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Hydrangea pests and diseases
Last Updated on January 21, 2020 by John
Hydrangeas are fairly easy in terms of their maintenance and care. Regardless of the form, you choose they will bring a great deal of beauty and joy to your yard with impressive displays of flowers and foliage. However, there are a few common pests, diseases, and other problems that might impact your hydrangea that you should be aware of.
Leaf spot disease
The most common disease you will see with your hydrangea is leaf spot disease. This is usually the result of a fungal infection. Fungal diseases like these manifest in situations where the ground remains too moist, the roots get too damp, or there is insufficient air flow throughout the plant.
This is more likely to take place during warm moist seasons. You can prevent this by being particularly cognizant of how often you water. Yes, hydrangeas need moist soil but no this does not mean you have to water them regularly. Consider that if you have added mulch to the top of your soil to help keep the roots cool, that will naturally retain moisture which means you don’t have to water as much. Similarly, you should avoid watering overhead on the leaves and instead, water directly at the base of the plant.
Tangentially powdery mildew is a common problem that won’t harm your hydrangea so much as impact the appearance. If you notice a physical powdery white mildew on top of the leaves and your flowers are also not blooming, you might need to cut away some of the branches in order to promote better air circulation and alleviate conditions.
Rose Chafers (beetles)
Rose chafers are a beetle that is known for eating the flowers of Hydrangea and the telltale sign is that you will notice small holes in the petals. They also eat the leaves between the veins leaving a leaf skeleton structure. The best non-chemical way to help prevent this is to check the leaves and remove affected leaves from the plant. Pesticides can also be successful and have more immediate results.
Bacterial leaf spot
Bacterial leaf spot can be problematic as well. This does not manifest in the form of mould spots so to speak but rather in the form of discolouration on the leaves themselves. You might notice black lesions on your hydrangea or brown spots that have a yellow perimeter. Regular, small brown spots like these will cause your leaves to dry up and eventually break. If the area in which your hydrangea is planted is exposed to severe wet and cool conditions this might promote the growth of bacteria. It could be something as simple as you remove bacteria-laden leaves from another part of your garden and in doing so some of the bacteria splashed off those leaves and onto your hydrangea. In any case, if you notice this use a bactericide immediately to treat it and prevent it from getting worse.
There are some common pests that adversely impact your hydrangeas. Spider mites are a common pests on hydrangeas however they are not a pest that you need to remove simply because they serve the purpose of feeding on the other insects that are cause for severe concern.
One of those is the spider mite. The spider mite is very small and it will eat away at your hydrangea leaves. It starts by piercing each of the leaves and removing fluid inside the leaves. You can tell when you have an issue with spider mites because this process leaves small yellow spots in its wake. If you notice spider mites you need to remove them by spraying water on them to physically knock them off the leaves.
Whiteflies, greenfly and aphids are other common pests that present problems for hydrangeas. The aphids will penetrate the leaves and remove sap from inside the hydrangea tissue. You can tell if you have problems with white flies or aphids because the result of this sap removal turns the leaves yellow, causes them to curl up from the edges inward, and in some cases fall off entirely. The leaves often also feel sticky as it leads to honeydew.
To remove these you can mix dish soap and water together but you must thoroughly coat every part of the hydrangea, literally the top of the leaves the underside of the leaves and everywhere in between. Do not do this when the morning sun is hitting your hydrangea or it can scorch the leaves. You can also use a pesticide to spray plants but we always recommend this is the last resort treatment we should use chemicals as little as possible.
Hydrangea scale is another more common pest that is hard to treat as they have a protective waxy coat that protects them from sprays, they can be identified by the oval white eggs that attach themselves to the stems of the plant. A painfully slow way to try and get rid of these is to remove the eggs manually but this takes lots of patience. The best way to treat hydrangea scale is by spraying with a pesticide but this needs to be done around mid-July to kill the young nymphs before they develop there waxy protective scale.
Slugs and Snails
Everybody knows what slugs and snails are and thankfully they are not to much of a problem with hydrangeas as they can be with softer plants. However young foliage is most at risk and they can be a problem sometimes. The best to treat is to simply put down some slug and snail pellets.
Aside from issues relating to pests or diseases you might notice that your hydrangea is not blooming. It might simply be blooming insufficiently especially in comparison to previous seasons or it’s just not blooming at all.
Hydrangea not flowering
Realistically in these situations, the culprit is likely unnecessary pruning at the wrong time of the year. It is fairly common for homeowners to mistakenly prune one season at the wrong time because they don’t necessarily know which variety of hydrangea they have so they remove the old would from the previous season unaware that that is the wood on which the following season’s flowers bloom. If that is the case simply continue your regular maintenance routine.