Posts Tagged ‘cucurbit downy mildew’

Timing Pumpkin Harvest

Friday, September 21st, 2012

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

Many pumpkin fields in the mid-Atlantic have poor foliage cover and weak vines at this time due to foliar diseases such as powdery and downy mildews (Fig. 1). Some growers are looking at their pumpkin field wondering if they should harvest now and store the pumpkins or wait a little longer. Maintaining vine health through harvest is one of the most important considerations for good fruit and stem hardiness. Once the fruit is mature (you can test to see if the pumpkin is mature by pressing the end of your thumbnail into the flesh of the fruit, if little indentation is left in the fruit the pumpkin is mature) the pumpkins can be harvested at any time. The best time to harvest mature fruit is while foliage is still green and relatively healthy. If there is poor foliage cover before pumpkins reach full maturity the fruit and stem quality will be diminished leading to premature fruit breakdown. This includes fruit rotting in the field, sunscald and collapsed stems. Fruit can appear healthy, but the stems still collapse (Fig. 2).

Over the last 2 weeks I have seen a great deal of sunscald damage to pumpkins. Sunscald starts as a reddish area on the fruit that becomes sunken and appears flat (Fig. 3). Over time, this area usually becomes tan with secondary pathogens often invading the area oftentimes causing a black ‘mold’ to cover the damaged spot. If you do have reduced foliage due to disease or insect damage it is best to harvest the fruit and store. Although some growers use chlorine solutions as a post-harvest dip to protect pumpkins taken early from fields our research has shown no value from these dips. Pumpkins can be stored in a well-ventilated shaded area with temperatures between 50-70°F. In general, fully mature, disease free fruit can be stored for months under these conditions. I have kept healthy pumpkins (not jack-o-lanterns) in good shape on my front door step from mid-September until mid-December (yes I like pumpkins a bit too much). Pumpkins should not be stored around apples as the apples emit ethylene gases that accelerate the ripening process, which could lead to premature breakdown.

Figure 1. Loss of foliage due to downy mildew

Figure 2. Healthy looking fruit, but rotting stem

Figure 3. Sunscald damage to pumpkin fruit

Watermelon Downy Mildew Altert!

Monday, August 20th, 2012

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

Downy mildew on watermelon was confirmed in Wicomico County, MD today. When downy mildew is present, watermelon growers need to modify their spray programs because the materials that are typically used for managing more common diseases are not effective on downy mildew. Growers should add additional materials to their spray program. Do not delay sprays because preventative applications are much more effective than applications made after disease is detected. Sprays should be applied on a 7-day schedule. Remember that materials with different Modes of Action (FRAC groups) should be alternated.

The following products have been effective on cucurbit downy mildew in our area. They should be tank-mixed with a protectant fungicide such as chlorothalonil.

● Ranman (2.10 to 2.75 fl oz. 400SC/A, see label for details, do not apply with copper);

● Presidio at 3.0 to 4.0 fl oz 4SC/A

● Previcur Flex at 1.2 pt 6F/A

Other materials for that are good when used in a tank mix or in alternation are

● Tanos at 8.0 oz 50DF/A

● Gavel at 1.5 to 2.0 lb 75DF/A (Gavel contains mancozeb, which is a protectant, and does not need a tank-mix partner)

● Curzate at 3.2 oz 60DF/A

Alternatively Presidio may be applied through drip irrigation. See label for additional details and application information.

Consult the Commercial Vegetable Production Recommendations for further information on resistance management and available fungicides (in Maryland, Extension Bulletin 236 and in Delaware, Extension Bulletin 137).

Pumpkin Downy Mildew Alert!

Friday, August 17th, 2012

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

Downy mildew on pumpkin and butternut squash is now present in many fields in Maryland and Delaware. Growers should scout their fields carefully. Preventative sprays are more effective than fungicides applied after the disease is established. On the lower surface the lesions are brown and angular. If viewed through a good hand lens, black flecks, which are the sporangia, may be visible. On the upper surface of the leaves the symptoms are more general and mimic many other diseases. Lesions on the upper surface appear as yellow angular spots that eventually turn brown and necrotic. Also, be aware that powdery mildew is also abundant in fields. Powdery mildew will appear as white granular spots, and is also prevalent on the leaves pictured below.

Downy mildew lesions lower surface

 Downy mildew lesions upper surface

There are several fungicides registered for managing downy mildew. The “targeted” products below should all be used in a tank mix with protectant product such as chlorothalonil or mancozeb. (These products are not effective on powdery mildew, so remember to include a product to control powdery mildew, also.)

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

 

Odd Year for Some Pests in Tomatoes and Cucumbers

Friday, August 10th, 2012

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

This has been a very hot dry summer so far and we would expect to see pests such as twospotted spider mites and their damage to be common, which we have. However, I have been surprised by the amount of worm (Lepidoptera larvae) damage in tomatoes. Usually worms are a problem in a few fields every summer where they do some damage, but the amount of damage they have done in some fields this year is much greater, around 15-20% of harvestable fruit in several instances. The biggest culprit seems to be yellow striped armyworm (YSAW) Spodoptera ornithogalli (Fig. 1). As the name implies the larvae have two bright yellow stripes on the upper part of the worm running the length of its body. The yellow stripe is often flanked towards the inside with black triangular-shaped markings. This worm species tends to feed on the foliage of many plants, but most of the damage I have seen this summer has been on the fruit with little feeding on the foliage. The fruit damage usually appears as surface feeding (Fig. 1) or feeding holes that are very shallow and do not penetrate too deeply into the fruit (Fig. 2). This often leads to a dry type of damage as opposed to the smaller, deeper holes that often lead to a wet rot (Fig. 2). The YSAW overwinters as pupa in the soil and becomes active in late May or mid-June in our area. This year it has become active much earlier than it normally does and has built its population earlier too. We usually do not see this much damage until late August. Management must take place early when larvae are small; once larvae become large they are difficult to control.

 Figure 1. Yellow striped AW and feeding damage on tomato

Figure 2. Yellow striped AW damage to ripening tomato fruit. Dry (yellow arrows) and wet damage.

Another surprise is that bacterial diseases are turning up in many tomato fields. Moist weather and splashing rains are most often needed for spreading bacteria. Maybe the presence of bacteria in the field is not too surprising, but what is surprising is the widespread nature of the bacterial spot, speck and sometimes canker diseases. Most tomato fields I have looked at in the last two weeks seem to have at least some if not a considerable amount of bacterial disease, usually on the lower leaves (Fig. 3) that in some cases has moved up to the pedicels of the fruit (Fig. 4). Infection of the flower or pedicel with bacterial spot is serious, causing early blossom drop (Fig. 5). From the pedicel the next stop for the bacteria, after a heavy thundershower, will be the fruit. A weekly mixture of mancozeb plus fixed copper or ManKocide should help with bacterial spot or speck, but once in the field, bacterial diseases are difficult to control. If a grower has an older tomato field that has bacterial spot in it that field should be plowed under as soon as possible as it will act as a nursery for spreading the disease to the younger tomato fields.

 Figure 3 Bacterial spot or speck on tomato

Figure 4. Tomato pedicels and blossoms with bacterial spot

Figure 5. Blossom drop due to bacterial infection (yellow arrows) and the start of a flower being aborted (red arrow).

The last ‘surprise’ pest has been the seemingly sudden appearance of downy mildew in cucumber fields (Fig. 6). This disease usually needs cooler weather that we have had little of this summer. But on the 21 of July we had a cool wet period when several areas in the mid-Atlantic set a record low for the daily high (77o F). Right after this brief cool down the downy mildew seemed to explode. Many of the cucumber fields I visited in southern and central Maryland that had been harvested at least once had downy mildew. Once it starts it can defoliate a patch of cucumbers very quickly leaving any fruit to sunburn (Fig. 7).

Figure 6. Downy mildew on cucumber leaf

Figure 7. Cucumber plants defoliated due to downy mildew resulting in sunburned fruit

Cucurbit Downy Mildew Update – August 10, 2012

Friday, August 10th, 2012

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

Within the last week cucurbit downy mildew has been confirmed in crops other than cucumber in the region, including a confirmation of CDM on butternut squash in Wicomico County, MD. Check the Cucurbit Downy Mildew IPMpipe at http://cdm.ipmpipe.org/ for information on all recent reports of CDM.

Disease ID for Pumpkin

Friday, July 20th, 2012

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

I recently wrote an update article about fungicide programs for pumpkin http://agdev.anr.udel.edu/weeklycropupdate/?p=4429. However, because many fungicides are effective on some diseases, but not others, it is important to be able to identify the diseases present in a field as you design your spray program.

Foliar Diseases
The most common foliar diseases of pumpkin are powdery mildew, downy mildew, white speck (Plectosporium), gummy stem blight and anthracnose.

Powdery Mildew

Figure 1a. Powdery mildew sporulation covering leaves and defoliating pumpkin plants.

 Figure 1b. Close up image of a leaf showing the “powdery” white sporulation on the upper surface of the leaf. Note that sporulation is usually seen first on the lower leaf surface. Scout a field by looking at the under surface of 45 old leaves in a field each week. Begin targeted sprays for powdery mildew when it is first observed.

White Speck (Plectosporium)

Figure 2. White speck or Plectosporium on the leaf causes tan spindle shaped lesions which form on the veins and result in distorted leaves. Plectosporium also causes lesions on the fruit (Figure 5).

Downy Mildew

Figure 3. Downy mildew lesions are initially seen on the upper surface as angular water soaked or yellow spots (3a) that are limited by the leaf veins. The angular nature of the lesions is especially evident on the lower leaf surface where sporulation occurs (3b). Look for grey angular lesions on the under surface of leaves after dewy nights. Lesions become necrotic over time.

Anthracnose

 Figure 4. Anthracnose will initially be small tan lesions with darker margins (image courtesy of B. Precheur, Ohio State Univ.). They will expand as they age and damage large portions of the leaf. They may develop small holes in the leaf. Anthracnose also causes lesions on the fruit (Figure 7).

Fruit Diseases
There are several pathogens that cause fruit rot on pumpkin. To manage fruit rot the single most important practice is to follow a good fungicide management program in the field. The same fungi that cause white speck, black rot and anthracnose also cause lesions on the leaves. If the leaves are protected from disease, the fruit will be less likely to become diseased. In addition to protecting fruit from rot, a good spray program will protect “handles” from damage and will maintain foliage health and keep sunscald at a minimum.

White Speck (Plectosporium)

Figure 5. White speck (caused by Plectosporium, formerly Microdochium) causes white or tan “pimples” on the fruit.

Black Rot

Figure 6. Black rot (caused by Didymella bryoniae the same fungus that causes gummy stem blight on the foliage) results in large grey lesions on fruit.

Anthracnose Fruit Rot

Figure 7. Anthracnose fruit rot (caused by Colletotrichum spp.) appears as smaller grey lesions on fruit.

Fusarium Fruit Rot

Figure 8. Fusarium fruit rot (Fusarium solani) causes a relatively dry fruit rot that initially appears as small white or pink spots as in this photo. Eventually however, the lesions may become black or tan because of saprophytic growth.

Southern Blight

 Figure 9. Southern blight on pumpkin fruit (Sclerotinia rolfsii) appears as a fan shaped white growth embedded with small round brown “seeds”.

Phytophthora Blight


Figure 10. A young target shaped lesion (10a) of Phytophthora blight (caused by Phytophthora capsici). Large lesion where fruit was in contact with soil (10b). Close up image of P. capsisi fruit lesion with felt-like sporulation (10c).

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).

Cucumber Downy Mildew Update – June 22, 2012

Friday, June 22nd, 2012

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

Downy mildew was confirmed on cucumber in Sussex County, Delaware this week. It was also confirmed on cucumber in the New Castle County CDM sentinel plot in Newark on Friday, June 22.  Continue with a good preventative program. The hotter weather is not as conducive to disease development.

Cucurbit Downy Mildew Alert!

Friday, June 15th, 2012

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

Cucurbit downy mildew was confirmed in Dorchester and Caroline counties in Maryland on June 12. Symptoms first appeared on June 8. This downy mildew occurrence is one month earlier than any occurrence in recent years. Growers should scout aggressively for this disease on cucumber and other cucurbits. This disease is favored by cool, humid weather including cool dewy nights. Weather during June 12-14 is forecast to be conducive to further spread. Tank-mix Ranman or Previcur Flex with a protectant fungicide and alternate sprays with a material with a different mode of action. Be careful not to rely on one fungicide class. Use excellent resistance management practices to avoid allowing the pathogen to develop resistance and to improve the efficacy of your fungicide management program. Presidio, which was commonly used in previous years, was not as effective as expected in 2011 University trials.

Downy mildew on the lower surface of a cucumber leaf. Notice the angular, water soaked lesions on this newly infected leaf. (Image courtesy of Bugwood and Gerald Holmes)

Consult the Commercial Vegetable Production Recommendations for further information on resistance management and available fungicides (in Maryland, Extension Bulletin 236 and in Delaware, Extension Bulletin 137). Because downy mildew has only been found on cucumber, targeted sprays on other cucurbits crops such as pumpkin, squash, watermelon, etc. are not necessary, at this time. Instead scout these crops aggressively and continue to apply a broad-spectrum spray program.

Cucurbit Downy Mildew Found in New Jersey

Friday, June 1st, 2012

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

Cucumber downy mildew was confirmed in Gloucester County, NJ on May 30 and reports of CDM from North Carolina are increasing. Cucumber growers are encouraged to apply preventative fungicides immediately and scout their crop for symptoms of disease. The progress of the disease can be monitored online at North Carolina State University’s Cucurbit Downy Mildew Forecasting Center at http://cdm.ipmpipe.org/index.php.