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Miss Floribunda: The great pumpkin vine decline

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Posted on: November 20, 2018

Dear Miss Floribunda,
Every year I grow pumpkins that I use for jack-o’-lanterns at Halloween and then for pies, breads and casseroles for Thanksgiving celebrations. Over the years, I’ve encountered a number of problems that I’ve been able to successfully research for myself. I spray with a milk and water mix to prevent mildew. I rotate the plants each year or so — generally to a part of my yard that I don’t want to mow. The vines sprawl all over even though I use a low-nitrogen, high-potassium fertilizer. I put waxed paper plates under developing fruit to keep burrowing “Peter Peter Pumpkin Eater” rodents from turning them into homes for their wives. During dry spells, I water to prevent leaf wilt and I hose off egg cases of insects.
But this October something terrible happened just when I thought I was home free. About two weeks before maturing to my satisfaction, the leaves on my pumpkins turned yellow and wilted almost overnight. I already had pumpkins, though not as large as I’d have liked. Of course they didn’t get any bigger and needed to be harvested early from the dead vines. I’ve seen leaf wilt in the past, but that always showed up earlier in the season, and even if I couldn’t stop it, at least I could start a new crop. What could this have been, and how can I prevent it in the future?
Blindsided on Livingston Street

Dear Blindsided,
My pumpkin-growing experts, Citrouille and Melonia Potimarron, believe that your pumpkins were attacked by a relatively new pumpkin blight called Cucurbit Yellow Vine Decline, also known as CYVD. It was first identified in Texas and Oklahoma in the late 1980s, and had travelled as far east as Pennsylvania by 2014. In October 2017, the University of Maryland Extension Service’s Vegetable and Fruit News reported its presence in our area. It is caused by the bacteria Serratia marcescens, for which the squash bug, Anasa tristis, is the vector. You probably stopped hosing your plants for insect eggs in August and September when we received so much rain in this area. The iridescent bronze-colored eggs of A. tristis take about two weeks to hatch, and it takes another four to six weeks for the insect to reach adulthood. The bacteria attack the phloem tissue of the pumpkin, while the adult insects suck sap directly from the leaves. The Potimarrons tell me that even were you willing to endanger pollinators by using insecticides, they wouldn’t work anyway. They believe that your best course is to attract some natural enemies of the insect. While ladybirds prey on the aphids that are vectors for other diseases, wasp egg parasitoids (Hymenoptera) are most effective for destroying this vector. Hubbard squash has been used as a trap crop, with some success. And of course, your practice of removing insect eggs whenever you find them is an excellent method of preventing all infestations.
What is most unfortunate is that the A. tristis overwinters very well in dry weeds and grass. You dare not compost dead vines, but should bag them for removal. In addition, you should mow wherever the vines meet the grass in your yard and dispose of the cuttings without composting them. Of course, you will want to rotate your pumpkin crop next year — perhaps in a grass-free area.  
To make up for bringing you bad news, let me invite you to an upcoming event that is sure to bring you some seasonal cheer. Please come to the Hyattsville Horticultural Society’s holiday wreath-making workshop on Saturday, Nov. 17. It will take place at the home of Mary Jane Stevens and Robert Meyer, 3925 Nicholson Street. After a brief meeting at 10 a.m., accomplished wreath makers will show you how to embellish your doors and tabletops for Thanksgiving and Christmas. Please bring plant cuttings and other decorative materials you would like to incorporate into them.



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