- Author: Ben Faber
With hot, dry winds, the question came up this week about whether the hot temperatures or the low humidity would affect pollen viability. It turns out that both day and night time temperatures will affect pollen tube growth. That in ‘Hass' approximately 48 hours about 50 deg F is needed to complete pollen tube growth and fertilization. If temperatures drop at night to below 50, there's not enough time for fertilization to occur. As temperatures increase, fertilization occurs more easily. In the tropics, there can be high temperatures and high humidities and good fruit set. But this question was not about fertilization, but how long the pollen would remain viable at high temperatures and low humidities. Work was done Loupassaki and Vasilakis for the World Avocado Congress III Proceedings and they basically found that when humidity dropped below 40%, viability was very low. This last week we have seen humidities below 10%. It probably means that even with bee visitation, non-viable pollen is being delivered to the flowers. When humidities come back up, there will probably be good fertilization, as long as we have decent day and night time temperatures.
Many years ago Gary Bender, down in San Diego, went to the Gulf Region of the Middle East to help establish an avocado orchard. The trees flowered, but never set fruit.
- Author: Ben Faber
Two years ago we set out to study the impact of native bees on avocado fruit set. We applied for several grants unsuccessfully and turned to growers to see if there was interest. We raised $6,000 to start the project and have established 4 sites in Ventura and Santa Barbara counties. in the meantime have gotten a Sustainable Agricultural Research and Extension grant. This grant does not start until October 2014. We need bridging funds to continue this study. Below is the original request from growers for funds. If you would help contribute it will keep this study going until the larger grant comes through. Thank you.
Dr. Gordon Frankie at UC Berkeley is teaming with Dr. Ben Faber from the Ventura County UCCE Extension to jointly work on a pollination study for avocados. Dr. Frankie is studying how to increase native bee pollinators in avocado orchards. To do this, we plan on surveying the native bees that are in the area, identify the plants that they are foraging on and then plant those species in orchards to lure indigenous bees + pollinators in to the orchards. These plants will also be monitored for their attractiveness to beneficial insects which could control avocado thrips, persea mite along with other pests. We will need some startup money to cover the costs of native plants plus travel for Dr. Frankie and his assistant to be able to come down to monitor the project. They are ready and willing to come do this important study. We have applied for UC grants and will apply to CA Avocado Commission and CDFA Specialty Crops for money, but we will not see that money until summer 2014 at the earliest. We need your help. It would help to plant the natives before the winter rains. They need the rain to bloom; so the sooner you can help, the sooner we can plant. We are trying to cobble together donations of about $3,000. Thank you in advance. Any contributions are tax deductible and can be made to: UC Berkeley Foundation (with a notation at the bottom of the check: Gordon Frankie Bee Lab) and sent to Dept of Environmental Sciences, UC Berkeley, 130 Mulford Hall #3114, Berkeley, CA 94720.
- Author: Ben Faber
Bob Hill, a local Ventura PCA, saw an interesting mite he had never seen before and asked if I could id it. Well, I sent it in to Mark Hoddle and UCR and he turned it over to his student Ricky Lara to id it. And this is what he says:
I started finding this type of mite infrequently in 2011, when I was sampling foliage in avocado orchards. Although seldom seen, they have a wide geographic distribution on avocado. I found them in Cambria (SLO), Santa Rosa Valley (Ventura County) and Irvine (Orange County). At the time I narrowed down the mite family to Winterschmidtiidae. I have to double check, but I believe their feeding habit is listed as fungivorous (The Manual of Acarology). They might feed directly on plant material too (no fungus on the avocado leaves I sampled) but no one has really studied them. I tried rearing them in the lab (without other mites as a food source, only pollen) but the colony only lasted for a couple of months. On avocado I have seen these mites at the leaf-vein junctions. This probably provides a natural home ("domatia") for them as it does for other mites (e.g. phytoseiids, tydeids, stigmaeids). On lemons, the calyx structure probably serves the same ecological function for these mites.
The tydeid mites are what I call the "tidy mites" since their basic function is to run around and clean up leaves, although there are some predatory and scavenging members of the family This little guy is just one of the many tidy mites found out there and its recent appearance is just a reflection of the weather/climate we have this time.
The red circled mite is the one we are talking about here. The structures next to it are some egg cases of another animal. The red dots are called opisthonotal glands which produce pheromones, the purpose of which is not clear.
- Author: Ben Faber
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.
potassium nitrogen uptake
- Author: Ben Faber
Assessing water quality for Southern California agriculture typically revolves around the total salinity of the water, its total dissolved solids (TDS), and the toxic ions boron, sodium and chloride. Salts are necessary to plants, because it is in the form of diluted salts that all nutrients are taken up by plants- the macro and micronutrients plants extract from the soil. High salinity leads to water imbalance problems much as if the plant were not getting adequate water. A toxicity problem is different from a salinity problem, in that toxicity is a result of damage within the plant rather than a water shortage. Toxicity results when the plant takes up the toxic ions and accumulates the ions in the leaf. The leaf damage that occurs from both toxicity and salinity are similar in that it causes tissue death known commonly as "tip burn." The damage that occurs depends on the concentration of the ions in the soil water around the roots, the crop sensitivity and crop water use, and the length of time the crop experiences the ions. In many cases, yield reduction occurs. Because crops can not excrete salts the way humans do, salts gradually accumulate in a plant. As a result plants need a higher water quality than humans do.
Much study in many countries has gone into evaluating water for crop use. Some of these studies have been on the effects of salts on soil characteristics. Generally, as sodium concentration increases, a soil will lose its aggregation, eventually leading to poor water infiltration. Many more salinity and toxicity studies have been done on plants themselves. Not all crops are equally tolerant of salinity and toxicities, and in general most plants respond to salinity and toxicities in a similar fashion. If a plant is intolerant of salinity, it will be intolerant of chloride, sodium and boron. Most annual crops are less sensitive to salts than tree crops and woody perennials, although symptoms can appear on any crop if concentrations are high enough. The reason for greater sensitivity for perennial crops is that the tree is sitting in the ground absorbing salts for a longer period than the lettuce plant that is harvested 3 months after planting. Furthermore, deciduous trees like walnut shed their leaves each winter, so they can handle salinity better than evergreens like citrus and avocado.
To manage salinity and toxicities, water management is the key. Depending on water quality, an excess of water will be applied to the soil to leach the previously applied salts away from the root zone. The poorer the water quality, the more excess water is applied.
Selecting a less sensitive crop is also an alternative when dealing with poor water quality. Some barley varieties can handle salinity similar to ocean water. Barley nets a grower $400 an acre, avocados $9,000 and $25,000 if the market is right for strawberries. Avocados are salt sensitive, so are strawberries and lemons and cherimoyas and star fruit and blueberries and raspberries and mandarins and nursery crops. We grow these because with our climate, very few other places can grow them and they return enough money for a grower to stay in business in an area where land, water and labor are expensive. We really don't have much in "alternative crops" to grow here.