Pumpkin and Winter Squash Harvest and Storage
Posted: September 10, 2015
Winter squash and pumpkin fruit that remain in the field face a daunting list of diseases, insects and weather events that could threaten fruit quality. Early harvest and careful storage is often preferable to leaving fruit in the field. This is especially true if you know that your pumpkins or squash are in fields that are infected with Phytophthora blight (Phytophthora capsici) as symptoms can develop on fruit even if they are asymptomatic at harvest.
Since the pumpkin market lasts from Labor Day to Halloween, pumpkins may need to be held for several weeks before they can be marketed. When is it best to bring then in, and when to leave them in the field? If the vines are in good condition, the foliage can protect the fruit from sunscald. If foliage is going down from powdery mildew or downy mildew, this may help with ripening and make harvesting easier, but also increases the risk of sunscald or injury to pumpkin handles.
There can be extra work involved in bringing fruit in early, especially for growers who normally have pick-your-own harvest. However, we recommend that growers harvest as soon as crops are mature and store under proper conditions, if it is feasible. If you need to hold fruit in the field for pick-your-own or any other reason, using a protectant fungicide (e.g. chlorothalonil) can protect against black rot and some of the other fruit rots. Scout for insects feeding on the fruit and handles, which may include squash bug nymphs or adults, striped cucumber beetle, and squash vine borer and control them if damage is evident. See the New England Vegetable Management Guide for treatment recommendations.
What about pumpkin stems, i.e. handles? In some cases, it’s the handle that sells the pumpkin. Pumpkins may not be marketable if the handle is broken off or dried up. Ideally, if the timing is right, pumpkins would be cut from the vine one to two weeks prior to marketing. However, if they are harvested now they may sit much longer before being sold. The discussion of how early to cut handles is an old one with many different opinions. One view is that it is advisable to cut the handles from the vine to save them from advancing powdery mildew and reduce shrinkage. Whether or not handles shrink and shrivel after cutting is affected by plant stress, genetics (variety), moisture and temperature conditions, and disease. There are many diseases that can affect handles, including Powdery mildew, Plectosporium, Fusarium, Black Rot, and Alternaria. Again, proper curing and storage conditions are key.
Ideally, pumpkins should be harvested when fully mature, with a deep orange color and hardened rind. Similarly winter squash should be harvested when mature, as indicated by corking of the stem, loss of rind surface sheen or gloss, groundspot yellowing, and die-back of the tendril nearest to the fruit. As long as pumpkins have started to turn color, they will ripen off the vine if held under the proper conditions. While not ideal, this may be preferable to leaving them in the field if conditions are not favorable.
If necessary, pumpkins can be ripened in a well-ventilated barn or greenhouse. The best temperatures for ripening are 80-85°F with a relative humidity of 80-85%. Night temperatures should not drop below the sixties. These are the same conditions as those used for curing. A period of curing is often recommended for squash or pumpkin showing non-hardened skin or surface damage. However, research on this subject has produced variable results, and shows that curing squash is not consistently beneficial when the squash shows no damage or is well matured in the field. The curing period is typically about 10 days. During this process the fruit skin hardens, wounds heal, and immature fruit ripens – all of which prolong the storage life.
Take care to avoid subjecting squash or pumpkin to chilling injury. Chilling hours accumulate when squash or pumpkin is exposed to temperatures below 50°F in the field or in storage. Injury increases as temperature decreases and/or length of chilling time increases. Storage life depends on the condition of the crop when it comes in and your ability to provide careful handling and a proper storage environment. All fruit placed in storage should be free of disease, decay, insects, and unhealed wounds.
When harvesting squash and pumpkins, it is important to handle the fruit with care to avoid bruising or cutting the skin. Despite their tough appearance, squash and pumpkin fruit are easily damaged. The rind is the fruit’s only source of protection. Once that rind is bruised or punctured, decay organisms will invade and quickly break it down. Place fruit gently in containers and move bins on pallets. Use gloves to protect both the fruit and the workers. Removal of the stem from squash (butternut, Hubbard, etc.) will also decrease the amount of fruit spoilage because the stems frequently puncture adjacent fruit, facilitating infection. These fruits need a period of curing to heal the stem scar, which can be done in windrows in the field if weather is favorable.
Growers often plan to store winter squash until January, February or March. Select fruit that are free from disease and haven’t been subject to much chilling (below 50°F). Chilling injury is of particular concern with squash intended for storage because it increases the likelihood of breakdown. If squash has been exposed to chilling injury it should be marketed first and not selected for long-term storage. Remove squash from the field if temperatures are likely to drop below fifty degrees for any length of time. Be sure that storage areas have the capacity to maintain temperatures above 50°F throughout the storage space.
Pumpkins and winter squash should be stored in a cool, dry, well-ventilated storage area. Ideal temperatures are between 55° and 60° F with relative humidity of 50 - 70%. High relative humidity provides a favorable environment for fungal and bacterial decay organisms. Lower humidity can cause dehydration and weight loss. Higher temperatures increase respiration and can cause weight loss. Temperatures lower than 50° F cause chilling injury.
In a greenhouse, temperature can be managed with ventilation on sunny days; heaters will be needed for storage into November and beyond. Fruit temperature should be kept as close to the temperature of the air as possible to avoid condensation, which can lead to rot. Under ideal conditions, disease-free pumpkins should have a storage life of 8-12 weeks and butternut squash up to three or four months. Even if it is difficult to provide the ideal conditions, storage in a shady, dry location, with fruit off the ground or the floor, is preferable to leaving fruit out in the field.
As you plan for storage and marketing, keep in mind that the market for pumpkins seems to get earlier every year. Fall decorative displays include pumpkins, and those displays begin showing up as Labor Day approaches. One of the best solutions to early-maturing pumpkins may be finding an early market.