Tour highlights pumpkin pathogens, insect pests
KEEDYSVILLE, Md. — At last month’s Twilight Tour held by the University of Maryland Extension at its Western Maryland Research and Education Center, Dr. Kate Everts, a vegetable plant pathologist and Peter Coffey, small farm and alternative agriculture educator based in Carroll County, combined forces to discuss disease pathogens and insect pests commonly plaguing pumpkin crops.
Focusing her presentation on three disease pathogens common to pumpkin crops in the Mid-Atlantic region, Everts began with an observation that “downy mildew on cucurbit crops was pretty widespread in the Mid-Atlantic region.” She further cautioned that producers “need to be really monitoring” their fields for it.
In a later conversation, Everts further explained that the downy mildew present in this year’s cucurbit fields was not the same downy mildew that plagued hops crops during last summer’s rains.
“The downy mildew that goes to hops is closely related to the downy mildew that goes to cucurbits,” she continued, “but the one that causes disease on hops can’t cause it on cucurbits and vice versa.”
In contrast, this summer was very favorable in keeping two of the most common bacterial diseases at bay.
She reminded the tour’s attendees that both angular leaf spot and xanthomonas leaf spot are seed borne diseases; thus, it helps if pumpkin producers ensure they are getting clean seed.
She also suggested producers rotate out their pumpkins and other cucurbit crops for at least 2 years for bacterial diseases. “Bacteria don’t overwinter as well,” she explained to reinforce the need for producers to rotate out from fields where those pathogens have made an appearance.
Everts’ last disease pathogen, fusarium crown fruit rot, unfortunately lives much longer in the soil than bacterial pathogens dictating that pumpkin and cucurbit crops need to be rotated out every 4 years. The disease’s common symptoms include wilting of the plant’s leaves, dark brown rot at the crown and a distinctive white or pink discoloration in the crown and roots.
And, thanks to its long soil life, it not only impacts the plant, but can also “infect the fruit from where it comes in contact with the soil, even if the plant’s not wilted. To add insult to injury, in both instances, infected plant and infected fruit, “there’s no fungicide to control its symptom or protect the fruit from rot,” Everts said.
Given the combination of a lack of fungicides to combat it and it soil life hardiness, Everts recommended producers “should find out what disease pathogen you have to put together an integrated program to manage it in your fields.” Even in the research center’s fields, she said, “we see a little bit of fusarium crown rot every year.”
Due to its insidiousness, “it’s one pathogen you definitely want to keep records for,” she said. “Even noting where in the field it surfaced will help you manage it.”
Coffey also singled out three different insect pests common to pumpkin crops, beginning with the squash vine borer, “a moth that is a wasp mimic.” Squash vine borers “lay eggs on the stem of the squash plant,” Coffey continued. “The eggs hatch into a maggoty-looking caterpillar that chews its way into the stem.”
Coffey recommended Bt products to control squash vine borers noting they “chew up the insect’s guts and cause sepsis.” He cautioned, however, the insecticide “has to be on the plant when the egg hatches and before the caterpillar chews through to the inside of the plant.”
“It’s a very narrow window of control,” he continued. “Once the caterpillar is inside the plant, squash vine borers are very hard to control.”
The saving grace for producers is that “squash vine borers are bad flyers. So, if you’re already rotating out for soil borne diseases then you’re also controlling for this insect,” Coffey said.
Squash bugs are another pumpkin insect pest controlled more effectively at its immature, or nymph, stage. In particular, Coffey mentioned insect growth regulators such as Novaluron.
The adult squash bugs can also be controlled with plywood traps placed at row ends. If using this technique, Coffey stressed the importance of crushing the bugs in the traps on a regular basis, noting when commercial producers do so, they “can numerically decrease the bugs present in your fields.”
Due to time constraints, Coffey originally hadn’t planned to discuss cucumber beetles, which he had listed on his handout. That quickly changed at the urging of one of the Tour attendees, who indicated that cucumber beetles were the biggest insect issue in his pumpkin fields.
Noting the two varieties of cucumber beetles, spotted and striped, “have preferences about the varieties of squash” they infest, Coffey pointed out that producers face a conundrum: Producers pick their cucurbit varieties based on commercial needs, but those also happen to be the varieties which are more attractive to the cucumber beetles.
Further, the cucumber beetles are “really great at vectoring a bacterial wilt. Transmitted by the insect’s feeding, which gums up the plant tissue,” the bacteria then take advantage of the plant’s vulnerability.
Coffey noted “seedlings are most sensitive to these issues.” He recommended producers consider putting larger transplants in the field as late as possible to avert such difficulties.
Everts later acknowledged their ideal recommendations, particularly their crop rotation periods, can sometimes be difficult to implement.
“Growers make decisions based on a variety of information,” she said, “but you can’t change the biology of the pathogen system.”
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