Pumpkin Season in Michigan: Tips for Successful Harvesting

As the pumpkin season in Michigan reaches its final stretch, it’s important to ensure that your pumpkins are in prime condition for harvesting. This is the time when the effectiveness of your growing season management practices becomes evident. While it’s normal to feel anxious before the October rush, it’s crucial to address any issues that arise. However, it’s worth noting that many problems discovered at this stage are often symptoms of poor early-season management or environmental conditions.

Powdery Mildew and Plectosporium Blight

One common issue that can affect pumpkins is powdery mildew and Plectosporium blight. Failing to control these diseases can lead to defoliation, sunburned fruit, and weak, brown handles. With limited effectiveness in rescue sprays, prevention is key.

Should you spray now? Yes, if the leaves, vines, and fruit you intend to harvest are still green. Poor handle quality can render the fruit unmarketable.

What to use? Start spray programs in August when heavy dews begin to form. Continuously rotate between at least two products with different FRAC codes. Tank mix with Bravo Weatherstik and a surfactant. The most effective products available include:

  • Inspire Super
  • Pristine 39WG
  • Procure 50WS
  • Quintec
  • Rally 40W
  • Vivando

Powdery mildew and Plectosporium blight
Image: A. Powdery mildew infestation of vines. B. Shriveled pumpkin handles are common when the vines die early from powdery mildew infection. (Photos by Ben Phillips and Mary Hausbeck, MSU Extension)

Fruit Rots

Fruit rots can be triggered by August rains in some fields, caused by a Phytophthora population. It’s advisable to avoid planting pumpkins from the round-stemmed Cucurbita maxima species in fields known to have a history of Phytophthora, as they are highly susceptible to fruit rots. The ridge-stemmed Cucurbita pepo and Cucurbita moschata species have some level of age-related resistance, which allows older fruit to resist rots better than younger ones.

Should you spray now? No. Preventative applications at fruit set, followed by a second application 14 days later, have been found effective in managing this disease. However, if wet conditions persist, additional applications may be necessary. It’s best to use a minimum of 40 gallons per acre with a boom sprayer or an air blast sprayer to penetrate the canopy and make contact with the fruit. Soil drenching is ineffective for fruit rots. Rotation away from other fruiting vegetables is crucial to prevent disease spread.

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What to use? The following products are effective against Phytophthora when applied proactively and rotated:

  • Forum 4.18SC
  • Gavel 75DF
  • Orondis Ultra
  • Presidio 4SC
  • Revus 2.09SC
  • Zampro

Fruit rots
Image: Fruit rots from excess moisture and disease can occur in the field or show up later in storage. (Photo by Ben Werling, MSU Extension)

Fruit Spots

Spots that appear on pumpkin fruits are often due to Angular leaf spot and bacterial leaf spot. These spots are caused by seed-borne bacteria that first infect the leaves and later the fruit. While mild cases are not a major concern, severe situations can lead to fruit rot. It’s important to refer to Michigan State University Extension’s “Bacterial disease of pumpkins: An old enemy and an emerging bacterial disease” for more information.

Should you spray now? No. Control at this stage is of no value. Preventative application of copper formulations is more effective than sprays after symptoms develop. It’s recommended to spray fruit when they are softball-sized until fruit set is complete.

What to use? Different copper formulations are available, but the tank mix solution should be within a pH range of 6.5 to 8 to decrease the risk of phytotoxicity in vine crops. Alternate and tank mix with other products, such as:

  • Mancozeb
  • Actigard 50WG
  • Tanos
  • Serenade Max WP

Bacterial spots on fruit
Image: Bacterial spots on fruit are suppressed by regular applications of copper and fungicides when leaves are infected. (Photo by Ben Phillips, MSU Extension)

Cucumber Beetles and Squash Bugs

Cucumber beetles and squash bugs can cause significant damage to pumpkin seedlings, particularly after planting. Mid-season growth is more tolerant of their feeding damage, but these pests can transmit bacterial wilt disease and cucurbit yellow vine disease. Control may be necessary if a significant number of fruit are in the green to orange transition phase and if you live in certain counties.

Should you spray now? Maybe. Control would only be necessary if you have a considerable number of fruit in the green to orange transition phase, especially if you live in the southern tier of counties where damage is prevalent.

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What to use? Pyrethroids are the primary mode of action for handling these pests mid-season:

  • Ambush 2EC
  • Assail 30SG
  • Brigade 2EC
  • Mustang Maxx
  • Pounce 25WP
  • Warrior II

Cucumber beetles and squash bugs
Image: Cucumber beetles and squash bugs can cause damage to pumpkin plants. (Photo by Ben Phillips, MSU Extension)

Aphids

Aphids are major vectors for viruses that can twist foliage and cause odd-shaped fruit. While spraying is not recommended at this stage, it’s important to note that aphids can colonize fruit after fruit set, resulting in defoliation and the presence of sugary honeydew. This honeydew can be colonized by a black sooty mold.

Should you spray now? Probably not. Unless your vines and fruits are still green, spraying them so close to harvest may not be economical. If aphid colonies have grown to form hotspots in your field, a few weeks ago would have been a more appropriate time to spray.

What to use? Scouting and spot treatments can prevent the spread of aphids. The following products are applied to the foliage:

  • Actara 25WDG
  • Assail 30SG
  • Beleaf 50SG
  • Exirel 0.83E
  • Fulfill 50WDG
  • Malathion 5EC
  • Warrior II

Aphid honeydew with sooty mold
Image: Aphid honeydew colonized by sooty mold. (Photo by Ben Phillips, MSU Extension)

Sunburn

When pumpkin plants lose their leaves or fruits are cut from the vines for field curing, the top sides of the fruit can be damaged by the sun on cloudless days with low humidity. Uncured fruit is particularly vulnerable, with shorter exposure to bright sun leading to discoloration and sunken areas.

What to do? Harvest pumpkins to cure in dappled or full shade or keep vines healthy to allow for curing in the shade of their leaves. This is similar to hardening off transplants in the spring but for fruit at the end of the season.

Sunburn on pumpkin
Image: Fruit showing sunburn damage. (Photo by Dan Egel, Purdue University)

Frost Damage

Pumpkins are also susceptible to frost damage. It’s important to note that the average first frost in the Lower Peninsula of Michigan occurs around October 15. Some years, the first frost arrives by mid- to late September. The northern Lower Peninsula and Upper Peninsula often experience earlier first frosts. Frost damage manifests as water-soaked spots on the upper surface of the fruit, softening the rind. Severely affected fruit may collapse in on itself, while ornamental and winter squashes may harden to some extent.

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What to do? Maintaining green leaves in the field helps shield fruit from frost damage. Additionally, covering wagon loads or piles in the yard can protect harvested fruit.

Water-soaked appearance on vegetables
Image: “Water-soaked” appearance is a common identifier of freeze damage on fruiting vegetables. (Photo by Ben Phillips, MSU Extension)

Ensuring a Successful Harvest

As we approach the main focus of picking and marketing pumpkins, it’s essential to consider a few key factors. The best-quality pumpkins are cured in the field, in the dappled shade of their own leaves. Maintaining green plants for as long as possible allows the fruit to mature on the vine. Harvesting is recommended when the leaves are dying, and the fruit is over 50% orange. Pumpkins harvested earlier than this may turn dull orange but won’t become hard, mature fruit and are prone to rot.

When removing pumpkins from the field, clean off as much soil as possible. Consider placing them in a 10% chlorine dip if you suspect fruit rots may become an issue. Avoid harvesting in wet areas or keep such fruit separate to minimize fruit-to-fruit contamination.

Displaying your pumpkins attractively is crucial for sales. Keeping displays well-stocked and promptly removing rotting pumpkins will maximize sales. Remember, there is a direct correlation between nice weekend weather in October and pumpkin sales, so ensure your displays are in great shape during those times. Finally, don’t slack off in these last four weeks. The effort you put in now can make the difference between a good year and a great year.

Pumpkins that will make it
Image: Pumpkins that will mature successfully if vines remain healthy. (Photos by Ben Phillips, MSU Extension)

Pumpkins that will not make it
Image: Pumpkins that may not reach maturity. (Photos by Ben Phillips, MSU Extension)

By implementing the right practices and ensuring optimal growing conditions, you can successfully complete the pumpkin season in Michigan and have a rewarding harvest.

For more information and resources, visit Ames Farm Center.