Tuesday, February 24, 2009

Dealing with Spider Mites Infestations

by Richard Chew

It is interesting to see that there are more interest in my postings on dealing with diseases and types of horticultural oil for pest control in my blog than my postings on feeding.

I thought my readers would be interested to know my approach in dealing with spider mites.

Incidentally 'The Prince' rose got infected with spider mites after I placed it at location where it received direct late morning/noon sun for about a week.

My immediate response was to jet spray the underside of the leaves to remove the mites.

However the next day, the mites came back again, it was like Houdini magic, appearing out of nowhere.

Upon checking AccuWeather (example report below), I learned that the sun was very intensed on that week when my rose plant got infected.

Just to give you an idea on understanding the report below. UV Index as indicated below in the report is the measurement of UV light intensity. At the time of writing this posting, it was measured at 3 (moderate) . If UV index is anything below 5, it is fine for most plants. If it exceeds 5 for few days consecutively, it can be hazardous to the leaves.

I extracted the definition of UV Index below.

UV Index is the Ultra Violet Radiation Index. The index is a value between 0
(none) and 15 (extreme). This value shows the part of the invisible spectrum of
light that reaches the earth from the sun. Although the Earth's atmosphere
protects us from the bulk of these rays, those that get through are still
harmful. UV has been linked to sunburn, skin cancer, skin wrinkling and aging,
cataracts, and other ocular damage.

Accuweather is a very useful tool for me to monitor the amount of rain, sun and weather condition in my garden, when I am away from home.

I checked the leaves and noticed speckled marks/textures were more distinct than it was before. This was a clear sign that it had been too exposed to intensed sunlight. Accuweather UV Index indicated level 8 which is considered harmful.

This was not the only rose plant with speckled leaves in my garden, I suppose this rose type, being less tolerant to sun, makes it more vulnerable to infestation compare to those originated from tropical climates.

The picture below is taken from the lower leave. I suppose this leave is more shielded from direct sun compare to the ones above.

Another observation, the silk-like webs and presence of spider mites tends to appear on the top of the plants where it receives most exposure to sun/heat. Very seldom we will find spider mites and web nesting at lower shielded part of the plant.

I believe spider mites thrive on leaves that are most 'cooked' by the sun and are attracted to most "litup" leaves (at upper part of the plant). The baby spider mites feed on simplified sugar 'cooked' by the sun/heat because it is easily consumed. Removing these leaves, may cause these spider mites to move their breeding ground to lower leaves. By retaining the infected leaves, in a way the mites are "contained".

The green in the leaves, suggests the presence of chlorophyl and that the leaves are still capable of manufacturing sugar. Unfortunately major portion of the food produced are consumed by these spider mites. But on the positive note, it discourages mites from moving to other leaves as food is easily accessible at current nesting place.

Pesticide is necessary, especially if regular jet water spray didn't work or you knew the rose plant was not in good health prior to infection, perhaps due to lack of feeding or water or lack of essential factors. In this situation pesticide helps to manage damage control but not neccessarily provide full aid to recovery.

To achieve full recovery, contrary to what we learn and know, the best way to fight against these pest, is actually a passive and indirect one.

Unlike humans and animals, plants do not have similar repair capabilities or immune system to heal itself. Plants heals by regrowth.

If you are reading this and are encountering recurring spider mites problem, perhaps you should consider nursing your rose plant to inbuild a stronger line of defence.

The following are some of the things that I did to 'The Prince'. These steps mentioned here is not a formula or technique that will solve all spider mites problems. The objective is to repel mites & nurse the plant back to health.

  1. Foliar Feed - I used seaweed extract, and spray about 3 to 5 times a week, depending on the severity of infestation.
  2. Relocate rose plant away from direct sun
  3. Use only organic fertilizer - I also include seaweed extract to moist the top soil after watering
  4. Jet spray with water regularly the underside of leaves - especially when the mites are visible
  5. Place large slices of garlic above the soil - it seemed the pungent smell of garlic repels the mites

Below are pictures of new growth.

I noticed some dramatic improvements after relocating the rose plant and carrying out the exercise above regularly. The mites were less visible the following day. However the mites emerged on 3 days later with webs at the top of the plant. I continued the jet spray and foliar feed. It is now day 8 since I first detected the spider mites. And there is no recurrence since I last jet spray 3 days ago. I won't say that it has completely recover from the spider mites because there could be small ones that are not visible to the naked eye.

From this case it is quite evident that the population of the mites is pretty much controlled. As long as there is new growth, new leaves, the rose plant is on the road to full recovery.

Spider mites are small, 8 legged, spider-like creatures which
thrive in hot, dry conditions (like heated houses). Spider mites feed with piercing mouth parts, which cause plants to appear yellow and stippled. Leaf drop and plant death can occur with heavy infestations. Spider mites can multiply quickly, as a female can lay up to 200 eggs in a life span of 30 days. They also produce a web which can cover infested leaves and flowers.

I believe when there is no recurrence of spider mites in 30 days, we can breath a big sigh of relief.


  1. Thanks for your tips. Now I know how to deal with them pest. :-)Winnie

  2. Thanks for the tip Richard. Been trying to grow roses the past few years but they have all died because of spider mite infestation and also simply pure ignorance on my part on how to grow roses. Just bought a new pot of roses to try again ... hope it works this time!

    ~ GMC

  3. It is very helpful tips for me. I defiantly use your tips in my work. Thank you for nice tips.
    Treat Spider Mites