It has been a wet summer across much of Indiana, and conditions became more challenging after historic rainfall hit east-central Indiana in mid-August. I recently had a chance to visit several pumpkin fields in the region. The amount of damage directly associated with the heavy rainfall varied considerably from field to field, clearly demonstrating how site selection can set the first bar for success.
Phytophthora Blight
In the most severe cases, fields or portions of the fields were submerged for an extended period. I saw dead vines and rotting fruit, with samples confirmed to have Phytophthora blight. In these fields, the immediate priority should be to prevent the pathogen from spreading to unaffected areas within the field or to other fields.
Roguing—removing infected plants and fruit—is one practice that may help slow the spread of disease. However, its success depends on several factors, including how early the disease is detected and how extensively the pathogen has already spread. Read Roguing as a Tool to Manage Phytophthora Blight of Pumpkin to learn more about when and why this practice may or may not be effective.
There is no single practice that can manage Phytophthora blight. As Dr. Dan Egel wrote in Phytophthora Blight of Cucurbits:
Management of Phytophthora blight with fungicides is not possible unless cultural methods are also implemented. Even the best management schemes, chemical and cultural, may fail to control Phytophthora blight completely when weather conditions are conducive to the disease.
Although managing Phytophthora is particularly challenging in wet years, understanding the disease’s biology and taking timely preventive measures can make a difference. The articles suggested above provide additional management recommendations.
Vines Decline
I also visited pumpkin fields where the fruit remained intact, but became exposed as vines wilted or declined. One farmer described vines that had been knee-high before rapidly wilting shortly after the heavy rain. In this situation, the decline was likely due to root injury from saturated soil and lack of oxygen in the root zone. Plants can be particularly vulnerable to these stresses when they are carrying a heavy fruit load.
Although many pumpkins in these fields had developed good color, their rinds had not fully hardened. This raises a practical question: Should these pumpkins be harvested now or left in the field?
There are several factors to consider, and there is likely a trade-off. Growers may hesitate to harvest because the pumpkins have not fully matured and market prices may not be at their best in August. However, once most of the functional foliage has been lost, the benefit of leaving fruit in the field to continue maturing and hardening diminishes significantly. At the same time, loss of the canopy exposes fruit to greater risks of sunscald, disease, and insect injury. These problems can quickly reduce marketability and fruit value.
Partially mature pumpkins can continue to develop and harden after harvest under appropriate curing conditions. Curing is generally favored by warm temperatures (around 80 to 85°F), good ventilation, and protection from direct sun. However, pumpkins harvested before full maturity may not store as well as fruit that fully mature on healthy vines. Another potential benefit of harvesting fruit that are close to maturity is reducing the fruit load on stressed plants. This may help the vines recover, which is essential to support the continued development of younger fruit.
Bacterial Spot
In addition to damage directly associated with heavy rainfall, bacterial spot of pumpkin, caused by Xanthomonas cucurbitae, was observed in several fields I visited, even though growers reported that copper products had been applied.
It is important to remember that copper products are protective rather than curative. Many factors can reduce their effectiveness, including repeated infection events, rainfall washing residues from plant surfaces, rapid canopy and fruit expansion, incomplete spray coverage, and infections that occurred before the most recent application.
Dr. Mohammad Babadoost at the University of Illinois has conducted extensive research on bacterial spot of pumpkin. He emphasized the importance of copper applications during early crop stages, noting that copper sprays become ineffective once an epidemic is underway (Illinois Fruit and Vegetable News, Vol. 17, 2011). It is worth noting that bacterial spot usually affects leaves first, then spreads to fruit. So early management is critical to slowing the spread of the disease.
Another disease, Plectosporium blight, which was also observed in multiple fields, can affect pumpkin fruit as well and may be confused with bacterial spot. Check the article “Plectosporium Blight of Pumpkin” for a comparison of symptoms between the two diseases.
For bacterial spot, Dr. Babadoost’s current program recommends two applications of Actigard after seedling emergence, followed by a spray program beginning at vine spread, alternating Manzate PRO-Stick + Kocide 3000 with Regalia + Kocide 3000. See the University of Illinois 2026 Recommended Pumpkin Spray Schedule for pumpkin spray recommendations.
I observed considerable differences in bacterial spot severity among fields and cultivars. In one field planted with multiple pumpkin and winter squash cultivars, one cultivar clearly had much more severe symptoms than the others. Although no commercial pumpkin and winter squash cultivars are marketed as resistant to bacterial spot, research shows meaningful differences in susceptibility among cultivars. In a study evaluating 81 commercial cultivars of gourds, pumpkins, and squashes, along with 300 Cucurbita accessions, C. pepo generally developed greater disease severity than C. maxima and C. moschata. However, there was also substantial variation among cultivars and accessions within the same species. Because it is difficult to directly compare many cultivars at once, growers can learn a great deal from their own fields by growing multiple cultivars. Take notes on which cultivars develop severe bacterial spot and which remain relatively clean under the same conditions. In a wet, disease-conducive year like this one, these observations can be particularly valuable when selecting cultivars for future seasons.
Yellowing Leaves
Lastly, I want to discuss yellowing foliage. Some leaf yellowing is not unusual as pumpkin plants approach the end of the season, but premature yellowing may be more common this year in wet areas because of root injury, nutrient loss, and disease.
In one field, I noticed premature yellowing associated with powdery mildew, with much of the visible fungal growth occurring on the undersides of leaves. This pattern is worth paying attention to when evaluating spray coverage. If a contact fungicide is deposited primarily on the upper leaf surface, the underside may receive less protection. Thorough canopy coverage is important when contact fungicides are the main component of a disease-management program.
Another disease that can cause pumpkin vines to turn yellow and decline is cucurbit yellow vine disease, a bacterial disease associated with squash bugs. Dr. Cesar Escalante recently confirmed the disease in Indiana. Growers should be particularly alert for this disease in fields where squash bug populations have been high. Read Pathogen Spotlight: Serratia ureilytica Causing Cucurbit Yellow Vine Disease for more information.
This wet season has created several challenges for pumpkin production, and the problems observed in individual fields often have multiple causes. Carefully examining field drainage, vine health, fruit maturity, disease symptoms, cultivar differences, and the timing of management practices can help growers make better decisions for the remainder of this season and provide valuable information for planning next year’s crop.