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Hibiscus Plant Care

Spider Mites

My Hibiscus Leaves are Turning Yellow!


Yellow Leaves on an Otherwise-Healthy Plant
The First Sign of Spider Mites
Spider mites are a warm weather problem for many hibiscus growers. They prefer hot, sunny, dry conditions and their levels can soar when the temperatures rise. If not dealt with they can cause all the leaves of a hibiscus to fall off and seriously damage the overall health of the plant.

How Can I Tell if My Hibiscus Have Spider Mites?

The first sign of spider mites is yellow leaves. A leaf or two first gets yellow mottling mixed in its normal green, then slowly the entire leaf turns bright yellow. At first you just see a few yellow leaves, here and there, and don't think anything of them. But very soon the spider mite population explodes and more and more leaves turn yellow at an increasing rate of destruction.


Spider Mite Webs in Bright Sunlight
As the spider mites spread, they become visible to the naked eye only in the brightest light with the closest inspection. A magnifying glass helps immensely at this stage. Look at the tips of the branches with yellow leaves, and you will see very fine webbing. These are the spider mites' webs. You can sometimes see little dots on the webs - the spider mites themselves. At this point, you have a severe infestation that must be dealt with quickly or these little pests will make every leaf on your plants turn yellow and fall off, which can eventually kill the hibiscus.

Tell-Tale Signs of Spider Mites


An Advanced Case of Spider Mites
Look Closely to See the Webs & Mites on Growing Tips
Leaves Show the Typical "Mottling" of Green & Yellow
Tiny Spider Webs: Look for tiny spider webs on the growing tips of your plants. You will need to look very closely, in bright sunlight, for very fine, tiny webs on the smallest growing tips or developing buds. If you have good eyes and bright light, you may see tiny dots along the webs. These are the spider mites. With a magnifying glass you can see that the dots actually look like tiny crabs scuttling along the web.

Growing hibiscus in the house or in a greenhouse offers a lot of protection from many forces of nature, including pests like thrips, ants, slugs, and even aphids much of the time. However, there is one bug that thrives in the warm conditions of the greenhouse, and positively flourishes in the warm, dry environment of a house - the spider mite. The warmer and dryer the environment, the more these little critters reproduce! So if your hibiscus are still indoors, watch carefully for signs of them.

Stippled Leaves: Leaves become stippled as the mites pierce the leaves and draw out chlorophyl from them, leaving colorless leaf spots behind. If you start to see leaves that look like this, with yellow stippling, search for spider mite webs on the stem tips.


Leaf Stippled by Spider Mites
Yellow Leaves: If the infestation continues, leaves that are badly infested will turn yellow and fall off. For many people, yellow leaves that fall off their hibiscus is the first clue that something is wrong. But by the time the infestation reaches this stage, it is already quite advanced. It's best to learn how to detect spider mites in the earlier stages.

Sick Plant: If the spider mite infestation continues unchecked, the whole plant begins to look tired, with the leaves slightly drooping despite being well watered.

Defoliation: If left untreated the mites can create a mass of webbing over the plants, and most or all of the leaves will become damaged, turn yellow, and fall off.

How Do I Get Rid of Spider Mites?


Plant Defoliated by Spider Mites
Over the years, we have written many articles on how to control spider mites. The methods below are the ones we have found to be most effective at killing spider mites with the least amount of harm to the hibiscus plants. The method each of us chooses depends on the circumstances - how many hibiscus plants we have, how big the plants are, whether they are indoors or outdoors, in a house or greenhouse, in pots or in the ground, etc. At HVH we have hibiscus growing in the greenhouse, in the ground in an outside garden, indoors in a house environment, and outside on porches and decks in pots. We use different pest control methods for each of these different sets of hibiscus. Very few of us have extra time to waste, so efficiency matters! All of these methods work. It's just a matter of finding the method that is quickest, easiest, and most efficient for you hibiscus and their growing circumstances.

DROWNING SPIDER MITES

This is our favorite method for all hibiscus growing in small-medium pots and for houseplant hibiscus. You only have to do it ONCE to kill all spider mites and their eggs. It kills every kind of spider mite, even the most microscopic ones that can hide in cracks in the bark. This method does require precision and care. You'll need a timer and a thermometer - a kitchen "candy" thermometer is perfect. If the water is too hot or you leave the plants too long, you can damage the leaves and they will all fall off after treatment. If the water is much too hot and you leave the plants much too long, you could actually kill a very young plant. But if the water is too cool or if you don't leave the plants in the water long enough, you won't dissolve the covers of the eggs and kill the growing larvae, which means the infestation will come right back.


A Large Sock on a Small Pot

  1. Wrap the hibiscus plant pots in some kind of fabric and use a twist tie to secure the fabric around the base of the plant. The fabric must let water through, so don't use plastic bags, or you will carefully protect any pests that are living inside the pot and soil. Large socks or pantyhose work well to wrap up small pots, and pillow cases work well for large pots.
  2. Lay several hibiscus plants on their sides, pots and all, in a bathtub. You can put many of them close together in a single layer in the bottom of the tub.
  3. Fill the tub with water that is bathwater temperature - about 90°F (32°C). It should not be so hot that you can't comfortably keep your skin in it. What feels too hot to skin will risk damaging your plants' leaves.
  4. Fill the tub until all the plants are covered, and weight the plants down to make sure all parts of all plants are submerged in the water. (An easy way to weight them is to cover the plants with two large towels, then to pull the two shelf racks out of your oven and lay those carefully over the top of the towels.)
  5. Leave the plants submerged in the water for 45-60 minutes.
  6. Drain out the water and stand the plants up in the tub until the excess water drains out of the pots.
  7. Remove the fabric covers, and scoop any loose soil in the fabric back into the plant pots.
  8. Leave the plants out of bright light for a few hours to rest, then put them back where they belong. Be careful not to water the plants again until the soil dries out after this thorough soaking.

Unless plants are recontaminated by exposure to another infected plant, plants should remain free of spider mites, aphids, and other pests for 4-6 months or more. This method has the added advantage of leaching out any build-up of fertilizer salts in potted plants, which needs to be done once or twice a year. So it is two plant-care activities in one.

WASHING OFF SPIDER MITES


BugBlaster
If your hibiscus are too big to put in a sink or bathtub, an alternative method is to wash your plants in a shower, under a faucet, or with a hose or BugBlaster. If done carefully and conscientiously, this method will wash off and drown adult spider mites, but it will not wash off or drown all eggs and nymphs. So you will have to repeat it 3-4 times, every 5-7 days, to get rid of all the spider mites as soon as they hatch out and grow into adults.

This method works for large hibiscus in pots or for hibiscus planted in the ground. It's especially good for people with smaller hibiscus collections, because it is very effective, and it is the least damaging to plants and to the environment. It is time-consuming though; each plant must be washed slowly and carefully.

  1. If plants are in pots, lay them on their side where the pots can be rolled over to all sides. If plants are in the ground, get a long enough hose that you can walk all around each plant.
  2. Using a hard stream of water, wash every single millimeter of each plant - the top and bottom of every single leaf, branch, stem, and twig. Spray systematically, making sure you don't miss one spot on the plant where spider mites could be lurking. Spider mites living mostly on the bottoms of leaves, so spraying the bottom of each leaf carefully is crucial.
  3. When finished, wash the ground with a very strong stream of water and enough water to drown any spider mites that fell off the plants.
  4. Repeat this washing process 2-3 more times every 5-7 day.

TREATING SPIDER MITES WITH SPRAYS

Another alternative method is to treat with either a miticide, such as Bayer Advanced 3-in-1, or with Horticultural Oil or Neem Oil. All three treatments work equally well, in our opinion, and we sometimes alternate between them, using one one week and the other the next week. Just like the washing method, sprays are effective at zapping adult spider mites, but in our experience they don't kill all the eggs or nymphs. So you have to repeat the spraying every 5-7 days for 3-4 egg-hatching cycles to make sure you get every emerging adult spider mite.

Breathing any of these products is very bad for you, so if you decide to spray, you should absolutely use a respirator mask. Oil droplets aren't poisonous, but breathing oil into your lungs is very harmful to your body. You can feel it in your lungs for quite a while afterwards if you make this mistake! It takes a lot of spraying to kill all the spider mites, and that amount of spraying without a mask is definitely bad for lungs.

One more note about spraying: All these products are best sprayed in the evening when the plant can be protected from the sun for the hours that the products are doing their work. If you spray in the evening, the products have 8-12 hours to work, and the sun won't burn the products into plant leaves and burn them or harm them in any other way.

  1. Put your hibiscus in a protected place outside with enough space to walk all around each plant.
  2. Put on your respirator mask.
  3. Carefully and systematically spray every millimeter of the plant: tops and bottoms of every single leaf, stem, branch, and twig, as well as the surface of the pot and soil. It takes time to spray this carefully, but you may as well not bother spraying at all if you don't do it this carefully! Spider mites living mostly on the bottoms of leaves, so spraying the bottom of each leaf carefully is crucial.
  4. Let the spray product dry for several hours before bringing the plants back into a house.
  5. Repeat this spraying process 2-3 more times at intervals of 5-7 days.

The trick with pest control is conscientiousness. Any one of these methods will work if applied conscientiously following the directions exactly. So find the method that's easiest and most comfortable for you to follow!


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