Posts Tagged ‘16:2’

Field Corn Soil Insect Management

Friday, March 28th, 2008

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

The following is a brief review of conditions favoring soil insects in field corn as well as observations from past seasons:

Corn Rootworm (Larval Control)
In general, rootworms continue to be more of a problem in continuous corn. Although generally more of a problem in heavier soils, we have also seen problems in continuous, irrigated corn fields planted in sandy soils. In our area, rotating out of corn is still a viable option for corn rootworm management. However, if you plan to plant continuous corn, control options include either a soil insecticide, a high rate of a commercially applied seed treatment, or a transgenic corn hybrid with resistance to rootworm larvae.

As far as seed treatments, reports from the Mid-West and areas in PA with heavy rootworm pressure state that “when rootworm densities and root injury have been low to moderate, seed treatments have provided acceptable protection of the roots. However, when rootworm densities have been high and root injury has been moderately high to severe, insecticidal seed treatments have not provided consistently acceptable control of corn rootworm larvae.”

Wireworms
High soil organic matter, sod covers, and heavy grass weed pressure the previous season all favor wireworm populations. In addition, damage from this insect is also higher in continuous corn. Commercially applied seed treatments i.e. Cruiser (thiamethoxam) and Poncho (clothianidin) have generally provided good wireworm control. NOTE – Labels for Cruiser and Poncho state seed and seedling protection.

Grubs
In general, grubs are favored by a number of factors including planting into soybean stubble, old sod, hay, pasture, or set-aside acreage. Cruiser and Poncho are labeled against white grubs. Although these 2 chemicals can work against low to moderate grub populations, in the past few years we have seen poor control with both products in commercial fields under high pressure, especially when the predominant grub species has been Asiatic garden beetle. If populations are high, you may still need to consider an in-furrow application of an insecticide. NOTE – Labels for Cruiser and Poncho state seed and seedling protection.

Black Cutworm
This insect is favored by late planting, broadleaf weed growth (especially chickweed) present before planting, poorly drained field conditions and reduced tillage. Rescue treatments can be applied for this soil insect if you are able to scout fields twice a week once leaf feeding is detected. Pheromone traps placed in the field by mid-March can be used to determine when to look for cut plants. So far, we have not caught any black cutworms in our pheromone traps. Look for pheromone trap counts in future reports. If you are unable to scout and you have conditions favoring cutworms, one of the following preventive approaches can be considered: (1) a granular soil insecticide labeled for cutworm control applied as a t-band, or (2) a tank mix of an insecticide with a pre-emergence herbicide or (3) a Herculex corn hybrid. In general, the seed applied treatments (Cruiser and Poncho) have not provided effective cutworm control in our area, especially if economic levels of larger larvae are present at planting.

Scout Alfalfa for Alfalfa Weevil and Pea Aphids

Friday, March 28th, 2008

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

Be sure to sample alfalfa fields for small alfalfa weevil larvae feeding in the tips of plants. Early damage will appear as a round, pinhole type of feeding. Once you detect tip feeding, a full field sample should be taken. You will want to avoid treating fields too early since it may result in multiple applications. Also, be sure that you do not confuse clover leaf and alfalfa weevil larvae. Cloverleaf weevils are generally larger at this time of year and have a distinct white stripe lined with red down the middle of their backs. Although cloverleaf weevils can cause damage during cool, dry springs, controls are generally not needed for cloverleaf weevils. For pictures of cloverleaf weevil and alfalfa weevil, please refer to the following links:

http://www.ipm.iastate.edu/ipm/icm/1997/4-21-1997/icloverweevil.html
http://www.ent.iastate.edu/imagegal/coleoptera/curculionidae/0212.47alfalfalarva6in.html

You will also want to sample fields for pea aphids. Heavily infested plants may turn yellow and wilt. Pea aphids prefer cool, dry conditions and can be a problem in both the first cutting and during spring seedling establishment. This species tends to congregate on the tips of alfalfa plants where they feed on young, succulent developing shoots. To sample for aphids, clip alfalfa stems at the base of the plant and record the number present per plant. You may want to examine plants over a white bucket to collect any aphids that are dislodged from the plants. In seedling stage alfalfa, a treatment should be considered if you find 5 aphids per stem. As a general guideline, you should consider a treatment in alfalfa less than 10 inches tall if you find 40-50 aphids per stem. The treatment threshold for alfalfa 10 inches or taller in height is 75-100 per stem.

Understanding FRAC Codes is Important for Managing Fungicide Resistance Development

Friday, March 28th, 2008

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

FRAC, or the Fungicide Resistance Action Committee, was developed to help provide resistance management guidelines for fungicide use. Remember, high-risk fungicides have a high probability of resistance development because of their modes-of-action (MOA). Those fungicides with chemistries that have a specific target site against fungal pathogens, unfortunately, will have a high risk for losing efficacy because of resistance development in the pathogen. Importantly, fungicides with similar chemistries and MOAs that belong to the same FRAC code may also be prone to cross-resistance, where a fungus that develops resistance to one fungicide in the FRAC group may also develop resistance to other fungicides in the group, even if those other fungicides haven’t been used.

With the recent influx of new fungicide chemistries on the market great lengths have been taken to reduce the risk of fungicide resistance development for many fungi where ‘high risk’ fungicides are used. There are currently 43 numbered FRAC groupings and 4 lettered groups. As new fungicides with new MOAs are released on the market, new numbered groups will be added to the list. For many vegetable crops many of the most common fungicides used fall into a few of these groupings, most notably:

Multi-Sites (M) or Low Risk FRAC Groups
M1 and M2, inorganics such as sulfur and copper
M3, Maneb or Mancozeb
M5, chlorothalonil such as Bravo

Higher Risk FRAC Groups
Group 3, triazoles such as Nova or Rally
Group 4, mefenoxams such as Ridomil
Group 11, strobilurins such as Quardris, Flint, Cabrio

Some of the newest fungicides labeled for use in vegetable production include Quintec (quinoxyfen, FRAC code 13) and Revus (mandipropamid, 40).

Knowing which fungicides belong to which FRAC code will have an impact on spray schedules, disease control, and resistance management. Protectant fungicides, such as those in the FRAC code M, have a low risk for fungicide resistance development and have less stringent restrictions. However, for those chemicals with a higher risk of fungicide resistance development the product labels are more stringent and labels should be followed precisely. Labels often require that high-risk fungicides be tank-mixed with protectant fungicides to reduce the chances for fungicide resistance development. In general, tank mixing high-risk fungicides with protectant fungicides is always a good resistance management strategy. For example and, in general, the strobilurin fungicides in FRAC code 11 should not be sprayed consecutively. Such that, if Quadris (azoxystrobin, 11) is sprayed one week, it should not be followed the next week with another Group 11 compound such as Flint (trifloxystrobin, 11) or Cabrio (pyraclostrobin, 11) or a compound containing a Group 11 fungicide (Pristine, pyraclostrobin + boscalid, 11 + 7). A simple way to remember what to use next in your fungicide rotation is to use a labeled fungicide with a different FRAC number or letter. FRAC codes can be found in the fungicide table at the beginning of each crop section in the 2008 Commercial Vegetable Production Recommendations to help growers learn what fungicides belong to what FRAC groups and to help them chose fungicides for use in rotations. A complete list of fungicides and FRAC groups can also be found in Table E-8 on pages E30 and E31 in the Vegetable Production Recommendations. Efforts in learning and using new chemistries with new modes of action along with knowing their FRAC grouping will ultimately pay off in the long run by reducing the chances for fungicide resistance development.

Delaware Growers – Fungicide Resistance Management Guidelines for Vegetables were distributed at Ag Week with the Vegetable Production Recommendations. If you did not receive one and would like a copy, request one from the county Extension office or stop by and pick one up. These guides were developed as a project directed by Andy Wyenandt at Rutgers assisted by the other plant pathologists in the mid-Atlantic region and funded in part by the Northeastern IPM Center and USDA/CSREES.

Lima Bean Fungicide Update

Friday, March 28th, 2008

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

There are several fungicide additions for 2008. BASF added soybean rust control on lima beans to the Headline label in addition to snapbeans. Dow Ag Products was granted a section 18 label for the use of Nova on lima beans for soybean rust control in DE last season, but Dow is no longer continuing the Nova trade name. Nova will be marketed as Rally for lima beans and other vegetable uses. Rally has been Dow’s myclobutanil product in fruit. Rally is the same formulation as Nova, a 40% wettable powder. I still do not expect soybean rust to be a threat to lima bean or snap bean production from the inoculation studies and field trials in the US and South Africa.

Seed Vigor in Sweet Corn

Friday, March 28th, 2008

 Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

A common problem that occurs each year in the field is poor stands due to low seed vigor in a particular lot of sweet corn seed. By its nature, sweet corn has lower stored food reserves (carbohydrates in particular) compared to field corn. With the advent of different endosperm types than the traditional sugary (su) such as homozygous sugary enhanced (se), shrunken supersweets (sh2), and the more recent augmented shrunken types, vigor became even more of an issue. In general, vigor of sweet corn rated from highest to lowest is: normal sugary su > se heterozygous > se homozygous > sh2 augmented > shrunken sh2. Newer synergistic sweet gene varieties may have seed with vigor characteristics of a se or a su sweet corn depending on the specific genetics (check with your sweet corn seed company for specifics on the vigor of these hybrids). Supersweet hybrids (shrunken sh2) are noted for having inherently low seed vigor due to reduced food reserves and it has been a standard recommendation to plant these varieties only when soil temperatures are above 60 °F.

With the earliest sweet corn being planted now (end of March) in Delaware, seed vigor is critical, particularly if planting without the use of plastic mulches or clear covers. Choose types and hybrids within a type that have cold tolerance and make sure that you get seed lots that have good vigor. Your sweet corn seed supplier will have cold tolerance ratings of the hybrids that they sell. A good seed treatment package with appropriate fungicides and insecticides is also critical to obtain good early stands.

It is also a good idea to have the seed vigor tested if there is any doubt about the particular lot that you are planting or if you are considering planting carried-over seed. Factors such as growing conditions during seed development and maturation in the sweet corn seed production region, mechanical damage during harvest or cleaning, drying regime, seed conditioning procedure, and seed storage can have great impacts on the vigor of a specific seed lot.

The standard seed germination test is performed under ideal laboratory conditions (temperature and moisture). This will not reflect field conditions. The standard germination test is designed to determine the germination of a seed lot under ideal conditions, the highest germination potential. It does not help to evaluate the ability of a seed lot to perform under suboptimal field conditions.

Alternative tests that are used to evaluate seed vigor that are available from different state and private seed laboratories include:

The Cold Test – Seeds are germinated using a specific cold, moist treatment regime. This will be useful in selecting those lots that will perform the best under early cold soil conditions.

Seedling Vigor Classification Test (SVCT) – In this test seedlings from a normal germination test are rated visually according to vigor (strong or weak). Visual ratings are based on whether or not the seedlings have normal developmental characteristics.

Tetrazolium (TZ) Test – This is a quick biochemical test that essentially stains living tissue in a seed a red color. The more red staining, the more viable the seed.

Accelerated Aging Test (AAT) – In this test, seed is put under a high temperature and humidity regime for a period of time and then is evaluated using a standard germination test. This is often used to check the storability of seeds under less than ideal conditions but also will do a good job of evaluating seed vigor. Modifications to the Accelerated Aging Test have been made to do a better job of evaluating sweet corn types such as shrunken sh2 varieties.

The seed laboratory at the Delaware Department of Agriculture can perform cold germination tests on sweet corn seed lots that you want to have evaluated for vigor.

Winter Temperature Index for Predicting Stewart’s Wilt in Delaware Sweet Corn, 1998-2008

Friday, March 28th, 2008

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

Prediction for 2008
Newark:        109.5 = Severe- average monthly temp (Dec, Jan, Feb) was 36.5°F Georgetown:  116.4 = Severe – average monthly temp (Dec, Jan, Feb) was 38.8°F

For processing and fresh market growers this means that if you are planting susceptible or moderately susceptible hybrids, flea beetle control is very important. A number of strategies are available including seed treatments, granular insecticides at planting and/or foliar applied insecticides after emergence.

Average monthly temperatures in °F at Georgetown, DE REC 1998-2008

  2007-08 2006-07 2005-06 2004-05 2003-04 2002-03 2001-02 2000-01 1999-00 1998-99
December 39.7 43.5 36.2 38.9 38.6 36.7 43.2 31.2 40.3 41.3
January 36.8 39.7 43.0 34.9 29.5 28.9 40.0 33.8 33.9 39.5
February 39.9 30.1 37.4 36.7 35.2 33.8 39.9 38.8 39.7 38.7
INDEX 116.4 113.3 116.6 110.5 103.3 99.4 123.1 103.8 113.9 119.5

Average monthly temperatures in °F at Newark, DE Experiment Station 1998-2008

  2007-08 2006-07 2005-06 2004-05 2003- 04 2002-03 2001-02 2000-01 1999-00 1998-99
December 37.5 42.5 34.0 35.5 34.0 33.5 43.3 31.1 39.1 41.0
January 35.5 37.3 39.5 31.0 26.4 27.1 39.6 31.5 32.6 34.8
February 36.5 27.8 34.5 34.2 33.1 29.5 40.1 38.4 37.8 38.0
INDEX 109.5 107.6 108.0 100.7 93.5 90.1 123.0 101.0 109.5 113.8

Severity Index: < 90, usually absent; 90-100, intermediate; >100, usually severe. The index is used to predict overwintering flea beetle populations that vector the Stewart’s wilt bacterium, Pantoea stewartii.

Note: Weather records from University of Delaware Carvel REC, Georgetown, DE and University of Delaware Ag Experiment Station Farm, Newark, DE. Thanks for the data go to Dean Dey at Georgetown and Scott Hopkins, Farm Manger, UD Ag Experiment Station, Newark.