MESOPHYLL COLLAPSE - SYMPTOMS OF WEATHER CHANGES SEEN IN CITRUS LEAVES
This question and concern has been a frequent citrus discussions here at the nursery. My citrus trees are suddenly showing crunch leaves on some outside branches, leaving green stems barren. Is the tree diseased? What is happening? Is there a treatment that should be applied?
This phenomenon is common during the fall in Arizona. Our daytime temperatures remain warm, but our nights are much cooler. The temperatures start falling around 4:00 p.m., as the sun is lowering, and you suddenly need a sweater. It is thought that the shock of abruptly cooling temperatures, worsened by winds, collapses the mesophyll, which is the internal tissue of leaves, resulting in sudden dehydration and defoliation. Lush new growth seems more susceptible to this peculiar disorder, particularly during the fall, when shortening day length is already a strong inducement to defoliate. A rather abrupt drop of otherwise healthy green leaves typically occurs. They may quickly wilt,dry, and remain on the tree. But, more often, affected leaves suddenly drop off, like over-night, abnormally leaving a noticeable number of their leaf stems remaining on green twigs. Occasionally some sap secretes and crystallizes at the place where shed leaves were previously attached. The more tender foliage on the north and east sides of trees seem more frequently affected. Grapefruit trees seem to be more easily affected, but other varieties, such as orange and lemon can also experience it. Mesophyll collapse is not serious, and the trees will recover normally the following spring with little or no loss of production.
What are some exotic varieties of citrus available for sale at the nursery? Is this time of year okay to plant citrus?
We are continually growing exotic varieties of citrus here at Greenfield. The freeze of 2006 was a "hard" freeze, with temperatures dipping to 19 degrees the first night, and only reaching 21 degrees the following night. We irrigated both nights, all night, and were spared the loss, except in small sized limes, and exotic citron varieties. Our lime trees are growing again,and we hope to have a good production this spring 2009. We do have the Kieffer Limes available now, read more below. The fall season is the best time to plant citrus, as the warm day time temperatures and cooler night temperatures provide the best "growing" components for the root system. The newly transplanted tree in the fall will have the longest time to begin growing again before our hot summer temperatures return. With good maintenance practices, citrus transplants can survive any time of year. Our nursery's longevity, and continual non-seasonal operation is testament to this.
For present, we have the traditional Washington-Navel orange trees available, whose fruit are ripe now, at the end of November into December. Theses oranges are the most popular, have no seeds, belly button bottoms, and are best for eating. You can't beat the taste of citrus grown on the sour orange seville rootstock, which is the rootstock, we at Greenfield use exclusively for our field-grown citrus here in the Salt River Valley.
Another popular Navel we grow at Greenfield is the Cara Cara Navel. This Navel variety originated in Venezuela. The fruit is pink fleshed, with the bright orange rind of a "regular" Navel. This variety is very sweet, with a slightly different flavor, but enjoyed by many who like it so much, they buy a second Cara Cara for their yard. Just cutting a piece of fruit brings a look of awe at seeing the bright pink flesh, almost the color of cantaloupe. The Cara Cara Navel ripens about the middle of December.
For a Grapefruit that ripens early here (meaning the end of November to early in December) in Arizona, the best choice would be the Oroblanco Grapefruit. This grapefruit is a hybrid of a Pummelo and White Marsh Grapefruit. This fruit is thick skinned, like the Pummelo, and produces a more textured flesh like the Pummelo. The fruit is very sweet, not the "bite" that grapefruit normally leaves in your mouth. If you think you don't like grapefruit, this variety will change your mind. This variety is very popular now. The Oroblanco Grapefruit leaves are large, larger than those on a "regular" grapefruit.
In the Lemon family, we grow the most popular, Improved Meyer Lemon now. Magazine articles, recipes, home and garden TV shows, have made this lemon "the one to grow". The Improved Meyer Lemon tree produces lemons more than once a year, and will grow slower than the traditional Lisbon Lemon grown here in Arizona for years. The Meyer lemon tree's fruit is not as acidic, and will produce a thin skinned piece of fruit, with orange tinged flesh. It is a hybrid between a lemon, and a sweet orange or mandarin.
For another choice in Lemons, we have the Pink Eureka Lemon, a beautiful varigated leaf tree, that produces a lemon with green and yellow stripes on the rind, and pink flesh inside. This tree also grows slower than the Lisbon Lemon. The rind of the fruit turns a pale yellow color when the fruit is ripe. This tree makes a great patio tree. The leaves are so different, you can't believe it is a citrus tree.
For Limes, we grow the Kieffer Lime, also known as the Kaffir, Kuffre, Indonesian Lime, Mahrut Lime, and Citro Hystrix. The"leaves" are used for flavoring in Thai and Cambodian cooking. The tree is a thorny shrub, with small rounded fruit, that isseedy, sour, light green flesh with bumpy, dark green rind that looks like alligator hide. Oil in the rind is thought to haveinsecticidal properties. We have this variety in our 14" B&B (ball & burlap) size for $60.00. The tree would plant at a height of 3 feet, with a 2 feet canopy width.
And, a most popular variety of citrus for growing in a pot, or even in the ground, is the Kumquat. The variety, the Fukushu, produces the round, golf-ball sized fruit that produces fruit almost year round, and the tree grows slower, reaching about 15 feet in 20 years. It is a very beautiful ornamental appearing tree, with the advantage of delicious fruit growing on it. Greenfield has the Fukushu Kumquats available in 15 gallon containers.