13 Reasons Your Pumpkin Plant Has Yellow Leaves

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Argue all you want, but fall is the season of pumpkins. These tender vegetables enhance the taste of pies and spiced lattes, and instill a sense of warmth with their earthy fragrance. They're also the stars of Halloween decor. However, you may lose hope if your pumpkin plants suddenly develop yellow leaves.

The good news is not every yellow leaf is concern-worthy. Sometimes, it's just too old or cold. But, your pumpkin patch may also just be unhappy in its location. Excessive heat, poor nutrient availability, and water stress can also induce yellowing in leaves. Correct these factors, and your plants can thrive again. Pathogens like spider mites, whiteflies, aphids, squash bugs, or squash vine borers can cause leaf discoloration, too. Diseases like downy mildew and bacterial wilt can also be responsible for yellowing leaves. 

Before we elaborate on these causes, here's one quick tip. When you grow pumpkins, change their location every year. This way, overwintering pathogens can't inflict damage on next season's harvest. Also, minimize the use of insecticides because they can kill pollinating bees and beneficial insects. Then, use these tips to focus on growing pumpkin plants with healthy, green leaves.

Perhaps your pumpkin plant's leaves are turning yellow due to aging. As the leaves mature, they get discolored and yellow. This is because essential nutrients, particularly nitrogen, move out of the region to support new growth, allowing the vines to continue growing and bearing fruit. Pumpkin vines also produce a slightly toxic sap that, over time, degrades the leaves. This damage first becomes apparent around the margins and gradually proceeds inward. Left unattended, these leaves will dry off and shed of their own accord.

Recognizing age-related yellowing isn't difficult. It's typically concentrated around the vine's base. Mature leaves will appear worn out, sport healed-over wounds (from pest damage), or be visibly battered from wind or rain action. While retaining them won't harm your plant, it's best to remove the old stalks intermittently throughout the growing season, especially near the harvesting stage. This should open the air flow around the plant's crown, dissuading rot or pathogens from hunkering down and spoiling your harvest. That being said, if you notice the new growth yellowing, poor care or pest outbreak may be at play.

If you've taken on the herculean task of growing giant pumpkins, a 'B' gene will be bred into some of their varieties. This enables these vines to produce more female flowers and, by extension, fruits. Moreover, these fruits may also develop faster. The downside is that this gene makes the vines even more sensitive to cold. Pumpkins are frost-tender plants and can't withstand temperatures below 50 degrees Fahrenheit. If your area experiences cool summers or is exposed to a short bout of cold winds, a few leaves may turn bright yellow in response.

Fortunately, such yellowing isn't concerning and is limited to the leaves that experienced cold stress the most. Once the warm temperatures are restored, the new growth will be green and healthy. Usually, varieties that boast some resistance to viruses (it'll be stated on the plant label) carry the 'B' gene, and that's how you can spot if the yellowing in question has simply to do with the variety.

Since pumpkins can grow to a considerable size, their water demands are significant to move the food and nutrients along the growth. When they're left thirsty, their chlorophyll production slows down, causing them to express yellow leaves in retaliation. To confirm if the plants are underwatered, re-examine your watering regime, the soil, and the location.

Generally, pumpkins require watering every week, dampening the soil to about 6 to 8 inches deep. But if your area is experiencing drought, heat stress, or is exposed to drying hot winds, without rainfall to supplement your irrigation regime, they'll likely feel dehydrated and develop chlorosis. The vines may eventually look wilted and shed their flowers. Giving them a good soak should help compensate for the water lost through increased transpiration and evaporation.

Your garden soil and location can also make things tricky. While you can grow pumpkins in sandy soils or on slopes, they tend to drain faster. Without more frequent soaks, they'll be left pining for water, and the leaves may grow pale yellow. Poke your finger into the soil or insert a tool, like General Tools' MMD4E Digital Moisture Meter, to gauge moisture levels. If it feels dry to the touch, it's time to water your pumpkin plants. Consider laying an even layer of mulch on top of fast-draining soil for improved water retention.

Excess of anything is bad, and sun exposure falls within this realm for pumpkins. While their vines love basking in the sunlight, they don't require more than 8 to 10 hours of direct exposure. Exceed these limits, and you might have an unhappy plant, or at least one cowering slightly for shade. The light intensity and air quality matter, too. In the summer, the sunny beams can be especially intense, causing the leaves to lose water at a rate greater than they can replace it. Coupled with poor air quality, this distress can take the form of ozone damage. The result? Leaves that appear crinkly, dry, and riddled with bleached yellow spots. These spots may metastasize into brown or gray parts, with complete defoliation as the final outcome.

The easiest way to tell if your pumpkin plants are feeling excessive light and heat is to note the direction of their growth. Plants experience phototropism, which is their ability to stretch their growth in the direction of sunlight. But if the vines — assuming they aren't contained by hardscaping — are growing away from the light, seeking shade, that yellowing may be due to overexposure to the sun. If you don't want them invading other beds, drape the plants with a shade cloth, like Windscreen Supply Co.'s Eyelets Shade Cloth Roll. Alternatively, put up an umbrella, tarp, or even an old bedsheet for sun protection.

Pumpkin plants are huge nutrient feeders and will exhibit chlorosis if you don't fertilize them adequately. For instance, in plants experiencing nitrogen deficiencies, old leaves turn yellow in their entirety. These leaves ultimately turn brown and die prematurely, stunting plant growth. In contrast, magnesium deficiencies start as interveinal chlorosis, with old leaves appearing yellow between the veins as the fruit is growing rapidly. These portions may grow red, then brown and fall out, riddling leaves with tiny holes. But if you notice interveinal chlorosis on younger leaves first, it might indicate iron deficiency.

That being said, pinpointing the exact mineral deficiency can be difficult without a tissue culture test. You can also test the soil's pH levels with this gardening DIY and check the drainage. In highly acidic soils (below pH level 6.0), pumpkins struggle to uptake nutrients and can even suffer manganese toxicity, which also leads to yellowing leaves. Sprinkle lime in your garden to rectify this issue. In case the soil becomes waterlogged from excessive rains (leading to nutrient runoff) or poor drainage, work compost into it. Rotten roots struggle to absorb nutrients, forcing the plant to show deficiency symptoms, despite growing in rich soils.

Did you notice weeds and grass overrunning your pumpkin patch so you tried eliminating them using herbicides, like glyphosate (Roundup)? Chances are, these chemicals drifted away from the target, either while spraying or when you watered the area. Unfortunately, this may have inflicted injury on your precious plants. Signs to look out for include yellowing around the plant's crown, especially on the older foliage. From these mature leaves, the chemicals may move into emergent leaves, with the yellowing first appearing around the veins and tips. These leaves may grow black (necrosis) and drop, reducing plant growth. 

Thankfully, pumpkins, whether they're in the seedling stage, sprouting true leaves, or mature enough to bear fruit, can generally withstand herbicide injury. While you may lose some yellow leaves, the plants will resume normal growth a few weeks later. Going forward, use hooded sprayers or avoid spraying on windy days to minimize drift. Keep the beds mulched so weeds can't access sunlight and don't get a chance to grow.

Even if your care routine is on point, your pumpkin plants may have attracted nuisance pests like spider mites. These eight-legged insects suck the sap from the leaves, causing yellow spots where they feed. Over time, these yellow markings coalesce across the leaf, turning it entirely yellow and later, brown. Flipping the leaf over may reveal gray undersides covered in red or bronze spots. You'll also notice fine, silken webs with dust-like bugs moving around. Spider mites are most prevalent in hot weather, when it's dry and dusty, so that's another sign to consider to hone in on the problem. This is also your cue to check if your plants are adequately watered.

Since mite-infested leaves and the stems they're sprouting from can die, it's important to get rid of spider mites to give your pumpkin plants a fighting chance. Hose the mites down with water for initial control. Swap out your fertilizer for a slow-release variant, as mites tend to congregate on nitrogen-rich plants. Deal with severe infestations by spraying horticultural sprays or neem oil. Bonide Captain Jack's Neem Max is a good option. 

If not spider mites, whiteflies may be terrorizing your pumpkin plants. These white-bodied individuals feed on the leafy undersides, marking their feeding areas in yellow speckles. Rather than webs, they lace the area in a sticky substance ("honeydew"), which can encourage sooty mold to develop on the foliage. In some cases, like when greenhouse whiteflies are in action, you may notice white wax on the bottom of the leaves. Yellow leaves often grow dry, misshapen, and drop off in massive numbers, slowing down plant growth. Another way to confirm their presence is to flick the leaves. If you notice any moth-like bugs flying around and landing back on the foliage, whiteflies may be present.

To limit damage, grab your hose to banish whiteflies from your garden and wash off any honeydew or sooty mold present on the leaves. This way, they'll photosynthesize better. If the infestation doesn't relent, use sticky traps, neem oil, or insecticidal sprays. As whiteflies usually piggyback on greenhouse-grown plants, always check your starts for these pests to avoid introducing them to your garden. If you're growing other vegetables in your patch, such as cucumbers, tomatoes, or cabbage, monitor their growth for whiteflies, or they'll spread. So, heavily infested leaves (or the entire plant) should be removed immediately to prevent further spread. 

Yellowing leaves during mid- or late summer may indicate an aphid infestation. Since many varieties, including green peach, bean, melon, and potato aphids, feed on pumpkins, you may notice them as green, yellow, brown, or black insects. They usually congregate on the undersides, and their incessant feeding turns the leaves yellow as they're zapped of nutrients. Since aphids excrete honeydew, you'll find sticky substances trickling down on the tops of lower leaves. Heavy aphid infestations may result in the plant developing black lesions on its curled leaves until they fall off. 

To wage your war against aphids, blast them with your garden hose. If the infestation is small, clip off the damaged leaves. Otherwise, you might have to remove the whole plant. Regular re-applications of canola, neem, rosemary, thyme, or peppermint oils can keep their populations in check. Row covers can be handy when you expect hot winds to blow aphids into your garden. Avoid using pesticides, as they will destroy beneficial insects like lady beetles that nosh on aphids, making your plants even more susceptible to untreatable viruses.

During early summer, you may notice black-dotted, orange-bodied insects buzzing around your pumpkin plants. They're squash vine borers on the hunt for lucrative sites to lay their eggs. Upon hatching, their babies, or white caterpillars, burrow into the stems. As their feeding deprives plants of essential resources, apart from disintegrating their food networks, the leaves turn bright yellow and droop down. Left untreated, the whole pumpkin vine collapses. Besides visual identification of the adult insects, spotting yellowish or greenish-gray dust (or frass) near mushy and wilted stems can confirm their presence.

If your pumpkin patch is already infested, try to recover the plants by cutting out the caterpillars from the damaged stems with a sharp knife. If that doesn't help, harvest as much fruit as you can before destroying the vines and cultivating the soil. Otherwise, the squash vine borers will overwinter in the soil and play havoc next year. Permethrin-based insecticides can be helpful if you catch the adult insects before they've laid eggs. In the future, either drape your plants in floating covers or wrap aluminum foil around the lower stems until the plants flower to keep boring insects away.

Another pesky insect that may induce yellowing in pumpkin leaves is the squash bug. Like borers, these bugs are active in the summer. But because they're black-bodied, they easily camouflage in the soil or mulch, making identification difficult. In contrast, their red-legged younglings and copper eggs are easily located on the leafy undersides. Tiny, white spots appear where bugs feed on the leaves. These, in succession, grow yellow and brown. Young pumpkin plants can't tolerate this stress and decline in health, growing crispy and molten back. Although their mature counterparts can still bear fruit, expect to lose a few vines. Worse, squash bugs can vector Serratia marcescens bacteria that cause yellow vine disease. When infected, pumpkin foliage turns a sickly lime-yellow and, then, bright yellow as the disease progresses. These vines can die quickly, right before fruiting. Food-transporting phloem tissues also appear honeyed, rather than their typical clear color.

When you detect squash bugs, their offspring, or their eggs in your pumpkin patch, pick them off and dunk them in soapy water. If you fear they're hiding in the soil, lay down boards overnight to trap them and destroy the gathered insects the next day. Prune damaged leaves to stem further spread and dispose of the foliage after harvesting. Neem oil, insecticidal soaps, or Sevin Insect Killer may help if you catch the insects early in action.

Generally, downy mildew is problematic in southern states where the warm temperatures paired with high humidity encourage the development and spread of the water fungus. However, if your garden is exposed to southern winds (like the eastern states), your pumpkin patch may contract downy mildew over the years. You'll notice angular, pale green spots in the plant's center on the upper side of the leaves. They'll eventually turn yellow, giving way to brown lesions and causing leaf curl and death.

Unfortunately, you must remove your plants if they contract downy mildew; pesticides offer limited efficacy. When you grow pumpkins next year, locate them in dry, sunny sites and trellis the vines for better air circulation. Since downy mildew takes hold of these plants around late summer or early fall, plant them early or choose early-maturing varieties to delay its onset. Also, monitor your plants for disease when temperatures are between 59 and 68 degrees Fahrenheit, when downy mildew is most aggressive.

Another reason for yellowing leaves is bacterial wilt. Initially, the foliage will grow dull and limp during the day (like an umbrella), but will recover overnight. In about two weeks, it'll show yellowing around the veins, with the region appearing water-soaked, while the tips become brown and shriveled. This disease can spread throughout the vine, killing it. If you have a magnifying glass, cut out an infected vine and split it. Press the two pieces together, then pull them apart. If you notice strands or material oozing out, you're most likely dealing with bacterial wilt.

Unfortunately, infected plants can't be saved and must be removed immediately to thwart their progression. As the bacteria are carried by striped and spotted cucumber beetles, it's important to control their population. Erect hoops or drape floating covers until pumpkin plants flower to exclude the yellow-bodied beetles. Spreading kaolin clay on them can also be effective.