Wet weather Brings Disease Pressure for Peanuts

Recent rains and cooler temperatures have maxed out out the risk for leaf spot and Sclerotinia blight of peanuts. In fungicide trials at the Tidewater AREC in Suffolk, VA I counted 9 hits of Sclerotinia blight in 70 row-ft in one untreated plot. Late leaf spot was evident at low levels in the lower canopy as well. Hopefully 2 preventive sprays have been made for leaf spot, but many growers may not have made an application for Sclerotinia blight at this time.

I know my above comments sound like doom and gloom, but growers typically have less disease pressure than we do at our experiment station as they use longer crop rotations. Most of our plots are on a 2-3 year rotation where most growers in Virginia rotate land to peanuts every 4 or more years. Crop rotation remains our best tool to reduce risk of disease losses in peanuts in the Commonwealth.

Peanut leaf spot can occur in all peanut fields, but soilborne diseases such as stem rot and Sclerotinia blight are problems in less than half of production fields, which is a good thing. Most growers know which fields they have problems with these diseases which allows them to treat them differently than most fields. With Sclerotinia blight risk high and already observed, growers need to make preventive fungicide applications of fungicides specific to this disease. if an application of Miravis/Elatus has been made in the last 10-14 days you should be good for another 10-14 days depending on weather conditions. If you haven’t applied a fungicide that effectively controls Sclerotinia blight, I recommend Omega 500 at 1 – 1.5 pts tank-mixed with a leaf spot fungicide in fields with histories of the disease. I also advise growers to scout these fields to determine if disease is present and to assess the effectiveness of fungicides already applied. The best place to look for Sclerotinia blight is in the largest, deepest vines in the field and in low areas that tend to hold moisture longer. The disease may cause leaves to wilt on individual stems (flagging) and tan, necrotic tissue that has white, fully fungal growth can be observed on these stems near the stem base beneath the canopy. See picture of typical Sclerotinia blight on peanut stems in the image below.

Tan lesions and white fungal growth on peanut vines affected by Sclerotinia blight. At the top of the picture just left of center you can see the small, black sclerotia on one of the stems.

You may see flagging from Tomato Spotted Wilt Virus (TSWV) but no lesions on stems or fungal growth is present. I have had to take a closer look at several plants that had flagging leaves only to find that it was TSWV causing symptoms.

Typically a follow-up spray for Sclerotinia blight is warranted 21 days after the initial application of Omega 500. If you are using the 2-spray program of Miravis/Elatus there is no need to make an application of Omega 500 unless you are more than 30 days prior to harvest and disease pressure and weather conditions pose a high risk of severe damage.

If you have questions related to peanut disease management please feel free to contact me.

David Langston – e-mail dblangston@vt.edu, cell (757) 870-8498, office (757)807-3536

Corn earworm moth report for July 29, 2021

Black light trap captures of corn earworm moths (average number per night) in southeast Virginia this week were: Prince George-Templeton=0.7; Prince George-Disputanta=0.9; Southampton=2.0; Suffolk=4.0.

Our pyrethroid (cypermethrin @ 5 micrograms per vial rate) vial tests currently have 14% of corn earworm moths surviving the 24-hour exposure period (n=243 moths tested).

Making decisions for the first peanut leaf spot spray

Right now most peanut growers are deciding when to apply the first leaf spot fungicide and which fungicide to use. The recommendation the past few years has been to start spraying peanut fungicides at R3 (beginning pod) but no later than July 10th. I recommend using a chlorothalonil product (Bravo, Echo, Equus and others) at the 1.5 pt/A rate. I also recommend using Alto at 5.5 fl oz/A + 1.0 pint/A of chlorothalonil as an alternative. Tebuconazole (Folicur) is often tank-mixed with chlorothalonil at 7.2 fl oz/A but I wouldn’t expect a lot of leaf spot activity with tebuconazole as resistance to that fungicide by the leaf spot pathogens is widespread. Tebuconazole may still provide some activity against southern stem rot (A.K.A. “white mold”). Subsequent fungicide applications for leaf spot can be made according to the last effective spray date (LESD) using the Virginia Leaf Spot Advisory on the Peanut-Cotton Infonet https://webipm.ento.vt.edu/cgi-bin/infonet1.cgi or using a 14-day calendar-based approach.

In some fields growers may see early spotting that could be from herbicide injury or irregular or “funky” leaf spot. Irregular leaf spot can look an awful lot like early leaf spot but generally occurs earlier in peanut development regardless whether environmental conditions are favorable or not for early leaf spot. According to the Virginia Leaf Spot Advisory the risk of developing leaf spot has been low to moderate across all location thus far, but with current rain conditions that may change. No known cause has been attributed for irregular leaf spot and it has not been shown to cause economic losses. My main concern is that irregular leaf spot may cause growers to react to what they think is the beginning of an early leaf spot epidemic and spray needlessly or use more expensive products to control leaf spot. With irregular leaf spot, brown spots may be surrounded by yellow halos or large yellowed areas, defoliation may or may not occur, and spores are never present on spots. Anytime you suspect irregular or actual fungal leaf spot you can bring or have samples sent to the Plant Diagnostic Clinic at the Tidewater AREC for identification. If you have question or concerns please don’t hesitate to contact me.

David Langston, Plant Pathologist, Virginia Tech Tidewater AREC 6321 Holland Rd., Suffolk, VA 23437 cell phone (757) 870-8498 office phone (757) 807-6536 e-mail dblangston@vt.edu

Plant bug pre-bloom surveys and insecticide recommendations

The entomology program at the Tidewater AREC has spent this week scouting cotton fields across Virginia growing regions. First, I want to thank our technicians, graduate students, ANR Agents, Johnny Parker, and especially, our cooperating farmers. Cotton surveys are made possible through funding by Cotton Inc. and the Virginia Cotton Board.

I want to emphasize that overall plant bug numbers are very low, square retention very high, and the majority of fields will not be blooming by next week. Fields above threshold at this time are rare and sporadic. Use restraint when making pesticide applications without scouting first because we have many weeks left to manage insect pests. The most important time to manage plant bugs is during the first two weeks of bloom (see below graph from Seth Dorman’s work) and late-planted cotton is at higher risk of yield loss. Spraying at threshold (pre-bloom = 8/100 sweeps and <80% square retention) is as good as spraying every week (which is a pretty bad idea for secondary pest infestations, logistics, and costs).

Until the 2nd week of bloom, scout fields using a sweep net. Pay attention to areas of the field where cotton is rank and or borders other crops, but do not make decisions based on hot-spots alone.

Several insecticides are effective for plant bugs in cotton pre-bloom including neonicotinoids (imidacloprid, thiamethoxam), acephate with or without novaluron (Diamond), flonicamid (Carbine), and sulfoxaflor (Transform). Rotating insecticides, opposed to spraying a broad-spectrum like acephate season-long, will save you trips across the field. See the below table from our 2020 experiments demonstrating that using sulfoxaflor (Transform) alone, flonicamid (Carbine) alone, rotating a neonicotinoid (Centric) with sulfoxaflor (Transform), and using acephate with novaluron (Diamond) resulted in fewer trips across the field when compared to acephate alone. Also note that acephate with novaluron (Diamond) resulted in a second spray only at the end of August when it is debatable whether we have time to make a harvestable boll (i.e., it is likely that yield protection was based on a single spray). ALL INSECTICIDE APPLICATIONS YIELDED THE SAME. I do not recommend pyrethroids because of documented resistance in Virginia. They may or may not work on your farm. Pyrethroid resistance increases as the season progresses. Please make the decision that is right for your farm based on your experience and knowledge.

Please let me know if you have questions and or concerns. Email, call, or text. I hope everyone has a safe and happy 4th!

Fungicide Use in Corn and Soybeans

Corn
Some corn may have been sprayed as early as V5 but now we are approaching tasseling and some fields have already begun to tassel. With the corn prices being what they are more growers are inclined to apply a fungicide. Multiple studies have shown that a single application of a DMI (FRAC Group 3) + QoI (FRAC Group 11) fungicide at VT-R1 provide the best chance of return on investment. The Corn Disease Working Group of the Crop Protection Network updates the corn fungicide efficacy table in the following link.

https://crop-protection-network.s3.amazonaws.com/publications/fungicide-efficacy-for-control-of-corn-diseases-filename-2021-03-09-163332.pdf

The last few years we’ve seen more Gray leaf spot on corn in Virginia than other foliar disease. Be aware that if you used Xyway in-furrow you may not be protected against Southern corn rust that comes in later in the season some years. Typically, by the time Southern corn rust is observed in Virginia it will not impact yield greatly. However, for late-planted corn fungicide application must be made by R3 (milk stage) to limit yield loss due to Southern corn rust.

Soybeans
In Virginia, our primary foliar disease of soybean are frogeye leaf spot, Cercospora leaf blight and Septoria brown spot. Scouting for these diseases at or prior to beginning flower (R1) will give an estimation on the amount of disease pressure in a given field if diseases are present. Fields with disease pressure early are more likely to benefit from a fungicide application. Fungicides have the best chance of potentially reducing yield loss to foliar pathogens when sprayed beginning at pod initiation (R3) through seed initiation (R5). If dry conditions are prevalent during this spray window a fungicide spray is not advised. Be aware that foliar fungicides do not offer much protection against seed decay organisms or soilborne pathogens of soybeans. Below is the link for the Crop Protection Network’s soybean fungicide efficacy table.

https://crop-protection-network.s3.amazonaws.com/publications/fungicide-efficacy-for-control-of-soybean-foliar-diseases-filename-2021-03-12-182833.pdf

It is not advisable to spray QoI (FRAC Group 11) fungicides alone as fungicide resistance to this group has been observed in the fungal pathogen that causes frogeye leaf spot.

If you have questions or concerns please don’t hesitate to contact me.

David B. Langston, Jr.
Professor and Extension Plant Pathologist
Tidewater Agricultural Research and Extension Center
6321 Holland Rd., Suffolk, VA 23437
Office (757) 807-6536
Cell (757) 870-8498
FAX (757) 657-9333
e-mail dblangston@vt.edu

Pest Alert: Cyclamen mites in Chesapeake strawberries

In the past weeks, a few strawberry growers have expressed their concern about the possibility of cyclamen mite infestations. After visiting some strawberry farms in the Chesapeake area this week, I found symptoms of cyclamen mite damage in a few fields. Because of the small size of the mites, I took leaf samples from the symptomatic plants and confirmed the presence of the mites in the laboratory.

The cyclamen mite is a serious pest of strawberries. It has been reported in most strawberry-producing states. Cyclamen mites are tiny mites (0.001 in long) that feed on the tissue of nonexpanded and newly unfolded leaves in the strawberry plants. Adults and immatures of the cyclamen mite are considerably smaller than two-spotted spider mites and cannot be easily seen with the naked or a hand lens. Symptoms of cyclamen mite infestation include severely crumpled and crinkled leaves, as well as stunted plants.

The presence of cyclamen mites was confirmed mostly on ‘Ruby June’ strawberries, but they can infest any strawberry cultivar. Strawberry growers in the Virginia Beach metropolitan area and the eastern shore should beware of the presence of this pest mite in their field. There are very few miticides available for the control of cyclamen mites. Unfortunately, the same products used for the control of two-spotted spider mites do not always provide control for cyclamen mites. The best performing product against this pest is Portal (fenpyroximate). Agri-mek (abamectin), is also labeled for cyclamen mites. Despite being miticides, Acramite and Magister are not labeled for control of cyclamen mite and may not provide enough protection against it.

Dr. Lorena Lopez
Department of Entomology
Virginia Tech | Eastern Shore Agricultural Research and Extension Center (ESAREC)
(954) 529 9042 | lorelopezq257@vt.edu

Do I plant soybean or wait for rain?

Until these big high-pressure systems sitting in the eastern part of the country move east, it looks as if we are in for another week or so of dry weather. This is not good for soybean planting, any way you look at it.  So, what should we do?

There are basically three options:

Plant shallow in dry soil and hope for enough rain to get the seed out of the ground. If you decide to take this approach, you want to ensure you achieve uniform seed depth and that you are not allowing the seed access to moisture below the seed that could lead to variable emergence. This approach would be less risky in clean-tilled situation where you are more confident that you have dried the soil out at shallow depths. Soybean seed will sit in the ground for several weeks and still emerge well when rainfall occurs. Some worry about “cooking” the seed during this period.  Although it is true that the seed will continue to respire and its ability to germinate will decline, the bigger risk is that you catch a small rain that allows the soybean seed to imbibe water but not enough to get it out of the ground.

Caution must be exercised in no-till systems.  With no-till the soil has not been uniformly dried out with tillage; therefore, there is non-uniform moisture distribution across the field.  This leads to uneven access to moisture and ultimately emergence variability. Parts of the field will have adequate moisture to get the soybeans out of the ground, other parts will be completely dry as in tilled conditions, and much of the field will be in between.  Those in-between areas are likely to have enough moisture to swell the seed and/or initiate germination but not have enough moisture to allow the seedling to emerge.  This is my least favorite option.

Plant deep to the moisture. Under most conditions, soybeans may be planted 0.75 to 1.5 inches deep. But I don’t usually like to go much over 1 inch deep, especially in May.  I want soybean to come out of the ground as fast as possible. With that said, we planted some at 1.5 inches last week. Soil temperatures are generally high enough right now for the seed to germinate and plants emerge relatively quickly. Soybeans should not be planted deeper than 2 inches. Many are not finding soil moisture at less than 2 inches. Even if there is moisture 1.5 inches down, exercise caution using this approach, especially your soils are prone to crusting, because a heavy rainfall could seal the soil before the soybeans emerge. In tilled conditions, the planter can push the soil down a little, creating a ridge of fluffy soil on each side.  A heavy rain will cause this soil to move into that furrow and possibly add another ½ to 1 inches of soil to your depth.  If you are going to go this route, check the emergence score on the variety.

Keep the seed in the bag until the next time we catch rain. This is the safest approach and the one that I am leaning to now. Based on historical data, we have another couple of weeks before we start seeing yield declines from delayed planting. Data from recent research throughout the Mid-Atlantic shows that each day delay in planting past mid-June can result in a ½ bu/A or more yield loss and in general these yield declines begin in the second or third week of June. We still have some time before we get to that point. The optimum planting date range for soybeans is late-April through mid-June, although it will vary from year-to-year and field-to-field based on rainfall, soil water holding capacity, and soybean maturity, but the goal is to get the soybean plants to lap the middles before reproductive growth begins. We still have still have time to do this in most cases. 

Waiting to plant is more of a concern for those who still have early-maturing varieties to plant (MG 3 and early-4), as these varieties will have less time for vegetative growth. I do suggest planting your earliest maturity groups first, whichever strategy you choose to employ.  Later maturity groups have more time for adequate growth when planting is delayed.

What about fungicide seed treatments? You have likely already decided on this and cannot change.  But fungicidal seed treatments are less likely needed in this situation where soils are warm. It looks as if temperatures will be warming all week, so I don’t see cold soils as a problem.

Whatever decision a grower makes, uniform seed placement in critical to achieve uniform emergence and ensure each seed has as equal of access to water as possible. I don’t get too concerned if some plants emerge just a few days apart, but we don’t need them emerging a week apart. Dr. Rachel Vann of N.C. State discussed the importance of uneven and delayed emergence in soybeans – How Important Is Uniform Emergence in Soybeans?  Still, keep in mind that although earlier emerging plants will usually yield more, the late emerging plant will still contribute to yield.  Due to soybean’s compensatory ability, the yield on the whole will differ little from only a few days difference in soybean emergence within the row.  If you know me, you know that I’m not a fan of planting with drills due to lack of equal spacing within the row.  This lack of even spacing will become increasingly important if plant emergence is not good. 

In conclusion, there are advantages and disadvantages to each planting option discussed, but we still have time to plant soybeans in our region before we see drastic yield declines. All options discussed will likely result in delayed emergence due to environmental conditions.

Wheat Disease Update April 29, 2021

After looking at some wheat fields this morning I believe most of Virginia’s wheat is between head emergence (Feekes 10.3) and flowering (10.5.1). Wheat disease pressure has been low but with rain chances increasing by the middle of next week that could change. I have seen some physiological damage caused by weather or hypersensitive responses (resistant responses) to disease but no real disease outbreaks. With the flowering stage here we typically begin spraying for wheat scab or Fusarium head blight (FHB). Right now risk of FHB is low. The risk of FHB can be monitored by the FHB Risk Assessment Tool provided by Penn State (http://www.wheatscab.psu.edu/). Fungicides such as Caramba, Prosaro, and Miravis Ace are recommended for FHB and DON control. Caramba and Prosaro will provide better control when applied at flowering while Miravis Ace has a wider window of activity from heading to 6 days after flowering. Remember to avoid using strobilurin (FRAC Group 11) fungicides after flag leaf as these fungicides can increase DON levels in grain. Fungicides applied for FHB will control the other major foliar wheat diseases. The 2019 Fungicide Efficacy for Wheat Diseases can be found at the following link. NCERA 184 Wheat fungicide table 2019_Final

If you have questions about wheat diseases you can reach me, David Langston, via e-mail or phone.

e-mail dblangston@vt.edu
office phone (757) 807-6536
cell phone (757) 870-8498

Label change for Velum Total in cotton and peanuts

Be aware that Velum Total now has a name and label change.  The new product is simply Velum.  The insecticide imidacloprid has been dropped from the product meaning that it no longer contains material to control thrips.

If you purchase the relabeled Velum product, you will need to apply an additional insecticide.  I recommend Admire Pro or generic products that include the active ingredient imidacloprid. Granular alternatives in peanut include Thimet 20G (phorate) and AgLogic 15G or 15GG (aldicarb).  Refer to label rates.

Thrips are capable of causing yield loss and plant death in certain scenarios. I recommend that you use an in-furrow product in peanut. Foliar sprays are generally insufficient on their own, but may be warranted as an additional input in very high-pressure years. Cotton has the option of having insecticidal seed coating applied in addition or instead of using an in-furrow product (imidacloprid and aldicarb are labeled for both crops). Seed treatments alone require scouting and foliar sprays if warranted.

Thrips injury ratings of peanut planted with different thrips products, with and without 8 oz./A of acephate applied at pegging. The red line indicates the injury level where economic damages begin to accrue. Dark blue line is untreated for thrips, light blue line is foliar acephate only.

Use existing quantities of Velum Total as you ordinarily would.

Dr. Sally Taylor, Asst. Professor

Row Crop Entomology

Virginia Tech TAREC

919-801-5366

Herbicide Resistant Weeds Workshop

Palmer amaranth infesting a soybean field
The workshops will be virtual via Zoom on Tuesday Dec. 8th and Tuesday Dec. 15th. On both days, choose the time that works best for you: 8-10 am OR 6-8 pm. Optional in-person “watch party” meetings offered at several locations.

Register at: https://go.umd.edu/IWM  

Topics: Session One: Tues Dec 8th 8-10 am OR 6-8 pm
Herbicide Resistance- What is It?
Mechanisms of Action-How to Choose Herbicides
Creating Effective Herbicide Plans  

Session Two: Tues Dec 15th 8-10 am OR 6-8 pm
IWM with a focus on Palmer Amaranth, Common Ragweed, and Marestail
Local Perspectives on Resistance Management
Putting It All Together: Creating a Weed Management Plan

Speakers:
Dr. Michael Flessner and Dr. Vijay Singh, Virginia Tech
Dr. Mark VanGessel, University of Delaware
Dr. Kurt Vollmer and Ben Beale, University of Maryland

CCA Credits will be offered.
For More Information Contact:
Ben Beale at 301-475-4481 or Kurt Vollmer at 410-827-8056 28