Stink bug numbers continue to climb

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Brown stink bug numbers have continued to increase in eastern Virginia from the Northern Neck to the Tidewater region. We have scouted fields in Suffolk and Caroline County with higher than threshold infestations spanning the entire field. Infestations in most fields remain confined to border rows and the majority of infested fields are near where wheat has been recently harvested.

Many growers are facing the decision to treat. Previously I had reported a threshold of 1 bug per 4 plants. In order to be extra protective during ear formation and elongation, treatment at the 1 bug per 10 plants threshold can be justified for heavily infested fields. More information about stink bugs in corn can be found here – NCSU corn stink bug management considerations. 

The ability of stink bugs to injure corn depends heavily on corn growth stage. Trials at the Tidewater Research Station have shown that stink bug feeding does not always reach developing ears. The photo below shows a healthy ear developing  (VT growth stage) despite multiple feeding lesions to the outside of the stalk. This may be good news for Virginia growers. We cannot determine if yield was effected in these plants until later this season.

This week, we will be rechecking fields  that were treated with aerial applications and post updates on the effectiveness of these sprays.

 

 

 

Herbicide Resistant Common Ragweed Plot Tour

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Having trouble controlling herbicide resistant common ragweed? Make plans to attend the field tour, this coming Thursday (June 22nd, 2017) near Lawrenceville, Virginia. Complete information is below. Please RSVP as soon as possible.

View a complete spectrum of preemergence and postemergence herbicides in soybeans in the field to see what works best for yourself. Also, learn about integrated weed management approaches that work within our cropping systems. 

Stink bug numbers increasing in corn

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Coinciding with the wheat harvest, brown stink bugs have been moving into pre-tassel corn in the southeastern region of our Virginia. The entomology department has scouted fields over threshold in Chesapeake and Virginia Beach. So far this season, stink bugs are present in low numbers in northern, central, and western regions of the state.

Thresholds for stink bugs in field corn are (From Dominic Reisig at NCSU):

one stink bug per four plants during ear formation, elongation, and pollen shed

one stink bug per two plants nearing the end of pollen shed to the blister stage.

Plant injury from stink bugs may include:

Holes in leaves and, in severe cases, twisted plants.

It is important to remember that this bug typically infests on edges of fields and in spotty locations. It is possible, though unlikely, that stink bugs will infest an entire field. Spray volume is critical if you decide to spray – use a high volume to ensure that sprays penetrate the canopy. Insecticides labeled for stink bugs in corn (e.g., Baythroid XL, Karate Z, Warrior II) must come into direct contact with insects to kill them.

 

 

Save the date: Virginia/Northeastern North Carolina Cotton Field Day on July 20, 2017

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You are invited to attend our cotton field day at the Virginia Tech Tidewater AREC on Thursday, July 20, 2017. The tour will begin promptly at 8:00 am, ending with lunch. The location is our research farm at 1045 Hare Road, Suffolk, VA. The event is free and open to the public, but pre-registration is required–please contact Gail White by phone at 757-657-6450 extension 430, or by email at guwhite@vt.edu by July 10th. Private Pesticide recertification credits (cat. 90, 91) are being offered. More information will be made available in the upcoming weeks. Thank you.

Greater Yields are Possible for Double-Crop Soybean in 2017!

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It appears that wheat harvest will be 1 to 2 weeks ahead of schedule this year.  We actually harvested some high-moisture wheat and planted soybean plots behind it today (May 31) in northeast N.C.  This is good news for soybean.  Earlier planting means greater yields!  This is clearly shown by the recent data obtained from our multi-state, multi-year double-crop project.

With earlier planting, have my recommendations for double-crop soybean changed?  In general no.  But below are a few things to consider.

Seeding Rate:  In general, you can probably back off on your seeding rates from what you were planning if you get your double-crop soybean in by mid-June.  I’d suggest that you start out with 120-160,000 seed/acre (depending on when you start planting) and gradually ramp that up by 20-30,000 for each week delay in planting.  For more information, see my recent blog, Soybean Seeding Rates for June and Later.

Relative Maturity:  Actually, my standard recommendation still stands, more or less.  Plant as late of a relative maturity (RM) as possible that will mature before the frost.  However, there are now some caveats.   By planting a week earlier, you’ll gain about 3 days in maturity.  Although a slightly later RM may work, I wouldn’t count on it – frost date will affect this more than planting date.  So, don’t plant a later RM.

But, can you plant an earlier RM, say go from an early-5 to a late-4?  Possibly.  Why do I say this?  Two things.  First, by planting a week or two earlier you have greater yield potential (see the above graph), which is due to the ability to grow more leaves.  So your yields are not necessarily so dependent on leaf area as they are with a late-June to early-July planting.  A slightly earlier RM planting in early- to mid-June will only have slightly less leaf area than a later RM.  And, we have generally found that under greater yield potentials, early RM will yield more than later ones.  Still, these are not great reasons to change your RM.  Generally, stick with what you planned.

Soybean Seeding rates for June and Later

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Due to the rainy weather over the past two weeks, we are still planting full-season soybean in some areas.  In addition, it appears that wheat harvest is not far off (some wheat at the Tidewater AREC was at 23% moisture today!).  So, should we be increasing our seeding rates?

In general, yes.  But, big increases probably will not be needed until late-June.  Below are some seeding rate data that we collected from soybean planted in early-June after barley.  First, we don’t have a lot of data of soybean grown after barley, so I don’t have as much confidence in the exact seeding rate needed.  Note that there is a wide range in the optimal seeding rates, illustrated by the area between the dotted lines in the graph.  Although, these data may not directly apply to full-season soybean (no small grain), it should be close.

I think that we should now be using 120,000 to 160,000 seed/acre.  The range will depend on the planting date.  In general, I’d suggest bumping up your seeding by 20-30,000 seed/acre per week through June.

If you remember the seeding rate data that I shared in this blog last month for May-planted soybean (see Soybean Seeding Rates – How Low Can We Go?), I stated that maximum yields could be obtained with only 95,000 to 110,000 seed/acre when the yield potential is greater than 40 bushels/acre.  That’s pretty low, but was adequate for maximum yield under good growth conditions.  For less than 40 bushel potential, seeding rates needed to be a little higher.   In the above graph, it appears that more seed is needed to obtain 55 to 70 bushels/acre after barley, I cannot fully explain why; therefore, I would assume that this response is primarily due to the location that we obtained the data (again, we don’t have a lot of data).

Once we get into mid- to late-June, I’d rather see a seeding rate of 180,000 to 220,000 seed/acre, depending on planting date.  This is based on the data to the right.    You’ll notice that, like full-season soybean, the optimal seeding rate falls with greater yields.  This is most likely due to greater leaf area with those high-yielding locations.  As I’ve stated often, the seeding rate response can usually be traced back to whether or not the crop developed enough leaf area to capture 90-95% of the light by early pod development.  Unfortunately, I don’t have any double-crop data planted following wheat with yields greater than 55 bushels/acre.  I hope to solve that problem this year with new experiments.

Potato Late Blight in North Carolina

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The following advisory is posted on behalf of Dr. Steve Rideout:

Late blight was found on potato in Camden and Pasquotank counties in North Carolina over the weekend. We will be processing the samples to determine more information on race/fungicide sensitivity. In the meantime, growers are encouraged to scout their tomato and potato fields for the disease.  Preventative fungicide applications are recommended, particularly near the outbreak area in NC.

If you have questions please let us know.  You can access current recommended materials for late blight in the commercial and homeowner vegetable production guides.  Also, you can visit the following web page for more information on this disease:

https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ANR/ANR-6/ANR-6_pdf.pdf

This is a serious threat to potato and tomato production in the Commonwealth.  Please let us know if we can help.

Warrant and Cool, Wet Soils

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Charlie Cahoon

Extension Weed Specialist, Virginia Tech

Warrant is an encapsulated formulation of the herbicide acetochlor and has widely become a part of our postemergence (POST) herbicide program in cotton.  Although Warrant does not control emerged weeds, it does provide excellent residual control of pigweed, other small seeded broadleaves, and annual grasses (with the exception of Texas panicum).  This makes it an excellent tank mix partner for glyphosate (Roundup) or glufosinate (Liberty) in our first, second, or both POST sprays, especially in fields heavily infested with glyphosate-resistant Palmer amaranth.  However, because of its encapsulated formulation, Warrant can also be applied preemergence (PRE) to cotton.  You may remember the days of using the EC formulation of acetochlor, known as Harness, in corn.  This formulation was not encapsulated and significant injury would result if applied PRE or POST to cotton.  This is not the case with Warrant.  The encapsulated version affords much more cotton safety that the old EC formulation.  In my experience, PRE applied Warrant has been very safe on cotton.  As is the case with all residual herbicides, environmental conditions influence cotton response to PRE applied Warrant.  Unfortunately, conditions we are currently experiencing in Virginia and northeast North Carolina; cool, wet soils and overall less than ideal weather for planting cotton are conducive to Warrant injury.

I saw this in my on research trials during the spring of 2016.  Our cotton planted at the Tidewater AREC (near Holland, VA) on May 15, 2016 took approximately 9 days to emerge whereas cotton planted May 26, 2016 emerged in roughly 5 days.  The weather was mostly to blame for the differences in vigor of the two plantings, but Warrant compounded the problem.  So why the difference?  We all know that cotton planted into cool wet soils is slow to emerge.  Cotton tolerance to Warrant all hinges on the breakdown of the tiny capsules used to encapsulate acetochlor versus the time it takes for cotton to emerge.  The key to avoiding injury from PRE applied Warrant is for cotton to emerge prior to the majority of these capsules breaking down and subsequent release of acetochlor.

Nontreated check plot.

Under ideal planting conditions this is not an issue.  On the other hand, if cotton is slow to emerge, giving the capsules more time to breakdown and the seedlings have to push through a higher concentration of acetochlor, the potential for injury is greater.  This is exactly what I saw in 2016 and have heard complaints about in years prior.  Cotton that laid in the ground longer than usual and received Warrant PRE was stunted about 25%.

Weed control by Warrant alone.

My cotton eventually recovered and by the end of the season no yield differences were observed.  Cotton that emerged quickly showed no injury in response to PRE applied Warrant and was one of the safest and cleanest treatments.

Weed control by Warrant plus 10 oz/A Reflex.

I routinely recommend Warrant PRE especially where Palmer pigweed is a problem.  The fact is that all of our residual herbicides are capable of injuring cotton if the weather does not cooperate.  As the planting progresses, I would advise you to factor in the planting conditions when choosing your PRE herbicides.  Any conditions delaying emergence of cotton is conducive to injury from Warrant PRE.  With that said, it may be wise to leave Warrant out of the tank until planting conditions improve.  Do not let this stop you from using a residual herbicide all together.  Alternatives to Warrant include Cotoran, Direx, Prowl, Reflex, and fluridone containing products (Brake FX and Brake F16).  With all the herbicide resistance issues knocking on our door, it is imperative that we continue to use residual herbicides early burndown, around planting, and in-season.  Once cotton land dries out and soil temperatures rise, Warrant will again be one of our best residual options.

Failed Corn Stand: Starting Over

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Charlie Cahoon and Michael Flessner

Virginia Tech Weed Science

Over the past few days we have had several questions concerning replanting corn behind an already failed corn stand.  Our biggest concern in this situation is how to terminate emerged corn from the first planting.  The best option for small corn (4-8 inch) is clethodim (Select Max or generics).  The label for Select Max (0.97 lb active ingredient/gal) specifies 6 oz/A must be applied at least 6 day prior to replanting.  Clethodim products that contain 2 lb active ingredient/gal and are labeled for this situation should be applied at 3 oz/A, while adhering to the same plant-back restriction.  As is the case with many weeds, timeliness is critical.  Control of larger corn by clethodim is variable (> 8 inches).

Poor corn stand as a result of bird damage. Painter, VA 2017.

Producers not wanting to wait 6 days before replanting should use paraquat (at least 3 pt/A of a 2 lb/gal product or 2 pt/A of a 3 lb/gal product).  Paraquat should not be used alone; adding atrazine (1 pt/A) and suggested adjuvants to paraquat will enhance control.  Research conducted by Dr. Kevin Bradley (University of Missouri) and Larry Steckel (University of Tennessee) concluded Liberty did not consistently control Roundup Ready corn.  Although not listed on the bag, many corn hybrids are tolerant to glufosinate (active ingredient in Liberty).  For these reasons, producers should be wary of using Liberty to terminate a failed corn stand.

Another common question when replanting corn is whether to reapply residual herbicides such as atrazine. Atrazine and other residual herbicides should not be reapplied. If additional atrazine is desired in a postemergence application, just note that the cumulative total atrazine for your first and second planting of corn cannot exceed 2.5 lb active ingredient per acre per year.  Other products have similar restrictions.

On a normal year, growers are usually asking if soybean can be planted behind corn.  And our answer to this is usually no.  This is mostly due to the fact that most everyone uses atrazine preemergence and planting soybean following atrazine if very risky.  The label of most atrazine products says “Do not rotate to any crop except corn or sorghum until the following year, or injury may occur” and “If applied after June 10, do not rotate with crops other than corn or sorghum the next year, or crop injury may occur”.