The Situation

I have heard from several growers and county agents that they have been seeing a lot of moldy ears lately.  Unfortunately, the drought in June followed by wet conditions in July and early August set the stage for ear rot fungi to infest corn this year. Ear rot diseases are Aspergillus ear rot, Diplodia ear rot, Fusarium ear rot, Gibberella ear rot, Penicillium ear rot and Trichoderma ear rot.  Pictures and symptoms and signs of each are below.

Aspergillus ear rot

Image by A. Robertson

Diplodia ear rot

Image by G. Munkvold

Fusarium ear rot

Image by A. Robertson

Starburst kernel pattern from Fusarium ear rot

Image by Pioneer Seeds

Gibberella ear rot

Image by A. Robertson

Penicillium ear rot

Image by A. Robertson

Trichoderma ear rot

Image by G. Munkvold

Damage Caused by Ear Rots

The most obvious losses due to ear rots are to yield and quality.  Probably the biggest concern with ear rots is that some of them produce mycotoxins that harm humans and livestock. Mycotoxin producers are Aspergillus ear rot (aflatoxin), Fusarium ear rot (fumonisin), Gibberella ear rot (deoxynivalenol or DON) and to a lesser degree Penicillium ear rot (PR toxin and Ochratoxin A).  Grain cannot be sold for food or feed if aflatoxin levels are 20 ppb (parts per billion), fumonisin levels cannot be higher than 30-50 ppb and DON no higher than 5 ppb.

Assessing Damage

Growers should hand pick 100 ears of corn from a representative area of a field and shuck them.   Pick out 10 ears showing the worst ear rot damage. Place these ears side-by-side to assess the average amount of kernel damage. If more than 25% of the kernels on these 10 ears are damaged, you have a problem.  If less than 25% of kernels on the 10 worst ears are damaged, check the field again after a rainfall event and plan on harvesting early. Harvesting at more than 20% moisture and drying to less than 15% moisture will significantly reduce harvest losses when compared to waiting for the corn to dry on its own in the field.  The extent of the problem can be determined by shelling all 100 ears, mixing the grain thoroughly, and sending a sample (usually 5.0 lbs) to a reputable mycotoxin testing facility.  Don’t mix grain from a field affected by ear rots with grain from a field that has not been affected.

What to do if You Have 10% or More Affected Ears

• Harvest early at higher moisture and dry to below 15% moisture
• Adjust combine to discard light or damaged kernels
• Clean harvest equipment between affected fields and clean fields
• Segregate poor quality grain from good grain
• Store affected long-term grain at less than 13% moisture and 30°F or below
• Don’t store affected grain for more than 1 year

A few disease issues have popped up within the past week on peanuts and soybeans. Some are pretty routine and some are not…

Peanuts

As you may expect, the wet, humid weather has been favorable for peanut diseases like leaf spot, southern stem rot (white mold) and Sclerotinia blight, but especially leaf spot. Sclerotinia is moving slowly due to the warmer weather over past two weeks, but with highs in the 70s today and possibly going forward I expect it to move faster. I have observed Sclerotinia blight in my trial plots. This late in the game I prefer Omega 500 for Sclerotinia blight over Miravis + Elatus. Miravis may not perform against leaf spot if there’s any out there already and Elatus is not a good stand-alone product for Sclerotinia. Remember, if you use Omega 500 you must use a leaf spot material with it. With leaf spot, just don’t extend your spray interval beyond 14 days. The leaf spot advisory has shown leaf spot risk to be steadily high and the last effective spray date jumps 2 days every day. If leaf spot is already showing up you may want to use a micronized sulfur product to temporarily arrest leaf spot along with a fungicide that gives residual control. The hot weather we experienced up until now has led to southern stem rot (white mold) showing up in some fields. If this is the case the best products for that are Excalia (3.0 fl oz), Elatus (7.0 – 9.0 oz) or Convoy at 32 fl oz.

Soybeans

Warm humid weather have led to outbreaks of FLS (frogeye leaf spot) and target spot in some fields. Frogeye will show up first in soybeans that have poor resistance to FLS, and some soybean varieties are more susceptible to target spot like AG49XF3. Both diseases can be very similar in appearance but FLS shows up more in the upper canopy and target spot starts in the lower canopy. I have seen pictures of soybeans defoliated from the bottom up by target spot recently. If you sprayed ahead of disease symptoms you shouldn’t have many problems, but you may see target spot start showing up. If you see disease is already there, use products that have an effective Group 3 fungicide that have curative disease activity. Examples would be Delaro Complete, Lucento, Revylok and Topguard or Topguard EQ.

If you have questions or concerns contact me via e-mail at dblangston@vt.edu or use my cell phone at (757) 870-8498.

With current rainfall from Idalia and cooler temperatures over the next three days, peanut fields with a history of SB (Sclerotinia blight) should be sprayed soon with a fungicide that can reduce losses to that disease.

SB is favored by rainfall and periods of high relative humidity, but what really triggers it is cooler temperatures. The current forecast is for daily highs to be in the upper 70s and 55 to 60° lows over the next three days. Those lows will really get SB cranked up! I have already seen SB slowly moving in my trials and I’ve heard reports that peanut growers are seeing it in some of their fields. According to Dr. David Jordan, peanuts are likely 1 week behind in maturity compared to last year due to the record cool temperatures observed in May, so there’s plenty of time for SB to do some damage.

This late in the game the second spray of Miravis tank-mixed with Elatus surely has been applied, or is about to based on when the first spray was applied. I do not recommend the first application of the Miravis/Elatus tank-mix be used this late, mainly due to it’s having no curative activity on either LLS (late leaf spot) or SB and for reducing risk of fungicide resistance to those chemistries. I’m quite hesitant even to recommend the second application at this time.

The safe bet is applying Omega 500 for SB tank-mixed with an effective fungicide for LLS. If you sprayed Miravis/Elatus the first week of August, I’d prefer to use Omega 500 at 1.0 pt/acre in the next few days to protect against SB. If you have a field that’s notorious for severe losses to SB, you can go to 1.5 pt/acre, but I haven’t seen a big difference in control between the two rates. I consider Omega 500 to have 3 weeks of activity against SB. So if it’s been 3 weeks or more since you applied Omega 500, I’d be thinking about that 2nd application right about now. Remember, Omega 500 has a 30 day PHI (preharvest interval). That’s 30 days prior to harvesting with a peanut picker, not 30 days until digging.

One saving grace is that temperatures go up again next Monday and maintain daily lows in the upper 60s/low 70s and highs in the upper 80s/low 90s until about September 11th according to the current forecast. Most peanuts in the region have fairly dense canopies now, so while the higher temperatures may slow SB development, the disease will continue to progress and potentially explode again if favorable conditions present themselves.

Within the past week two outbreaks of FLS (frogeye leaf spot) have been reported in southeastern Virginia. Southeastern Virginia has experienced warm, humid conditions and frequent rain events which favor FLS development. Both outbreaks were found on soybean varieties susceptible to FLS in the R1 stage. This creates an issue as the recommendation for fungicide timing on soybeans is R3-R5. Having disease already in the field is also less than ideal as fungicides perform better if applied prior to symptom development. To deal with this situation I recommend:

Scout fields for FLS and Target…

• fields planted to FLS-susceptible varieties and with a history of frogeye leaf spot
• fields in continuous soybean production
• fields in short rotations between soybean crops
• fields with conservation tillage
• low-lying areas of fields

If you have fields that meet the above risk factors you should use a preventive fungicide application no sooner than R1. If you find FLS in R1 soybeans spray immediately with a FRAC Group 3 (DMI, triazole) fungicide as these fungicides have some curative activity. University pathologists in the U.S. have had the best results with Domark, Topguard, Lucento, Revytek, and Miravis Top when spraying after FLS is detected. Follow-up sprays may be needed if FLS continues to progress.

When I look at how small my peanuts are today, spraying them for leaf spot seems hard to imagine.  We’re at least 40% behind in peanut heat units compared to previous years.  Slow, late development tells me we will likely be digging peanuts later than usual.  How does that affect initial fungicide spray program decisions?

To me, digging later means there’s potential to apply more fungicide sprays, which can get expensive.  My response to late-developing peanuts is to delay the first leaf spot application.  The rule of thumb NC and VA have used for initiating leaf spot fungicide programs is 60 DAP (days after planting), but no later than July 10^th.  But with peanuts so far behind I’d consider shifting that back to no sooner than July 15^th, maybe a little later to extend disease control later in this season and to avoid “extra” leaf spot sprays.  Not only for leaf spot, but also for soilborne diseases like SSR (southern stem rot/white mold) and SB (Sclerotinia blight).  This may be especially true for SB as temperatures cool down as we approach harvest and cool temps favor SB.  Saving expensive SB fungicide applications in lieu of a later harvest makes sense to me.  I recommend keeping up with peanut heat units and the leaf spot and SB advisories on the Peanut Cotton InfoNet (url link here) or call the Peanut Hotline at 1-800-795-0700.  That way you can gage peanut maturity and disease risk to help make fungicide timing decisions. 

If questions arise concerning peanut disease management this season please don’t hesitate to reach out to me. My contact info is below:

address: 6321 Holland Rd., Suffolk, VA 23437 office phone: (757) 807-6536; mobile phone (preferred): (757) 870-8498 email: dblangston@vt.edu

I’ve been getting questions about peanut in-furrow fungicides and nematicides lately. The primary question is what to use in-furrow since Proline availability is limited, but should be available for later plantings.

Let’s start with why in-furrow Proline was initially recommended for peanuts. In-furrow applications of Proline were found to reduce losses to CBR (Cylindrocladium black rot ) in the early 2000’s by Dr. Pat Phipps. While not as effective as the fumigant Vapam, growers used it because it was less expensive and much easier to apply than Vapam. This caused widespread use of Proline in-furrow in Virginia and North Carolina and became a standard practice to reduce losses to CBR. The early trials evaluating Proline in-furrow did not demonstrate activity on any other peanut disease in Virginia. Thus, Proline in-furrow was used specifically to reduce losses to CBR.

Fast forward to 2023. Due to past and continued breeding efforts towards CBR resistance in Virginia-type peanuts coupled with longer peanut rotations, CBR has become a disease of the past. We have not observed a single peanut sample in the Tidewater AREC Plant Diagnostic Lab where CBR was confirmed as causing disease on peanut since I started here back in 2014. I have not heard anyone mention problems with CBR in Virginia or North Carolina nor have I seen it in my peanut trials or grower fields. So why are some growers still using Proline in-furrow, especially since the disease it was meant to control is not a problem. Good question! I have not used Proline or any other in-furrow fungicide in my peanut trials for years with no issues.

So what’s the bottom line? To me, Proline in-furrow is an added expense that doesn’t provide measurable disease control in our area unless you’re growing Valencia peanuts or another type besides Virginia-type peanuts. Also, there is no replacement product currently labeled for peanut except Propulse which contains the active ingredients in Proline and Velum. I have had someone ask about using Provost Silver as an in-furrow replacement for Proline because it contains the active ingredient in Proline (prothioconazole), but Provost Silver is not labeled for use in-furrow and the tebuconazole component will cause delayed emergence and growth in seedling peanuts. What about Velum? Velum in-furrow is labeled for Aspergillus crown rot, early season leaf spot, early season southern stem rot (white mold), and nematodes. In Virginia, the utility of Velum in-furrow is primary against nematodes. In my opinion, the “must have” in-furrow products on peanuts across the board should be inoculants and thrips control insecticides. I don’t see dropping Proline in-furrow on peanuts causing any disease issues.

If you have questions about in-furrow fungicides in peanuts, please feel free to contact me by e-mail (dblangston@vt.edu) or by phone: office (757) 807-6536; cell (757) 870-8498. If you want to drop in, my address is 6321 Holland Rd., Suffolk, VA 23437.

Nematodes consistently rank as a top yield robber of soybeans. Please plan to join us virtually on December 5 from 1:00-3:00 PM for the Nematode in Atlantic Soybean Production Webinar. This webinar will include results from Soybean Cyst Nematode seed treatment trials, Root-Knot Nematode on-farm trials, emerging management strategies, and feature a panel discussion on needs to improve nematode management in the region. The webinar is free, but registration is needed for access to the zoom link. Registration information can be found athttps://www.pcsreg.com/2022-nematodes-in-atlantic-soybean-production-webinar.  Please email Alyssa Koehler akoehler@udel.edu with any questions. 

I have received a lot of questions regarding leaf spot fungicide treatments in the past two weeks. A lot of this is driven by either: 1) fungicide failures in fields with high disease pressure; or 2) fields under heavy drought stress. In both cases I have advised growers and consultants to look at low cost options. I’ll cover both situations below.

Fields with high late leaf spot pressure Late leaf spot outbreaks have shown up in fields that have been sprayed with Miravis that has traditionally performed well in past years. In each case the fields were in a 4 year or less rotation, most of these fields were irrigated, and growers were using the 4 week extended spray interval to take advantage of the residual activity provided by Miravis. What growers and consultants are interested in now is what to do to hold the leaves on until digging. I try to reduce fungicide costs this close to digging while providing late leaf spot management that reduces excessive defoliation. My “go to” has been Microthiol Disperss (dry sulfur formulation) mixed with a Group 3, DMI fungicide. University researchers, including myself, have observed favorable results with this combination in field trials. The hesitancy in using this program is the added complexity of using a dry formulation and sourcing Microthiol Disperss. Some grower opt for liquid formulations of sulfur because of the two reasons just mentioned, but most of the positive results reported have been with Microthiol Disperss and the amount of sulfur provided by liquid formulations is variable depending on each product, and often the amount of sulfur used with liquid formulations is less than what is provided with Microthiol Disperss. I prefer Microthiol Disperss because it has proven effective in managing high levels of late-season late leaf spot and because it is inexpensive (about $1 per pound which is $5/acre at the recommended 5 lb rate). The sulfur provides instant reduction in leaf spot inoculum but little to no residual activity. That’s why I recommend mixing it with a DMI fungicide like Provost Silver or less expensive Alto. DMI’s provide some curative activity, but most importantly residual activity. Group 7 (SDHIs) and Group 11 (strobilurins) don’t provide curative activity and are most active when applied preventively when little-to-no leaf spot is present.

Fungicide decisions on drought stressed peanuts In many areas peanuts are under severe drought stress with many fields exhibiting wilting 24 hours a day with growers being reluctant to apply leaf spot fungicides due to dry conditions. In many cases these fields are 10-14 days away from digging. This is really a situation where I tend to favor no fungicide applications or at least one application of a very inexpensive fungicide. During dry conditions we often avoid using chlorothalonil (Bravo) due to it’s propensity for flaring spider mites. In my opinion the fungus that parasitizes spider mites to keep them in check is already absent due to the severe drought which is why many growers are seeing outbreaks of spider mites in certain areas. Since the fungus that keeps spider mites at bay (and that chlorothalonil reduces) is already absent, if chlorothalonil is chosen I see that as a low-risk application. Another less expensive option would be Alto which shouldn’t flare spider mites. My personal favorite is to not apply a fungicide at all because: 1) there is little to no leaf spot in these wilted peanuts; and 2) leaf spot outbreaks take a good bit of time to get going and by the time you see any leaf spot in these fields it will be too late for the disease to cause yield damage by the time they are dug. In Suffolk, VA the extended forecast shows no rain chances over 20% for 9 days, at least with the weather app I use. So leaf spot pressure will be low until digging in most cases which further decreases the chance of outbreaks occurring. Deciding not to spray a fungicide is a low risk option in my opinion.

Aflatoxin potential It’s been many years since growers have had to think about dry conditions leading to aflatoxin-contaminated peanuts, which is a good thing. This year is different due to the drought stress near harvest. I recommend keeping peanut field harvests separate between fields with low and high risks of aflatoxin contamination. In other words, avoid mixing peanuts from severely drought-stressed and fields that have not had as much drought stress (possibly irrigated). If peanuts that have had drought stress are to be used for seed, they should receive a quality seed treatment to reduce poor stand due to the aflatoxin fungus in peanuts planted next spring.

The system that brought rain on August 10th seems to have broken our streak of hot weather for Virginia’s peanut growing region. Dailey high’s in the 80s with lows in the 60s will continue until August 23rd according to my weather app. The temperature Saturday the 13th may not get above 80^o F and the low may be in the upper 50s, which is very favorable for the development of Sclerotinia blight. I anticipate the risk of Sclerotinia blight to be high the next 2 weeks, so fungicide sprays may be warranted in fields with a history of that disease. If growers have sprayed the second spray of Miravis + Elatus fungicides within the past 2 weeks they should be covered. I do not recommend spraying the Miravis + Elatus fungicide tank-mix now if you haven’t sprayed it already due to fungicide resistance concerns with late leaf spot and the lack of curative or “kick back” activity if leaf spot already exists. If the Miravis + Elatus tank-mix has not been sprayed twice already I recommend using Omega 500 at the labeled rates for Sclerotinia blight sooner than later. Typically we recommend growers scout for Sclerotinia blight when the risk of that disease is high according to the Virginia Sclerotinia Blight Advisory. Omega 500 will have greater efficacy if applied prior to or at the initial onset of disease. Follow-up sprays may be made using Omega 500 21 days after the first application if favorable disease weather persists.

As always, if you have questions or concerns about diseases of agronomic crops please feel free to call or text me at (757) 870-8498 or e-mail me at dblangston@vt.edu.

Corn

Virginia growers are over the hump so far as corn disease management is concerned.  Late season diseases such as tar spot and southern corn rust have not been observed in Virginia at this time and we are past the R3 (milk) stage which is the cutoff for making effective fungicide applications for each disease.  Click the link for updated maps showing where each disease is currently in the U.S. https://corn.ipmpipe.org/diseases/

Peanuts

As of August 1st, peanut growth and development is a little behind in areas that have experienced periods of severe drought.  Heat units for peanuts planted on May 1st so far are on par with 2021, which was a record-breaking year so far as yield is concerned.  Growers in Virginia have made at least one fungicide application for leaf spot by August 1st, and many have made 2 applications.  The risk of Sclerotinia blight has been variable based on the differences in vine growth due to drought in certain areas, however, recent rainfall events have been more numerous in the region and I expect disease pressure will continue to increase.  Increased rainfall and relative humidity will shorten the LESD (last effective spray date) for leaf spot for most fungicide chemistries and growers using Miravis should consider spraying at 21 days after the first application if disease risk for leaf spot is continually high since the last spray of that product.  Growers that have already made applications of Miravis tank-mixed with Elatus will have some protection against Sclerotinia blight and growers that are opting for Omega 500 should be scouting fields with histories of that disease, especially in those fields where peanut canopies are dense, to make applications at disease onset.  If Miravis or the Miravis/Elatus combo was not applied as the first or second fungicide application I do not recommend using it in August or later due to concerns with fungicide resistance and the lack of curative or “kick back” activity associated with those chemistries.    If peanut leaf spot severity becomes high due to weather and the inability to get equipment in fields to make timely fungicide applications, rescue treatments using Microthiol Disperss or chlorothalonil tank-mixed with Group 3 fungicides, such as Provost Silver, to reduce defoliation prior to digging.

Soybean

Fungicides have recently been going out for foliar diseases recently as most soybeans are in the R1 – R5 growth stages.  Recent weather patterns have brought and continue to bring rain events and high relative humidity which favor the development of frogeye leaf spot and other foliar diseases.  My main concern for fungicide applications is to avoid using Group 11 (strobilurin) fungicide chemistries alone as fungicide resistance to those has been previously documented in the frogeye leaf spot pathogen in Virginia.  There are plenty of Group 3 (triazoles), Group 7 (SDHI) and Group 11 fungicide combinations available to manage foliar soybean diseases.  Also, I’m thinking of naming August as “SDS (sudden death syndrome) month” as that is when SDS usually starts showing up.  The first clinic sample with SDS came in Tuesday on soybeans planted April 15th.  Typically, SDS symptoms occur in early planted and early maturing soybeans first and continue as soybeans mature.  Soybeans planted early in cool (at or below 60°F), moist soils are more at risk of infection by the pathogen that causes SDS, Fusarium virguliforme.  The most visible symptoms occur at the late R5 growth stage and into R6.  Managing this disease is strictly preventive through the use of crop rotation, delayed planting, resistant varieties and the fungicide seed treatments ILeVO and Saltro.  We are gathering data on SDS outbreaks in Virginia so please contact us if you suspect this disease in your fields.

As always, feel free to contact me if you have questions regarding disease and nematode issues in your fields. e-mail: dblangston@vt.edu, cell: 757-870-8498