Posts Tagged ‘vegetable diseases’

Vegetable Fungicide Updates for 2012

Thursday, March 29th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

The following is a very brief overview of recent fungicide registrations and new updates that may be of use to vegetable growers in 2012. This is not meant to be a comprehensive list. Also, I have not run research trials for most of these product uses, and therefore cannot say anything about efficacy in comparison to other products. Remember to follow all label directions carefully. Before use, check each label for rates, information on resistance management, tank mix incompatibilities and other information.

  • · Prophyte and some other phosphorous acid fungicides are available for use on bean cottony leak (Pythium cottony leak).
  • · Quintec now has a Section 2ee label for the suppression of bacterial leaf spot on pepper in some states in the mid-Atlantic (including DE and MD, but not PA).
  • · Both chlorothalonil and Manzate Pro Stick labels have added anthracnose fruit rot on pepper.
  • · The Ranman label now includes spinach white rust as well as club root and downy mildew of cole crops (brassicas).
  • · Quilt Xcel and Stratego YLD are labeled for sweet corn rust.
  • · A new OMRI approved copper, Nordox, has a broad label that includes many vegetables and use in the greenhouse on some crops.
  • · Quash fungicide is labeled on potato and sweet potato for many diseases including early blight and white mold.
  • · A label expansion for Cabrio lists management of stem rots caused by Rhizoctonia and Sclerotinia and Southern blight (Sclerotium rolfsii) on tomato, pepper and eggplant.
  • · Fontelis has received a label for many vegetables including brassicas (Alternaria, gray mold, powdery mildew, Sclerotinia); tomato and other fruiting vegetables (early blight, gray mold, powdery mildew, Septoria leaf spot, etc.); Leafy vegetables (Alternaria, Cercospora, Septoria, etc.); Legume crops (Alternaria, anthracnose, Ascochyta, Botrytis, etc.); and some root vegetables (early blight, Cercospora leaf spot, Sclerotium rolfsii, etc.)
  • · Luna Experience has received a label for use on watermelon in DE and the label is pending in MD. Diseases on the label include gummy stem blight, anthracnose, and powdery mildew.

Vegetable Disease Updates – September 17, 2010

Friday, September 17th, 2010

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

Nematodes in Veggies
Fall is the best time to soil sample for nematode pests such as root knot, lesion, and other plant parasitic nematodes. After fall harvest but before any fall tillage is done, take soil cores six inches deep between plants in the row. Samples should be taken in the root zone of the old crop. Twenty cores/ sample should be taken from random spots in the field and placed in a plastic bucket, gently mixed, and a pint of soil submitted for analysis. Large fields should be subdivided into blocks of 15- 20 acres each and sampled separately. Nematode test bags and instructions are available for purchase from the county Extension offices. Samples cost $10.00. Fall sampling for root knot nematodes is strongly recommended for fields that will be planted in cucumbers, watermelons, cantaloupes, lima beans or other high value vegetables where root knot could reduce production. Forms and instructions are also available on the web at http://ag.udel.edu/extension/pdc/index.htm. Just a reminder, as I mentioned last week, do not take nematode samples until we get some rainfall if the soil is very dry.

Fall sanitation
In vegetable production it is not a good idea to leave old crop residue in the field any longer than necessary. If the crop is allowed to survive after harvest, fungi that cause many diseases continue to increase on the surviving plants. This allows higher numbers of the fungi to potentially survive until next season. Sanitation (plowing or disking the old crop) will help prevent pathogen carry-over.

Lima Beans
To date, I have not heard about or seen any samples of downy mildew in lima beans. The weather has not been favorable for infection.

2010 Fungicide Update for Vegetables

Thursday, March 25th, 2010

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

There are some new additions and a few deletions:

Beans
Folicur 3.6F has been added for the control of common bean rust on snap beans. The section on soybean rust on snap and limas beans was removed. This disease has not developed on any other host other than soybeans and kudzu. At this time it is not a threat to snap and lima bean production. Omega 500F is labeled on snap and lima beans for white mold control. It also has good activity on downy mildew on limas. Hopefully by application time there will be a 2(ee) registration for downy mildew as well.

Cucumber, Cantaloupe, Pumpkin, Winter Squash and Watermelon
Switch and Folicur (tebuconazole) have been added for gummy stem blight control. The fungus that causes gummy stem blight has developed resistance to Pristine in South Carolina and may be occurring here. The addition of these two products is very important to control this important disease. Folicur has also been added to these crops and summer squash for powdery mildew control in addition to the other two triazole fungicides Rally and Procure.

Peppers
Chlorothalonil (Bravo) has been labeled to replace maneb which is no longer being manufactured for anthracnose fruit rot control.

Sweet Corn
Maneb is no longer being manufactured for use on sweet corn.

Tomato
Revus Top was added this year for control of leaf spots and late blight. Scala is labeled for early blight and gray mold control in the field as well as in the greenhouse and high tunnels.

Potatoes
Tanos was added for early blight control. Revus and Revus Top were added for late blight control.

Maneb is no longer being made but existing stocks can be used until maneb is gone.

End of the Season Vegetable Disease Notes

Friday, September 18th, 2009

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

Nematodes in Veggies
Fall is the best time to soil sample for nematode pests such as root knot, lesion, and other plant parasitic nematodes. After fall harvest but before any fall tillage is done, take soil cores six inches deep between plants in the row. Samples should be taken in the root zone of the old crop. Twenty cores per sample should be taken from random spots in the field and placed in a plastic bucket, gently mixed, and a pint of soil submitted for analysis. Large fields should be subdivided into blocks of 15-20 acres each and sampled separately. Nematode test bags and instructions are available for purchase from the county Extension offices. Samples cost $10.00. Fall sampling for root knot nematodes is strongly recommended for fields that will be planted in cucumbers, watermelons, cantaloupes, lima beans or other high-value vegetables where root knot could reduce production. Forms and instructions are also available on the web at http://ag.udel.edu/extension/pdc/index.htm.

Fall Sanitation
In vegetable production it is not a good idea to leave old crop residue in the field any longer than necessary. If the crop is allowed to survive after harvest, fungi that cause many diseases continue to increase on the surviving plants. This allows higher numbers of the fungus to potentially survive until next season. Sanitation (plowing or disking the old crop) will help prevent pathogen carry-over.

Scout for Spinach Downy Mildew and White Rust

Friday, April 17th, 2009

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

Scout spinach for downy mildew and white rust on a regular basis, especially if spring plantings are near overwintered fields. Beginning 2 to 3 weeks after emergence (and prior to symptom development), apply the following on a 7 to 10-day schedule: Quadris (azoxystrobin, 11) at 6.0 to 15.5 fl oz 2.08F/A (use high rate for downy mildew), or Cabrio (pyraclostrobin, 11) at 12.0 to 16.0 oz 20EG/A (use lower rate for white rust only). Rotate to one of the following fungicides: Actigard (acibenzolar-S-methyl, P) at 0.75 oz 50WG/A, or Aliette (fosetyl Al, 33) at 3.0 lb 80WDG/A, or fixed copper (FRAC code M1) at labeled rates (copper containing fungicides may cause some phytotoxicity), or Ridomil Gold Copper (mefenoxam + copper, 4 + M1) at 2.5 lb 65WP/A (on a 14-day schedule). For more information please see the Delaware Commercial Vegetable Production Recommendations Guide.

Fumigation Alternatives – Biofumigants

Friday, April 17th, 2009

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

Crop rotation is a key to successful vegetable production. However, land limitations often make long term rotations difficult. Shorter rotations lead to a buildup of pests, with soil borne diseases being a major challenge for many vegetable crops. One approach to tighter rotations is to fumigate soils using commercially available chemical fumigants. Methyl bromide has been phased out and can only be used for certain exempted critical uses in specified states as listed by the EPA (go to http://www.epa.gov/ozone/mbr/cueinfo.html for more information). Other fumigants such as chloropicrin; dicloropropene + chloropicrin; metam-sodium, metam-potassium, and iodomethane + chloropicrin are being used in this region where labeled. Numerous experimental materials are being studied for use as soil fumigants and may receive labels in the future. A major drawback to chemical fumigation is material cost. There are also application requirements and equipment considerations to take into account.

There has been considerable interest in the use of certain crops as biological fumigants ahead of vegetable production to reduce the need for chemical fumigation, especially in tight rotations. These are crops that would be grown for their naturally occurring compounds that kill soil borne pests. Plants in the mustard family, such as mustards, radishes, turnips, and rapeseed, and Sorghum species (sudangrass, sorghum-sudangrass hybrids) have shown the potential to serve as biological fumigants. Research in this region and across the country has shown some promise in using these crops to reduce soil borne pests. Plants from the mustard family produce chemicals called glucosinolates in plant tissue (roots and foliage). These glucosinolates are released from plant tissue when it is cut or chopped and then are further broken down by enzymes to form chemicals that behave like fumigants. The most common of these breakdown products are isothiocyanates. These are the same chemicals that are released from metam-sodium (Vapam) and metam-potassium (K-Pam), commonly used as chemical fumigants. Sorghums produce a cyanogenic glucoside compound called Dhurrin that breaks down to release toxic cyanide when plant tissue is damaged.

While rapeseed, mustards, radish species, sudangrass, sorghum-sudangrass hybrids and other related species have shown some promise as biofumigants, results in Delaware have been inconsistent, often with minimal benefits. It is important to note that success with biofumigant crops depends on a number of factors. The following are some suggestions to achieve the best results:

● Plant biofumigant crop varieties selected or bred for higher levels of active compounds if available.

● Produce as much biomass of the biofumigant crop as possible. This requires that you have a good stand, fertility, and sufficient growing time. The more biomass that is produced and that is incorporated, the more chemical is released. However, as plants mature, the will reach a point where levels of these active chemicals will decline and you should not let the plants go to seed. There is also the practical consideration that it is difficult to do a good job of incorporation with too much biomass. With a crop like sudangrass, this means you cannot let it get too tall.

● The plant material must be thoroughly damaged so that enzymes can convert glucosinolates into isothiocynates or so that the Dhurrin is converted into cyanide. This means that you need to chop the material as much as possible and work it into the soil as quickly as possible so as to not lose the active compounds to the air. A delay of several hours can cause significant reductions in biofumigant activity. The finer the chop, the more biofumigant is released.

● The material should be incorporated as thoroughly as practical to release the biofumigant chemical throughout the root zone of the area that is to be later planted to vegetables. Poor distribution of the biofumigant crop pieces in the soil will lead to reduced effectiveness.

● Sealing with water or plastic after incorporation will improve the efficacy (as with all fumigants). Soil conditions should not be overly dry or excessively wet.

Biofumigant crop systems include overwintering rapeseed; early spring planted mustards, cover-crop type radishes, or turnips; and late spring planted sorghum/sudangrass. Each has the potential to fit different vegetable cropping sequences for early, mid, or late season production.

Different species and cultivars of biofumigant crops contain varying levels of active compounds. There have been significant efforts to evaluate species, and varieties within a species, for levels of biofumigant chemicals produced, as well as some breeding and selection efforts to increase levels of these compounds. This work is on-going in different parts of the US. Where varieties with higher levels of active chemicals are available, they should be used.

A major limitation to biofumigant crop use is the fact that you cannot deliver high enough levels of the active chemicals to do a complete fumigation job and the biofumigation effectiveness is also limited by the depth of incorporation. However, you are adding organic matter and do get the benefits associated with that addition.

The bottom line: biofumigant crops can suppress soil borne pests but are not a full replacement for chemical fumigants, nor are they a substitute for adequate rotations. However, using biofumigant crops in combination with disease tolerant vegetable varieties can allow for a greater chance of success in tight rotation situations.

There also has been considerable research into the effect of cover crops (such as hairy vetch), compost, and other organic additions on disease suppression in vegetable crops with some positive results. The mechanisms for these benefits may include some chemical suppression. However, other mechanisms such as increasing diversity of the soil microbial community (resulting in increased competition with pathogens) and promoting growth of beneficial microbes that serve as biocontrol agents may be more important.

Vegetable Diseases in the Greenhouse

Friday, March 6th, 2009

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu 

As vegetable transplant production in greenhouses gets underway, remember that the potential for disease can be minimized by using certified, tested, and treated seed. Sanitation is the most important management practice. Walls, benches, hand tools, pots and transplant trays should be sanitized with 5% commercial bleach. New potting mix should be used each year. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Once seed is planted, seedlings should be watered early in the day so that the foliage dries quickly and, if possible, watered at the seedling base to reduce moisture on leaves.

Provide good air exchange throughout the greenhouse to minimize periods of high humidity (high humidity favors pathogens). Even after careful sanitation and good practices for managing disease, disease may develop in the greenhouse. Most fungicides are not labeled for greenhouse use. Do not use unlabelled fungicides because the lack of a greenhouse label indicates that there are problems with safety, phytotoxicity, or resistance development risk associated with a fungicide.

The following table, which is modified from the Vegetable Management Guide 2008-2009 New England Region is a good summary of available fungicide options. Please note that Ridomil is not labeled for use in the greenhouse. Please follow label directions carefully.

Please follow link below for table:
Selected Fungicides and Bactericides Labled for Greenhouse Use 2009

Fall Sanitation in Vegetable Fields

Friday, September 19th, 2008

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

In vegetable production it is not a good idea to leave old crop residue in the field any longer than necessary. If the crop is allowed to survive after harvest, fungi that cause many diseases continue to increase on the surviving plants. This allows higher numbers of the fungus to potentially survive until next season. Sanitation (plowing or disking the old crop) will help prevent pathogen carry-over.

Plant Management Network Publishes Latest Plant Disease Management Reports

Thursday, August 28th, 2008

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

The following article is a news release about the Plant Management Network and specifically about the Plant Disease Management Reports. This resource is valuable to all those who use fungicides and those that recommend them to growers.

The 2008 volume of Plant Disease Management Reports (PDMR), an online resource developed to give growers, consultants, pesticide applicators, and extension specialists the latest in disease management information, is now published.

This latest volume contains more than 560 searchable reports on the effectiveness of fungicides/nematicides, resistant varieties, and other biological controls that defend against diseases of agricultural and horticultural crops.

All volumes of PDMR and its preceding publications, F&N Tests and B&C Tests, contain 5,000-plus reports, covering more than 1,500 chemical and biological controls.

“Many professionals in agriculture and horticulture depend on PDMR to develop disease management recommendations or make better pest management decisions,” said Dan Egel, Ph.D., Extension Plant Pathologist at Purdue University and Editor-in-Chief of Plant Disease Management Reports.

Each one to two-page report consists of a summary outlining trial conditions and results. Test plot trial data, also in the report, includes treatment rates, application timings, and pertinent efficacy data for each product tested.

Users can search the reports by keyword or section. Keyword searches can include product names, active ingredients, host crops, and authors. Sections include cereals and forage crops; citrus, tropical, and vegetable crops; field crops; ornamentals and trees; pome fruits; seed treatments (for all crops); small fruits; stone fruits and nuts; and turfgrass.

PDMR’s efficacy reports were first published in 1946 as a section in the USDA publication, Plant Disease Reporter. In 1960, the American Phytopathological Society (APS) published these reports independently under the title Fungicide and Nematicide (F&N) Tests. In 1986, APS developed a new publication, Biological and Cultural Tests for the Control of Plant Disease, or B&C Tests. By 2001, both resources became electronically accessible. In 2007, they were merged into Plant Disease Management Reports. A full history is discussed in this volume of PDMR.

Users can have continuous access to all volumes of Plant Disease Management Reports, F&N Tests, and B&C Tests online for $45 yearly. This subscription also includes access to other Plant Management Network resources, which include Arthropod Management Tests, a similar publication covering the effectiveness of insecticides; applied crop science journals, webcasts, targeted extension searches, image collections, proceedings, and more. To subscribe or learn more, visit http://www.plantmanagementnetwork.org/pub/trial/pdmr/.

PDMR is distributed online through the Plant Management Network (http//www.plantmanagementnetwork.org), a nonprofit publisher of applied plant science resources. The Plant Management Network is jointly managed by the American Phytopathological Society, the Crop Science Society of America, and the American Society of Agronomy. The Plant Management Network’s nonprofit publishing mission is to enhance the health, management, and production of agricultural and horticultural crops.

Vegetable Crop Diseases

Thursday, July 3rd, 2008

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

Tomato Spotted Wilt Virus
Tomato spotted wilt virus was indentified and confirmed today by ELISA on tomato plants from across the line in MD. We don’t see this very often but the symptoms are pretty obvious most of the time. It can be a problem when tomato transplants are produced with ornamental bedding plants, which harbor the virus. The virus is often then transmitted to tomatoes by Western flower thrips. The virus can be transmitted from weeds and perennial ornamentals as well by nine species of thrips. Young leaves are bronze colored and later develop numerous small dark spots. Growing points may die and stems of terminals may be streaked.

 

Tomato spotted wilt on tomato

Bacterial Wilt in Cucurbits*
Symptoms of bacterial wilt will vary depending on the cucurbit crop. In general, plants may wilt during the day in hot weather and ‘recover’ during cooler parts of the evening and morning. Margins and interveinal areas of leaves become necrotic which cause leaves to appear ‘scorched’. Look for beetle feeding scars on cotyledons and stems of young plants. Healthy green plants will turn chlorotic (yellow) with time and infected plants will eventually collapse and die, exposing fruit to sunscald injury. Cutting through stem tissue at the base of infected plants often reveals a coppery-tan color where the bacterium causes the vascular tissue to ‘plug up’. Control of bacterial wilt begins with controlling striped and spotted cucumber beetles which vector the pathogen early in the growing season as plants emerge. Late-season beetle control will remain important as fruit begins to mature. Late-season beetle feeding may cause injury to stems ruining aesthetic quality. For more information on cucumber beetle and bacterial wilt control please see the 2008 Delaware Commercial Vegetable Production Recommendations Guide.

Anthracnose of Pepper
Symptoms of anthracnose infection in pepper fruit include sunken, circular spots which develop blackish-tan to orange concentric rings as lesions develop. Lesions on stems and leaves appear as grayish-brown spots with dark margins and can easily be overlooked.

Control of anthracnose begins with using clean-free seed and/or transplants. A three-year crop rotation with non-solanaceous crops is recommended. After the harvest season, pepper fields should be disced and plowed under thoroughly to bury crop debris. Beginning at flowering and as small fruit begin to set, alternate maneb (M3) at 1.5 to 3 lb/A 75DF with one of the following FRAC code 11 fungicides:

azoxystrobin (Quadris at 6.2 to 15.4 fl oz 2.08F/A)
or
Flint (trifloxystrobin) 50WDGat 2 to 4 oz/A
or
Cabrio (pyraclostrobin) 20EG at 8 to 12 oz/A
or
Tanos (famoxodone + cymoxanil, 11 + 27) at 8 to 20 50WDG/A.

 

Anthracnose on pepper fruit

Bacterial Leaf Spot of Pepper*
Symptoms of bacterial spot on pepper leaves include small, brown water-soaked lesions that turn brown and necrotic in the centers. Spots may coalesce and form large blighted areas on leaves and premature defoliation can occur. On fruit, brown lesions can form which have a roughened, cracked wart-like appearance. High temperatures, high relative humidity and rainfall favor bacterial spot development. Loss from bacterial spot can be reduced somewhat by maintaining high levels of fertility, which will stimulate new growth. Applying a fixed copper (M1) at labeled rates plus maneb (M3) at 1.5 lbs 75DF/A or 8 to 10 oz Tanos (famoxadone + cymoxanil, 11 + 27) may help suppress spread. For more information on control of Bacterial leaf spot of pepper please see the 2008 Delaware Commercial Vegetable Production Recommendations.

*From Andy Wyenandt, Rutgers University