Posts Tagged ‘wheat’

Thoughts on Planting Soft Red Winter Wheat Early

Friday, September 14th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

With corn harvest proceeding much earlier than in ‘normal’ years, many growers could be considering whether to go ahead and plant their wheat or barley crop in the next few weeks. The recommended or suggested planting date varies from county to county based on the Hessian fly-free date. (For more information on Hessian fly see the article by Joanne Whalen “Agronomic Crop Insects – September 7, 2012” in issue 20:25 of the Weekly Crop Update) The fly free dates are Oct. 3 for New Castle County, Oct. 8 for Kent County, and Oct. 10 for Sussex County.

For barley, we have conducted planting date studies in Sussex County comparing early-planted (September 26) barley with a close to suggested planting date (October 7). Our results indicated a fairly consistent 5 percent reduction in yield with September planted barley as compared with the October 7 planting date. Winter weather in the years the study was conducted did not result in significant visual winter injury to the barley so the impact appeared to be more of a general nature. Barley planting was dramatically affected by late planting unlike wheat. Delaying barley planting by just one week to October 15 resulted in a (four year average) yield reduction of over 15 percent and delaying two weeks to October 25 resulted in an over 20 percent yield reduction. Delaying planting barley until November increased the yield potential reduction to over 40 percent.

For winter wheat, experience has to be our guide with respect to planting date. We have evaluated the ideal planting date versus later planting dates but not against a September planting date for wheat. However, we can use both past experiences and basic agronomic knowledge to evaluate the risk involved with early planting wheat.

Since September planting dates are before the Hessian fly-free date for all our counties, we can surmise that the risk of lodging during grain fill will be increased versus planting after the fly-free date. You do need to keep in mind that the fly-free date is based on temperature averages and during warmer than normal falls fly emergence and egg-laying activity can extend past the listed dates. Larval activity can cause lodging, stunting, and yield loss since wheat tillers can be severely injured. In past variety trials, we have seen significant injury and yield reductions on susceptible varieties. Early planting of wheat can increase your risk of an infestation especially if wheat is planted in fields with wheat stubble or in fields next to one with wheat stubble.

For wheat that is planted following dryland corn, the greatest risk this year likely is due to excessive soil residual nitrogen (N); or, if the fall weather is warm and moist, to fall N mineralization from the high levels of nitrate in the dryland corn residue. High fall N availability can lead to excessive growth that will be more susceptible to winter kill or injury if we have a cold, open winter. In past years, we have had many growers asking what they could do about all the excessive top growth that occurs when wheat is planted in September and fertility levels are high. In some areas of the country, the extra foliage is used to graze cattle or sheep but most Delaware farmers do not have this option. The option tried has been to mow off and sometimes remove the excessive top growth. This has at least in part been successful in reducing winter injury but there are significant costs associated with the practice.

Another concern that again depends on fall weather conditions as well as insect populations and a residue of disease inoculum is the development in September planted wheat of disease or insect problems. In particular, barley yellow dwarf virus, which is transmitted in the fall by aphids feeding on the lush growth, can cause more severe injury than spring infections. The lush growth of early planted wheat could be more of an attractant for aphids but certainly will have a longer exposure to the risk of infestation.

All these cautions are not to say that you should never plant wheat or barley before the fly-free date only that you should be aware of the possible consequences and make a decision on when to plant and how many acres to plant from a position of knowledge.

Considerations for Small Grains Weed Control

Friday, September 7th, 2012

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

For no-till fields, a non-selective herbicide needs to be used prior to planting. If grasses are present glyphosate is a better choice than paraquat. Fields worked with a vertical tillage implement for residue management still need a non-selective herbicide. These implements are not weed control tools.

There are few effective herbicides labeled for preemergence applications. Sharpen is labeled but we have limited data in the region to recommend it for either residual weed control or crop safety. Valor can be used at 1 to 2 oz with the burndown application, but there must be a 30 day period between application and planting wheat due to concerns with crop safety.

A few products can be used shortly after the crop has emerged. Axiom and Prowl H2O can be used at crop emergence (Axiom at the spike stage and Prowl H2O at 1 leaf stage); however they need to be tankmixed with other herbicides or followed by postemergence herbicides to provide a broad spectrum of control.

Products that provide postemergence control include: Harmony, Harmony Extra, Starane Ultra, Osprey, PowerFlex, Axial XL, 2,4-D, or dicamba. Others labeled with a limited fit include metribuzin, Finesse, and Maverick.

Aphids Prevention and Barley Yellow Dwarf Management

Thursday, August 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu, Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu and Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

As discussed in the article, Review of Barley Yellow Dwarf in 2012, the spread of barley yellow dwarf virus (BYDV) is completely dependent on aphids transmitting the virus which causes the infection. There are four aphid species occurring in Delaware that are capable of transmitting BYDV from infected grasses into wheat including the English grain aphid, bird cherry-oat aphid, corn leaf aphid, and the greenbug. For photos to help you identify aphids go to: http://kentagextension.blogspot.com/2007/10/know-your-small-grain-aphids.html

Aphids can infest small grain fields in the fall and again in the spring. The number of aphids arriving in fields in the fall is often dependent on the growing conditions the preceding summer. In general, cooler summer conditions with adequate rainfall followed by a warm, dry fall favors aphid development, especially in early planted fields. In drier summers, fewer aphids are produced due to reduced host plant quality. It should be noted that greenbug aphids (which cause direct damage to small grains as well as transmit BYDV) are favored by cool, late summer conditions. Aphid population densities in the fall are also affected by when the first hard frost occurs in relation to wheat seedling emergence. Crops that emerge long before a hard freeze have a greater potential for aphid infestation (and exposure to BYDV). Planting after the fly free date can help to help to manage aphids as long as the freeze occurs when expected. Aphids arriving in the fall will continue to feed and reproduce as long as temperatures remain above 48°F.

In areas where you have seen BYDV in the past, where you are planting early (before the Hessian fly-free date), or you have seen direct damage by greenbug aphids, a commercial applied seed treatment which includes an insecticide would be a good control option for fall infestations. Another option would be to scout fields and apply a foliar insecticide. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. The most important time for controlling aphids in the fall is the first 30 days following emergence. The second most important time is the second 30 days following emergence. So it will be important to scout wheat starting at plant emergence if you plan to use a foliar insecticide for fall aphid management. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp).

Since the incidence of BYDV has not been widespread in past years in Delaware and Maryland, we do not have current data from our area evaluating thresholds to time sprays for fall aphid management. The following thresholds from Kentucky (included in the above fact sheet) could be considered when making a decision to apply a fall foliar insecticide : (a) the first 30 days after planting treat if you find an average of three or more aphids per row-foot, (b) from 30-60 days after planting treat if you find six or more aphids per row-foot, and (c) more than 60 days after the plants emerge treat if you find ten or more aphids per row-foot. Depending on weather conditions, a second application could be needed, especially if temperatures remain warm. As we saw this past season, aphid populations remained high throughout the winter and early spring so you will need to continue scouting if conditions remain mild again. They also indicate that in some years these thresholds may be too high and in others too low but currently this is the best available information. In addition, the risk of BYD infection varies from year to year. At this point, we are still not certain if the 2012 season was just an unusual one for BYD or if we will continue to see an increase in problems. We hope to survey for aphids this fall and evaluate these thresholds under our conditions.

Review of Barley Yellow Dwarf in 2012

Thursday, August 2nd, 2012

Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu, Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu and Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

As we approach the upcoming small grains planting season, it is a good time to discuss barley yellow dwarf management. Barley yellow dwarf (BYD) can be found most years in a few wheat fields in Delaware. It is not uncommon to see a few infected plants, primarily in the spring. In 2012, the number of fields with infected plants appeared to be generally higher compared to most seasons. Impact on yield was variable, though it was estimated that some fields experienced a 5% yield loss. The dry spring weather in Delaware had a larger impact on yield, therefore it was difficult to estimate the true impact of BYD. It is important to understand the causal agents, symptoms, and disease cycle in order to best manage BYD. Barley yellow dwarf is the most widespread virus disease of cereal crops worldwide and can infect other crops such as rye, barley, oats, and corn, though the greatest concern in our area is in wheat.

Causal Agents
There are numerous virus types that actually cause BYD. While the taxonomy of BYD can be complicated, it’s important to note that some strains are more severe than others. The ones that are of greatest concern in our area are (in order from least severe to most severe): BYDV-MAV, BYDV-PAV (severe strain), and CYDV-RPV. CYDV-RPV, cereal yellow dwarf, was named and then later found to be a related strain of BYD. Both CYDV-RPV and BYDV-PAV were confirmed in the samples submitted this past spring from wheat fields in Delaware.

Vector
The BYD viruses are limited to the phloem and can only be transmitted from plant to plant by aphids which have piercing/sucking mouthparts. The infection occurs after aphids feed on infected hosts, such as wild grasses, and then move into and feed on wheat fields. The wild grasses may be infected yet show no symptoms. It can take as little as 12-48 hours from the time aphids feed on the infected grasses until infection has occurred in wheat plants. This can occur anytime that aphids are actively feeding, which would typically be in the fall and spring months when the weather is warmer. Since the spread of barley yellow dwarf depends on aphids, management of the aphids may be helpful in fields with known problems of barley yellow dwarf in the past. Remember that the viruses causing BYD are only transmitted by aphids and are not known to be seed-borne. Read the Aphids Prevention and Barley Yellow Dwarf Management article in this issue of WCU for more on management.

Symptoms
Symptoms include leaf discoloration (Figures 1- 3), shortening of the internodes, and general stunting of the plant. Leaf discoloration typically has a characteristic purple to yellow color. Symptoms become exacerbated by cool weather and high light intensity. Hot spots (cluster of infected plants) may occur near field borders, field corners, or near woods depending on how the aphids moved. To further complicate matters, the plant’s reaction to the infection may vary depending on when the plant was infected and the variety of wheat. Fall infections usually result in more stunting and less tillering while spring infections tend to discolor the flag leaf and are thought to cause little yield loss. Other viruses such as wheat spindle streak and/or wheat soil-borne mosaic virus may infect the plant causing additional symptoms (see Figure 4). The other viruses are not transmitted by aphids. To learn more about the other viruses we encounter in Delaware, read Bob Mulrooney’s article on Viruses in Winter Wheat at: http://agdev.anr.udel.edu/weeklycropupdate/?p=2745.  It’s difficult to identify viruses in the field and samples should be submitted to a lab for testing to confirm virus infection.

Figure 1. Wheat plant infected with barley yellow dwarf (BYDV-PAV).

Figure 2. Wheat plants infected with barley yellow dwarf (BYDV-PAV).

 Figure 3. Wheat plants infected with barley yellow dwarf (BYDV-PAV).

 Figure 4. Wheat Plant infected with BYDV-PAV, CYDV-RPV, wheat spindle streak mosaic virus, and wheat soil-borne mosaic virus.

Figure 5. Close up of wheat infected with BYDV-PAV, CYDV-RPV, and wheat spindle streak mosaic virus.

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.

Small Grain Disease Updates – May 11, 2012

Friday, May 11th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Stripe rust in wheat has been seen in both DE and MD this week. The outbreaks at this time are small and for most of the state wheat is past flowering, so the impact of increased rust development at this time should be minimal. Anyone who applied a fungicide such as Tilt, Prosaro, or Caramba at boot stage or heading will have 2-3 weeks of control, depending when it was applied and when stripe rust spores arrived from the south of us. We have not seen stripe rust in our region for several years. There have been population changes in the rust and it may be more aggressive than what we have seen in the past. We would be interested to know if you see it and what varieties get infected and the severity of the infection. Initially it might be found in a small area or several small areas but if the continued rain and cooler temperatures prevail it could spread quickly. If the wheat is past flowering, check fungicide labels for timing. See the next article for more information on stripe rust and effect on yield as well as fungicide choices.

 Close-up of stripe rust symptoms showing rust pustules in a line or stripe.

 Stripe rust on wheat.

Several more wheat samples were confirmed with Barley yellow dwarf virus. Most of the symptoms are mild but very widespread when it is found in a field. There is little impact on yield as best we know, but there is still much to learn about this virus in this region.

 Barley yellow dwarf showing reddening of flag leaf.

Wheat Disease Update
The following was written by Arv Grybauskas, Extension Plant Pathologist, University of Maryland and adapted for Delaware by Bob Mulrooney, Extension Plant Pathologist, University of Delaware

The risk of scab development this season has been very low and most of our wheat will be scab‐free or, at worst, have infection levels well below 10%. Vomitoxin levels should therefore be well below the 2 ppm threshold for acceptance at mills for most of the crop. The last few days, however, indicate that there are a couple of regions in the state that might still develop some scab. Much of the wheat in the hot spots in eastern Sussex County should be past flowering, and therefore past the label growth stage limitation for treatment with fungicides. However, there may be late planted fields or later developing varieties that can be treated. Leaf rust has been present on susceptible varieties since early spring but has been kept in check by unfavorable temperature or moisture conditions. It still has the potential to develop and spread if temperatures warm into the 80s at daytime and drop only to the mid‐60s at night as long as showers continue or dew and RH is high. Treatment of susceptible varieties may be warranted if leaf rust is present and is threatening to reach the flag leaves.

Stripe rust has also made an appearance this season. It was just confirmed in Dorchester and Caroline Counties in Maryland as well as in Delaware on Monday, May 7. These outbreaks are in small pockets (foci) in fields and their appearance is consistent with long‐distance spore transport from either NC or KY on storm fronts that came through about 2 weeks ago. Stripe rust, unlike leaf rust, requires cooler temperatures. In fact, at temperatures above 77°F lesions will stop producing spores and secondary spread is reduced, and at temperatures above 85°F the pathogen dies. The question now is, what is the potential damage and do I need to apply a fungicide? The short answer is, in my opinion, the worst‐case scenario for either rust disease (susceptible variety, and continuous disease favorable conditions through grain‐fill, and a focus of rust is present in the field now) would potentially produce a 10% yield loss. Realistically the weather will probably be less favorable sometime during grain fill so losses are more likely in the 1‐7% range (Table 1). For either rust disease it takes 7‐14 days to go through an infection cycle (infections giving rise to more spores that cause new infections) under ideal conditions. With that in mind, by the end of the grain‐fill period it is possible that the plants will look nasty (100% of the plants with 40 to 65% flag leaf severity) but between hard and soft dough stages this typically only produces 1 to 7% yield losses.

Table 1. Approximate Yield Loss in Relation to Severity of Rust on the Flag Leaf at Various Stages of Growth

Growth Stage Flag Leaf Area Infected with Rust
10% 25% 40% 65% 100%
Flowering 10 15 20 30 35
Milk 2 5 8 14 20
Soft dough 1 3 4 7 10
Hard dough 1 1 1 3 5

From: Hunger, B. and K. Jackson. Foliar Fungicides and Wheat Production in Oklahoma.

At this stage the only products that can be considered are triazole fungicides. The products registered for scab management, Prosaro and Caramba, are also effective against leaf and stripe rust. Rust susceptible wheat varieties that are still eligible for a fungicide application (pre‐ or just at flower) that are not at risk of developing scab may be sprayed with Folicur or a properly labeled generic tebuconazole product for rust control. Note that Prosaro, Caramba and Folicur have a 30 day Pre‐Harvest Interval as well as the growth stage restriction. Tilt has a 45 day PHI, and therefore would only be an option on earlier stage wheat where the risk of scab was low.

Another Risk of Frost on the Small Grain Crop

Thursday, April 26th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

Although the various forecasting sites differ in what morning will be the coldest over the weekend and into early next week, several suggest the possibility that frost pockets will develop in the Mid-Atlantic region with the greatest risk for the northern areas of the region. The winter wheat crop is beginning to reach heading and will be at one of its most susceptible stages for frost injury. It’s hoped we won’t have freezing temperatures which can completely destroy the seedhead turning it into a watersoaked mass that will not recover (See Photos 1 and 2).

Photo 1. Freeze damage to winter wheat in northern Delaware causing tiller injury, seedhead death, and leading to infection with many secondary pathogens. (Photo taken two weeks after a severe frost.)

Photo 2. Emerging flag leaf following severe frost injury.

Although there’s nothing producers can do to effectively prevent frost damage on their small grains, they should scout their fields to assess the amount of damage a few days to a week or so after the injury occurs. This should help with their marketing plans.

When the frost injures the pollen containing anthers, the seedhead will emerge normally but you may be able to detect white awns or white florets or heads that may remind you of wheat scab (Photo 3). In his “Wheat Disease Update” in this issue of WCU, our Plant Pathologist, Bob Mulrooney, comments on the possibility of scab in wheat this year and indicates that even in irrigated fields the chance is rather low due to the extremely dry spring weather. Therefore if you see heads that remind you of scab, the more likely explanation will be frost or freeze injury. Unfortunately, the impact of this type of injury on yield is severe. A number of good publications are available on the internet showing photos of injury symptoms and discussing yield implications. In particular, the University of Kentucky and Dr. Lloyd Murdock has had a lot of experience with this problem.

Photo 3. White, water soaked florets from frost/freeze damaged wheat in 2012

Wheat Disease Update – April 27, 2012

Thursday, April 26th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

BYDMV
We have had several more reports and a sample of Barley yellow dwarf mosaic virus in wheat. Irregular patches of varying height reductions, yellowing and purple flag leaves indicate BYDMV infection. Since this virus is aphid transmitted there are no controls at this time.

Fusarium Head Blight
With the much needed rain that came and the forecast for more Thursday and possibly Saturday as well some have been asking about the possibility of head blight or scab appearing. The forecast at the present time is the probability is low. The corn residue on the surface needs to be wet for a long time before spores are produced that can infect the wheat at flowering and the temperatures need to be in the mid-70s for significant infection to occur. The temperatures have been and are too low now for infection. As long as the wheat flowers between now and next Wednesday when the forecast is for warmer temperatures the wheat will no longer be in a susceptible stage of development for scab to infect. I think the risk of scab it very low and specific sprays for scab control are unwarranted at this time.

Keep up to date with scab by visiting the website and using the 2012 Predictor. http://www.wheatscab.psu.edu/ This will be important if we should get more rain later in the week.  Make sure the predictor says 2012 across the banner. For some reason my browser is going back to the 2011 site. If you run into the same problem here is the 2012 link http://www.wheatscab.psu.edu/riskTool_2012.html

Leaf Rust & Stripe Rust
More of a possibility is the occurrence of some late season leaf rust and stripe rust. There has been stripe rust reported in NC earlier in the week and now a report of leaf rust and stripe rust from Mt. Holly, VA in university test plots. These reports are fairly close and after a big rain event like we had with some more possibly on the way we may see some develop within the next two weeks. If growers have a variety that is susceptible to leaf rust or stripe rust, there is a chance that we could see more rust two weeks from now depending on the temperatures. Again that might justify application of a fungicide at flowering if you have rust present now or are growing a susceptible variety. With the lack of water there may be undetected leaf rust in the lower canopy and with the recent rain there could be spread to the upper canopy. Be sure to get out and check the wheat before making a spray decision. Prosaro plus a non-ionic surfactant can be applied to wheat until 30 days before harvest; for scab control it needs to be applied at early flowering in 5 gal/A if applied by air. Tilt can only be applied until full head emergence. With the low risk of scab, strobilurin fungicides such as Headline and Quadris could also be considered for protection against leaf and stripe rust as well as tan spot, and the Septoria complex if those diseases are present, which have not been seen because of the dry weather. Be sure to check labels for application restrictions. Our past experience has shown that diseases that appear late (after flowering) usually do not have time to infect the upper leaves that are important for grain fill and reduce yield. If diseases are present in the canopy at flowering there is more of a risk of diseases reducing yield and/or quality of the grain.

Some information from Dr. Christina Cowger from USDA at NC State Unversity indicates that the following varieties are susceptible to stripe rust and might warrant spraying especially if any rust is present now. There are some gaps in our knowledge about susceptibility to stripe rust, so this is a very limited list of known susceptibility for varieties that are grown in the Mid-Atlantic:

Coker 9436, DG Shirley, NC Cape Fear, NC Neuse, NC Yadkin, P26R12, SS520, SS560, USG3209, USG3592, USG3665, SS8404

Freeze Injury
We just received a wheat sample from Kent County, DE with random bleached awns as well as tips of some heads. If you see some irregular bleaching of heads don’t panic about scab. We suspect at this point since no fungus appears to be present on this sample that the damage is from freezing. From spike emergence through flowering, freezing can cause symptoms that range from minimal bleaching of the awns to severe grain yield loss, depending on the duration and degree of freezing.(See Photo 3 in the article by Richard Taylor, “Another Risk of Frost on the Small Grain Crop”, which is in this issue of WCU) If normal kernel development does not occur, then freeze injury can be suspected.

Small Grain Disease Update

Thursday, April 12th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The dry weather and low humidity has been very unfavorable for diseases at the present time. There are still some fields of barley with powdery mildew and leaf rust. If they needed treatments they should have been treated by now. Wheat is looking a bit better in that powdery mildew levels are low and except for some barley yellow dwarf mosaic virus in some areas the crop looks good. Rainfall is desperately needed. The risk for Fusarium head blight or scab is low at the present time. To keep track of the threat of scab be sure to check the website http://www.wheatscab.psu.edu/.

Dry Spring and Small Grain Irrigation

Thursday, April 12th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

Available soil moisture is becoming a critical issue in small grain fields across the entire state. For producers fortunate enough to have the means to irrigate small grain fields, now is the time to replenish the top and subsoil moisture supply, especially for winter wheat. Barley is much further along developmentally (most has already headed out) and matures earlier in the year than does winter wheat. Although I might hesitate to spend the money to irrigate barley that is already past flowering, I would not hesitate to irrigate wheat, which, for the most part, has not reached the heading stage as yet. In some irrigation work we did on wheat a number of years ago, we found that irrigation after head emergence tended to decrease yield potential, although only by a small amount and this decrease may have been related to disease pressure encouraged by higher humidity conditions created when irrigating. My preference for small grain irrigation is to apply enough water before heading to build the topsoil and subsoil moisture levels back to near field capacity. This should provide the water the crop needs to mature since wheat and barley are excellent at using available soil moisture.

As a side benefit, irrigation can help with emergence in the crop following the small grain crop. Without adequate early irrigation, it can prove difficult to rewet the soil, and especially recharge the deeper layers of soil, with enough moisture to adequately support the second crop if the dry weather continues.