Which yellow leaves are the cause of Spider mites.

[davidwood]

In the photo left to right 1to 5 which would you say are the cause of Spider Mites[if any].These leaves are from 5 different cv's and i have just about tried everything to get rid of Spider mites which makes me think that maybe its not all mites,certainly leaves 2 and 3 every leaf on these cv's are the same as the ones shown and they have been bathed sprayed etc for a long time.
Also leaf 2 has that bubble affect,is this ok as i have this on 2 or 3 cv's but no yellow.

Sorry if it is yet another topic on Spider Mites but with this photo I and a few others could use it as a reference.
Personaly i think only number 1 is mites so i will be interested[and hopefully praying]that i am right.

[Darkhorse]

Hate to be the bearer of bad news but they all look like they could potentially be mites to me.  4 and 5 are most typical of mites but in my experience different cultivars show mites differently.  With most it is textbook leaf stippling but for example both Silver Memories I've had have shown mites by having yellow veins first, then the whole leaf yellows.

If you have good vision you can flip the leaves over and look for the mites, or webbing with eggs.  The webbing/eggs looks like there could be tiny bits of white dirt stuck to the bottom of the leaf in a little spider's web.  They're tiny but you can see them with the naked eye.  If you need extra help try looking for them with a magnifying glass.


A note on leaf #2, some cvs I have just have leaves like that naturally.  Sometimes it's caused by pests, though.

[davidwood]

Jordan i tend to agree with you except i am not sure about number 3,i think that is just sun burn.
I am like everyone else and it seems to be a constant battle to get rid of the dam things,I spray each leaf both sides every night with water and once a week they either get oil or Bayer.Most of them have even had a bath last week.
Obviously you cant give up on mites but maybe i will just have to learn to live with a few.Out of 20 cv's i only picked of 7 leaves this morning which is not to bad,but its an on going battle.
Lets see what Charlie says,maybe its not as bad as we think.

[Charlie]

We love photos - thousands words and all...

The underside of the leaves can be more instructive than the tops, but based on the tops any of these could be showing mite damage. Mites are specialized feeders. Their favorite food is chlorophyl and they have mouth parts that allow them to penetrate the big cells of chlorophyl and suck out the contents. As these cells are destroyed the green color they impart to the leaves is also lost and the leaves show it, first as yellow dots and then increasing areas of yellow. At some point the plant recognizes the damage to the leaf and starts the process of shedding it altogether. When that happens the leaf dies and the yellow spreads rapidly and then the leaf is abscised (look it up, good botanical term to know).

Anyhow, this is why we cannot control mites with a systemic pesticide the way we can almost all the other pests of hibiscus. Systemics are absorbed into the plant where they circulate in the xylem sap but do not enter into chlorophyl cells. Most pests of hibiscus are "sap suckers" and when they feed on the sap they are killed by the systemic pesticide. Since mites consume little sap, preferring the chlorophyl, they do not consume the systemic pesticides and we have to use contact treatments that actually hit the mites to control them.

By the way, systemics usually do not enter into flower buds either which is why thrips are the next most difficult pest after mites. Fortunately, the organic and fairly benign pesticide Spinosad is highly effective in killing and repelling thrips.

This message turned into a digression but I hope it's helpful to know why the leaves turn yellow.

Charlie

[Charlie]

Jordan, I agree with your comments. Different cvs can react in unique ways to any type of stress, including mite damage. Even so, the best way to confirm mites is to use a magnifier that is between 10x and 30x and examine the underside of the leaves. In advanced infestations webbing is often present around the tips of the stems. Mite damage is not reversible by the leaf - once the pinprick holes show from feeding damage they remain for the life of the leaf. That makes it hard to tell if mites are still there or not without looking for them with a magnifier.

Leaves also die for other reasons and as they do so the chlorophyl degrades and they turn yellow - think fall leaves of trees. Hibiscus leaves are not supposed to last the life of the plant and are regularly replaced. This contributes to the confusion so what can you do. I don't know of any other method that is reliable other than to view the undersides of the leaves with a magnifying device. Live mites look like little crabs and are clearly alive when seen at 30x.

ln most garden situations there are also plenty of predator mites and insects that feed on spider mites. These do a lot to prevent bad infestations of spider mites. In such a situation you might see some limited mite damage but it won't spread because the predators clean up the mites. The problem with that is you don't know if the predators will do the job or not and if you wait too long to treat, the mites can do a lot of damage. Once again, a real inspection with a magnifier is the only way to keep track of what is actually happening.

So, I can't say whether your leaves represent an ongoing mite infestation or not. If the yellowing gets worse it's likely the mites are gaining the upper hand. If the yellowing stays at low levels that are not increasing then it is likely there is another cause or that predators are taking care of them for you. Nothing beats Mother Nature's own balances but when a lot of one species such as hibiscus are grown together with few other plants around (as in a commercial greenhouse) the balance is disturbed and pests can go quickly out of control unless treated.

One last point, Jordan. The bumps and bubbles you sometimes see in leaves are usually the result of uneven growth that happens when the leaf is first forming. It can be the result of insects chewing on the emerging new growth, or a reaction to environmental conditions such as pesticide application or even internal variations in the plants chemistry. One part of the leaf grows faster or slower due to the disturbance and the bubble occurs. These are not dangerous or a problem for the hibiscus. The one time that it is a problem is when it is due to a rare type of mite called the erinose mite. The leaf distortions then are extreme and treatment is needed to get rid of this mite that is not visible to the naked eye. These mites are a problem in Australia and Hawaii and other places but rarely seen in the continental US.

Charlie