Mysterious leaf spots in peanut

Posted on August 28, 2014 by Maria Balota

In the past two weeks or so, there were discussions among specialists about peanuts showing a “mysterious leaf spot” of non-pathogenic origin (credit to pathologists Barbara Shew and Hillary Mehl); but the spot is similar in appearance to the early leaf spot when it starts and becomes irregular at later stages.

“Mysterious” leaf spot found in Suffolk, VA. At the initial stage, the spot looks like early leaf spot, but it has non-pathogenic origin.

Dr. Jay Chapin with Clemson University thinks it is a physiological leaf spot; he calls it “irregular leaf spot”. He observed it to be more prevalent on runners, in particular GA09B, and resulting in yield reduction under certain circumstances. Dr. David Jordan calls it “peculiar leaf spot”. I also found it in research peanut fields in Suffolk and Southampton, VA; the spotting was under 25% of the total leaf area. To solve the “mystery” and get information on the frequency of this issue in NC, Dr. Jordan recently launched a survey and asked the Extension Agents to assess the presence and severity of the spot in approximately 20 fields in each county (4 to 5 areas in each field) using the table below. Because I also found the spot in several fields and I know of growers growing GA09B this year, I suggest we do the same in Virginia. Please use the table below; under “comments” please include information on the cultural practices used in each field, if possible, so we can better explain the cause of the spotting. This assessment can be used at winter meetings and presented at the APRES next year together with the NC Extension Agents.

Documentation of Leaf Spots in Peanut that is not early or late leaf spot or web blotch


Field ID (your designation)	Spots present (yes/no)	Severity (none, low = 25% or less leaflets with spots, moderate = 25 to 50% leaflets with spots, high = 50 to 75% leaflets with spots, very high = 75 to 100% leaflets with spots) relative to entire peanut canopy	Comments

Black light trap report for the week ending August 21, 2014

Posted on August 21, 2014 by Sean Malone

This week’s corn earworm moth nightly black light trap counts increased for most reporting stations; brown marmorated stink bug catches tended to be lower this week. Please click on the pdf file below (BLT_21_Aug_2014) for the data tables. Thanks to the following for their reports this week: David Moore, Chris Drake, Watson Lawrence, Mike Parrish, Keith Balderson, Mary Beahm, Mark Kraemer, Scott Reiter, and Ames Herbert and his entomology team.

BLT_21_Aug_2014

Late Blight Found in Montgomery County

Posted on August 21, 2014 by Elizabeth Bush

Late blight has been confirmed on tomato in Montgomery County, VA, by the Virginia Tech Plant Disease Clinic. Potato and tomato growers should take precautionary actions and increase scouting. Cool and wet conditions favor development of this disease and fungicide sprays should be in place before the disease is present in a field or garden. For more information on late blight and late blight management, refer to the Extension publication available at: http://pubs.ext.vt.edu/ANR/ANR-6/ANR-6_pdf.pdf . Late blight was previously identified in Loudoun County, VA, on July 22 and Rappahannock County, VA, on August 8.

Brown marmorated stink bug distribution in Virginia–August 21, 2014 report

Posted on August 21, 2014 by Sean Malone

BMSB was found in soybean in nine new Virginia counties this past week: James City, Caroline, Stafford, Culpeper, Fauquier, Nelson, Rockbridge, Henry, and Montgomery. The highest numbers of BMSB occurred in a Warren field (5 nymphs and 4 adults per 2-minute visual inspection), followed by Augusta (5 nymphs and 1 adult per 2-minute visual), Fauquier (5 nymphs), Buckingham (4 nymphs), James City (3 nymphs, 1 adult), and Appomattox (3 nymphs, 1 adult). Thanks to our soybean scouts and to Dr. Tom Kuhar for their updates this week.

Kudzu bug distribution in Virginia–August 21, 2014 report

Posted on August 21, 2014 by Sean Malone

Our soybean scouts detected kudzu bug in two new Virginia counties this past week (Halifax and Greene); both of these locations had low numbers. The highest numbers of kudzu bugs reported by our scouts for the past week were in a Pittsylvania soybean field (8 nymphs and 3 adults per 15 sweeps), followed by Goochland (4 adults per 15 sweeps) and Henry (3 nymphs and 2 adults per 15 sweeps). Additionally, VCE Agent Scott Reiter reported high numbers of kudzu bug adults along the edge in a Prince George soybean field that was bordered by kudzu (50 adults in 15 sweeps in the first 30 feet of field, diminishing to 3-4 adults per 15 sweeps at 100 feet from the field edge). Scott found other fields with 0-3 kudzu bugs in 15 sweeps.

Invitation to the Virginia Tech Tidewater AREC’s Pre-Harvest Field Crops Tour

Posted on August 18, 2014 by Sean Malone

Please click on the pdf document below (Fall tour 2014) to view details for the September 11, 2014 “Pre-Harvest Field Crops Tour” at the Virginia Tech Tidewater AREC’s Hare Road Research Farm. Pre-registration instructions, times, and topics are detailed in this document.

Fall_tour_2014

If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in this activity, please contact the Tidewater AREC at 757-657-6450* during business hours of 8:00 a.m. and 4:30 p.m. to discuss accommodations 5 days prior to the event. *TDD number is (800) 828-1120.

Peanut Disease Update – August 14, 2014

Posted on August 14, 2014 by Hillary Mehl

Sclerotinia blight risk has been, and continues to be, high this summer and timely fungicide applications based on advisories (Peanut-Cotton Infonet, http://webipm.ento.vt.edu/cgi-bin/infonet1.cgi) and scouting are needed to avoid devastating outbreaks of this disease. Unfortunately, it has been reported that Omega, the most effective fungicide for Sclerotinia blight control, is in short supply, and growers are looking for alternatives. At this point we are recommending Fontelis at a rate of 1.5 pints per acre. According to Barbara Shew, Extension Plant Pathologist at North Carolina State University, 1.5 pints per acre of Fontelis provide Sclerotinia control similar to one pint of Omega. Note that lower rates of Fontelis typically used for leaf spot control are not adequate for control of Sclerotinia. A follow-up Fontelis application should be made 2 to 3 weeks after the first application or according to the Sclerotinia blight advisory, but keep in mind that only two applications of this fungicide class (SDHI, group 7) should be made per year to minimize the risk of fungicide resistance. In fields with high Sclerotinia pressure, avoid using chlorothalonil (Bravo and generics) in August or early September for leaf spot control since this can increase the severity of Sclerotinia blight outbreaks. Alternatively, use strobilurin fungicides such as Abound or Headline or a triazole such as Provost for leaf spot control. However, the final leaf spot application of the season should be chlorothalonil for the purpose of fungicide resistance management.

Southern Rust in Corn – Update

Posted on August 14, 2014 by Hillary Mehl

Southern rust continues to be reported on corn in Virginia. Southern rust was first confirmed August 3 on corn samples from Chesapeake and Suffolk. Since then, reports of southern rust have been made from Sussex and Albermarle counties, and it is likely that the pathogen is throughout much of the state. Yield of corn at or near the dent stage is unlikely to be impacted by the disease, but late planted corn in fields with good yield potential (120 bu/ac +) may need to be protected with a foliar fungicide. Strobilurins are good preventative fungicides whereas triazoles are recommended once sporulation is observed in a field due to their curative activity. A combination fungicide is a good option as long as a strobilurin fungicide has not been applied previously. Wet, warm weather favors disease development. Once sporulation occurs, symptoms of rust are relatively obvious. Lesions start out as raised, blister-like pustules then break open to reveal orange spores. Samples of corn plants with symptoms of southern rust can be submitted to the disease clinic at the Virginia Tech Tidewater AREC (contact Dr. Hillary Mehl, hlmehl@vt.edu).

Late Season Weed Control in Peanut

Posted on August 14, 2014 by Maria Balota

Yesterday a farmer asked what herbicide to use for ragweed control at this time of year. I am not a weed researcher so I asked the expert: Dr. David Jordan with the North Carolina State University. He recommended Cobra, but also cautioned with its use at this stage of development. Cobra cannot be applied within 75 days of harvest. This means that if the farmer sprays it now, he will have to postpone harvest until end of October. 2,4-DB (40 to 65 days pre-harvest interval) and Select (40 days pre-harvest interval) were also recommended for late season broad leaf weed control.

Ragweed mature plant.

Dr. Hillary Mehl’s Peanut Cotton InfoNet (http://webipm.ento.vt.edu/cgi-bin/infonet1.cgi) service shows that peanut accumulated from May 1st and until mid-August across peanut growing region in Virginia from about 1840 heat units (at Waverley) to 1980 (at Skippers). The number of heat units accumulated only from August 1st to mid-August is about 200. Bailey and Sugg require about 2600 heat units to mature; this is approximately 690 more heat units needed to reach maturity. Assuming similar temperatures for the rest of August and September, the 690 heat units can be achieved by the first week of October, or the second week of October if September gets cooler, for a May 1st planted peanut. This means that some herbicides still can be used for weed control in peanut at this time, in particular for late planted peanut; but herbicide label needs to be carefully checked.

Determining the optimum harvest maturity is more complicated than checking the heat units and counting the number of days from planting, as you very well know. Therefore, I recommend that growers take advantage of the pod-blasting clinics that Extension Agents will organize in September. One will be on September 5th at Emporia. I will also send advisories with peanut maturity starting after the first week of September.

Black light trap catches for the week ending August 14, 2014

Posted on August 14, 2014 by Sean Malone

Corn earworm moth catches are increasing; please click on “BLT_14_Aug_2014” below for your local trap catches of this insect and also the brown marmorated stink bug. Thanks to the following for their reports this week: David Moore, Keith Balderson, Watson Lawrence, Kelvin Wells, Mark Kraemer, Chris Drake, Mary Beahm, Mike Parrish, Janet Spencer, and Ames Herbert and his entomology team.

BLT_14_Aug_2014