Posts Tagged ‘18:23’

WCU Volume 18, Issue 23 – August 20, 2010

Friday, August 20th, 2010

Volume 18, Issue 23 – August 20, 2010

PDF Version of WCU 18:23 – August 20, 2010

In this issue:

Vegetables
Vegetable Crop Insects
Late Summer and Early Fall Considerations for Vegetable Growers
Cucurbit Downy Mildew Update
Watch for Tomato Late Blight
Scout Lima Beans for Disease
Pumpkin Spray Programs

Agronomic Crops
Agronomic Crop Insects
Soybean Rust Update
Charcoal Rot is Showing Up in Soybeans
Plan Ahead to Deal with Corn Stalk Rots, Ear Rots and Toxins in Grain
The Decisions You Make Pre-Season Have the Greatest Affect on Wheat Scab and its By-Product Vomitoxin
Grain Marketing Highlights

General
Insecticide Updates
Reducing Weed Seed Production in Harvested Fields and Non-Cropped Areas

Announcements
Twilight Tour with Bees – August 30
Pole Lima Bean Open House – September 21
Regional Women in Ag Conference – January 25-26, 2011

Weather

Regional Women in Ag Conference

Friday, August 20th, 2010

January 25-26, 2010
Dover Downs Hotel and Casino
Dover, DE

More information is available at: http://ag.udel.edu/extension/kent/womeninag.htm  
or contact Laurie Wolinski at (302) 831-2538

Reducing Weed Seed Production in Harvested Fields and Non-Cropped Areas

Friday, August 20th, 2010

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

Many annual and some perennial weeds are beginning to flower now, particularly those that emerged early in the summer. Removing now the flowering portions of the plant or seed heads will prevent most of these plants from producing mature seed. If these plants are mowed off, they are likely to regrow and eventually produce seed, but the quantity of seed produced will be dramatically reduced. Many of these fields will need at least one additional mowing to prevent seed production. However, delaying a mowing for a few weeks will allow a greater proportion of the developing seeds to mature and contribute to the seedbank. Another option is a herbicide treatment, however few herbicides will kill these large weeds. Glyphosate is one option, but be sure to match the herbicide rate with size and stage of the weeds.

Insecticide Updates – August 20, 2010

Friday, August 20th, 2010

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

Belt SC – (flubendiamide) – This federal label was recently expanded to include soybeans and legume vegetables. However, as of Aug 17 it is not included on the Delaware Department of Agriculture’s state registration list. Materials must be labeled both federally and in-state to be used on a crop. We will let you know when it has received a state label as well or you can check their website:
http://www.kellysolutions.com/de/pesticideindex.htm

Bayer Agrees to Terminate All Uses of Aldicarb (News Release)In a recent EPA Pesticide Update released from the EPA Office of Pesticide Programs, they indicated that EPA and Bayer CropScience have reached an agreement to end use of the pesticide aldicarb in the United States.

More information: http://www.epa.gov/oppsrrd1/REDs/factsheets/aldicarb_fs.html

To view the dockets: http://www.regulations.gov

Grain Marketing Highlights – August 20, 2010

Friday, August 20th, 2010

Carl German, Extension Crops Marketing Specialist; clgerman@udel.edu

Countdown to Harvest
The first load of new crop corn on the Eastern Shore was delivered on or about August 5. Reports are also trickling in concerning new crop corn deliveries now being made in the Corn Belt. The 2010 harvest is now underway. It is going to be early and near record breaking for both U.S. corn and soybeans. A Perdue grain merchant predicted this morning that the Eastern Shore will be heavily into harvest by next week. The same is true for large portions of the Corn Belt.

The extent of harvest pressure on corn and soybean prices is likely to be minimized by production concerns in other parts of the world. Russia is in the news again concerning the possibility of having to make large increases in the amount of grain imported for the 2010/2011 marketing year due to their worst drought in over 100 years. The most recent estimate for Russian grain production indicated their 2010 grain harvest to be slashed by at least one-third of normal.

USDA Export Sales Report 08/19 07:35
Pre-report estimates for weekly export sales of soybeans (combined old-crop and new-crop) ranged from 69.8 to 80.8 million bushels. The weekly report showed total export sales of 82 million bushels, with old-crop sales of 6.7 million bushels bringing year-to-date sales to 1.51 billion bushels, above USDA’s demand projection of 1.47 billion bushels. Total shipments of 18.3 million bushels were below the 21.8 million bushels needed this week. This report should be viewed as bullish.

Pre-report estimates had weekly corn export sales at 51.2 to 66.9 million bushels. The weekly report showed total export sales of 107.3 million bushels, with old-crop sales of 23.4 million bushels bringing year-to-date sales to 2.06 billion bushels, above USDA’s revised demand projection of 1.975 billion bushels. Total shipments of 39.6 million bushels were below the 76 million bushels needed this week. This report should be considered bullish.

Pre-report estimates for wheat ranged between 34.9 to 45.9 million bushels. The weekly report showed total export sales of 51.9 million bushels, well above the 19.3 million bushels needed this week to stay on pace with USDA’s revised projection of 1.2 billion bushels. Shipments of 21.2 million bushels were below the 24.8 million bushels needed this week. This report should be viewed as bullish.

Market Strategy
Currently, Dec ‘10 corn futures are trading at $4.34 per bushel; Nov ‘10 soybean futures at $10.23; July ‘11 SRW wheat futures at $7.16 per bushel; Dec ‘11 corn futures at $4.39; and Nov ‘11 soybean futures at $10.07 per bushel. These prices represent good pricing opportunities for both the 2010 harvest and for pricing a portion of the 2011 crop.

World production concerns will make it necessary to revisit sales decisions on any unsold portion of the 2010 harvest later in the season to determine whether storage is warranted.

For technical assistance on making grain marketing decisions contact Carl L. German, Extension Crops Marketing Specialist.

The Dexisions You Make Pre-Season Have the Greatest Affect on Wheat Scab and its By-Product Vomitoxin

Friday, August 20th, 2010

Arvydas (Arv) Grybauskas, Extension Plant Pathologist, University of Maryland; arvydas@umd.edu 

Fusarium head blight (FHB) or head scab is a serious disease of small grains that does not develop every season. As a consequence we tend to drop our guard or just operate as we always have done because it is not front and center in our minds. The last big one was now two seasons ago, and only a few growers experienced vomitoxin (DON) levels above 1 ppm last season. Vomitoxin is the toxin produced by the fungus that could result in rejection of loads at the elevator or mill. Diseases are always the result of a combination of factors. We have a general rotational sequence of field crops that puts us at risk of scab every season. A serious outbreak of scab is highly dependent on weather conditions just prior to flowering through grain development. Weather is obviously something we cannot control but that does not mean there aren’t things we can do to reduce the risk of scab and ensure a harvestable crop.

We have been conducting scab management research with funding from The Maryland Grain Producers Utilization Board, the US Wheat and Barley Scab Initiative and the University of Maryland Experiment Station, which illustrates the importance of integrating management practices. The data that follows demonstrates that:

1) No one tactic (ie. fungicide or resistant variety) is sufficient in a serious outbreak;

2) Fungicides, although vastly improved and still an important tactic, provide the smallest increment in reducing DON;

3) Distance to a source of inoculum (primarily infested corn stubble) has the largest effect on scab, followed by resistant varieties and fungicides.

4) Management of scab is best achieved by integrating practices that minimize in-field inoculum and take distance to a local source into consideration, selecting varieties with some resistance, and using fungicides when needed.

The management research was conducted using 6 wheat varieties representing the range of resistance to scab that was known and was commercially available. To keep things brief we will focus on DON levels to illustrate the effects of resistance and other management practices. Varieties were ranked on the basis of DON levels based on trials conducted over several season in inoculated nurseries and naturally infected State wheat trials. A percentile was then calculated so that a variety with a 0.9 percentile means it is in the 90th percentile or is in the top 10% of resistant varieties tested. A variety that had a percentile of 0.1 means it had high levels of DON on average and is in the bottom 10% of tested varieties. Wheat trials were planted with all six varieties at the Wye and Beltsville facilities of the University of Maryland Experiment Station. All sites were turbo-tilled and each location had a planting where the previous crop was corn and another planting where the previous crop was soybean. A major difference between locations is that wheat planted into soybean stubble at the Wye was surrounded by corn, whereas at Beltsville the nearest corn stubble was about 300 ft to the south for the soybean-wheat rotation. This difference greatly affected scab development and DON levels. At the Wye wheat following soybeans had DON levels only 10% lower than wheat following corn, whereas at Beltsville DON levels were 40% lower in wheat following soybeans (Table 1). This illustrates that the most important source of spores for scab development is within the field, and that nearby sources provide background levels of spores that can still infect a crop regardless of rotation. Nevertheless, by reducing the spore load with a rotation away from corn (or wheat) even in a very disease favorable year and a highly susceptible variety, DON levels are close to 1 ppm and could be mixed with clean seed to be marketed.

Variety selection is clearly a very important tool to reduce the potential for DON levels that could make or break your season. Even varieties in the middle percentiles have a huge advantage over highly susceptible ones. Yet no variety by itself under high disease potential consistently had DON levels below 1 ppm. Fungicides provided another increment of DON reduction averaging about 40%. Yet 40% of 2 ppm is still above the stringent FDA guideline of 1ppm for human consumption. Combining resistance to DON from a variety that is in the 75th percentile or above with the recommended fungicides can get us very close to 1 ppm or at least to levels that could be mixed with clean seed to market. Combining all three tactics, rotation with resistance and fungicides when needed is the best way to keep scab and DON from destroying your crop. Rotation and variety selection is a pre-season management decision. The time is now to make the best management choices, a table on varietal rankings based on DON levels is provided to help make the choices.

Table 1. Scab Management Research 2009 – Effect of rotation, cultivar and Prosaro fungicide on DON (ppm) in wheat. Dr. A. Grybauskas and E. Reed, Univ of Maryland.


Highest risk of scab following no-till corn. Wye 2009 soybean site within 100 ft of corn stubble, therefore risk was practically unchanged. Whereas at Beltsville, source of spores (corn stubble) further from soybean site and disease reduced dramatically.

Summary of Vomitoxin (DON) Levels Due to Scab Infection and Percentile Rankings of Cultivars in Wheat Trials in Maryland

 

1The proportion of cultivars that have higher levels of DON under the same conditions, eg. 0.9 = 90th percentile where 90% of the population had higher levels of DON, or entry was in the top 10% of the population. Percentiles calculated over all available trials.

Red Text top 30% based on DON assessed over all trials.

Data from Dr. Jose Costa, U of MD; includes inoculated and misted scab nurseries 2008 & 2009, and naturally infected State Wheat trials at Queenstown and Keedysville in 2009.

Summary prepared by Dr. Arv Grybauskas, U of MD (revised 5/19/2010).

Note: Resistance to the visual blighting, bleaching of spikelets and poor grain fill is not completely correlated to resistance to DON development. Thus some low DON cultivars still suffer yield loss due to scab. For example, Pioneer 26R15 has greater resistance to symptom development than Chesapeake but Chesapeake tends to have lower DON levels.

Plan Ahead to Deal with Corn Stalk Rots, Ear Rots and Toxins in Grain

Friday, August 20th, 2010

Arvydas (Arv) Grybauskas, Extension Plant Pathologist, University of Maryland; arvydas@umd.edu

Corn harvest will begin earlier this season due to the high average temperatures increasing the speed with which growing degree-days (GDD) have accumulated. Typically in seasons characterized by high temperatures and droughty conditions there is an increase in stalk rots and certain ear rots. Most notably two fungal ear rots that can produce toxins in the grain, Aspergillus and Fusarium ear rot, are favored by these conditions. The more dangerous of the two is Aspergillus. Aspergillus infected kernels can contain the carcinogenic toxins known as aflatoxins.

Aspergillus is a fungus that is highly tolerant of high temperatures. Because of its high temperature tolerance it is the most prevalent ear-infecting fungus during hot dry conditions. The fungus survives is soil and crop debris and is spread to silks by wind and insects. The use of certain types of BT corn have helped reduce the incidence of Aspergillus infection by reducing the insect-associated infections but direct infections are still possible. Stressed corn appears to be more susceptible to infection. Typically only a few kernels near the tip are infected by Aspergillus, but tolerance levels for aflatoxin are in parts per billion (e.g. 20 ppb for human consumption). A blacklight is commonly employed as a quick preliminary test for aflatoxin contamination. A sample of cracked or coarsely ground kernels is illuminated with a blacklight and viewed for a yellow-green fluorescence. It is important to know that the fluorescing material is not aflatoxin itself but often is an indicator of (correlated with) aflatoxin. Other material will fluoresce under blacklight like corn glumes (a.k.a. beeswings), certain weed seeds, and uninfected kernel tips, so that false positives are possible. Since the advisory limits are at ppb levels false negatives are also possible with the blacklight test. There are commercially available rapid test kits that provide better and in many cases quantitative detection, as well as commercial labs that will test for toxins.

Similarly, Fusarium ear and kernel rot is favored by high temperatures and droughty conditions especially when they occur near flowering. There are several species of Fusarium that are involved but generally are different from the primary species that cause scab in wheat. Fusarium ear and kernel rot is important because of a production of a class of toxins known as Fumonisins. Fumonisins are known to cause equine leukoencephalomalacia, “blind staggers” in horses and pulmonary edema in swine, and have been linked to human cancers in other parts of the world. Different tests are required to detect Fumonisins.

Stalk rots caused by fungi leading to premature lodging are also generally favored by stressful growing seasons. In general any stress on the corn plant can lead to insufficient capacity of the plant to provide photosynthate to the developing ear. When the capacity is exceeded the plant mobilizes stored carbohydrates from the stalks to fill the demand. This leads to premature senescence of stalk tissue and predisposes the plant to colonization by any number of opportunistic stalk rotting fungi.

Regardless of the stalk rot or ear rot, there are a few things that can be done to minimize losses and improve the harvestablity. First, harvest the corn at high grain moisture (25 to 27%), and make sure the combine is adjusted properly to minimize cracking. Harvesting as early as practical reduces the time that the damaging fungi have at colonizing the tissue. This reduces lodging due to stalk rots, kernel infection and toxin development. Cracked kernels are more susceptible to post-harvest colonization and toxin development. You can also use simple pre-harvest stalk testing to determine which fields are at greater risk for lodging to schedule harvest accordingly. You can pinch stalk internodes to determine a percentage that are soft and likely to lodge if left in the field, or you can use the push test. The push test is simply pushing corn stalks at arms length and determining the percentage that break. In both cases the greater the number of plants and sites scouted the better the information. A rule of thumb I like is 10 stalks in 10 sites for every 10 acres. It is also important to note that fungicides used near tassel will not have a direct effect on stalk rotting. If there was a foliar disease then fungicides reduce the stress associated with the foliar disease and this indirectly reduces stalk rotting. There is no fungicide residue available by the time stalks are predisposed to stalk rotting fungi to directly affect the colonization by these fungal organisms.

Secondly, to reduce the damage from ear rots and in particular to keep toxin development to a minimum, after harvesting corn at high moisture with careful attention to reduce cracking, dry the corn as soon as possible (within a day or two) to 15.5% moisture or lower. The ear rotting fungi continue to grow in high moisture corn in the bin. Controlling moisture and temperature of harvested corn is the most cost-effective method of preventing spoilage.

Figure 1. Healthy stalk (left), stalk rot (right).

Figure 2. Fusarium ear rot.

Charcoal Rot is Showing Up in Soybeans

Friday, August 20th, 2010

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

Charcoal rot was identified this week on a late Group III soybean variety. Charcoal rot is favored by dry weather that follows wet weather soon after planting. Usually irregularly sized patches of infected stunted, dying plants are seen in the field, but sometimes you can see individual plants in the row infected, and dead or dying. When this happens you see scattered plants dying either singly or several in a row flanked by healthy ones. Carefully dig up plants and look at the roots and lower stem. They will often be gray and if you scrape the gray lower stem or roots you can see many small black flecks that look like the tissue was covered with powered charcoal. Often if the plants are dead and you split the stems the pith is full of these tiny microsclerotia as well. Rotation will help to some degree as well as planting later maturing varieties. This disease will always be a threat to Group II and III soybeans planted full season, if planting in fields previously cropped to soybeans when a season is wet early and then the crop is drought stressed during pod fill like this year. Double-crop soybeans are not usually infected with charcoal rot. We will likely be seeing more of this disease as the month progresses.

Charcoal rot on split soybean stem. Note the powdered charcoal appearance of the microsclerotia imbedded in the stem tissue and scattered in the pith.

Soybean Rust Update – August 20, 2010

Friday, August 20th, 2010

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

It looks like most soybean areas in the US may escape soybean rust this season. It has yet to be seen on soybeans in the South. To date it has only been observed on kudzu.

The linked pdf file shows the 30-day Soybean Rust Risk Outlook.

Agronomic Crop Insects – August 20, 2010

Friday, August 20th, 2010

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

Alfalfa
Be sure to watch for fall armyworm, beet armyworm, webworms and corn earworm, which can quickly defoliate alfalfa. Mixed populations of larvae can be found in fields and controls should be applied before significant defoliation occurs. Also, larvae must be small to achieve effective control.

Defoliators can be destructive in last cuttings, especially during drought conditions. When defoliators are present, early harvest may eliminate the problem. Although there are no specific thresholds, as a general guideline if the crop is more than 2 weeks from cutting and 25 to 30 percent of the terminals are damaged, treatment is suggested.

Soybean
Be sure to continue to scout carefully for earworms during the next few weeks. Local trap catches as well as traps to our south continue to have high moth activity.

Economic levels and hot spots of high levels continue to be found in fields throughout the state but they are not present in every field. In addition they are being found in both full season and double crop fields so the only way to know if you have an economic level will be to scout. In the past, we have used the treatment threshold of 3 corn earworms per 25 sweeps in narrow fields and 5 corn earworms per 25 sweeps in wide row fields (20 inches or greater). However, these are static thresholds that were calculated for a 10-year average soybean bushel value of $6.28. A better approach to determining a threshold is to access the Corn Earworm Calculator (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter. With the recent rains, I have been asked if it will help to reduce/and or crash populations. Although extremely small larvae may be susceptible to the rains, we have not seen any indication of disease in worms so it is too early to decide if weather will play a role in moderating populations.

As far as defoliators, grasshoppers and bean leaf beetles are starting to cause economic levels of defoliation in some full season fields so be sure to watch for these two insects as well as corn earworm. Remember, that in addition to defoliation both can feed on and/or scar pods. There are also beet armyworms present in some fields. It also appears that in some cases they may be confused with yellow striped armyworms. The following links have pictures of both larvae :

Yellow Striped Armyworm
http://www.ent.iastate.edu/imagegal/lepidoptera/armyworm/nystripedarmyworm.html

Beet Armyworm
http://www.utextension.utk.edu/fieldcrops/cotton/cotton_insects/images/BAW-larva-close.jpg

Kentucky Pest News – Aug 10 newsletter – has good pictures of defoliators in soybeans –http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_10/pn_100810.html

Although population have been lower this season in our area as well as in a number of Midwestern states, you should continue to scout for soybeans aphids, especially in later planted fields. This aphid can increase if the temperature turns cooler. Remember the threshold is 250 aphids per plant with the populations rising up until the R-5/ and in some cases R-6 stage of plant development. You should also watch for beneficial insect activity that can help control populations.

Lastly, although populations have been moderate this season, there are reports of an increase in populations of green stinkbugs. You will need to continue to scout for stinkbugs in fields that are in the pod development and pod fill stages. Economic damage is most likely to occur during these stages. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. We are currently following the same guidelines that are being used in Virginia. Thresholds are based on numbers of large nymphs and adults (green and/or brown stink bugs), as those are the stages most capable of damaging pods. As a general guideline, current thresholds are set at 1 large nymph/adult (either brown or green stink bug) per row foot if using a beat sheet, or, 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans.

For more information on what is occurring in Virginia, you will want to look at the Virginina Ag Pest Advisory (http://www.sripmc.org/Virginia/).