Avocado Leaves Last and Last

Avocados come from a wet environment. The Guatemalan and Mexican races come from cloud forest environments that are dripping much of the year from if not rain, a high humidity that creates a cloud-like condition. These are conditions that leaf fungi love, so in order to protect from leaf fungi, they have developed a waxy cuticle so that water runs off. This also protects the leaf from water that would dissolve nutrients in the leaf. This is one reason that foliar nutrient sprays don't work well with avocado. They can get into flowers, so floral sprays can work. But then you might mess up pollination.

 

Greg Alder photo

Another consequence of this cuticle is that the leaves are resistant to decay. One reason for the thick leaf duff/mulch/layer found in avocado orchards.

I tagged leaves that had newly fallen with different colored propylene string at time different times of the year. Leaves were 1 month, 6 months and one year old. The leaf on the right is one year old. That waxy layer is really resistant.

 

New Weatherman at ANR

weather map

Leps - Leaf Eating Jewels

They can be so destructive, but they sure are beautiful. Leps or worms can be found on fruit tyrees.

Citrus Lepidoptera (“Worms”) https://ipm.ucanr.edu/agriculture/citrus/

ID Key: https://ipm.ucanr.edu/legacy_assets/pdf/pmg/key_to_caterpillars_lepidoptera_larvae_in_california_citrus_3.pdf

 

California Orangedog· Papilio zelicaon

Amorbia (Western Avocado Leafroller)· Amorbia cuneana

Citrus Leafminer· Phyllocnistis citrella

Fruittree Leafroller· Archips argyrospila

Loopers· Cabbage looper: Trichoplusia ni· Citrus looper: Anacamptodes Fragilaria

Omnivorous Leafroller· Platynota stultana

Orange Tortrix· Argyrotaenia franciscana (=A. citrana)

(Photo of M.J.W. Cock & D.H. Burris)

Pink Scavenger Caterpillar· Pyroderces rileyi

Western Tussock Moth· Orgyia vetusta

 

Avocado Leps

As well as Orange Tortrix, Omnivorous Looper and Amorbia: https://ipm.ucanr.edu/PMG/C008/m008bpcaterpillars.html

In avocado look for:

Avocado Leafroller/Leafminer ·Caloptilia sp.

worms of citrus avocado Page 1

worms of citrus avocado Page 2

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One Last Act of 2024

Get the Latest and the Last

Dec 23, 2024 | View All Issues

This edition includes the following:

• Preparing Frost Protection Measures
• The National Clean Plant Network, with emphasis on the National Clean Plant Network — Citrus
• Development of integrated pest management for huanglongbing (HLB) in Florida

topics in sub masthead

Horticultural Myths

Horticultural Myths

These are practices and or products that many people working in our industry may hold to be useful but have no scientific basis for their method of action. They are formed from misinformation passed on over the generations or from common observations that are misinterpreted. A good example is that of placing gravel or rocks in the bottom of a planting hole to increase drainage for the rootball. This is borne out by the fact that these drawings exist in old books. Even though the mistakes are corrected in modern texts the myth that rocks in the bottom of a planting hole creates drainage, lives on today, and actually shows up in some modern landscape architectural specifications.

Another myth is the notion that pruning woody plants stimulates their growth. The more severe the pruning, the more the plant is shocked into good growth. Although the growth of latent buds from major limbs that have been headed back leads to copious regrowth, if you compare the overall growth of this tree to a similar unpruned tree, the pruned tree will have grown less on the main trunk over the same amount of time. Transplanted trees do not need to be pruned to compensate for their root loss. Sometimes when trees are moved, compensatory pruning is done to “balance” the roots with the shoots. Research has consistently shown that as mentioned above, pruning is a growth retarding process, and thus slows the establishment of transplanted trees.

There are many funny ideas about mulches. Almost any mulch can be applied to the soil surface with few bad affects. There are some exceptions where the mulch contains toxic acids or contains weed seeds. However, the belief that high C:N ratio mulches (contain a lot of wood) will extract nitrogen from under the soils to which they are applied has little or no scientific evidence to support it. Just the opposite is true. Over time, woody mulches decay and release nitrogen to underlying root systems.

A product that has attained Horticultural Urban Legend status is Vitamin B1.  In the 1930's, Caltech's James Bonner discovered, that Thiamin (vitamin B1) was able to restore growth to pea root tips that had languished in tissue culture. It was concluded to be essential in plant growth media. Bonner later found that B1 had little growth promoting effects on most whole plants in hydroponic culture, but that some plants such as camellia, and cosmos showed dramatic growth increased to added B1 vitamins. Bonner latter discovered that thiamin production was associated with the foliage of growing plants. The hoax was on in 1939 when Better Homes and Gardens magazine ran an article that claimed thiamin would produce five inch rose buds, daffodils bigger than a salad plate and snapdragons six feet tall! In1940, Bonner entered into collaborative research with Merck pharmaceutical company to master the growth promoting effects of B1, account for the wide variability in his experimental results and develop a product that gave consistent good results. Bonner proved during this period that B1 was phloem mobile was made in leaves and transported downward in stems. Bonner's experiments with Cosmos continued, but with varying results, so he sought cooperative research with University experiment stations around the country. Results were mixed, some showed growth promotion, most not. By 1940,other physiologists widely reported negative results. By1942 Bonner was debunking his own discoveries, stating that the effect only ever occurred in very few plants and that since thiamin was found in soil itself, field applications were unlikely to benefit plants. Bonner ultimately fully retracted his claims of efficacy by saying “It is now certain, however, that additions of vitamin B1 to intact growing plants have no significant or useful place in horticultural or agricultural practice”. The public craze and fanatical headlines about thiamin continued but Merck withdrew all interest and funding in the concept so as to distance itself from a product that does not work.

New products come and go. Snake oil products often disappear rapidly, when their efficacy fails to materialize after application. Products that confound their purported results with fertilizers or growth stimulators can persist, but eventually they too fail to live up to expectations at some point and will fade from popularity. Try to obtain some kind of consensus with university based research or other peer reviewed research reports, field efficacy trials that you run for yourself, and not on the testimonials of others. If you decide to conduct your own trials, they must be replicated and statistically analyzable, otherwise they are little more than anecdotal observations that have little value in quantifying the effects of the above mentioned products and practices. For more help with trials, seek out University Extension agents and specialists. This is their job, and they are willing partners in field research. After awhile, you will be able to ascertain the nature of the “oil” before you purchase it.

avocado big leaf homrone - Copy

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