Noticing Yellowing Pumpkin Leaves? These Are the Most Common Causes

Whether you’re growing them for pie or Halloween Jack ‘O Lanterns, pumpkins, Cucurbita pepo, are often planted out later in the season for fall harvest.

Growing during the heat of summer can present problems, and yellowing leaves are one sign you need to investigate and take action. Here are 8 reasons pumpkin leaves turn yellow and how to fix the problem.

Poor Drainage

Pumpkins have shallow but extensive roots that feed the vines. Poor drainage leads to a host of problems that start with yellowing leaves and wilting. Vines can grow 20 to 30 feet long with roots to match, so well-draining soil is critical.

Prepare the pumpkin bed before planting, adding compost, sand, and other organic material to improve drainage. Avoid low spots that collect water and consider sowing seed in mounds or raised beds. Let the soil dry between watering.

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Insufficient Nutrients

Pumpkins require plenty of nutrients to produce large fruits. When leaf margins yellow and turn brown, plants lack sufficient potassium. Yellowing between leaf veins indicates low magnesium. If the entire leaf is pale or yellow, the plant may need nitrogen.

Have your soil tested for macronutrients, secondary, and micronutrients.

Your cooperative extension office can do a thorough check and advise you on amendments. Tests also measure soil acidity. Pumpkins need a pH between 6.0 and 6.8 for good nutrient absorption.

Once vines begin to run, fertilize every two weeks with a formula high in nitrogen to generate vine growth. When flowers appear, switch to a high-phosphorus product to promote blooming. Switch to potassium-rich fertilizer once fruits start to form.

Crowding

Pumpkins need lots of growing space. Overcrowding and poor air circulation invite pests, diseases, and nutrient deficiencies, indicated by yellowing leaves and stunted vines and fruits. Tangled vines hinder efficient watering, fertilization, weeding, and harvesting.

The square feet needed to grow pumpkins depends on the variety, but a general rule of thumb is to provide 100 square feet of space for each hill.

Smaller types need less, and larger pumpkins may need more. Refer to your seed packet for proper spacing and thin plants, if necessary, to provide adequate space.

Heat Stress

Signs of heat stress include wilting, yellowing, browning, curling leaves, and sunscald. Temperatures above 95°F combined with high humidity lead to fungal diseases like powdery mildew.

Provide afternoon shade in climates with high temperatures. Plant next to a tall crop like corn or cover plants with shade cloth. Mulch to cool the soil and water deeply at ground level.

Improper Watering

Too much and too little water both cause foliage damage. Overwatered plants present pale, soggy, wilted leaves, while inadequate moisture causes leaves to wilt, yellow, and dry up.

Pumpkins need an inch of water per week. It’s better to water deeply less frequently than to water often but not enough to hydrate the roots. Aim to irrigate when the soil is dry about an inch below the surface.

Drip irrigation is ideal. Use a moisture meter or a simple finger test and check the soil often.

Disease

Pumpkins are vulnerable to mildews, leaf spots, and leaf blights. Prevalence of a specific infection differs according to your climate and USDA growing zone. Inspect vines often for signs that usually start with wilting, leaf damage, and loss of healthy green color.

Preventive treatments for pumpkin diseases can save your crop. When spotted early, most can be managed and controlled. If you discover leaf damage and are unsure what it is, take a sample to your cooperative extension office to find the cause and solution.

Remove diseased plants as soon as possible to avoid spread. Use drip irrigation or irrigate at the soil level and water early or late in the day.

Pests

Vine borers and cucumber beetles are two notorious pests of pumpkins. When healthy leaves near the base of the vine yellow and begin to wilt, vine borers are likely present.

Inspect the vine base for cracks, holes, and chewed plant material. If caught early, you can open the vine, taking care not to cut all the way through. Find and remove the small white grub, then cover the opening with fresh soil.

Check leaf surfaces and undersides for eggs and scrape them off. Biological sprays, including BT (Bacillus thuringiensis) and spinosad, are effective against cucumber beetle larvae and borer grubs. Follow label instructions for application.

Improper Use of Herbicides

Weeds and grasses can become troublesome, but improper use of herbicides can also damage pumpkin leaves and plants.

Non-selective herbicides kill all plants. Instead, opt for pre-emergent products or those that target specific types of weeds. Plant a cover crop as living mulch and avoid overhead watering.