2013 University of Delaware Weed Science Field Day

Wednesday, June 26, 2013
University of Delaware
Research and Education Center
(old office building)
16686 County Seat Highway
Georgetown, DE 19947

Registration begins at 8:15 at the Grove near the farm buildings.

A variety of herbicide programs for conventional tillage and no-till production are being evaluated. Many of the registered corn and soybean herbicides will be shown on the tour. The strengths and weaknesses of various approaches to weed management will be discussed. In addition, we have a number of trials integrating cover crops with chemical weed control. Herbicide evaluations for sorghum, watermelon, sweet corn and other vegetables are underway but these will not be part of the tour.

Lunch will follow the tour.

Recertification credit for pesticide applicators and Certified Crop Advisor are also available

There is no charge for this event. To register, please call Karen Adams at 302-856-7303 ext. 540 or adams@udel.edu. For more information, contact Dr. Mark VanGessel at 302-856-7303 or mjv@udel.edu.

University of Delaware Welcomes New Extension Plant Pathologist

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

My name is Nathan Kleczewski and I am the University of Delaware’s new Extension Specialist in Plant Pathology. I am really looking forward to being a part of the UD Extension team, and am excited to work to address Delaware issues with plant diseases. I earned a B.S. in Plant Science from the University of Wisconsin-Oshkosh in 2004 and a Ph.D. in Plant Pathology from The Ohio State University in 2009. I worked as a Postdoctoral researcher at Indiana University from 2009-2010, and Purdue University from 2010-2012. I worked as a Research Plant Pathologist for FMC prior to starting this position. Through my extension and research activities, I will assist growers improve crop productivity by combating disease. My main focus will be field crops, but undoubtedly my role will expand as I settle in. My office is located in 145 Townsend Hall on the University of Delaware’s main campus, but I will also be in the fields this summer meeting growers, agents, and other professionals. You can reach me by email nkleczew@udel.edu and phone (302)-300-6962. Feel free to contact me with any plant pathology related questions!

Effect of Cereal Cover Crop Species on Full Season Soybean Performance

Robert Kratochvil, Extension Specialist – Grain and Oil Crops, University of Maryland; rkratoch@umd.edu

Does choice of cereal cover crop species affect full season soybean? Does cereal cover crop kill date matter? These are questions that soybean farmers are asking as Maryland cover crop acreage continues to increase.

To address these questions, three years of research was conducted by planting three cereal species (barley, wheat, and rye) as cover crops at the Wye Research and Education Center (fall 2009 and 2010) and Central Maryland R&E Center-Beltsville (fall 2010 and 2011). A no cover crop treatment (only fall-winter weed growth) also was included. Three (Wye) and two(Beltsville) cover crop spring kill dates that supported varying amounts of cover crop biomass production were used. The kill dates at Wye are defined as 1) extra early kill for only the rye and the no cover treatments (mid-late March during the two study years); and at both Wye and Beltsville 2) early kill date for all treatments (ranged from 13 April to 23 April); and 3) late kill date for all treatments (ranged from 2 May to 16 May). Soybean varieties Asgrow brand3539RR2 (mid-MG 3) and Asgrow brand 4630RR2 (mid-MG 4) were planted into all cover crop treatments between 2 and 3 weeks after the last kill date. Soybean harvest dates were considered normal ranging from 17 October to 3 November during the three years.

Approximately three weeks post-planting, stand emergence was assessed to see if the cover crop species or kill date treatments impacted stand establishment. Over the three year period, no emergence differences were observed indicating that neither choice of cereal cover crop nor spring kill date had a detrimental effect on soybean germination and emergence. The most important criterion when planting full season soybean into a cereal cover crop is attainment of good seed-soil contact.

Starting approximately mid-June each year, a weekly measurement of growth stage progression was done by randomly selecting 5 plants in each plot, determining the growth stage according to Fehr and Caviness (1971), and averaging the growth stage. The primary growth differences observed were associated with the two varieties. Both varieties progressed through vegetative growth similarly. The onset of reproductive growth always was observed for the earlier of the two varieties, as expected. The weekly readings continued until early-mid September. Occasionally, only very minor differences in growth stage progression for the soybeans were observed for either the cover crop species or the kill date treatments. These differences were inconsistent across the assessment dates and are considered to have no influence on soybean growth and performance.

Soybean yield (72 bu/acre average) was excellent during the three years. The most consistent yield difference observed was associated with variety, however there was no consistent trend favoring one over the other. At Wye, the MG 3 variety produced better than the 6 MG 4 variety during 2009-2010 and the opposite occurred during 2010-2011. During 2010-2011 at Beltsville, the MG 4 variety was best and during 2011-2012, there was no yield difference between the two.

Response of soybean yield performance to cover crop species and kill date varied by location. During the two years at the Wye, a cover crop species × (by) kill date interaction was observed. For the March kill date (extra early), soybeans planted into the no cover crop treatment produced 10% (2009-2010) and 4% (2010-2011) better than soybeans following rye.

For the 2010 April kill date (early), soybeans planted following any of the three cover crop species produced the same (62 bu/acre) but soybeans following the no cover treatment yielded nearly 10% more (68 bu/acre). In 2011, the April kill date produced no yield differences (~67.5 bu/acre average) among the four cover treatments.

For the two years the study was conducted at Beltsville, there was no cover crop species × kill date interaction during 2010-2011 but in 2011-2012 this interaction was significant. At Beltsville in 2010-2011, soybeans planted where cover crops were killed during April produced over 6% greater than soybeans following the May kill date. However during this study year, there were no differences in soybean yield associated with any of the cover crop treatments.

During 2011-2012, soybeans following either barley or wheat cover crop produced the same for the two kill dates. However, soybeans that followed either rye or the no cover crop treatment, produced approximately 12% greater following the May kill date. Based on three years of data collected in this study, answers to the two primary questions about soybean performance following cereal cover crops are:

1. Does choice of cereal cover crop species affect the performance of full season soybean?
The performance of full season soybean following a cereal cover crop cannot be predicted by the cereal species grown. Differences may occur but they will be associated with location and kill date.

2. Does cereal cover crop kill date influence soybean performance?
The optimum kill date for cereal cover crops followed by full season soybean is difficult to predict. Factors that can affect soybean performance for any particular kill date are location, year, weather, and variety.

Wheat Head Blight Update for Delaware

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Updated on May 13, 2013

Disease models at http://www.wheatscab.psu.edu/ currently are listing much of Kent County and portions of Sussex County as being at high risk for FHB (See photo below).  Growers in these regions should consider applying appropriate fungicides (Prosaro, Caramba, Proline) if wheat is at early flowering (Feekes 10.5.1).  All growers should continue to monitor the growth stage of your wheat and the wheat scab modeling website to determine if and when fungicide applications may be needed.  See last week the article below for more information on FHB management.  


Original Article:
We are entering the period where outbreaks of Fusarium head blight are possible on winter wheat. This disease is caused by a fungus (predominantly Fusarium graminearum) that resides in crop residue (corn stalks, wheat straw, and other host plants). The fungus produces spores on this residue, which are dispersed by rain or wind to the flowering wheat. Once wheat is infected, wheat heads may become bleached (Figure 1) and pink to orange fungal growth may be seen at the base of diseased spikelets. The fungus also produces mycotoxins such as vomitoxin (aka: DON), which are toxic to humans and animals and can be present in infected wheat grain. In this article I will go over some important factors that impact head blight severity and discuss fungicide use to help suppress this disease.

Growers should consider applying fungicides to wheat if the environment favors disease and plants are in a susceptible growth stage. Over the past two weeks Delaware has experienced wet weather associated with persistent cool temperatures. The cool temperatures likely have slowed the development of Fusarium spores and the risk for severe head blight outbreaks. However, the risk for head blight will rise if moisture remains high (>90% RH) and temperatures increase. Optimal temperatures for head blight infection are between 59 and 86°F. I encourage all growers to visit the FHB Risk assessment tool at http://www.wheatscab.psu.edu to keep abreast of the blight risk in their area. As of May 7th, the forecasting model shows a small section of southeast Sussex County with moderate to high levels of head blight risk.

The severity of Fusarium head blight is not only impacted by weather, but also by the growth stage of the plant. Fusarium infections are most severe at flowering; consequently, this is when you should apply a fungicide. Fungicide treatments will be most effective if applied preventively at early flowering. A link to identifying this stage in wheat can be found at http://www.youtube.com/watch?v=7NJNE1wbVaU. Fungicides applied earlier or later will be ineffective at controlling this disease. In addition, fungicides applied before heading or at the flag leaf stage will not provide scab control. Even if timed properly and applied preventively, a fungicide may only result in approximately 50% disease control. However, the goal of a fungicide application is to reduce the impact of this disease on yield and to reduce mycotoxin levels in grain. Therefore, it is important that you choose the correct fungicides to maximize the benefit of the fungicide treatment.

headbleachingFigure 1. An example of head bleaching that may occur from infection by the Fusarium head blight/scab fungus.

What fungicides should you apply? The best fungicides for control of head scab belong to the triazole class of fungicides (Group 3), but they vary greatly in their level of activity. The two best products for wheat head scab control are Caramba™ (active ingredient: metaconazole) and Prosaro™ (active ingredients: prothioconazole+tebuconazole). Proline™ (active ingredient: prothioconazole) provides some control but often is not as effective as Prosaro™. Products containing only tebuconazole (e.g. Folicur™) have been used in the past to control head blight. However, research from The Ohio State University indicates that Caramba™ and Prosaro™ provide between 10 and 15% greater control of blight, and between 20 to 25% greater control of DON than Folicur™. The nice thing about Caramba™ and Prosaro™ is that they will also give you some control of Septoria/Stagonospora glume blotch, rust, and tan spot. Fungicides containing a strobilurin (group 11) should not be applied to heads or flowers because strobilurins may increase DON levels in grain. Examples of these products include Quadris™ Headline™ Stratego™ and Quilt™.

In closing, remember that fungicides are only one part of Fusarium blight management and work best when combined with other practices. There are several options that you have to proactively reduce the risk of head blight. These include using resistant wheat varieties, tilling, removing crop debris from the field, and spreading risk by planting several varieties at different dates. Even if these management practices are followed, head scab outbreaks are possible given the right environmental conditions. Visit the FHB risk assessment tool often and monitor the growth stage of your wheat to determine if and when a fungicide treatment is needed. I encourage growers to contact University of Delaware Extension personnel to assist with your wheat disease management needs. Additional information on Fusarium head blight management can be found at http://www.scabsmart.org/ and http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/Fusarium.aspx.

Agronomic Crop Insects – May 10, 2013

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

In general, alfalfa weevil populations have been higher in many fields this spring. For alfalfa over 16 inches tall, the threshold increases to 2.5 larvae per stem. Early harvest is often the best option once fields are greater than 16 inches tall and populations exceed 4 larvae per stem; however, there must be enough “stubble heat” after harvest for this technique to provide control. If populations were above threshold before cutting, be sure to check for alfalfa weevil adults and larvae within a week of cutting. Feeding from both stages can hold back re-growth. A stubble treatment will be needed if you find 2 or more weevils per stem and the population levels remain steady.

Field Corn
At this time, we can find both cutworms and slugs feeding in newly emerged corn fields. In addition to black cutworm, which generally attacks later planted corn, we can find a number of other cutworm species present in corn fields at planting time. They include the dingy cutworm, claybacked cutworm and variegated cutworm. Information from the Midwest indicates that the claybacked cutworms can cause economic loss in corn. They overwinter as half-grown larvae in the soil so they can get a “jump” on black cutworms when it comes to cutting each spring. Since they are larger in size, this species can damage very young corn plants. Scouting fields at plant emergence is important, even if at planting materials were used, to catch any potential problems. In addition, a higher rate of an insecticide will be needed to control larger cutworms. As a general guideline, a treatment is recommended if you find 10% leaf feeding or 3% cut plants. If cutworms are feeding below the soil surface, it will be important to treat as late in the day as possible, direct sprays to the base of the plants and use at least 30 gallons of water per acre. For cutworms, fields should be sampled through the 5-leaf stage for damage.

With the continued wet weather, we have seen an increase in slug damage on recently emerged corn. If slugs are damaging plants, you will be able to see “slime trails” on the leaves. Since corn was planted later this year and in many cases fields are just emerging, we could see more injury from slugs that have been hatching and beginning to grow. As indicated in previous newsletters, Deadline M-Ps is available for slug management this year in field corn. This is the only product that we have local experience with in regards to slug management in field corn. We continue to see very good control with Deadline MPs when applied at the 10 lb/A rate as long as you get good distribution of the product (5 pellets per square foot). The best control with the Deadline M-Ps has also been observed when applications were made and there was at least one day of sunny weather after an application. There are also a couple of other products available for slug management in field corn: Sluggo (iron phosphate) and IronFist (sodium ferric FDTA). At this point, we do not have local experience with these two products so will be evaluating them in replicated plots. We hope to get our first applications out today so we should have more information on their efficacy by next week. Please see the following link for comments from Ohio regarding slug management in field crops this season (http://corn.osu.edu/c.o.r.n.-newsletter#2).

Small Grains
Grass sawflies and true armyworms have been found in fields in Kent and Sussex counties. In addition, cereal leaf beetle adults have been found laying eggs and we are seeing the first larvae. Population levels remain variable throughout the state so scouting fields will be the only way to determine if an economic level is present. Depending on the temperature, cereal leaf beetle larvae will feed for up to 3 weeks. Research from Virginia and North Carolina indicates that the greatest damage can occur between flowering and the soft dough stage. Although armyworm can attack both wheat and barley, they can quickly cause significant losses in barley.

You will also need to watch for aphids feeding in the heads of small grains. With the continued cool wet weather and projection for cool weather again next week, populations could continue to increase and beneficial insects will have a hard time keeping up with populations. The treatment threshold is 20-25 aphids per head with low beneficial insect activity.

24c Label for Malathion for SWD Control in Blueberry

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

We recently received a 24c label for Gowan’s Malathion for Spotted Wing Drosophila (SWD) control in blueberries. This 24C supports an increased rate for better performance and residual. Be sure to read the label for use rate, number of allowed applications, as well as other restrictions. As a reminder, you must have a copy of this 24c label in your possession when you are using this pesticide. To obtain a copy of the label go to http://www.cdms.net/LDat/ld833021.pdf or contact Joanne Whalen at (302) 831-1303.

Gray Mold (Botrytis Fruit Rot) in Strawberries

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Most growers should have had at least 2 fungicide sprays for Gray Mold on strawberries already in 2013.

Gray mold is caused by the fungus Botrytis cinerea. The reservoir for this fungus is mycelium in dead strawberry leaves. This mycelium becomes active in the spring and starts to produce spores on this old leaf tissue which then spread to blooms. Most infections start at the bloom stage but symptoms usually do not develop until close to harvest (the fungus does not become active until the fruit enlarges). Ripening fruits can also be infected. Conditions conducive for infection are temperatures between 70 and 80°F and wet conditions (rain, dew, fog, irrigation. The most critical period for applying fungicides to control gray mold is during bloom.

Fungicide Recommendations From our Commercial Production Recommendation Guide: http://extension.udel.edu/ag/files/2012/03/DEvegrecs2013.pdf

Start sprays at 5 to 10 percent bloom, because 90% of fruit infections occur through the flower, and repeat every 7-10 days. Increase spray intervals during persistent dry periods, but decrease intervals to 5-7 days during very wet periods.

Four weekly sprays starting at 5-10% bloom are usually sufficient for season-long control. Tank-mix and rotate fungicides from different FRAC codes to reduce the chances for fungicide resistance development.

Suggested Program:
Application #1, apply one of the following:
Captan–4.0 lb 50WP/A plus Topsin M–1.0 lb 70WP
Switch–11.0 to 14.0 oz. 62.5WG/A

Application #2, apply one of the following:
Elevate–1.1 to 1.5 lb 50WDG/A
Pristine–18.5 to 23.0 oz 38 WG/A

Application #3:
same as Application #1

For subsequent applications, rotate between two or more of the following fungicides:
Captan–4.0 lb 50WP/A,
Captevate–3.5 to 5.25 lb 68WDG/A
Elevate 1.1 to 1.5 lb 50WDG/A
Switch–11.0 to 14.0 oz. 62.5WG/A
Pristine–18.5 to 23.0 oz 38WG/A

If Botrytis is a problem it can often be traced back to poor sanitation (removing old leaves from plantings), mistiming of bloom sprays, or a combination of the two. However, we are seeing resistance of Botrytis to several fungicides. If fungicide resistance is suspected, resistance testing may be warranted. There is a laboratory at Clemson University that is doing Botrytis resistance testing.

The following is information on that testing program from Dolores Fernández-Ortuño and Guido Schnabel, Clemson University

“If you are a strawberry grower and you are interested in getting your farm-specific resistance profile to identify ineffective fungicides, send us around 40 dead strawberry flowers or collect spores from newly infected, decaying fruit with a cotton swab. We need about 10 to 15 of those swabs (each from a different fruit and each fruit from plants far enough apart to represent an acre or so). Make sure that you only collect the fungus spores, do not touch the fruit. Mail the flowers or the swabs to Guido Schnabel, Clemson University, 114 Long Hall, Clemson, SC 29634 and tell us the origin of the sample, your name, and e-mail so that we can send you the report electronically. Upon receipt, we need about 3 (for cotton swabs) to 5 (for flowers) working days to get a report to you outlining farm specific gray mold management recommendations.”

Garlic Problems — Again

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Last year at about this same time there were calls from growers about their garlic plantings turning yellow and wilting (Fig. 1). When dug up the bulbs were often times blackened and rotting with some or much of the basal plate or roots missing (Fig. 2). The calls are coming in again this year with the same complaint and unfortunately, the same problems—bulb mites and garlic bloat nematode.


Figure 1. Bulb mite/bloat nematode infested garlic field

Bulb mites are a problem of garlic and sometimes of onion that usually go unrecognized. These pests can reduce stands, decrease plant vigor, and increase post-harvest diseases by their feeding on the roots and the stem plate. Bulb mites have a very wide host range, but cause most of their damage to onions and garlic. These mite pests are usually not seen on the bulb and prefer crawling into crevices between the roots and stem plate. Early in the growing season, bulb mites can cause poor plant stands and stunted growth as they feed on roots. Infested plants easily can be pulled out of the soil because of the poor root growth (Fig. 2).

The mite is bulb shaped with its legs moved forward and a bulbous rear end and many long fine hairs (Fig. 3). The mouthparts and legs are purplish-brown while the main body is creamy white. These mites have been described as looking like tiny pearls with legs. The mites are extremely small (from 0.02 to 0.04 inches) and are very slow moving. They are usually found in clusters underneath scales and at the base of the roots.

The garlic bloat nematode Ditylenchus dipsaci can destroy a crop of garlic in one season. Symptoms of bloat nematode in garlic plants include: bloated, twisted, swollen leaves, distorted and cracked bulbs with dark rings (Fig.4). These nematodes also can move to the inflorescence and remain in seeds for long periods of time in some plant species, i.e., beans, clover, and alfalfa where they are major sources of nematode dispersal. The nematodes can be spread around fields by equipment or on clothing and shoes. Garlic bloat nematodes can overwinter in soil or crop debris.

It is not just the direct feeding of the nematodes and mites on garlic and onions that causes problems, their feeding also allows pathogens to enter through the wounds they create. These wounds are very good entry points for pathogens like Fusarium spp., Sclerotium cepivorum (causes the disease white rot), and various soft-rotting bacteria. The white rot fungus does best in cool temperatures, and symptoms include white fungal growth on the stem or bulb with small, dark structures called sclerotia in the decayed tissue. Later in the season, higher than normal amounts of soft rot and Fusarium dry rot may be seen because of the wounds caused by these mites (as we saw in a couple of the garlic fields).

There is no program that certifies garlic as nematode-free. Commercial suppliers of garlic bulbs are aware of this important problem, and may send a portion of their crop to a laboratory for nematode testing, but this does not certify a crop as nematode-free. Because the nematode and mite can survive for long periods on infected plant material, to prevent build-up of the nematode or mite populations in a field, you MUST rotate away from any Allium crops (garlic, onions, and leeks) and control nightshades for at least 4 years. DO NOT keep any bulbs or seed from an affected field no matter how clean it looks. You should start from fresh seed or bulbs. Rotation to areas of the farm that have not had garlic or onion plantings for many years with new garlic or onion seed is the best method of control. Growers can, however, use soil fumigants to reduce or eliminate the nematodes from infested areas of the field. Growers also can use bio-fumigant cover crops that can be planted after harvesting garlic. Mustard and sorghum-sudangrass have been shown to reduce nematode populations due to the bio-fumigant constituents they produce. Be sure to clean equipment and storage areas with meticulous sanitation techniques.

allium2a allium2b Figure. 2 Infested garlic bulbs, misshapen or rotting bulbs, sometimes roots are intact other times there are no roots

 allium3Figure 3. Bulb mite

allium4Figure 4. Severe garlic bloat nematode damage to the two bulbs on the right vs. non-infested bulbs on the left