With the start of pumpkin harvest, it is a good time to review important considerations for harvest and postharvest storage of pumpkins and winter squash (butternut, acorn and hubbard squash etc.).
Pumpkin and winter squash should be harvested fully mature to reach their optimal quality and fulfill their potential for long shelf lives. Characters indicating fruit maturity include loss of rind surface gloss, ground spot yellowing, and hardening of the skin to the level that it is resistant to puncture with a thumbnail. Except for some striped varieties, mature fruit should have solid external color. If fruit have to be harvested pre-mature because of plant decline, these fruit won’t store as well as mature fruit. The best practice is to harvest the fruit as soon as they are fully mature and then store under proper conditions. If mature fruit are left attached to the vines, it increases the chance of disease infection on stems and fruit. For example plectosporium blight causes cosmetic damage on handles, and bacterial spot reduces quality and longevity of fruit. In addition, if diseases such as powdery mildew and downy mildew cause significant loss of foliage, fruit left in the fields are likely to suffer sunscald (Figure 1) and low quality handles as explained in this article https://vegcropshotline.org//article/powdery-mildew-of-cucurbits/. The high temperatures and bright sunshine experienced over the past few weeks in Indiana might help explain the increased reports of sunscald (or sunburn) that has been reported. Sunburn may start as minor skin discoloration in the field. The symptoms of such fruit may expand upon harvest, particularly if the fruit is stored in the sun.
In some situations like pick-your-own where mature fruit have to be held in the field, scout carefully to manage diseases and insects to maintain healthy vines and protect fruit. Recommended fungicides can be found at the Midwest Vegetable Production Guide for Commercial Growers.
Figure 1. A pumpkin fruit with sunscald due to lack of vine canopy (photo: Dan Egel)
After harvest, pumpkins may benefit from curing, especially when fruit show non-hardened skin and surface damage. Curing is conducted under temperatures between 80 to 85°F in a shaded area for about 10 days. Studies have shown that curing heals wounds, hardens the rind, enhances fruit color and increases sugar content. If pumpkins are washed after harvest, be sure to dry them thoroughly before curing. It should be noted that curing is detrimental to acorn squash; it accelerates skin color change, deteriorates fruit texture and taste, and stimulates fruit decay.
Pumpkins and winter squash are best stored at temperatures between 50 to 55°F and relative humidity between 50 to 75%. With higher storage temperatures, excessive loss of weight, color and eating qualities might be experienced. When temperatures are above 55°F, the surface of acorn squash becomes yellow and flesh becomes stringy. Under the optimal storage conditions, acorn squash can be stored for 5 to 8 weeks, pumpkins and butternut squash for 2 to 3 months, and hubbard squash for 5 to 6 months. Both pumpkins and winter squash are sensitive to ethylene. They should not be stored near apples, ripening tomatoes or cantaloupes. When temperature is below 50°F, fruit might develop chilling injury (Figure 2). Pumpkins, butternut and acorn squash may survive one or two cold nights in the field, however, a frost might lead to fruit rot. If fruit is displayed in the field or a farm stand, they should be protected if frost is anticipated.
Figure 2. Chilling injury on butternut squash.