Category: Crops

Using the PSNT and Tissue Testing for Nitrogen

Kelly Nichols, Agriculture Agent Associate
University of Maryland Extension, Frederick County
kellyn@umd.edu

With all of the rain that we have had earlier this spring in some areas, nitrogen deficiency is likely to show up, if it hasn’t already. Nitrate (NO3–) is the main form of nitrogen that plants take up. When soils are saturated, the bacteria in the soil do not have access to oxygen in the air, so they use the oxygen in nitrate instead. During this process, called denitrification, nitrate is converted to a gaseous form of nitrogen. The nitrogen gas then is lost to the atmosphere and is no longer available to plants.

The symptoms of nitrogen deficiency will show up on the lowest leaves of the plant first. Nitrogen is mobile in the plant, so if it runs out of nitrogen, it will pull nitrogen from the lower leaves and send it to the newer leaves. The nitrogen-deficient leaves will be yellow; this yellowing will start at the tip of the leaves and move along the middle of the leaf.

If your plants are starting to show nitrogen deficiency, don’t panic! There is still time to correct this by adding additional nitrogen. There are two tools that farmers can use to determine if and how much additional nitrogen should be added.

The first tool is a tissue test. This test can be used for not only nitrogen deficiencies, but also to detect other nutrient deficiencies. A majority of the soil testing labs in the region also offer plant tissue analysis. After choosing which lab you will send your samples to, make sure you find the tissue sampling instructions on the lab’s website. Samples will need to be taken from a specific part of the plant at a specific growth stage of the plant. The lab has calibrated their tests to those plant parts and growth stages; a different method of sampling will result in a useless report.

Take two samples – one from the area that is deficient, and one from an area that is not deficient. Both areas should have similar management practices. Once you have the results, you can compare the two areas and determine practices to mitigate any nutrient deficiencies. If additional fertilizer is needed and you have a nutrient management plan, work with your plan writer to ensure that you are in compliance with applying the additional fertilizer.

The second tool is the Pre-Sidedress Nitrogen Test (PSNT). This test is offered by University of Maryland Extension Nutrient Management Advisors and can be used on corn. The PSNT is a soil test that can be taken when the corn is 6-12 inches tall. This is just prior to when the corn is about to rapidly take up nitrogen. The results of the PSNT will tell if you there is enough nitrogen in the soil to get the corn through its next growth spurt.

The PSNT can be used in fields that have a previous crop of a legume and/or have had manure or biosolids applied. The PSNT cannot be used in fields that have received more than 50 lbs/A of commercial fertilizer nitrogen, or in fields that have a history of receiving commercial fertilizer as the only nutrient source.

Contact your county’s nutrient management advisor if you would like to schedule an appointment for a PSNT. Below are the steps for taking a soil sample in order to prepare for a PSNT. Remember that the soil sample needs to be taken when the corn is 6-12 inches tall.

Soil samples should be taken 12 inches deep (or as deep as you can get them) midway between the rows. Thirty to forty cores should be taken. Put the samples in a bucket, break up any clumps of soil, remove any rocks or other foreign material, and mix the soil. Spread the soil out on newspaper to dry. The samples should be dried immediately after they are taken.

A few soil testing labs around the region also offer the PSNT. If you choose to use one of these labs, check their sampling procedure on when and how to take samples, as it may differ. Also check with your nutrient management plan writer once you have the results to ensure that you are in compliance with your nutrient management plan if you sidedress nitrogen.

One last note – there are a couple of other nutrient deficiencies that have symptoms similar to nitrogen deficiency. Potassium deficiency looks like a yellowing or burning also on the lower leaves. However, it will appear on the edges of the leaves (as opposed to nitrogen which appears in the middle of the leaves). Sulfur deficiency also results in yellow leaves. However, sulfur is not a mobile nutrient in the plant. When the plant runs out of sulfur, the top leaves will become yellow. (Nitrogen deficiency starts in the bottom leaves.)

 

Guess the Pest! Week #13 Answer: Ozone Damage

Guess The Pest Logo

 

 

 

 

 

Bill Cissel, Extension Agent – Integrated Pest Management, University of Delaware; bcissel@udel.edu

Congratulations to Keith McGowan for correctly identifying the damage in the photo as ozone damage and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #13 Answer: Ozone Damage

Photo and article by Nancy Gregory

Ozone damage on vegetables is observed during hot and humid weather in our region. The most susceptible crops include potato, watermelon, cantaloupe, pumpkin, squash, snap bean, and lima beans. Symptoms occur on the top, younger leaves, and show up as dark spots on potato. On cucurbits, ozone damage shows up as yellowing with spots having a white crusty center. Watermelon is the most susceptible in this group. On beans, spots are small and bleached looking, and leaves may have a bronzed appearance on the top surface. Affected leaves may yellow and drop. Ozone is easily misdiagnosed and hard to accurately confirm, since an episode of air pollution cannot be chemically tested for. Inversion layers in hot humid weather result in trapped air at the field level that has a high level of air pollutants. Air remains at field level until winds pick up and disperse it, and four or five hours at levels of 80 ppb can result in damage. Some cultivars have some tolerance, and keeping plant stress low can help to avoid damage.

2018 Commodity Classic

Farmers are invited to attend the Maryland Commodity Classic on Thursday, July 26, 2018, at Queen Anne’s County 4-H Park. Hosted by the Maryland Grain Producers Association, Maryland Soybean Board, Maryland Grain Producers Utilization Board, and Mid-Atlantic Soybean Association, the annual meeting is the premier event for grain farmers in the region.

Keynote Speaker Bill Northey, Under Secretary of Agriculture for Farm and Foreign Agricultural Services, is a well known grain farmer, serving as president of the National Corn Growers Association from 1995-96 and most recently Iowa’s Secretary of Agriculture. Northey will be covering the latest news in agriculture from Washington DC. USDA’s current focus is to help new farmers get started in agriculture, assist rural communities, help farmers operate with less regulation, increase exports, address crop damage, and pass the 2018 Farm Bill.

“This year’s classic offers farmers a great opportunity to get the latest on farm research and current industry topics, particularly from the national level,” states Dr. Robert Kratochvil, Maryland Commodity Classic chairperson.

Research presentations from 9:30-10:30 a.m. will update farmers on checkoff-funded projects designed to make their operations more productive and profitable. Exhibits and informational displays to present the latest innovations in technology, research and equipment will open at 10:30 a.m. The afternoon program begins at 1:30 p.m. and will include awarding college scholarships and the National Leaders Panel.

The Classic will conclude with the famed Crab Feast, Pork and Chicken Barbecue. Event tickets are $10 before 2:30 p.m. and $20 after 2:30 p.m. No entry is permitted after 3:30 p.m. For more information, call 443-262-8491 or email lindsay@gmail.com. Maryland Grain Producers Association members received a free ticket  – join today!

Guess the Pest! Week #11 Answer: Thrips Injury on Soybean

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Bill Cissel, Extension Agent – Integrated Pest Management, University of Delaware; bcissel@udel.edu

Congratulations to Travis Kinnison for correctly identifying the damage in the photo as thrips injury and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #11 Answer: Thrips Injury on Soybean

Thrips are small bodied insects that use piercing-sucking mouthparts to feed on plants. The damage in the photo is of thrips feeding injury on soybean. The threshold for thrips is 8 per leaflet and leaf damage. However, we rarely reach populations high enough that the physical feeding injury warrants treatment. In fact, thrips are most known for their ability to vector plant diseases such as soybean vein necrosis disease (SVNd).

Adult Soybean Thrips

There are at least three species of thrips, including soybean thrips, which are capable of vectoring SVNd. From 2015-2017, we conducted a state-wide survey for SVNd, sampling 88 fields for thrips and disease symptoms. Our findings determined that the disease is prevalent in Delaware. We detected SVNd in 11.6% of the full season and 22.8% of the double crop soybean fields included in the survey averaged across all three years.

Here is a link for more information about the SVNd survey results,: https://cdn.extension.udel.edu/wp-content/uploads/2015/10/30120518/SVND-grower-summary-and-report.pdf

Soybean Vein Necrosis disease (SVNd) Symptoms.

Here is a link to a short Youtube Video Discussing SVNd symptoms:https://youtu.be/7gXDLjm5x7Q

Fun Entomology Fact: Thrips is the proper terminology used whether it is singular and plural. So you can have one thrips or many thrips.

Guess the Pest! Week #10 Answer: Stagonospora nodorum Leaf Blight and Glume Blotch

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Bill Cissel, Extension Agent – Integrated Pest Management, University of Delaware; bcissel@udel.edu

Congratulations to Buzz Lowe for correctly identifying the disease in the photo as Stagonospora nodorum leaf blight and glume blotch and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Stagonospora nodorum Leaf Blight and Glume Blotch

By Nancy Gregory

Stagonospora nodorum leaf blight and glume blotch can cause yield loss on wheat, especially if infection occurs before grain fill. Stagonospora overwinters in crop residue and can be spread in infected seed. Disease is favored by environmental conditions of high moisture and wind, resulting in spore movement up through the canopy. Disease spread slows when weather turns dry. Symptoms include oval to round, brown leaf spots with yellow halos. The glume blotch phase is characterized by gray to purple brown discoloration on the outer seed coverings. Closer look with a hand lens may show a dusty cast to the heads when the fungus is producing spores. Management strategies include rotation to soybean, corn, or other on-hosts, as well as proper plant density to avoid over-crowding. Fungicide applications of a labeled triazole or strobilurin product at heading can be a part of a management plan. Resistant varieties are available for fields with a known history of glume blotch.

What Can I Do To Manage Head Scab in 2019?

Andrew Kness, Agriculture Extension Educator
University of Maryland Extension, Harford County
akness@umd.edu

Wheat head with bleached spikelets from FHB
Figure 1. Wheat head with Fusarium head blight. Image: Andrew Kness, University of Maryland

If you grew wheat this year, chances are you don’t have to look too hard to find head scab/Fusarium head blight (FHB). The excessive rainfall, humidity, and warm temperatures that we had around wheat flowering provided the perfect habitat for Fusarium graminearum, the causal agent of FHB, to thrive. If you have FHB, you have few options to manage it at this point in the season as you read in Bob’s article above; but what can you do in 2019 to better your odds (besides hope for little rain during flowering)?

To understand your options you need to understand the lifecycle and biology of F. graminearum. The pathogen survives on residue, particularly that of wheat, barley, and corn and will persist through the winter on this material. During periods of wet, humid, and warm temperatures in the spring, the fungus will produce spores. If wheat or barley is growing in the field, the spores are splashed up onto the heads via rain or irrigation, or carried by the wind. If the wheat or barley is flowering, the spore can germinate and infect the plant through the flower; it cannot get into the plant any other way. This is why we recommend fungicide application at flowering. Once the pathogen infects the wheat, it grows within the spikelet, bleaching it in the process (Figure 1) and infects the developing grain, causing shriveled, light weight, discolored kernels called tombstones. Infected grain may contain deoxynivalenol (DON) vomitoxin. FHB not only reduces yield, but has the potential to contaminate your grain with DON.

With that in mind, here are some tips for managing FHB in 2019:

  • Know your variety! If you plan to grow and market quality grain, then you need to know your varieties. Unlike barley, wheat does have some resistance to FHB, although it is not complete resistance. Some varities are more resistant than others, so my suggestion is to grow a variety that has the best resistance and yield potential. Consult with your seed rep and utilize the data from our wheat variety trials. A collaborative project between the University of Maryland and University of Delaware screens wheat varieties for resistance to FHB. The data can be found here, or call your Extension Office for a copy.
  • Use a fungicide at flowering. Unless we have an exceptionally dry spring, you’ll likely need a fungicide application to protect against FHB. Use the Scab Risk Assessment Tool to help assess your risk. Time your application at the start of flowering (Feekes 10.5.1) and up to 5 days thereafter. Triazole fungicides work best, particularly Caramba (metconazole), Proline (prothioconazole), and Prosaro (prothioconazole + tebuconazole). Do not use strobilurin fungicides! See my article in the April issue for more information on fungicide strategies.
  • New for the 2019 growing season will be a new product from Syngenta, called Miravis Ace (adepidyn). This will be a new mode of action fungicide (SDHI) to be used on FHB, and should help us with managing resistance by rotating it with the Triazoles. Preliminary University testing shows that Miravis Ace does well against FHB; however, claims of a wider application window seems questionable at this point, so application timing will still be critical.
  • Select your best fields. Since F. graminearum can survive on small grain and corn residue, planting wheat or barley behind soybeans is better than following corn. F. graminearum doesn’t survive well on soybean residue. If you are following corn, consider a light tillage pass with a vertical till tool to size residue. This will accelerate residue decomposition, killing some of the surviving F. graminearum.

It is important to utilize as many management strategies as possible for FHB. Host resistance can only provide about 50% FHB suppression in wheat (and 0% in barley), and fungicides can only provide 50% suppression at best. Growers must use a combination of variety selection, fungicides, and cultural practices to achieve a high quality wheat or barley crop.

Fusarium Head Blight (Head Scab) in Small Grain This Year Cause for Concern

Bob Kratochvil, Extension Agronomist
University of Maryland, College Park
rkratoch@umd.edu

 

wheat heads infected with Fusarium graminearum
Figure 1. Healthy (outside two heads) and Fusarium head blight diseased wheat heads. Image: APS.net

During the past two weeks, I have had the opportunity to walk a number of small grain fields (wheat, barley, triticale) across the state. Many of those fields are infected with Fusarium head blight (FHB), aka head scab (Figure 1). I have seen fields with very low levels of infection (less than 1% of heads infected) to some that have over 50% infected heads. Thus, the reason for concern. The reason for the high number of infected fields this year is the rainy weather we have had during May. The rains coincided with flowering of the wheat, barley, and triticale. Rain splashes spores of the causal agent of the disease, F. graminearum, onto the heads allowing infection to occur. Temperatures ranging between 75 and 85°F are considered optimum but lower temperatures during periods of high humidity and moisture can also enhance infection. The over 10 inches of rain much of the state has received created ideal infection conditions.

Head scab often results in significant yield loss and grain quality reduction. Grain quality reduction is primarily the result of the mycotoxins (chemicals) that are produced by F. graminearum. These mycotoxins can be toxic for humans and animals if the concentrations exceed minimum limits. The most concerning mycotoxin is deoxynivalenol (DON), also known as vomitoxin. The Food and Drug Administration (FDA) advisory level for DON is 1 ppm for foods consumed by humans. In the case of wheat, the level is 1 ppm for the flour. Often elevators and mills will accept wheat with DON levels 1.5 – 2 ppm without penalty because they can blend infected grain with sound grain to meet the FDA advisory level. Wheat with DON levels that exceed 2 ppm can be acceptable livestock feed. Swine are the most sensitive with the recommended level of 5 ppm DON with the DON infected grain not to exceed 20% of the ration. For ruminants and poultry, grain with 10 ppm DON can be used as long as no more than 50% of the ration is composed of the infected grain.

 

FHB-infected wheat kernels (tombstones)
Figure 2. Healthy and head scab damaged wheat kernels.

When you harvest your grain and notice shriveled, whitish looking kernels (tombstones), there is a strong likelihood that DON is present (Figure 2). If you have head scab infected wheat or barley fields, you will want to do what you can to minimize the impact of DON that is concentrated in the shriveled tombstone kernels (Figure 2). These light-weight kernels can be separated from sound grain at harvest by increasing the combine’s fan speed so don’t be concerned that you are losing too much good grain if you see lots of tombstones behind the combine, because you are not.

combine harvesting wheat
If you are storing the grain do so properly to prevent further contamination. Dry newly harvested grain that is infected to 13-14 percent moisture. This will stop pathogen growth and mycotoxin production. DON is an extremely stable mycotoxin. This means that drying and properly storing grain will not reduce the DON levels, however, DON concentration will not increase in properly stored grain. Bin any infected grain you harvest separately from sound, good quality grain. If you have a cleaner, you can remove fines from the wheat before you bin it and possibly lower the DON concentration. Before you deliver your grain, I suggest you check with your elevator or mill to see if they test for DON. It will be easier to take samples to them for testing prior to delivery than to learn that your grain is rejected after you have loaded the truck and taken it to the elevator.

Should I Be Worried About Mega-Pests?

Peter Coffey, Agriculture Agent Associate
University of Maryland Extension, Carroll County
plcoffey@umd.edu

If you’re a farmer in the United States then you’re acquainted with the corn earworm, Helicoverpa zea. Maybe you know it as cotton bollworm, tomato fruitworm, sorghum headworm, soybean podworm, or maybe you remember when scientists used to call it Heliothis zea. To keep things from getting confusing we’ll just call it H. zea. No matter what you call it, it’s the same tan colored moth with caterpillars we all remember picking out of the tip of an ear of sweet corn as a kid. As you can guess from the variety of names, H. zea feeds on a lot of different crops. It’s actually been documented to eat over 100 different plants, usually the reproductive part of the plant (the fruit/grain/bean part).

Adult corn earworm
Figure 1. Adult Helicoverpa zea moth. Image: Peter Coffey, University of Maryland.

While H. zea is a devastating pest throughout North and South America, it has a bigger badder older brother. In Europe, Africa, Asia, and Australia they also call this moth the cotton bollworm, but it’s a different species, Helicoverpa armigera (we’ll call it H. armigera). In fact, H. armigera is the parent species to our H. zea. Scientists estimate that about 1.5 million years ago some H. armigera moths made their way over to the Americas, and over time they evolved enough that does we consider them to be a different species, H. zea. To put it another way, if dogs evolved from wolves, then H. zea is a bulldog, and H. armigera is the wolf. This is important because H. armigera as the older original species is more genetically diverse, which is probably why it’s better at evolving pesticide resistance.

In recent years, increasing global trade has increased the occurrence of introductions of invasive pests worldwide, and H. armigera has been one of the species that people are the most worried about. It has been caught at the borders several times in North America, but unfortunately in 2013 it was confirmed to be established in Brazil. Additionally, scientists have known for a while that H. armigera and H. zea could mate and create viable hybrids in the laboratory, and just this winter a paper was published documenting the first wild hybrids discovered in Brazil.

Hybrid moths are concerning, because even though H. armigera is the more genetically diverse species, H. zea has spent the last 1.5 million years developing its own unique set of genes. This means that the hybrids combine the genetic diversity of both species. If you’re wondering why genetic diversity is important, remember that when a population lacks genetic diversity we call it inbred, so you could think of hybrids as the opposite of inbred. Scientists worry that these hybrids could attack an even wider range of crops, and that they could evolve pesticide resistance even faster. There’s no reason to think that individual caterpillars would be more damaging, both species are cannibals, which is why you rarely see more than one worm in an ear of corn.

So what does this mean for you? It means that sometime in the future, if these hybrids make it here, pesticide resistance may become even more of a concern than it already is. For now, if you’re spraying corn remember to rotate your chemical families. You can also check out what the corn earworm population is doing at www.mdmothmap.com, or call your local extension office and ask.

Maryland Department of Agriculture Announces 2018-2019 Cover Crop Sign-Up

ANNAPOLIS, MD – The annual sign-up period for Maryland Department of Agriculture’s cover crop program will take place June 21 – July 17 at soil conservation district offices statewide. This popular grant program provides farmers with cost-share assistance to offset seed, labor, and equipment costs to plant cover crops on their fields this fall to control soil erosion, reduce nutrient runoff, build healthy soils, and protect water quality in streams, rivers and the Chesapeake Bay. Governor Larry Hogan has allocated approximately $22.5 million for Maryland’s 2018-2019 Cover Crop Program.

“Planting cover crops this fall is a great way to recycle or scavenge any nutrients that were not used by corn and other cash crops by the end of the growing season,” said Secretary Joseph Bartenfelder. “To give farmers more planting options, several new small grain/legume cover crop mixes were approved for payment this year. I urge farmers to take advantage of our popular cover crop program.”

Cover crops help protect waterways from nutrient runoff, control soil erosion, and improve soil health. As they grow, cover crops recycle unused plant nutrients remaining in the soil from the preceding summer crop. Once established, they work all winter to protect fields against erosion spurred on by wind, rain, snow, and ice. In addition to their water quality benefits, cover crops help build healthy soils, increase organic matter in the soil, reduce weeds and pests, and provide habitat for beneficial insects. They can even help farm fields recover more quickly from drought and extreme rainfall. Studies have shown that planting cover crops in the fall can increase yields of cash crops like corn and soybeans after only a few years.

Maryland’s Cover Crop Program provides grants to farmers who plant small grains such as wheat, rye, barley, and oats, brassicas, and forage radish on their fields following the fall harvest. To help create diversity, eligible cover crop species may be mixed with radish and legumes including clover, Austrian winter peas and hairy vetch using a variety of two and three-species mixes.

Cover crops cost-shared through this program receive a base rate of $45/acre and up to $30/acre in add on incentives for planting early and using other highly valued planting practices. The aerial seeding deadline is October 7. Maryland’s nutrient management regulations require farmers to plant cover crops to help protect water quality when organic nutrient sources are applied to fields in the fall. Double-crop soybeans may be planted aerially at a reduced reimbursement rate and farmers may harvest their cover crops, but payment for this option is no longer offered. Program eligibility requires that the farm has a current nutrient management plan.

Maryland’s Cover Crop Program is administered by the Maryland Department of Agriculture and the state’s 24 soil conservation districts through the Maryland Agricultural Water Quality Cost-Share (MACS) Program. Applicants must be in good standing with MACS and in compliance with Maryland’s nutrient management regulations. Other restrictions and conditions apply. Funding is provided by the Chesapeake Bay Restoration Fund and the Chesapeake and Atlantic Coastal Bays Trust Fund. For more information, farmers should check their mailboxes for announcements or visit the department’s website.

Herbicide Options for Monsoon Season

By Matt Morris, Agriculture Extension Educator
University of Maryland Extension, Frederick County
mjmorris@umd.edu

While I am usually very cautious to complain about the rain, enough is enough! There isn’t one farm in this State that isn’t weeks behind because of our recent weather. Most all the hay is nearing straw quality and there’s still a good amount of corn that is yet to be planted. Not to mention the sheer number of soybean acres that haven’t gone in the ground. One thing this weather has done a good job of is ruining the best laid herbicide plans for corn and soybeans. I’ll outline some scenarios and what post-emergence options you might have.

Let’s say you planted corn May 15th and were planning to spray after you planted, but before the plants emerged. Then it started raining. Now your corn is up and at the V3 or V4 stage (3 or 4 visible leaf collars). Weeds are emerged and racing the corn. The obvious go-to would traditionally have been glyphosate (RoundUp) for tolerant corn varieties. However, in the day and age of herbicide resistance this probably won’t be enough. For tough to control broadleaf weeds I’d suggest throwing a product like Status or Diflexx Duo in with your glyphosate to pick up weeds like marestail, lambsquarter, or pigweeds. These are “safened” dicamba products. The caution is that these products cannot be applied to corn before the V2 stage. Also remember, most herbicides have a maximum height for application ranging anywhere from V2-V8.

You’ll also want to think about throwing a residual product in the tank since we missed that before planting. This is where atrazine or S-metolachlor (Dual) can work well. Atrazine can help control a lot of our broadleaf weeds and works really well on morning glory if you have pressure in your fields. S-metolachlor won’t kill emerged weeds, but will keep any small seeded weeds from germinating for several weeks. A word of caution: atrazine cannot be applied to corn greater than 12” in height. S-metolachlor has a maximum application height of 40”.

Soybeans present a much more challenging problem due to herbicide resistant broadleaf weeds and their widespread prevalence in the area. Here’s our first scenario: You sprayed a combination of burndown and residual herbicides on May 15th with hopes to plant that weekend. Then it started raining. You still can’t get into the field to plant. Whatever you do, resist the temptation to plant without another residual application. If you can’t, the weeds will come up long before your crop can canopy. You may need to go back in with a product like S-metolachlor, metribuzin, or Valor to hold weeds back until the crop canopies. If you need another burndown because weeds are emerged, adding in a product like paraquat with your residual can help. The key is starting clean. A word of caution: most herbicides have a maximum application rate per season so read the label to make sure you don’t exceed that amount.

Here’s the second scenario: you planted soybeans on May15th and planned to come in and spray the next day. Then it started raining. Now your soybeans are up and no burndown or residual herbicides were applied. The first thing to do is remember that most all of our marestail are glyphosate and ALS (Firstrate, Synchrony, Raptor, etc.) resistant so I will not consider them here. That being said there are areas they still may work, but I caution against them being used alone. Post-emergence options are limited and work best on 4” or smaller weeds. The PPO herbicides like Reflex or Blazer can be applied post-emergence for small, annual broadleaf weeds, but can cause minor crop injury. Since there was no opportunity to apply a residual herbicide it may be a good idea to include S-metolachlor or Zidua to try and hold back any weeds yet to germinate. Zidua must be applied by the 3rd trifoliate growth stage.

If you planted dicamba tolerant soybeans or Liberty-Link soybeans they can provide excellent post-emergent weed control. Again, I caution using dicamba or Liberty on weeds greater than 4” or in the tank alone as that is the path to herbicide resistance.

There are a million different scenarios you can be faced with in the field and we’re dealing with Mother Nature. That means we can still get rains delaying us even further. If you have questions about your options don’t hesitate to give your local Extension office a call and one of us can work up something specific for your scenario.

 

Matt Morris
301-600-3578
mjmorris@umd.edu