Posts Tagged ‘pumpkin’

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

How Late is Too Late for Pumpkins?

Friday, August 31st, 2012

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

Delayed fruit set in pumpkin can be due to many factors including late planting, heat and water stress, poor pollination and excess fertility (too much N). When set is delayed until August, the question is will the pumpkin develop and color in time for sales.

Under favorable summer growing conditions pumpkins will start to color about 4 weeks after fruit set and will be completely colored by 7 weeks after set. If fruit set is delayed until August, reduced day lengths and cooler temperatures may increase the time for full color development. Varietal differences in days to maturity also come into play.

In research at Purdue University, reported by Liz Maynard in the Purdue Vegetable Crops Hotline, pumpkin fruit (Magic Lantern and Gold Medal Varieties) that set in August were tagged and then evaluated for maturity in October. They found that “for pumpkins planted June 16 or June 25, out of 88 flowers that opened between Aug. 10 and Aug. 21, at least 70% produced pumpkins that were either turning or fully orange by Oct. 2 and 10, respectively. The remaining 20 to 30% either never set a fruit, or the fruit was still immature at the time of harvest. Of 14 flowers that bloomed between Aug. 22 and Sept. 3, 43% produced turning fruit by October 10, and none produced fully orange fruit by that date”.

This indicates that pumpkins set in mid-August will be ready for October sales. In fields with delayed set, it will be critical to keep vines healthy through September. This will mean additional fungicide sprays through the month with special attention being paid to powdery mildew and downy mildew.

Poor Fruit Set in Pumpkins

Friday, August 17th, 2012

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

Each year we see pumpkin fields with poor fruit set or fruit carry. Remember that in larger pumpkin sizes, each plant will only carry 1-2 fruits. The large vining plants also need considerable space – 25 to 50 square feet per plant. While planting Jack-o-lantern types at higher densities might at first seem to be a way to achieve higher yields, interplant competition will increase and you can decrease fruit carry because of this competition.

Too much available nitrogen can also delay pumpkin fruit set so that many of pumpkins that are produced do not reach maturity in time. Pumpkins do not normally need more than 80 lbs/acre N to grow a crop. Anything above 100 lbs/acre N will cause the pumpkins to put on excessive vine growth and limit fruiting.

A major reason for poor fruit set in some fields this year is high temperatures during flowering in July. Day temperatures in the 90s or night temperatures in the high 70s will cause flower and small fruit abortion. For pumpkin growers that do wholesale and start shipping right after Labor Day, this will limit early pumpkin availability. Varieties vary considerably in their ability to tolerate heat and to set under hot conditions. Inadequate irrigation and excessive water stress can also reduce fruit set, increase abortions, and reduce fruit carry. High temperatures and water stress reduce photosynthesis and the ability of the plant to carry fruits. Drought can also cause a higher than normal male/female flower ratio, thus affecting the amount of fruit per plant.

Another major factor that will reduce fruit set is poor pollination. Misshapen fruit can also result from inadequate pollination. A pumpkin plant has both male and female flowers and the first female flower opens one week after the first male opens. The flowers only last a few hours, blooming at dawn and closing later in the morning but well before noon. Pollinators need to be active during this short period.

Native pollinators can be very effective in pollinating pumpkins and some research has shown that most of the fruit set is occurring because of these native pollinators. In particular, bumblebees and squash bees are active in pumpkins. The squash bee is of particular interest because it has evolved along with pumpkins and squash in the Americas and is dependent solely on pollen from pumpkin and squash plants.

Other research has shown that honeybees do provide additional pollination benefits above what native pollinators are providing. In research from Illinois, Walters and Taylor found that while pumpkin fruit number was not increased with the addition of honeybees, pumpkin weights and size were increased significantly.

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

 

Striped Cucumber Beetle Populations Still Very High

Friday, July 27th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu and Karen Rane, Extension Specialist Entomology, University of Maryland rane@umd.edu

We have seen very high populations of striped cucumber beetles on squash, pumpkins, cantaloupe, watermelon and other cucurbits over the last few weeks. These populations at times have reached over 20-30 beetles per plant. If a spray was missed or plants were not thoroughly covered with an insecticide application the beetles would soon consume that unprotected area very rapidly (Fig. 1). This area is often times the base of the plant. This is especially true if the cucurbits are sprayed with an air-blast sprayer. While air-blast sprayers do a good job of covering leaves with material, they often do not do a great job of covering the base of a plant and heavy feeding can occur (Fig. 2). The feeding can lead to plants being girdled by beetles or can lead to bacterial wilt infection—even though the leaves of the plant show almost no feeding. This feeding by the beetles also opens the base of the stem to infection from soil organisms and greater rates of Fusarium and bacterial soft rots are possible. When beetle populations are this high the base of the plant, even more so than the foliage, needs to be protected from heavy feeding.

Figure 1. Two squash leaves fed upon heavily by striped cucumber beetles because of the lack of good spray coverage.

Figure 2. Base of pumpkin plants damaged by striped cucumber beetles due to poor spray coverage

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).

Pollination Disorders in Cucurbits

Thursday, July 12th, 2012

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

Watermelon harvest is underway on Delmarva; cantaloupe harvest started early this year, squash and cucumbers have been producing for over a month; and pumpkins and winter squash are setting fruit in earlier plantings. Each year, we see pollination problems with vine crop fruits, especially when weather conditions are unfavorable.

Signs of incomplete pollination in cucurbits include bottlenecked fruit or fruit with a pinched end, crooked or lopsided fruit, fruit small in size or nub-like; and fruits with prominent lobes or that are triangular in shape. Causes of incomplete pollination may be inadequate pollen transfer by pollinating insects; inadequate pollen sources (pollenizers); or hot, dry weather that reduces pollen viability or that desiccates flower parts during pollination. Research has shown that a minimum of 1,000 grains of pollen are required to be distributed over the three lobes of the stigma of the female flower of a watermelon to produce a uniformly shaped fruit.

Hollow cavities in fruit and vacant seed cavities are related to lack of seed formation, again traced back to poor pollination. Fruit tissue separation, such as hollow heart in watermelon, may also be due to inadequate pollination and may be worsened by rapid fluctuation in environmental conditions affecting fruit development.

Fruit Loads in Vine Crops

Friday, June 29th, 2012

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

Early watermelons are sizing now, later plantings are setting fruit, pickle harvest is underway, and pumpkin planting is finishing up. A common question from growers and crop consultants is how many fruit should a plant carry and what will affect fruit set and fruit “carry” in vine crops.

For watermelons, a healthy, vigorous plant may set 3-7 fruits initially. However, for mid-size and larger watermelons, the plant will only carry 2-4 fruit at any time. Smaller fruited varieties will more fruits per plant but essentially the same amount of pounds as larger types. This is the carrying capacity of the plant and is directly related to the quantity of photosynthates being produced by the plant, mostly in the leaves. Any additional fruits, even if initially set, will be aborted. Once the first fruit ripens and is harvested, additional sets can be carried. To carry the maximum amount of fruit, it is necessary to maintain high plant vigor and good foliage health. This requires paying close attention to irrigation and fertility programs; having excellent disease, insect, and mite control; and having good pollinator activity during pollination and fruit set. If average fruit carry is less than 2 per plant in watermelons, that is a sign that the plants have reduced vigor and are under stress. Repeated fruit set depends on maintaining vine health through the season.

Another factor to consider is where fruit set is occurring. Crown sets are desired in watemelons, especially in early plantings. Crown sets are those that occur on nodes closest to the base of the plant, within the first 8 nodes. Having good crown sets requires that plants have good early growth so that adequate leaf area is produced that can support early set fruit as well as proper pollination (sufficient bees). Lack of crown set is a sign of poor early growth, early plant stress, or of problems with pollination.

With pumpkins the carrying capacity is similar; however, because pumpkins are not repeat harvested as are watermelons, harvest is limited to those fruits set initially. Medium sized Jack-o-lantern types will carry 1-2 fruits, larger types closer to 1. All others will be aborted. Smaller types will carry more depending upon their size in pounds (for example a variety with 5 lb. average will carry 4-7 fruits). Maximum carrying capacity in pumpkins is largely affected by variety (varieties with some heat tolerance will carry more fruits in our climate) and foliage health. Excess nitrogen fertilization will often delay fruit set in pumpkins.

In gynoecious cucumbers grown for once over pickle harvesting, there will be two fruits set on adjacent nodes that are ready for harvest at any one time. These will be set on nodes 2-6 commonly. The pollinizers that make up a small percentage of the population will set pickles every fifth node generally and therefore only one fruit will be ready for harvest. Yield reductions in gynoecious pickling cucumbers occur when there is a loss of set so that fruits are not on adjacent nodes. Parthenocarpic pickle varieties that set fruit without pollination will commonly have 4-6 pickles on 3-5 adjacent nodes ready for harvest at any one time. This allows them to be planted at much lower densities.

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).

Leaf Aging in Cucurbits

Friday, June 22nd, 2012

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

We are starting to see the oldest leaves (crown leaves) in watermelons, cantaloupes, squash, cucumbers, and pumpkins with large areas that are discolored (white, tan, or bronze). These leaves will be brittle to the touch and may start to tear or shred with high winds and storms. This condition is common in cucurbit crops and can be due to a number of leaf aging factors including mineral nutrient scavenging (export of mobile nutrients from oldest leaves to newer leaves), ozone air pollution damage, chemical phytotoxicity, repeated stress cycles, and wind injury. Leaf cells that die will leak their contents, releasing enzymes and oxidizing chemicals affecting nearby cells thus accelerating the “aging” process. This results in large patches of dead leaf cells that then dry, making the leaf feel brittle. If leaf veins are damaged, water and food transport will be compromised, accelerating leaf decline. This leaf aging is not to be confused with damage from mite feeding which is also concentrated on oldest leaves.