Posts Tagged ‘soybean’

Harvest Aids for Soybeans

Friday, September 21st, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

A few herbicides are labeled as harvest aids for soybeans. Glyphosate and paraquat will have the broadest spectrum of control, with paraquat having quicker activity on the weeds. Aim is also labeled, but it has a very narrow spectrum of control. Be sure to read the label of the product you are considering for all the precautions and restrictions. Application of these products is after the pods begin to lose their green color. Applications made this late in the season means they will have little to no impact on reducing weed seed production.

Agronomic Crop Insects – August 31, 2012

Friday, August 31st, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to sample fields on a weekly basis for defoliators including earworm, webworms and all armyworm species. Economic levels of defoliators, continue to be found causing damage.

Soybeans
We can still find fields with economic levels of corn earworm (mainly double crop), stink bugs and defoliators. There have also been a few fields that need a second corn earworm spray for recently hatched larvae.

As soybeans begin to mature and insects are still active in fields, there is always the question regarding the susceptibility of fields to insect damage, especially full season soybeans. So let’s discuss each group and what we know and/or what experience we have from past seasons.

Stink Bugs
As a general rule, soybeans are still susceptible to damage from stink bugs through growth stage R6.5 (“mid R6”). This has been described by some agronomists as the stage when pods are still green and the lower leaves are just beginning to yellow from natural senescence and not drought stress – approximately 10 days after R6.0 (full green seed). It has also been described by others as mid-way from full seed development until maturity. However, there are a few studies from the south indicating that scouting is needed until beans are in the R-7 growth stage (beginning seed maturity) to avoid damage from stinkbugs which can include underdeveloped or aborted seeds, green stem syndrome, reductions in pod fill, seed vigor and viability, yield loss and a reduction in the storage stability of harvested seeds. In New Castle and Kent Counties, we are starting to see fields with high levels of Brown Marmorated Stink Bugs on field edges of full season soybeans (most fields are growth stage R6). If a treatment is needed, an edge treatment (one spray boom width – at least 50 ft wide) was effective last year, and we are working on a regional project to document the outcome of this strategy in 2012. There are also areas of the state with high native brown and green stink bug populations so be sure to scout for them as well.

Corn Earworms
As far as corn earworms, the experience of most entomologists in the region is that soybeans are most susceptible to corn earworm damage when beans are in the R-5 and early R6 stages although there are cases where we see damage through the R6.5 stage. As of Aug 27, a number of our corn earworm pheromone traps where still catching high numbers of moths so it is too early to say for sure if populations are on the decline (http://ag.udel.edu/extension/IPM/traps/latestblt.html). In addition, trap catches in North Carolina are still high and weather patterns could bring these moths north. We sometimes see a late summer/early fall corn earworm flight which could result in new worm infestations. Most full season fields should be in the “bug-safe” late R6-R7 stage if this occurs; however, double crop soybeans will still be susceptible to attack.

Defoliators
When it comes to defoliators, especially soybean loopers, it is important to keep scouting for them as well through the R6.5 stage. We continue to find pockets of soybean loopers and beet armyworms. If leaves are beginning to yellow up the stem, not from drought but from the maturity process, and there are any pods on the plant that are beginning to yellow, the field should be safe from most defoliators. The exceptions would be grasshoppers and bean leaf beetles, which can scar pods later in the growth stage of soybeans.

NOTE: As we get closer to harvest, be sure to check all labels for the days from last application to harvest as well as other restrictions.

Small Grains
With the increase in no-till wheat acreage as well as our typical rotation of wheat following corn, it will be important to consider a number of insect pests that can present problems. The following article provides a good review of insect pests that pose a threat to wheat in the fall including aphids, the wheat curl mite, Hessian fly and fall armyworm. (http://www.uky.edu/Ag/kpn/kpn_08/pn080825.htm#wheins). In addition to the insect pests listed in this article, true armyworms have been a pest in the past as well as slugs if we have a wet fall.

Nitrogen Fertilization and Irrigated Soybean Production

Friday, August 24th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

A number of people have been asking about applying nitrogen (N) fertilizer to irrigated soybeans so I thought I would make a few comments about the practice in case they might help you in making the decision as to whether to spend the money in hopes of getting a yield response.

To begin with, I have tried this practice on both full-season and double-cropped soybeans at one time or another. I’ve tried applications of N at both 25 and 50 lbs N/acre at R2 (full flower) and R4 (full pod) and for double-cropped soybean I’ve tried these rates broadcast at planting. I never got a significant response to the treatments although for double-cropped soybeans I was close to seeing an increase in early plant height and pod set. For yield, the treatments were all within a bushel or two of each other.

That being said, I should point out that significant responses have sometimes been reported from down South but only when the N was applied through an irrigation system (for the reports I’ve seen) and when both boron (B) and N were applied in combination. At the time of the research that I conducted, we did not have the capability to apply N to my plots through the irrigation system. I had to apply the N with a back-pack CO2 sprayer while walking through the soybeans. I did have the studies irrigated immediately after applying the treatments to minimize the chance of foliar burn. I remember hearing from the southern researchers that they felt that the leaf damage caused by walking on N or applying N with a ground rig would negate the slight yield response that they were able to obtain using fertigation. I also did not apply B along with the N which may have also reduced the chances of obtaining a positive yield response since B is important in sugar transport and in helping flower set.

I understand that some people suggesting that N should be applied to irrigated soybeans are suggesting the inclusion of sulfur (S) (probably as ammonium sulfate) along with the N. This makes some sense from a biological point-of-view in that the plant requires enough S to make the S-containing amino acids required for protein synthesis. However by the time soybeans reach the full bloom or full pod stage, the root system has reached or will soon reach its deepest penetration of the soil. Even the sandy soils in Sussex County, Delaware, were found to have large quantities of S (typically 300 to 500 lbs S/acre) stored in the clay lenses found in the 1 to 2 foot depth of soil and soybean roots should be able to tap into this S reserve by reproductive stage.

Let me summarize below some of my thoughts on trying to increase soybean yields with N fertilizer.

● If soybeans already have matured to the full seed stage (R6) where a full size seed is found in a pod at one of the four upper most nodes with a fully expanded leaf, it is much too late for N application to increase yield potential in my opinion. All the research that I’ve seen involves the application of N at full bloom (R2) to full pod (R4) stage.

● I doubt that the addition of S as ammonium sulfate is going to increase your chance of obtaining any return on your investment since soybeans are very likely to have more than an adequate supply of S available by this time of year due to root growth. An exception would be where there is a root restricting compaction layer in the top 12 inches of soil but in this case the chance that fertilizer will improve yield is very low.

● If your expected yield potential is not at least 60 to 70 bushels/acre, N fertilization will not help. Next year, try using either the liquid seed Bradyrhizobia inoculants or some of the new graphite soybean inoculants since the new strains available can really help increase your yield potential.

● If you still plan to apply N fertilizer to your soybean crop, be sure to add about 0.5 pound of boron per acre. The data I’ve seen where a yield response was obtained with late season (R2 or R4) N application were always where B had been included with the N.

● I would suggest limiting any N application to no more than 30 lb N/acre since levels higher than this have often been shown to reduce the nitrogen fixing activity of the soybean nodules. If this occurs, you’ll be trading dollars essentially since the nodules will either stop N fixation or reduce fixation to a degree where the plant will need the N you apply just to produce the original crop’s yield potential. Some studies with early season manure applications have shown yield reductions because the crop ran out of N during the reproductive stages and had to reinitiate nodulation because the crop ran out of available N.

● Do not consider N applications on non-irrigated soybeans. Keep in mind that in the case of a dryland soybean crop, the overall limiting factor is water availability not nutrient availability.

● Also if your field has a history of soybean cyst nematode (SCN) infestations, do not add N fertilizer since SCN will be your yield limiting factor not N or S or B fertilizer.

Charcoal Rot of Soybeans

Friday, August 17th, 2012

Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

Charcoal rot was diagnosed on soybean plants in early August, much earlier than we normally see this disease. We usually see charcoal rot near maturity, and these plants had small pods about ¾ inch in length. Charcoal rot is a stem rot caused by Macrophomina phaseolina, a soil-borne fungus with a wide host range, infecting many bean species and corn. Charcoal rot often shows up in Delaware fields in the late summer season, as soybeans mature, especially in drought stressed beans. Plants may show a loss of vigor or smaller than normal leaves. Leaflets may yellow, but stay attached at the petioles. Dark lesions may extend up the stem from the soil line. Eventually, the fungus colonizes the water-conducting tissues of the bean stems, and plants die. The fungus produces small survival structures called microsclerotia; I think of them as small rubber-band-balls of fungal strands. The numerous small dark microsclerotia look like charcoal dust, giving the disease its name. These microsclerotia can survive in soil and debris for several years; however, they do not survive well in wet soils. The fungus can survive on seeds in small cracks. Often, infections occur early, when soil moisture is good, and symptoms become obvious late in the season as plants become stressed from drought. To control, rotate away from fields that have been heavily infested, for at least two years. Irrigation and cultural practices such as good fertility and average seeding rates should help avoid the stress that brings on symptoms of dieback. There are no good resistant varieties, but breeding work is ongoing. Foliar fungicides are not effective for controlling charcoal rot.

Dayflower in Soybeans

Friday, June 15th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Last fall there was a sample of spreading dayflower brought into the office (http://www.ppws.vt.edu/scott/weed_id/comco.htm). The field was treated once or twice with glyphosate and the plants were not controlled. The grower was concerned about resistance. As it turns out, dayflower is one of those species that glyphosate will not control. FirstRate is the best option for dayflower control in soybeans.

Double-Cropped Soybean Burndown Considerations

Friday, June 15th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

As we move into small grain harvest and considering weed control prior to planting soybeans, we have limited options. And we need to view the options as the best of a difficult situation and be realistic on what we can expect for control. Some things we need to consider are:

Weeds present at time of planting. Horseweed is the one of biggest concern, but horsenettle, ragweed, lambsquarters, grasses, etc are also present. Which of the weeds present can also be controlled after the soybeans have emerged? Are Liberty Link soybeans used, because glyphosate could be used prior to planting and then Liberty (or Ignite) used postemergence. Need to decide what problem is most critical and develop a program to target that species.

What herbicides options are available: product availability, crop rotation constraints, or environmental/soil issues. Liberty/Ignite might be the best product for some of these fields, but it is in very short supply and may not be available. Kixor products may be an option for some fields with medium-texture soils. Always consider what will be planted in the field next season and be sure there is adequate time for the intended crop rotation (it maybe only 9 months until you plant the 2013 crop!)

When glyphosate-resistant horseweed is present and it is the species you are targeting for control, you will need to rely on a herbicide other than glyphosate to control them. No product will consistently control horseweed this late in the season; and we are compounding the problems with cutting the plants off with the combine. If Liberty (or Ignite) is not available and your soil texture prevents use of Kixor, one option to consider is Gramoxone in combination with Canopy, along with crop oil concentrate and nitrogen fertilizer. Canopy is the product I would suggest because it contains metribuzin and chlorimuron. Metribuzin may improve the effectiveness of the Gramoxone. The chlorimuron at the rates used prior to planting, will have some activity on the horseweed as well. The use of crop oil and nitrogen sometimes improve Gramoxone activity, but will also maximize the effectiveness of the chlorimuron. This program is not ideal, but in my experiences it provides the best level of control under many situations. Perennial species (horsenettle or yellow nutsedge) will probably regrow and they will need to be controlled with a later glyphosate application.

If horseweed is not present in the fields then often glyphosate plus a residual herbicide may be the best option for it will control summer annual broadleaves and grasses, as well as start to “work on” the perennials. But since most plants have been damaged during small grain harvest, glyphosate activity may be reduced. But glyphosate will be used again after the soybeans have emerged and should improve overall control.

Postemergence Control of Glyphosate-Resistant Horseweed

Friday, June 15th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Options for controlling horseweed resistant to glyphosate after the soybeans have emerged are very limited. Liberty Link soybeans are an exception, because Liberty 280 is fairly effective on horseweed (be sure to keep your rates up).

For non-Liberty Link soybeans the options are very limited. Liberty Link soybeans can be treated with Liberty (or Ignite) for fair control of horseweed. For non-Liberty Link soybeans, FirstRate or Classic are effective on small, newly emerged seedlings. However, neither will consistently kill large horseweed plants, nor plants that were “burned off” and are recovering (FirstRate is better option than Classic after the soybeans have emerged). These herbicides may provide some suppression, but results have been quite erratic the past few years. Horseweed plants are generally not very tolerant of shade and most soybeans will begin to canopy over the horseweed and out-compete them. Additional glyphosate applications will provide some suppression of horseweed and sometimes the soybeans have a chance to outcompete them.

Glyphosate Tankmixed with Reflex

Friday, June 15th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

There are many situations where both fomesafen (active ingredient in Reflex) and glyphosate will complement each other for weed control. Syngenta has a premix of fomesafen plus glyphosate called Flexstar GT. Also, Reflex and glyphosate can be tankmixed, but there have been some situations of these two products not mixing well. The following is an article from Ken Smith from University of Arkansas entitled “Problem Solving Incompatible Tankmixes of Glyphosate and Reflex®”

“Some growers have experienced cottage cheese spray mixtures when Reflex® and glyphosate were tankmixed in an effort to burn down existing weeds while applying Reflex® prior to cotton or soybean planting.

“It seems that the potassium salts of glyphosate (WeatherMax, Touchdown, PowerMax etc.) are not very compatible with Reflex® . . . . Many of the generic glyphosate formulations are isopropyl or diammonium salts (not potassium salts) and will mix fine. A quick check of the label will give the salt used in the formulation. 

“If a mistake is made and Reflex® and the potassium salt of glyphosate is mixed and found to be incompatible, it can likely be brought back into solution by adding household ammonia. Start with 1% ammonia and begin agitation. More ammonia may be added if needed.”

Control of Volunteer Corn in Soybeans

Friday, June 15th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

I have looked at some soybean fields with heavy volunteer corn pressure. The corn is Roundup Ready, so none of the glyphosate formulations will control it. The postemergence grass herbicides (Select Max, clethodim, Assure II/Targa, Fusilade, or Poast) will control emerged corn. In a trial at Purdue University, control was slightly better when these products were applied to 10 to 15 inch tall corn compared to 22 to 25 inch tall corn. If tankmixing these products with glyphosate, many of them recommend including an adjuvant and nitrogen regardless of the glyphosate formulation. Be sure to read the labels.

Small Grain Harvest Began Early

Friday, June 1st, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

Believe it or not, a number of growers have begun to harvest barley around the state and our winter wheat crop is advancing in maturity very rapidly. This is the earliest that I can remember growers beginning barley harvest and if wheat comes on as early as I think it will we also will have a record early harvest season for wheat. Although the very much shortened growing season for the small grains could signal lower yields for barley and wheat, I think we will find that double-cropped soybeans will have at least the potential for excellent yields. Weather and/or irrigation availability will determine the final yield potential for the double-crop soybean crop but with as much as a two week longer growing season, the soybeans could help make up for any shortage in the small grain yield.

So the message here is to not feel that you don’t need to plant soybeans as soon as possible after the small grain crop is harvested. Although the extra time may seem as if it gives you the opportunity to not be as pressured to plant soybean quickly, there is the possibility of a substantial reward for remaining aggressive in planting the soybean crop as soon as possible after removing the small grains. With the current price of soybeans, that reward could mean a significant return to you come this fall.