Since pumpkin plants often continue growing into the fall when temperatures are dropping and trees are changing colour, it may seem natural that your pumpkin leaves change colour as well. While in certain circumstances this may be true, in most cases it is a sign of a problem with the pumpkin plant that requires attention.
A lack of sufficient nitrogen causes pumpkin leaves to lose their colour and begin turning yellow, often beginning along the edges. Although pumpkins do not need a large amount of nitrogen, and too much can actually result in less fruit on the vine, they do require some nitrogen to grow and bear fruit. Add a 6-10-10 fertiliser at the time you plant your pumpkins. When the first blooms appear, provide 1 tablespoon of ammonium nitrate per plant. Repeat the treatment three weeks later. If older pumpkin plants are showing signs of nitrogen deficiency, repeat the ammonium nitrate treatment.
Squash Vine Borer
Squash vine borers inhibit a pumpkin plant's ability to take in nutrients, which causes the edges of the leaves to turn yellow. What starts out as a mild symptom will become more pronounced as the entire vine wilts and dies. Prevent squash vine borers from attacking pumpkins by using floating row covers, which consist of fabric draped over hoops above the plants. Insecticides can bring the pests under control but won't save a pumpkin vine that has already been attacked. Look for insecticides that contain carbaryl, bifenthrin, permethrin or esfenvalerate. Remove the infected vine, or attempt to save it by seeking out and killing the borer. Locate the point of entry, usually near the base of the stem, and slice the stem in half until you find the borer. Kill the borer. You can try to salvage the cut portion of stem by burying it in soil and watering well; it may root and continue to grow.
The first sign of Fusarium wilt is a wilting vine, but sometimes in very early stages it will show up as yellowing along the edge of leaves. It quickly progresses to wilting, however, and the entire vine soon dies. Fusarium is a fungus that lives in the soil. It rots the roots, making it impossible for the pumpkin plant to take up necessary moisture and nutrients. There is no cure for Fusarium wilt rot. Prevent it by planting fungus-resistant seeds and varieties of pumpkins and by rotating crops.
Sometimes there is a good reason for the leaves on a pumpkin plant to turn yellow. When pumpkins on the vine are ripe and ready for harvest, the vine will begin to die. This is a natural process and part of the life cycle of pumpkins. Leaves may turn yellow, then brown and the vine will start to shrivel and dry up. If the pumpkins on the vine are full-size and the rinds are hard, they likely are ripe and the change in the leaves is the result of the plant reaching the end of its life cycle.
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- University of Illinois Extension; Ask Extension - Pumpkins; Maurice Ogutu
- University of Minnesota Extension; Squash Vine Borer Management in Home Gardens; Jeffrey Hahn, et al.; 2007
- Purdue University Cooperative Extension Service; Growing Cucumbers, Melons, Squash, Pumpkins and Gourds; B. Rosie Lerner, et al.; April 2001
- Cornell University Extension; Fusarium Diseases of Cucurbits; Thomas A. Zitter; January 1998