Large aphids populations have been observed in alfalfa this year following insecticide applications targeting alfalfa weevil. If you haven’t scouted for alfalfa weevil in Virginia, you should. See the bottom of this post for a weevil summary.
Aphids, typically pea aphids, can be problematic when their natural enemies are disturbed. They can reduce vigor and cause wilting in first cuttings. If early cutting is not an option, several insecticides (mostly pyrethroids) are labeled for their control. Low label rates are generally effective as long as you ensure good coverage. Scout for aphids by pulling 30 random stems per field and counting the number of aphids. This guide from Iowa State can help you make treatment decisions.
Most of the aphids I have seen in Virginia alfalfa are pea aphids (left) and cowpea (right). If you think you have another species, please give me a call or send an email.
Photos Erin Hodgson, Iowa State
My thanks to Lane Grow from Southern State Cooperative for his ongoing efforts to scout and report problems in western Virginia.
Alfalfa weevil information
Scout fields by pulling 30 random stems and inspecting foliage for weevils. Weevil larvae are small, can be white, yellow, or green, and have black heads. They are often tucked tight into new growth. It’s possible to dislodge larger larvae so be careful or collect stems into some container that catches these. I use a plastic freezer bag and insect stems in the shop or truck. This guide from Penn State can help you make spray decisions. Cutting alfalfa is an option if you don’t want to use pesticides. I recommend using clorpyrifos based on spray tests in 2018 and 2019. Some people have been successful with indoxacarb (Steward) or pyrethroids (many brand-name and generic options). Coverage is essential with any product.
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.
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!
November 15-17, 2016
Princess Royale Hotel in Ocean City, MD
Registration is open for the 22nd annual Mid-Atlantic Crop Management School. This year’s school will feature 2 ½ days of timely presentations in the areas of crop management, nutrient management, pest management, soil and water management, and climate. This year, the school will also feature the popular Crop School on Wheels field tour (limited to 50 participants). Nutrient management (VA, MD, DE, PA), pesticide, and certified crop adviser (CCA) credits will be available. Register early for the best selection of sessions.
The session schedule is online at: https://cdn.extension.udel.edu/wp-content/uploads/sites/12/2016/09/23151701/2016_CMS_Program_Final.pdf
Registration information is posted at: http://www.cvent.com/events/2016-crop-management-school/event-summary-bbd4a7d2717545af9770626ef761a930.aspx?tw=E3-C1-0B-14-32-A0-CB-AB-1C-D6-9A-06-46-74-20-5F.
Contact Amy Shober (firstname.lastname@example.org) or Jarrod Miller (email@example.com) with questions about the school. We look forward to seeing you there.
The Mid-Atlantic Crop Management School is organized by Extension Specialists from Virginia, West Virginia, Delaware, and Maryland featuring speakers from across the nation.
Scott Baker, Bedford Co. extension agent, reported aphids in an alfalfa field. I recommended an application of a pyrethroid labled for use against aphids in alfalfa.
The DD model value for 4/15/11 is 290 DD, about 10 DD over threshold. It’s time to make a management decision based on presence/absence of paired feeding holes detected within 20 ft of field edges. You can reach me at 540-231-9118 or firstname.lastname@example.org Thank you
The number of accumulated degree-days (DD) for bluegrass and hunting billbugs in orchardgrass since 1/1/11 are starting to move. As of 4/6/11, 214 DD have accumulated. Model forecast for 4/13/11 is 284 DD. Recall that at least 280 DD are needed before taking any action. Within the next week or so you need to start checking your field borders for paired-field holes. My contact information is, 540-231-9118 (office), 540-357-2558 (cell), email@example.com. Thank you.
According to the Agmaster degree-day collection service – same
company we’ve been using. Given a Jan. 1, 2011 start date, and as of
Mar. 23, 172 DD have accumulated. Model predictions for April 2, are
Recall, 280 DD represents the start of billbug adult activity moving
back into orchardgrass. At this point and beyond you need to start
monitoring field edges for the paired-feeding holes that adults make.
This is a presence/absence sample that gives you an idea on whether
or not they’re in a field. There are no thresholds for spraying or
not spraying – personal judgement call.
As always, if you need more information, contact your local extension
agent or me. My office number is 540-231-9118, cell 540-357-2558, email firstname.lastname@example.org