Posts Tagged ‘cucurbit phytophthora blight’

Pumpkin Spray Program 2012

Friday, June 29th, 2012

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

I frequently am asked for a “good” spray program for pumpkins. This is always difficult because a spray program depends on field history (i.e. has Phytophthora crown rot occurred in the field), production practices (no-till vs. bare ground), and the grower’s philosophy about control (Cadillac treatment program vs. minimal inputs).

Preventative practices are more effective than trying to minimize the damage from a disease after it occurs. Practices such as growing pumpkin on a no-till cover crop and using a powdery mildew tolerant cultivar will allow growers to stretch their spray interval.

Powdery mildew is the most common disease – it will damage leaves and the pumpkin “handles”. Downy mildew is an extremely damaging disease, however it does not overwinter here and sprays for downy mildew should only be applied when it is present in the Mid-Atlantic. Other diseases that occur, such as Bacterial wilt or virus diseases need to be treated by managing the vectors.

Keep the following in mind:
● Know what diseases are the most common on your farm. Previous problems with black rot, Phytophthora blight, anthracnose, scab or other diseases may indicate that these diseases are likely to be problems again.

● Begin spraying when vines begin to run.

● Use a protectant such as chlorothalonil every time (don’t worry about resistance developing).

● Spray every 7 to 14 days.

● The most common disease in our area is powdery mildew. However it is not always present early in the season. Scout 50 old leaves in your field for powdery mildew lesions. If powdery mildew is present in the field, apply materials that are targeted for it. If it is not present, spray with a protectant, then scout again before your next spray and adjust the spray accordingly.

● Familiarize yourself with the extension publication “Commercial Vegetable Production Recommendations” section on pumpkins. Fungicides included in the “Recommendations” have been tested and performed well in the Mid-Atlantic region.

● A good fungicide spray program will increase yields and improve quality. The single best way to improve handle quality is to control foliar and fruit diseases with fungicides.

The program:
The best way to save money on your spray program is to start with a protectant program such as either chlorothalonil plus copper or mancozeb plus copper. Add targeted products to your protectant program based on what diseases are in the area or known to be on the farm (downy mildew, powdery mildew, Phytophthora crown and fruit rot, etc.)

Powdery Mildew: The following are targeted for powdery mildew and have been tested in our region. Apply them with a protectant. Select two that are in a different FRAC code groups, and alternate them.

Product (FRAC Code) Efficacy on Powdery Mildew
Quintec (13) excellent
Micronized Wettable Sulfur (M2) very good (may cause injury at high temperatures – see label)
Procure (3) good
Rally (3) good
Tebuconazole:Folicur, etc. (3) good
Inspire Super (3 + 9) good
Pristine (11 + 7) good

 

Downy Mildew: Management of downy mildew should use the following products tested in our area. Select two that are in different FRAC code groups, and alternate them.

Product (FRAC Code) Efficacy on Downy Mildew
Presidio (43) excellent
Ranman (21) excellent
Previcur Flex (28) good (the pathogen may be developing resistance)
Tanos (11 + 27) good in alternation or tank mix
Curzate (27) good in alternation or tank mix
Gavel (22 + M3) good in alternation or tank mix

 

Plectosporium can be managed with applications of Quadris Top, Cabrio or Flint.

Phytophthora crown and fruit rot needs to be managed intensively. In fields with potential problems, apply Mefenoxam (Ridomil Gold or Ultra Flourish) pre-plant for early season control. Once the canopy closes, subsoil between the rows to allow for faster drainage following rainfall. Fungicide applications will only suppress Phytophthora, and reduce spread.

When conditions favor Phytophthora crown and fruit rot development, tank mix one of the following fungicides with fixed copper:
Revus (FRAC code 40), Ranman (FRAC code 21), Presidio (FRAC code 43), Forum (FRAC code 40), or Tanos (FRAC code 11 + 27).

Vegetable Disease Update – August 26, 2011

Friday, August 26th, 2011

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

With the impending hurricane we will probably see large amounts of rainfall. For vine crops fields with a history of Phytophthora fruit rot it will mean more Phytophthora fruit rot if any marketable watermelon or cantaloupe remain but it will really threaten the pumpkin crop. No fungicide will protect fruit from fruit rot if we get huge amounts of rainfall. Standing water in the fields will be the biggest indicator of possible fruit rot damage. There would be some benefit to protecting foliage with fungicides before the storm arrives if there is time and there is no history of Phytophthora fruit rot. This would be true for many vegetables including vine crops, tomatoes, and others. If there is no Phytophthora fruit rot present in a pumpkin field, fungicides such as Presidio, Ranman, Revus or Forum plus a fixed copper could be considered to suppress Phytophthora fruit rot, if Phytophthora spores moving in water from other fields should be introduced. Fruit have to be covered for the materials to have a hope of having an effect.

For other vegetables such as tomatoes, peppers and other fruiting vegetables that may be planted for late harvest fungicide applications should be made before the rains arrive not after. Prevention is the key to control. If the label allows, adjuvants that help products adhere to the plants should be considered. Spreader-stickers would be encouraged if the crop and label warrant it.

In crops where cottony leak caused by Pythium could cause crop loss, such as snapbeans and lima beans, application of one of the phosphonate fungicides such as ProPhyt or Phostrol would be suggested at maximum rates, or Ridomil Gold/Copper on snapbeans only. There is a 24c label for Ridomil Gold/Copper (2.0 lbs/A) in DE, MD and VA for cottony leak on snapbeans. Lima bean growers will want to scout carefully once this storm clears out for downy mildew. Wet soil and cool temperatures will favor downy mildew infection.

Cucurbit downy mildew is present on pumpkin now in the sentinel plot in Newark in New Castle County. This is the first report of downy mildew on pumpkin. It has probably been there for several days. Growers should continue to apply fungicides for leaf diseases including downy mildew.

 

Phytophthora Fruit Rot on Cucurbits

Friday, June 24th, 2011

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

Conditions have not been very favorable for fruit rot lately but we always seem to run the risk of scattered thunderstorms and frog-strangling rain events at this time of the year. Phytophthora blight is a tough disease to control, but if you have cucurbits in fields that had fruit rot in the past you are at very high risk if the soil stays saturated even for a few hours. This is a fungus that moves in water and the spores will move where water goes. (Spores will not move more than a few feet in the air.) Some additional cultural controls would be rotation (5 years or more) for watermelons, sub-soiling between the rows before they close to help water drain faster and to keep the fruit out of standing water. Fungicides will only suppress the disease and those that have the best activity are the following: Presidio, Revus, Ranman plus a surfactant (see label), Forum, Gavel and Tanos. Depending on the test, the season, and the location, the efficacy of these fungicides varies. However, proper application of these products will result in better yields than in untreated fields. Remember that Revus and Forum are Group 40 fungicides and have the same mode of action, so they should not be applied in succession. All of these fungicides except Ranman should be tank mixed with fixed copper if the label allows. Fixed copper is not compatible with Ranman plus the surfactant. Good coverage of fruit is very important. For more information on fungicides check the 2011 Commercial Vegetable Production Recommendations.

 

 

Watch for Phytophthora Fruit Rot on Cucurbits

Friday, June 25th, 2010

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

Be on the lookout for Phytophthora fruit rot on cucurbits, especially watermelon. After last seasons’ losses from Phytophthora fruit rot due to the excessive rainfall in 2009, growers should be thinking about the possibility of fruit rot this season. We are at risk for Phytophthora blight if the scattered thunder storms, along with the frog-strangling rains that we can get, occur like they did Tuesday evening. Phytophthora blight is a tough disease to control, but if you have cucurbits in fields that had fruit rot last season you are at very high risk if the soil stays saturated even for a few hours. This is a fungus that moves in water and the spores will move where water goes. (Spores will not move more than a few feet in the air.) Some additional cultural controls would be rotation (5 years or more) for watermelons, sub-soiling between the rows before they close to help water drain faster and to keep the fruit out of standing water. Fungicides will only suppress the disease and those that have the best activity are the following: Presidio, Revus, Ranman plus a surfactant (see label), Forum, Gavel and Tanos. Depending on the test, the season, and the location, the efficacy of these fungicides varies. However, proper application of these products will result in better yields than in untreated fields. Remember that Revus and Forum are Group 40 fungicides and have the same mode of action, so they should not be applied in succession. All of these fungicides, except Ranman, should be tank mixed with fixed copper if the label allows. Fixed copper is not compatible with Ranman plus the surfactant. Good coverage of fruit is very important.

On pickling cucumbers, fruit rot fungicides should be applied soon after flowering when the fruit are one inch long and repeated once they are three inches long for the best results. Data from Michigan State indicate that Presidio, Revus, Gavel , Forum (Acrobat), and Ranman provide suppression of fruit rot. Remember that Revus and Forum are Group 40 fungicides and have the same mode of action, so they should not be applied in succession.

Phytophthora Blight on Watermelons

Friday, August 21st, 2009

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

In the past three weeks I have received many reports of Phytophthora blight in watermelon fields on Delmarva. This disease appears to be especially common this year on watermelons. We have had a few periods during the summer where we had high volume rain events. The threshold that usually triggers disease development is 2 inches of rain that falls over a short enough period of time to pool in the field. If soil is saturated for 5 to 6 hours, the zoospores are released and a new infection cycle will begin. Optimum temperature for spread is 28C (82°F). There are several reasons that disease might be especially severe this year. In addition to high volume rain events, soil compaction may be greater this year because growers had to work in fields during June when soil remained wet from frequent rains. Soil compaction would slow drainage and increase the length of soil saturation.

Management practices for this disease must begin prior to planting. Remove infected debris from fields, including, where possible, diseased fruit. Cultural practices for management of Phytophthora blight are to improve soil drainage through tillage, use raised beds and reduce soil compaction. Alternate hosts include beans (snap and lima), cucurbits (pumpkin, melons, cucumbers, etc.), eggplants and tomatoes.

Fumigants such as K-pam. Vapam and Telone will reduce plant death, but fumigation should not be used as a stand-alone practice. Fumigants and fungicides, used in an overall disease management program, which includes cultural practices, is the best approach.

The fungicides available for Phytophthora blight control are, at best, suppressants of disease. Forum, Gavel, Tanos, Presidio, Revus and Ranman are labeled. Bob Mulrooney wrote a good overview of treatments in a Weekly Crop Update article a few weeks ago http://agdev.anr.udel.edu/weeklycropupdate/?p=1209

phytophthora fruit rot on watermelonPhytophthora fruit rot on watermelon

"felt-like" Phytophthora sporulation on watermelon fruit“Felt-like” sporulation on fruit

 

Phytophthora Fruit Rot on Cucurbits

Friday, June 26th, 2009

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

As harvest approaches for some cucurbit crops and other plantings are beginning to flower this is the time to be planning controls if the crop is at risk from Phytophthora fruit blight. Although Gavel and Revus are not effective on cucumber downy mildew they do suppress Phytophthora fruit rot. To help suppress development, apply mefenoxam or metalaxyl at planting. The following materials will help provide suppression of the fruit rot phase only:

● Forum (dimethomorph, 40) at 6.0 fl oz 4.18SC/A – must be tank mixed with another fungicide active against Phytophthora blight on muskmelon, such as fixed copper

● Gavel (zoxamide + mancozeb, 22 + 3) at 1.5 to 2.0 lb 75DF/A (Note: some muskmelon cultivars are sensitive to Gavel)

● Tanos (famaxodone + cymoxanil, 11 + 27) at 8.0-10.0 oz 50DF/A

● Ranman (cyazofamid, 21) at 2.75 fl oz 400 SC/A plus an adjuvant, see label for details

● Presidio (fluopicolide, 43) 4.0 fl oz/A – plant back or rotation restrictions of 180 days for all crops other than cucurbits and fruiting vegetables. See label for details.

● Revus (was inadvertently omitted last week) (mandipropamid, 40) 8.0 fl oz/A – must be mixed with a fixed-copper fungicide.

phtophthoracucPhytophthora fruit rot on pickling cucumber

 phytophthorafruitrot1Phytophthora fruit rot of watermelon

Phytophthora Blight on Cucurbits

Friday, June 19th, 2009

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

Phytophthora blight is beginning to show up in summer squash fields in New Jersey. This should be a warning to us here in DE that our cucurbits are also at risk, especially if cucurbits, peppers or other susceptible crops have been grown in the fields. As the early pickles begin to flower this is the time to be planning controls if the crop is at risk from Phytophthora fruit blight. To help suppress development apply mefenoxam or metalaxyl at planting. The following materials will help provide suppression of the fruit rot phase only:
● Forum (dimethomorph, 40) at 6.0 fl oz 4.18SC/A (must be tank mixed with another fungicide active against Phytophthora blight on muskmelon, such as fixed copper

● Gavel (zoxamide + mancozeb, 22 + 3) at 1.5 to 2.0 lb 75DF/A (Note: some muskmelon cultivars are sensitive to Gavel)

● Tanos (famaxodone + cymoxanil, 11 + 27) at 8.0-10.0 oz 50DF/A

● Ranman (cyazofamid, 21) at 2.75 fl oz 400 SC/A (plus an adjuvant, see label for details)

● Presidio (fluopicolide, 43) 4.0 fl oz/A; plant back or rotation restrictions of 180 days for all crops other than cucurbits and fruiting vegetables. See label for details.

phytophthora fruit rot on watermelonPhytophthora fruit rot of watermelon

Increase in Soil Rots May Be in Store for Area Cucurbits

Friday, June 5th, 2009

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

Last week Gordon Johnson wrote an excellent article, “Tough Year for Early Peas,” about problems with peas due to the wet soil conditions we have had in our area resulting in “soil rots”. We have had anywhere from 2-5 inches above average rainfall for the month of May throughout the Delmarva area, which has resulted in the second wettest May over the last 50 years for many areas. Last year we also had a very wet May; it was the third wettest May in many areas of Maryland, which resulted in many more root rot problems in cucurbits, i.e., watermelons, cucumbers, cantaloupes, pumpkins, etc. We can probably count on similar problems this year in the field as the June forecast calls for wetter than normal conditions.

The symptoms in watermelon fields usually begin with leaves flagging on a few plants down a row and then a few days later a total collapse of those same plants. Sometimes the wilting occurs within certain rows while in adjacent rows the watermelon plants look fine (Fig 1a). If wilted plants are dug up you can see reddish-brown discoloration of the crown of the plant (Fig 1b). The roots will be decayed as well. There are several fungi that can cause crown and root rot diseases, including Fusarium, Pythium and Phytophthora. To identify the specific fungi involved, samples should be sent to a diagnostic laboratory for testing. The disease often starts with a few plants in one row then moves down that row. Water, either through irrigation or heavy rains is usually responsible for the movement of the disease down a row. High plant loss can occur in the lower areas of fields where water stands after heavy rains. In the last month we have had several days of heavy rains with water sitting in fields, which will stress young plants and allow root rot diseases to get started.

 watermelon rows with and without fusarium crown rot

Fig 1a. Watermelon rows with and without Fusarium crown rot

plant with crown rot 

Fig 1b. Watermelon plant with crown rot

One thing growers can do for root and crown rot diseases is to be sure to not over water the plants or apply excess nitrogen. Rotation helps somewhat, especially for Fusarium wilt, but the root and crown rot pathogens can infect many hosts, making crop rotation less effective in reducing disease. Environmental conditions are probably the most important component for the development of root and crown rot diseases. Well drained fields will have less of a problem than poorly drained fields.

Besides seed treatments containing fungicides which will protect the seed from rots, there is a biological control that can be seed applied (preferred application method) or drenched onto the transplant that will help protect the plant from soil rots. The product is T-22 a naturally occurring fungus, Trichoderma harzianum, strain T-22. Trichoderma grows on the surface of roots, where it provides disease control and enhances root growth. Its spores survive in the soil, but the food it exists on is secreted from the root surface. The fungus multiplies on its own, protecting the roots over the growing season. The fungus, however, does not work very well if fields have standing water in them over a period of days, so it is important to keep your fields well drained.

Phytophthora Blight Management in Cucumber

Friday, July 11th, 2008

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu and Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Heavy localized rainfall in our region has resulted in pockets of Phytophthora blight, especially on cucumber. While there is no way to avoid these rain events, there are practices and products that can alleviate some of the losses to Phytophthora blight. Management of Phytophthora blight should be based on cultural practices that minimize standing water on the crop. This means planting only in fields with good drainage, not planting in low areas, subsoiling fields before planting, avoiding over-irrigation, etc.

Several fungicides are registered for managing Phytophthora blight. While the labels may say “control”, it is more accurate to say these fungicides will “suppress” Phytophthora blight because the control is easily overcome if the weather favors disease development. The organism that causes Phytophthora blight is related to the one that causes downy mildew, therefore some of the fungicides can be used to target both diseases.

Below is a table that indicates which products are effective on downy mildew, and have some suppression on Phytophthora blight. Relative efficacy is not listed for Phytophthora blight because little comparison data exists.

Fungicide Efficacy on Downy Mildew and Phytophthora Blight

Product FRAC Code Efficacy on downy mildew Registered for Phytophthora blight suppression Comments
Ranman 21 Very Good Yes Use 2.75 fl.oz./A for Phytophthora blight
Presidio 43 Very Good Yes  
Previcur Flex 29 Very Good No  
Tanos 11 + 27 Good – Very Good Yes Use higher rate 8 to 10 oz./A for Phytophthora
Forum 40 Poor Yes  
Revus 40 Poor Yes  
Gavel 22 + M3 Good No  
Prophyt/Phostrol   Poor Yes  
Curzate   Good No  
Ridomil Gold combinations 4 Resistance Foliar formulations not labeled Soil applications can be used for Phytophthora suppression where no resistance occurs
Reason 11 Resistance Not labeled