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Test completed 7-27-07 - See below for results
What would another year be without continuing research on the mites. Although checking them out close up and real personal has been fun, observing their methods of transportation has been interesting too. Since the greenhouse presented an opportunity to increase the number of plumerias I can keep, it has also presented the problem of where to place them around the yard during the summer, as keeping the greenhouse cool via fan or other methods is not yet cost friendly. Plumerias enjoy the heat but there are limits.
Placement of plants. This year I have placed plumerias in three areas around my yard. I am not keeping any plumerias on my west facing deck (very isolated, except from humming birds) as done in the previous years, but instead am exposing the plants to various more "natural", less isolated conditions.
Red arrow points to the grapefruit in the citrus grove. To the left of the image are five plumerias which are exposed to the breezes which flow through and are approximately 15' away from the nearest citrus tree (orange). To the right of the red arrow is the blind area which houses multiple plumerias, plus tomatoes, cucumbers, sunflowers, etc..
Plants directly exposed.
Plants somewhat protected by the blind.
Plants around my lab. This area provided for easy maintenance last year. I am hopeful it will be this year too.
Choice of treatment. Since I have dogs which rule my yard, I'm careful about what I apply to my plants. Since insecticidal soap is safe, doesn't appear to burn the leaf tissue as easily as horticultural oil may, and is widely available, this is my choice of treatment.
What? Since I have been able to track a source of these mites in my yard (citrus grove), this year I have set up a test to determine whether one can clean up these plants of the mites and keep them mite free if they are close to alternate hosts. I started the year out treating all plants via a dial-sprayer attached to the garden hose with a concentration rate of 2.5oz insecticidal soap per gallon water. Although that worked fairly well keeping the plants in the blind area mite-free, those in the direct wind path near the citrus orchard continued to demonstrate damage. Seeing that this wasn't keeping them under control I have now (6-17-07) switched back to using the hand pump up sprayer. One thing I do know is apparently I can use plumeria as sentinel plants/traps for these particular mites and it is most apparent that my entire citrus grove needs treatment, not just the grapefruit (severely collared and treated 4 times so far this year), which is a preferred host but by all means not the sole one.
RESULTS: Plants kept within the blind area were easily maintained mite-free while those in the direct air-flow area continued to demonstrate mite damage, even with the decrease in application periods to every two days instead of three and the use of the hand pump-up sprayer.
Red shell seedling which demonstrated the most damage.
It produced a bloom cluster, which appears to be nubbing.
In this spot it may recover and finally be clean of mites.
A bloom cluster on a plant with least amount of damage of the five. Note the necrosis on the unopened bloom behind the other open one.
Another angle.
Each of the five directly exposed had mite damage of some form.
Blind area which contains >5 plants. No mite damage evident.
Blind vs. breeze-way. Why the difference? Although the plumerias placed in the blind area certainly were not entirely surrounded by netting, both the shade fabric and bird netting which is encasing the sunflowers, cucumber, and tomatoes appears to have provided just enough buffer/barrier so as to prevent transport of the mites from the citrus in such numbers that treatment was able to effectively keep any passing creatures from causing damage to the plants. For the breeze-way it appears that no matter the application method, treatment with insecticidal soap, even every other day, could not prevent continuing mite damage to the plants. It should be noted that various creatures do visit these plants and the five placed in the breeze-way were visited this year every afternoon by a mud-dauber wasp, seeking sugars from the nectaries located on the petioles from recently elongated leaves. The same wasp was noted visiting the citrus, although what it sought from there is unknown. But, hairy creatures (hairs on the legs of the wasp - hairs all over the back of the mites) can interlock, and perhaps my little visitor was being a bit too helpful. The plants around the lab demonstrated some anthocyan production (purple/red spots) on a few leaves which may be associated with mite feeding. Beyond that damage was limited to what birds did to a few emerging leaves on those plants.
Why should one care? If you have mites and have not yet figured out your hosts/source areas, it is hoped that this demonstration may help those who are seeking answers.
Will 2008 be my first mite-free year since that glorious first year back in 2002 when I received my first cuttings and seed?
Images taken in February of 2002