Saturday, September 15, 2012

Hazards of Citrus in Zone 9a


I live in USDA plant hardiness zone 9a. What that means is in the winter it freezes here, sometimes getting down to 18 degrees Fahrenheit. And, further, that means it is not a good place to grow citrus. Except, well, being from Arizona originally, specifically The Valley of the Sun, I am drawn to the scent of blooming citrus. To satisfy my spring citrus scent desires, I first got a Mock Orange plant (P. gordonianus, if you're keeping track) that is strictly an ornamental, blooms it's heart out with heavenly citrus-y smelling blossoms. Being frost hardy, it thrives here, is a full 20 feet tall, has grown way beyond it's allotted location and may well consume its neighboring vegetation.

Then a few years later, knowing my citrus weakness, a good friend offered me a grapefruit tree she had started from seed. Just a little plant that perhaps would winter over as hers had done for several years. I took the plant and was successful in keeping it alive for a few winters and thus encouraged, for eight dollars I purchased from Walmart what is reportedly the hardest of citrus, a Meyer Lemon. With so little invested if the small tree succumbed to the frost not much would be lost. Now with the two trees I decided to plan a winter home for them and so constructed a PVC pipe and plastic sheeting "hoop house", this long before the structures and term had been coined.



Some years later I added a ten dollar Walmart Mandarin orange and three years ago two kumquats joined my citrus collection. The kumquats came from a local nursery at the price of upward to $40 each, but with their pedigree and fancy upbringing I thought them worth it. With the five trees in my winter hoop house (greenhouse is far too fancy a word) a warm sunny spring day is an aroma filled experience, second only to being in Arizona driving past a citrus orchard in February. Amazingly, all the trees have borne fruit, except the grapefruit started from seed.

Here begins my tale of woe. Last winter I noticed that one of the kumquats started to look all wilty and sad. And, very sad it was due to an infestation of a nasty bug that loves citrus! After an internet search and much digging I discovered that the nasty bug had a name, Cottony Cushion Scale, scientific name Icerya purchasi. From the University of California Intregreted Pest Management (UCIPM) website I learned:

California citrus pest cottony cushion scale
Adult female Cottony Cushion Scale on dying grapefruit
The most distinguishing feature of the cottony cushion scale female is the fluted cottony egg sac that she secretes. About 600 to 800 eggs are laid in the sac. Hatching occurs within a few days in summer, but can take up to 2 months in winter. Adult females settle and begin to form the white, elongated egg sac. Males are rare and females can reproduce without mating. There are three generations a year.
 
Cottony cushion scales extract plant sap from leaves, twigs, and branches, thus reducing tree vigor. If infestations are heavy, leaf and fruit drop can occur along with twig dieback. The scale secretes honeydew, which promotes the growth of sooty mold. (And lots of "farmer" ants that share in collecting the honeydew!)

Now the good part. The preditor of the Cottony Cushion Scale is the vedalia beetle; better know to you and me as Lady Bugs (or beetles)! UPICM goes on to say:  Lady beetles are easily recognized by their shiny, convex, half-dome shape and short, clubbed antennae. Most lady beetles, including this species, are predaceous as both larvae and adults. Young lady beetle larvae usually pierce and suck the contents from their prey. Older larvae and adults chew and consume their entire prey. (Gross but apparently effective!) Larvae are active, elongate, have long legs, and resemble tiny alligators. Many lady beetles look alike and accurate identification requires a specialist.

Now the not so good part. Unless disrupted by pesticide use or other adverse conditions, the vedalia beetle and the parasitic wasp, Cryptochaetum iceryae, provide complete biological control of the Cottony Cushion Scale. R. cardinalis was introduced into California citrus groves in 1888 and saved the citrus industry from destruction by the Cottony Cushion Scale. Due to its success, the vedalia's introduction is now viewed as the beginning of classical biological control.

Following this warning I decided not to use a pesticide, even a so called "natural" one, and to hand pick as many of the little buggers as I could to maintain control until the cavalry arrived. Now remember I have the growing conditions that mimic summer when hatching can occur within a few days and each female is producing 600 to 800 eggs. Yikes, I was out numbered!

Now the really bad part! The cavalry never arrived. I lost the kumquat that was the original carrier (so much for the pedigree and fancy upbringing) and the grapefruit. I almost lost the Meyer lemon, but it rallied this summer after shedding all of its fruit and many of its leaves. I continue to hand pick and seem to have the little buggers under control. However, I will use "something" before I put them back in the hoop house for the winter. Sadly, there will only be three citrus trees - well, and the avocado - but that's another story!


2 comments:

  1. Citrus, I still need to figure that out. Your zone 9a sounds much like our 8a, rarely gets below 20. But when I go to our local Home Depot, they have many different citrus trees, for the past several years.

    I have a friend who grow lemons here, he'd protect and cover his plants when it got cold, his lemon tree did awesome. He got MS and wasn't able to keep it covered and he lost it one year.

    I found a lady in Home Depot and asked, is everyone growing these in like a green house? Or do they plant they in the ground. She was telling me after the first few years (in the ground) you didn't have to protect them unless it got really cold. One thing was to keep them well watered and mulched in the winter.

    We have an avocado tree, in a pot. Some day I'll have some citrus, other things to do first. Before I try one in the ground, I want to find who ever it actually doing it, and learn their secrets.
    Good luck on your trees.

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    Replies
    1. When citrus is iffy in your zone, Meyer Lemon is usually one you can grow. My dad put Christmas lights in his to keep it just warm enough not to frost. Mind you the lights were the old fashioned BIG ones, 7 watts each, not the little twinkle lights and certainly not the LED ones that give off no heat whatsoever. We were down to 22 degrees overnight here the last couple of nights. It can get into the teens sometimes, so rather than risk it my citrus go into the greenhouse! =) I have some kumquats ripening and can't wait to pop the first one in my mouth! Thanks for stopping by and commenting!

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