shore AREC field day scheduled for Wednesday, September 13, 2017 has been canceled. Let’s hope Hurricane Irma keeps tracking further west. We certainly do not need any more rain!

Insect update for Sep. 7, 2017

Most reporting black light trap stations this week had decreased corn earworm moth captures (except for Chesapeake remaining constant). Nightly averages were Chesapeake = 11; Southampton = 1; Suffolk = 8; and Warsaw = 4 moths. Here is the data table:  BLT_7_Sep_2017

No brown marmorated stink bugs were caught this week in the black light traps.

Eastern Shore AREC Field DAY: September 13th, 2017

Please join us for Virginia Tech’s Eastern Shore Agricultural Research and Extension Center (ESAREC) 2017 Research Field Day on Wednesday, September 13th. Registration is free, open to the public and will begin at 8:00 AM at the ESAREC complex located at 33446 Research Drive, Painter, Virginia 23420. The field tour will begin at 9:00 AM and conclude with lunch at 12:30 PM.  See the attached flyer for specific projects to be highlighted and more information.

If you would like more information or are interested in sponsoring this event, please contact Lauren Seltzer at 757-414-0724 ext. 11 or email at mlpeyton@vt.edu.

2017 ESAREC Field Day Announcement

Insect update for Aug. 31, 2017

This week, corn earworm (bollworm) moth captures in the black light trap were down at most locations (steady at Chesapeake and Prince George-Templeton), perhaps partly due to the rainy weather, but some “down” numbers are still pretty high (Suffolk, for example). The table is here: BLT_31_Aug_2017

We had no reports of any brown marmorated stink bugs captured in the black light traps this week.

We have vial-tested close to 1,000 corn earworm moths in Dr. Taylor’s pyrethroid resistance monitoring program in 2017, with an average of 38% survival.

Insect update for Aug. 17, 2017

Corn earworm moth captures in the black light traps ranged from 2 to 45 moths per night; brown marmorated stink bug catches ranged from zero to 2.6 per night. Here are the data tables: BLT_17_Aug_2017

In our corn earworm (bollworm) vial tests, we are averaging 39% moth survival, with 832 moths tested to date.

Insect update for Aug. 10, 2017

Black light trap captures of corn earworm/bollworm ranged from 5 to 78 moths per night this week. Brown marmorated stink bug captures ranged from zero to 2 per night. Here are the data tables: BLT_10_Aug_2017

Resistance monitoring of corn earworm/bollworm shows that this season in Suffolk, an average of 39% of moths survived the 24-hour exposure period to the pyrethroid, cypermethrin.