If you grow pumpkins in your garden, you may have seen white spots on the leaves and vines. What is this all about? Most likely, your plants are infected with a fungal disease. Powdery mildew on squash is very common and in many cases can be successfully treated. However, if allowed to spread, in severe cases the plants can drop their leaves and expose the fruit to sunburn.
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What is powdery mildew?
Powdery mildew on squash is a very common plant disease caused by hundreds of different types of fungi. While the infection does not usually kill mature cucurbit plants, it can cause problems in developing fruit and stunted growth in young plants. In pumpkins, this disease is primarily caused by Podosphaera xanthii (formerly known as Sphaerotheca fulginea). In temperate regions, cucurbits typically show initial symptoms in summer when plants begin to bear fruit. However, severe infections can occur earlier in the season and result in bud drop and stunted vine growth.
Symptoms begin with the appearance of white spots on the underside of leaves, which can easily go unnoticed. The fungus can spread and cover the entire leaf, which eventually turns yellow and, in severe cases, dark brown. When this happens, the leaves fall off, and the exposed squash can be scalded by the sun, ripen poorly, and become much smaller than expected.
Conditions conducive to powdery mildew in squash.
Unlike most fungi that reproduce under moist, wet conditions, powdery mildew can infect squash even under dry conditions. As long as there is enough moisture, the spores can spread. The likelihood of these fungi infecting your plants is greatest when it is hot, dry during the day and cool and humid at night. Daytime temperatures of 20 to 27 °C are ideal for infection. However, when temperatures rise above 37 °C, the fungus is no longer active.
Dense foliage on the vines increases the susceptibility of the plants to this disease, as the lack of air supply allows the infection to spread quickly. In addition, plants that are crowded out by weeds or grow in shady locations create ideal conditions for powdery mildew to spread. Lush plants that have been overfertilized with nitrogen are also more susceptible to infection. The fungi infect the new growth, causing it to stunt.
Shrubby squash varieties that grow in a more compact form can also become infected when the plant’s dense canopy increases moisture in the plant medium. This results in high humidity, which encourages powdery mildew development.
Inspect your plants weekly
Because it is a widespread and, in some cases, potentially serious disease, you should inspect your plants regularly. This will help prevent the infection from spreading and damaging your crops. Early stages of powdery mildew appear as small white spots that can be successfully treated. Check the underside of older leaves first, as this is where the infection usually begins. Don’t forget to also check the crown of the plant and the vines.
Powdery mildew on zucchini – how to deal with it? You can find out here !
Make sure that it is not downy mildew
Powdery mildew in Кürbis – A complication in determining this diagnosis is that there is another pathogen that can infect pumpkins and also causes whitish spots: downy mildew. While it acts like a fungus, the pathogen that causes downy mildew is a completely different organism – a water mold or oomycete. This means that completely different control methods are used for the two pathogens. Fungicides that are effective on downy mildew are ineffective on powdery mildew and vice versa.
You can recognize downy mildew infestation on pumpkins by the yellowish spots on the top of the leaves and the purple to gray spots on the underside. In contrast, powdery mildew shows white spots on the underside of the leaves. Another way to tell the two infections apart is that downy mildew’s spots are angular. They stop growing at the veins, so they look like a patchwork. You can see this most clearly on the underside of the leaves.
Fight downy mildew on cucumbers – what measures can you take? You can read about it here !
Home remedies for downy mildew on cucurbits
Milk: The general advice is to dilute milk with water in a 1:10 ratio and spray it on your plants at the first sign of infection. You can use milk in powder or liquid form. However, based on research to date, higher concentrations of milk prove to be most effective. Try using a 50/50 mixture of liquid milk and water for moderate to severe infections. If you don’t have a large area to treat, even use whole milk. Put the liquid in a spray bottle. Make sure you cover all infested areas of your plants, including the stems and undersides of the leaves. Continue applying twice a week until you see results. Repeat the application when it has rained.
Sulfur is another organic compound that can be very effective against powdery mildew on squash if applied before the infection spreads too far. BUT: Do not apply sulfur to plants that have been treated with horticultural oils for at least two weeks. Still avoid application when temperatures are expected to exceed 27°C.
Biofungicides are also often effective against this disease.
Baking soda for powdery mildew: Researchers have tested the effectiveness of baking soda (sodium bicarbonate) as a fungicide since the early 1930s and found it to be ineffective as a fungicide on plants, although it can inhibit the growth of molds in the laboratory.
What tricks and other home remedies can you use to naturally control powdery mildew on plants? Find out here !