At a recent avocado meeting, Carol Lovatt of the Botany Department at UC Riverside pointed out that avocado fruit take up more potassium than nitrogen, almost twice as much, and that much of that uptake occurs later when the fruit is expanding. She reminds growers that all to often, the potassium needs of the tree are overlooked.
Click on "attached files, potassium nitrogen uptake" to view graphs.
A recent visit with Spanish researchers and packers was of interest. Virtually the whole industry uses a snapping method to harvest fruit. It is faster and often leads to fewer fruit rots than with clipping. In a past article by Reuben Hofshi in the CA Avocado Commission's AvoResearch is a review of the practices and results in various countries. It was well worth rereading:
Evaluating Damage to Baby Trees Requires Patience
Earlier temperatures and forecasted temperatures do not appear to be cold enough to freeze baby trees in the citrus belt. Time will tell. Semi-dormant wood in the winter looks dry even when it is healthy, so any final evaluation should be conducted in the warmth of spring. With warmer temperatures, frozen bark will peel easily from the young trunk and the degree of damage easily estimated. A tree, even those frozen down to the top of the wrap, can make an amazing recovery. Growers, in the summer after the 1990 freeze had some success budding onto the rootstocks that remained after the scions were killed by frost.
It may be better to replace a tree if it is still alive under the trunk wrap but badly damaged. Badly frozen trees regrow fairly slowly, and often are not able to resist pathogens that grow into the wood such as fungal Fusarium species causing dry root rot. Slow growing Fusarium in the wood can take up to 10 or 15 years to kill a tree.
Badly Frozen Young Trees
Badly frozen fruit may start dropping from the tree shortly after the freeze, but other fruit may hang on the tree longer than unfrozen fruit. Many growers resist picking or dropping frozen fruit in that it is another expense, at a time of little income. Reasons for dropping the fruit, even if it cannot be sold for juice, include:
Ensuring that the frozen fruit does not interfere with spring fruit set. Navel oranges, for example, will not set as much fruit if last season’s fruit remains on the tree.
Old frost-damaged fruit may harbor fungal pathogens that may infect the new crop, such as clear rot (Penicillium sp.), tear staining (Colletotrichum sp), brown rot (Phytophthora sps.) or Septoria organisms.
Avoiding having to separate last year’s partially frozen fruit from the new crop at harvest next year.
Preventing partially frozen fruit from providing habitat for insect pests.
A note just caught my eye of China requesting to export fresh apples to the US. They already are the major exporter of apple juice to the US, and now fresh fruit. I went online to see what other countries are requesting to send here and was impressed that the Philippines, Ecuador, Argentina, South Africa, Australia and Columbia all want to export 'Hass' avocado here and Swaziland, Chile and Mexico all want to send more citrus here. The link is to the USDA-APHIS website:
It's been a dry year and you don't expect it, but there's been a lot of "tear staining" of fruit. It has become most apparent this spring with the dew along the coast and the humidity. I've had a number of calls from growers this year because it has downgraded their fruit. One 'Meyer' lemon grower has had virtually all of her fruit affected. Here's the word from the IPM website - http://www.ipm.ucdavis.edu/PMG/r107102111.html
Pathogen: Colletotrichum gloeosporioides
In this Guideline:
Symptoms of anthracnose on citrus include twig dieback, premature leaf drop, dark staining on fruit and postharvest fruit decay. Dying leaves and twigs become covered with dark fungal spores by which the pathogen spreads.
Anthracnose may blemish the rind tissue of mature Valencia and navel oranges, grapefruit, and occasionally lemon. The disorder affects mainly fruit on stressed trees with old, dead wood.
Comments on the Disease
The anthracnose fungus usually infects weakened twigs. The disease is most common during springs with prolonged wet periods and when significant rains occur later in the season than normal. During wet or foggy weather, anthracnose spores drip onto fruit, where they infect the rind and leave dull, reddish-to-green streaks on immature fruit and brown-to-black streaks on mature fruit (tear stains). Anthracnose tearstain often occurs with Septoria spot. The Septoria fungus itself and possibly certain environmental conditions may also cause tear staining. The stain cannot be washed off, but the disorder is generally not severe enough to require preventive actions. Certain conditions, however, such as applications of insecticidal soaps, which damage the protective wax on the fruit peel, can increase the severity of this disease./h4>/h4>/h4>/h4>/h3>